Methods and apparatus for stress relief using multiple energy sources
Methods are presented for modifying a physical property of a structure, such as reducing or relieving remaining internal stress, in which two or more energy types are concurrently applied to the structure to change the physical property of interest in an accelerated fashion. A first energy type, such as heat, is applied according to time values and operational settings derived from a first order rate relationship for the first energy type and from a first order rate relationship for a second energy type. The second energy type, such as vibration or other time-varying energy form, is applied concurrently for the time value. Methods are also provided for determining operational settings for concurrent application of multiple energy types to a structure.
This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 60/404,020, which was filed Aug. 16, 2002, entitled A PROCESS AND DEVICE FOR METAL OR METAL ALLOY STRESS RELIEF, the entirety of which is hereby incorporated by reference.
FIELD OF INVENTIONThe invention is generally related to the field of changing physical properties of structures and more particularly to methods and processes for changing physical properties of structures using two or more energy sources.
BACKGROUND OF THE INVENTIONManufactured parts are often fabricated using a variety of mechanical and thermal processing steps, such as heat treating, welding, and others, that cause mechanical stress within the materials. Residual stress remaining in a manufactured part has been found to adversely affect fatigue life, corrosion susceptibility, and strength, wherein areas near weld joints have been found to be particularly susceptible to stress problems. In many machines and structures, component parts may suffer early degradation in load bearing capability, corrosion resistance, and/or catastrophic failure due at least in part to internal stress remaining after fabrication or welding. Furthermore, the repair and/or replacement of components is costly in many situations.
Localized internal stresses may cause accelerated failures due to stress corrosion, fatigue, and premature overload fractures. These failures can occur in bridges, aircraft structures, ship hulls, pipelines, liquid storage tanks, rails, and reactor vessels, as well as in many other structures. Relieving or reducing internal stress in large structures is sometimes difficult, particularly where the structure is in a remote location. For example, stress may occur as a result of welding pipes together in remote areas to create an oil pipeline, or from welding, forming, and/or assembling structural components in bridges, ships, or airplanes. For large and small structures, premature degradation or failure of the structure may result from remaining internal stresses. Durability and performance of welded parts are affected by internal stresses that can reduce fatigue life and corrosion resistance. Welding involves providing high temperatures to melt a welding rod or other filler metal used to join two sections of plates. The base metal joining surfaces are also heated to melting temperatures during the welding process. The presence of thermal gradients adjacent to the weld line affects the microstructure of the plate. Thermal gradients are the primary cause of residual stresses along the weld lines and contribute to diminished mechanical properties and reduced corrosion resistance in the heat-affected zone compared to the base material. In addition, welding, especially when coupled with variations in thickness, leaves significant internal stresses as the material attempts to adjust to the varying thermal gradients.
Accordingly, techniques have been developed for relieving internal stresses in manufactured parts that may be employed during or after fabrication or welding operations. However, conventional stress-relief processes are typically time-intensive, requiring application of energy to the stressed parts for long periods of time. In a manufacturing setting, lengthy stress-relief processes are costly in terms of total fabrication time, throughput, and energy. Time and energy are also an important consideration in stress-relieving structures in the field. For example, performing a stress-relief operation on an aircraft in a commercial airline fleet requires that the aircraft be grounded during the stress-relief operation. For large structures, such as welded pipes in a remote pipeline, ship or aircraft hulls, etc., the energy for the stress-relief operation often needs to be brought to the worksite, wherein time-intensive conventional stress-relief techniques are particularly costly. Accordingly, there remains a need for improved stress-relief techniques and systems for reducing stress in manufactured parts and/or welded structures.
SUMMARY OF THE INVENTIONThe following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended neither to identify key or critical elements of the invention nor to delineate the scope of the invention. Rather, the primary purpose of this summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. The invention relates to techniques for changing physical properties of a structure using concurrent application of multiple energy types to the structure, and methodologies for determining operational settings for concurrent application of multiple energy sources to a structure.
The concurrent provision of multiple energy types in accordance with the present invention may be advantageously employed to significantly reduce the time and/or energy required to change a physical property of interest, such as reducing remaining internal stress in manufactured parts or other structures, compared to previous techniques. The invention may find utility in technology areas of solid diffusion, including but not limited to heat treating and aging, surface diffusion treatments for metals (e.g., oxynitriding, nitriding, carburizing, etc.), zone refining of metals, battery manufacturing, doping semiconductors (e.g., to speed processing or lower temperature in semiconductor manufacturing), or other technologies where time is spent while atoms diffuse through a material. The invention may also be employed in areas of liquid diffusion, including but not limited to osmotic membranes (e.g., water purification, chemicals separations, etc.), liquid chromatography (e.g., chemicals separation, etc.), and chemical mixing.
In accordance with one aspect of the invention, a method is provided for changing a physical property of a structure, wherein the physical property can be creep rate, creep, strain, stress, residual stress, internal stress, aging, mixing, motion through a membrane, or any property, such as those that may be controlled according to an Arhennius-type first order rate equation. The method comprises providing a first energy type to a structure by performing a first energy process according to an operational setting. The operational setting and/or a time value is selected according to a first order rate relationship for the first energy process, a first order rate relationship for a second energy process, and according to a desired physical property value for the structure. In one example, the physical property may be internal stress, where the desired physical property value is one of a remaining internal stress value and an internal stress reduction value. The relationship for the first energy process relates application of the first energy type to the structure and a physical property of the structure, and the relationship for the second energy process relates application of the second energy type to the structure and the physical property. The method further comprises providing energy of the second type to the structure at an energy level above an activation energy for the structure, where the first and second energy types are provided concurrently for at least the time value.
The first and second energy types may individually be any form of energy applied to a structure. In one example, the first energy type is thermal and the second energy type is time varying, such as oscillatory mechanical vibration. The first order rate relationships may be Larson-Miller (L-M) relationship curves that relate the application of thermal and oscillatory energy to the structure and the physical property of interest. A first L-M parameter is determined according the first L-M relationship, corresponding to the desired physical property value, and a second L-M parameter is determined according to the second L-M relationship, also corresponding to the desired physical property value. For example, the first L-M parameter may be determined according a first L-M relationship (e.g., L-M curve, etc.), wherein a desired remaining internal stress value is selected along the Y axis of the first L-M curve, and the corresponding parameter (“P”) value is ascertained along the X axis (P1). A second L-M parameter is determined for the desired physical property value according to a second L-M relationship (e.g., a second L-M curve) by locating the desired internal stress value on the Y axis of the second L-M curve, and locating the corresponding second parameter value (e.g., P2) along the X axis. A third L-M parameter (e.g., P3) may optionally be determined according to the first and second L-M parameters (P1 and P2), such as by subtraction (e.g., P3 =P1- P2).
An operational setting and a time value are then selected according to the third parameter P3 using the first order relationship for applying the first energy type to the structure. One of a temperature setting and a time value is selected for applying the first energy type to the structure, for example, based on structural, equipment, economic, or other considerations, or randomly. The other value is then determined or selected according to the third parameter P3 (e.g., based on P1 and P2), the first L-M relationship, and according to the previously selected value. For instance, a temperature value may be selected based on thermal heating equipment limitations, structural material properties, etc., and a time value is then determined by solving a first order rate equation using the pre-selected temperature value and the third parameter. In another implementation, the time value may be selected first, and the temperature setting is then determined according to the time value, the first and second parameters, and the first order rate equation.
In accordance with another aspect of the invention, a method is provided for determining operational settings for concurrent application of multiple energy types to a structure. The method comprises determining a first parameter according to a desired physical property value for the structure and according to a first order rate relationship for a first energy process that relates application of a first energy type to the structure and the physical property. A second parameter is determined according the desired physical property value and according to a first order rate relationship for a second energy process that relates application of a second energy type to the structure and the physical property. A time value or an operational setting for the first energy process is selected, for example, according to structural, equipment, economic considerations, etc. The remaining time value or operational setting is selected according to the first and second parameters (e.g., or a third parameter that relates the first and second parameters), according to the first order rate relationship for the first energy process, and according to the previously selected one of the time value and the operational setting. The method may further comprise determining the first order rate relationships for the first and second energy processes.
Other aspects of the invention provide methods for changing a physical property of a structure by applying two or more energy types concurrently, methods for determining operational settings for concurrent application of multiple energy types to a structure, which employ a combined first order rate relationship for multiple energy types, and systems for concurrent application of multiple energy types to change a structure property. In these methods, the first order rate relationship characterizes a relationship between concurrent application of the first and second energy types to the structure and a physical property of the structure. Operational settings are selected by determining a parameter corresponding to a desired physical property value and deriving one or more settings from the L-M parameter.
To the accomplishment of the foregoing and related ends, the following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
One or more implementations of the present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. The invention relates to methods for stress-relieving or changing other physical properties of a structure using concurrent application of multiple energy types to the structure, as well as to methods for determining operation settings for concurrent application of multiple energy sources to a structure. The invention finds particular utility in association with stress relieving structures such as manufactured parts, assemblies of multiple parts, welds, or other structures, wherein concurrent application of a thermal energy type and one or more time varying energy types can provide for temporal acceleration of the stress-relief operation not previously attainable using conventional stress-relief techniques. However, the invention may also be utilized in association with any property changing processes, such as those that may be modeled according to first order rate equations, wherein a plurality of energy types or sources are employed to accelerate the change in one or more physical properties, such as remaining internal or residual stress. In this regard, the invention is not limited to the particular examples set forth herein.
Referring initially to
The method 2 illustrates characterization of two energy application processes at 6 and 8, correlation of first order rate relationships and first order rate parameters (“P”) for different energy types at 10-14, selection of operational and time values or settings at 16-18 and application of multiple energy types at 22. It is noted at the outset that certain aspects of the invention provide methods including the characterization, correlation, setting selection, and energy application features described herein, while other methods of the present invention do not require all these acts. As one example, the invention provides methods for changing physical properties of structures that may require only certain of the acts illustrated for the exemplary method 2. The invention also provides methods for determining operational settings for concurrent application of multiple energy types that may not require all the acts illustrated in the exemplary method 2.
Beginning at 4, a first order rate relationship is determined at 6 for a first energy process and another first order rate relationship is determined at 8 for a second energy process. The first order rate relationships determined at 6 and 8 may be curves, mathematical expressions resulting from curve-fitting a series of data points, or any characterization or expression of a relationship between application of the corresponding energy type to the structure and a physical property of interest, for example, including but not limited to Larson-Miller relationships and/or equivalents thereof. Thus, the first order rate relationship determined at 6 relates application of the first energy type to the structure and the physical property of the structure, and the first order rate relationship determined at 8 characterizes the relationship between application of the second energy type to the structure and the physical property.
A first order rate relationship may be expressed as an equation used to model or represent a process that relies upon diffusion or dislocation motion over time. For example, stress-relief may be expressed as a first order rate equation representing passage of dislocations through a material. In one implementation of the invention, L-M equations may be derived by taking the log of the Arrhenius equation, and may be plotted as a curve of a physical property such as remaining internal or residual stress on a Y axis vs. a first order rate parameter (e.g., a Larson-Miller parameter) “P” on the X axis. In the example of stress-relief through application of thermal energy, a first order rate relationship can be plotted as remaining internal stress vs. a thermal first order rate parameter Pt, which incorporates both time and temperature. Alternatively, actual structures may be stressed and processed using thermal stress-relief operations at various times and temperatures in order to create a plot of several remaining internal stress vs. first order rate parameter values.
It is noted at this point that the physical property or characteristic of interest may be plotted on reverse scales along the Y axis of such relationship curves or plots within the scope of the invention. These and any other suitable techniques may be employed at 6 and 8 to determine the first order rate relationships for the first and second energy processes in accordance with the present invention. It is noted that more than two energy types may be provided to the structure in accordance with the invention and the appended claims, wherein corresponding first order rate relationships are employed to determine one or more operational settings and/or time values for acceleration of the change in the physical property of the structure. It is further noted that the first order rate relationships may be determined using any samples made of the same or similar materials as the structures to be processed, wherein the samples may, but need not, be of the same size, shape, etc., as the structures of interest. In this regard, the first order rate relationships and the first order rate parameters are applicable to any structure made of the material of interest, whereby the first order rate relationships and the parameters derived therefrom are universally applicable to any structure made from that material.
At 10-14, first order rate parameters and first order rate relationships are correlated for different energy types. Alternatively, as discussed below with respect to
In
The operational settings for concurrently providing two or more energy types to the structure are selected at 16 and 18 according to the first order rate parameters. One of a time value and an operational setting for the first energy type are selected according to one or more selection criteria, including but not limited to structural, equipment, or economic considerations, or arbitrarily. The other variable is then selected or determined according to the first and second parameters P1 and P2 using the first order rate relationship associated with the first energy process.
Toward that end, a third parameter P3 is optionally determined at 14 according to the parameters P1 and P2, such as by subtracting P2 from P1, wherein the time and/or operational settings can then be selected or determined in accordance with P3 at 18. The correlation of the first order rate parameters P1 and P2 in determining the operational and time settings for application of the first energy type results in the third parameter P3 that reflects a temporal acceleration achievable within the scope of the invention. This acceleration, in turn, facilitating stress-relief or implementation of other multiple energy type processes to change a physical property of a structure in less time and using less energy than was possible using previous methods. The inventor has appreciated that dislocation motion within a structure (e.g., such as during stress relief) occurs by a diffusion process and can be described by a first order rate equation:
where
D=rate of diffusion at some time, t
D0=initial rate of diffusion
Q=activation energy for reaction to begin
R=universal gas constant
T=temperature in degrees K (Kelvin).
Generally, the rate of stress relief obtained using thermal methods is driven by diffusion and can be described using the Arrhenius first order rate equation (2), named after the chemist Svandte Arrhenius:
where
r=rate of stress relief at some time, t
A=constant
H=free energy of the reaction
R=universal gas constant
T=temperature in degrees K.
The level of stress relief can be related to a first order rate relationship or equation. In one example, a Larson-Miller (L-M) equation is obtained by taking the log of the Arrhenius equation (2).
Assuming
and rearranging, the L-M equation for thermal stress relief may be expressed as:
where P is the L-M first order rate parameter. Other specific forms of first order rate expressions may be used, which are logarithmic expressions of an Arrhenius equation, wherein Larson-Miller or “L-M”, as used herein, is intended to include all such first order rate relationships and associated parameters which characterize a logarithmic expression of the Arrhenius equation. The first order rate equation (3) may be plotted as shown in
The inventor has appreciated that internal or residual stress relief can primarily be achieved by moving dislocations and reducing the overall dislocation density, and/or the density of other lattice defects such as stacking faults. A component of the overall stress state may be due to local lattice strains, but is anticipated to be of absolute values. This component is pure elastic strain and is local within the lattice. The formation of a dislocation will result when the strain reaches a certain value equivalent to the activation energy. No dislocation interaction will occur unless it is energetically favorable to do so. When energy, whether in the form of heat or any time-varying (e.g., oscillatory, periodic, pulsed) applied energy that can cause a pressure wave to be generated, is applied to a crystalline solid, energy is added to the dislocations that results in exciting their motion. Since any system will move to the lower energy state, the dislocations will try to attain a lower energy configuration by combining or annihilating, thus reducing the internal stresses in the material.
In addition, the inventor has appreciated that similar mathematical relationships should hold for any stress relief or other property changing method that causes dislocation motion using a diffusion process, and can thus be described by the Arrhenius first order rate equation (2) above. In accordance with the present invention, an acceleration results in the diffusion process through the concurrent application of multiple energy types to a structure for changing a physical property (e.g., stress relief) where the time and operational settings are determined as described herein. To further illustrate the acceleration results, the following derivation is provided for an example wherein thermal energy and vibration energy are concurrently applied to stress-relieve a structure.
Assuming that the matrix of the material or part in question can be partitioned into strained and non-strained portions, each with a concentration C, the total concentration may be expressed as:
C(total)=Cs(strained)+Cn(non-strained) (4)
In the case of strain relief, the following relationship holds:
Cs→Cn (5)
The rate of change of concentration of the strained portion during stress relief may be expressed as:
for the rate change of a reaction, where
where kv, is the Arrhenius equation for an oscillatory (vibratory) second energy type, and:
where kT is the Arrhenius equation for a thermal energy type.
The total for the combined method is:
Cs(t)=A e−(k
Cs(0)=A e−(k
Cs(t)=A·0+B=B (12)
A=Cs(0)−Cs(∞) (13)
Cs(t)=[Cs(0)−Cs(∞)]e−(k
Cs(t)=Cs(0)e−(k
from the boundary conditions of Cs (0)=1 and Cs (∞)=0. Thus:
Cs(t)=e−(k
Applying L'Hopital's rule and substituting for t at completion:
Cs(t)=e−(k
For the case of two diffusion-controlled processes occurring simultaneously then, where k=Arrhenius equation:
Taking the natural log:
Rearranging and converting to log:
Thus, for any combination of simultaneously applied stress relief processes, the sum of the stress relief process rates can be related to the first order rate parameter P. The oscillatory process, whether using sound, mechanical vibration, laser impulses, or some other oscillatory or time-varying applied energy process, is usually performed at a fixed temperature, where time, frequency, and amplitude are the variables. The vibration frequency and amplitude settings can be determined according to any suitable techniques so as to provide energy at or above the activation energy of the material of interest within the scope of the present invention, for example, by identifying a resonant frequency for the structure and the system in which the structure is to be mounted during processing, and selecting a frequency at or near the resonant frequency. In this regard, the frequency may be adjusted during processing as the resonance point changes, wherein the invention is not limited to fixed frequency or fixed amplitude implementations for providing time varying energy to the structure. The inventor has also appreciated that frequency may have a weak dependence on temperature, that can be calculated as follows:
c=8f, (21)
where
c=speed of sound in a material
8=f (specimen dimension)
f=frequency of harmonic.
Also:
where
Y=Young's modulus
ρ=density of material.
The relationship between density and temperature is expressed as:
ρ=ρ0(1+βT),
where β=3 cte and cte is the coefficient of thermal expansion. Solving for frequency:
Including the variation with temperature, the frequency is expressed as:
Consequently, as the temperature T changes, the working frequency will shift as well. Thus, for greatest efficiency of stress relief, frequency can be adjusted to a final value once the processing temperature is reached. For some oscillatory techniques, this is believed to be a very weak relationship at best and so adjustments in the oscillatory operational frequency setting may, but need not be made in accordance with the invention. Because of the cyclic lattice displacement by wave energy is proportional to Young's modulus E and to Poisson's ratio within a single method, the frequency/modulus relationship will be unique to an alloy and product form and thus may be advantageously determined by experimental procedures on the specific part in question.
Furthermore, the resonant frequency may change as a structure is stress relieved, wherein adjustments to the frequency of a time varying energy type may be made accordingly. In addition, frequency may also be highly dependent on part dimension. In general, though, specific frequency ranges for alloys can be predetermined for a specific method of frequency generation, whether sonic, laser, electrical, magnetic, mechanical, and microwave, or some other type, wherein adjustments according to specific structures and mounting systems are contemplated as falling within the scope of the invention.
Returning to
At 18, the other one of the operational setting and the time value is selected or determined according to the first order rate parameter P3 (e.g., or simply in accordance with P1 and P2), and also in accordance with the previously selected (e.g., independent) variable. For the above example where a temperature setting was selected at 16, the time value is determined at 18 according to the temperature setting and the parameter P3 for application of the first energy type to the structure using the first order rate relationship for the thermal energy process. The first order rate relationship is used, for example, by evaluating a corresponding first order rate equation (e.g., equation (3) above) for the first energy process, using the parameter P3 and the temperature setting as independent variables, and solving for the dependent variable, which is the time value in this example.
Operation settings for the second energy process can be selected according to other criteria for concurrent application of energy together with the first energy process. For example, frequency and/or amplitude settings may be selected for an oscillatory second energy process, wherein the structure, together with the system in which it is mounted for processing, is scanned to determine a resonant frequency. The processing frequency may then be chosen to be at or near the resonant frequency, wherein the frequency may be adjusted during processing. The frequency and amplitude of such an oscillatory second energy process are also adjusted such that the energy provided thereby is above an activation energy for the material of the structure.
It is noted in this regard, that whereas the first order rate relationships and first order rate parameters determined at 6-14 above are generally material specific and structure independent, that one or more of the operational settings for application of the energy types to the structure may be chosen according to material specific considerations (e.g., activation energy, etc.), as well as according to the specifics of a particular structure and/or a system in which the structure is being processed, such as mass, size, shape, or other system or structure characteristics. Once the operational and time settings or values have been selected at 16 and 18, the method 2 proceeds to 22, where the first and second energy processes are performed to apply the first and second energy types to the structure concurrently for at least the selected time value to achieve accelerated change in the physical property of the structure, before the method 2 ends at 24. In certain implementations of concurrent energy application in which one of the energy types is thermal, the heat may preferably be turned off first, leaving the oscillatory energy running until the part being processed (e.g., stress-relieved) achieves a minimum temperature for dislocation mobility.
As exemplified in
It is further noted that the various aspects of the invention may be employed in concurrent application of more than two energy types. Thus, the invention contemplates concurrent application of any integer number N different energy types, where N is a positive integer greater than 1, wherein first order rate relationships (e.g., derived or pre-existing) may be employed in determining N first order rate parameters (e.g., P1 . . . PN) corresponding to a desired physical property value. One or more operational settings and/or a time value may then be determined according to these parameters, or the parameters may be correlated using another parameter (e.g., PN+1=P1−(P2+P3+. . . +PN)). In addition, as illustrated and described below with respect to
Referring now to
In
The following table 1 illustrates the data points used in constructing the exemplary L-M curve plot 151 in
The method 102 continues at 108, where an oscillatory Larson-Miller curve (e.g., first order rate relationship) is determined for a vibration stress-relief process, such as the exemplary plot 152 in
The following table 2 illustrates the data points used in constructing the exemplary L-M curve 152 in
With the L-M relationship curves 151 and 152 for the thermal and oscillatory processes determined at 106 and 108, respectively, a first thermal L-M parameter Pt is determined at 110 that corresponds to a desired remaining internal stress value for the structure. In the illustrated example, 3% remaining internal stress was selected (e.g., 97% stress reduction) as the desired physical property value. Using this value along the Y axis 151y in
Referring again to the thermal L-M curve plot 151 in
At 120, the dependent variable is selected. In the illustrated example, the processing time t is determined according to the final L-M parameter Pf determined at 114 above (e.g., 6,000). In this example, the L-M equation (3) is solved for the time value t using the temperature T selected at 116 (e.g., 300 degrees F.), the constant (e.g., C=10 for aluminum), and the parameter Pf (e.g., 6,000), to yield a process time t=about 28.25 seconds for concurrent application of thermal and vibrational energy to achieve the desired 3% remaining internal stress value. One or more vibrational settings may be selected, for example frequency and/or amplitude, in order to provide oscillatory or time-varying energy at or above an activation energy of the aluminum material. One technique that may be employed involves determining a resonant frequency for the structure and the system in which the structure is to be processed, and selecting a frequency at or near (e.g., slightly below) the resonant frequency, wherein the frequency may be adjusted during processing. In this example, it is noted that separate application of heat at this temperature or of vibration alone for this time would not yield the desired stress-relief goal. Thus, the invention facilitates significant acceleration of stress-relief, as illustrated further below with respect to
As illustrated further in
The above techniques can then be used to determine Pt, Pv, and Pf using the first and second L-M relationships from either two first order rate relationships or from a single combined first order rate relationship characterizing concurrent application of multiple energy types. For example, where a thermal L-M curve and an oscillatory L-M curve are available, P3 may be calculated by subtracting P2 from P1. Once P3 is obtained, the previously selected temperature value may be used to determine the time for the concurrent energy application. The first and second energy types are applied concurrently for the appropriate time, beginning once the structure has reached the temperature value selected above, and then the thermal energy application is discontinued. The second (e.g., oscillatory) energy type may be continued thereafter until the structure temperature drops below activation energy for dislocation motion for improved stress relief results. This technique of continuing the second energy type after removal of the thermal energy source may advantageously prevent new residual stresses from being created by the thermal gradients inherently present during cooldown.
Sample #1 was stress-relieved using vibration only at a frequency of 53 Hz for 4 minutes, yielding the remaining internal stress shown in the curve 191. Sample #2 was stress-relieved using vibration only under similar frequency conditions for 24 minutes, resulting in the stress shown in curve 192. Sample #3 was stress-relieved using a thermal only process (no vibration) at 300 degrees F. for 4 minutes.
The fourth sample (#4) was stress relieved using concurrent application of thermal and vibratory energy for 4 minutes according to the invention, wherein the stresses are seen in the curve 194 to be approximately zero throughout the depth of the measurement. In the illustrated example, the fourth sample was processed generally according to the operational settings set for in the description of
To develop a first order rate relationship (e.g., curve, equation, model, etc.) that combines the effects of concurrent application of two or more energy types for stress relief or other property change, the following technique may be used at 206. For the example of thermal and oscillatory energy types, the frequency dependence on temperature is believed to be strongly dependent on alloy and part configuration (e.g. including the mass, size, shape, etc. of the structure being processed and the system in which the structure is mounted during processing) and weakly dependent on temperature. Therefore, a frequency may be selected that is appropriate to the system and alloy. Fine-tuning may be done but generally the frequency will not vary greatly over a wide range of temperatures if the rest of the system is stable. Test coupons or samples, preferably from a single lot of material (alloy, etc.) of interest, can be used to derive test results for plotting a combined first order rate relationship curve. For residual or internal stress relief, generally tensile specimens may be produced per ASTM E8 or some suitable test method and tested appropriately to failure. One half of each broken tensile coupon is used for testing (e.g., measuring) the baseline residual stress. The other half of each tensile coupon is stress relieved using concurrent application of thermal and oscillatory energy (e.g., using the frequency setting determined above) at varying times and temperatures chosen to yield a wide range of L-M parameters within the limits of the heat source and time available. The resulting (e.g., measured) remaining stress values (e.g., or calculated amounts of stress relief) can then be plotted vs. the corresponding L-M parameter to generate the combined relationship curve, wherein at least five points are ideally used to determine the L-M curve for the combined (e.g., concurrent) processes.
The resulting combined first order rate relationship curve from 206 (e.g., or a suitable pre-existing combined first order rate relationship) is then used to determine time and temperature settings and parameters for process application. A combined first order rate parameter Pc is determined at 208 from the combined first order rate curve or relationship, corresponding to a desired value of the physical property of interest. Time and operational settings are selected at 210 for the concurrently applied energy types according to the first order rate parameter Pc, and the first and second energy types are concurrently provided to the structure at 212 according to the selected operational and time settings, and the method 202 ends at 214.
Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (blocks, units, assemblies, devices, circuits, systems, etc.), the terms used to describe such components (including a reference to a “means”) are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”
Claims
1. A method of changing a physical property of a structure, comprising:
- providing energy of a first energy type to a structure by performing a first energy process according to an operational setting, at least one of the operational setting and a time value being selected according to a first order rate relationship for the first energy process, according to a first order rate relationship for a second energy process, and according to a desired physical property value; and
- providing energy of a second energy type to the structure at an energy level above an activation energy for the structure by performing the second energy process;
- wherein the first and second energy processes are performed concurrently for at least the time value;
- wherein the first order rate relationship for the first energy process relates application of the first energy type to the structure and a physical property of the structure; and
- wherein the first order rate relationship for the second energy process relates application of the second energy type to the structure and the physical property.
2. The method of claim 1, wherein the first energy type is thermal and wherein the second energy type is oscillatory.
3. The method of claim 2, wherein the operational setting is a temperature setting, wherein one of the temperature setting and the time value is selected according to the first order rate relationship for the first energy process, according to the first order rate relationship for the second energy process, according to the desired physical property value, and according to the other one of the temperature setting and the time value.
4. The method of claim 3, wherein the first order rate relationship for the first energy process is a first Larson-Miller relationship that relates application of thermal energy to the structure and the physical property, and wherein the first order rate relationship for the second energy process is a second Larson-Miller relationship that relates application of oscillatory energy to the structure and the physical property.
5. The method of claim 4, further comprising:
- determining a first Larson-Miller parameter according the first Larson-Miller relationship, the first Larson-Miller parameter corresponding to the desired physical property value;
- determining a second Larson-Miller parameter according to the second Larson-Miller relationship, the second Larson-Miller parameter corresponding to the desired physical property value;
- selecting a first one of the temperature setting and the time value;
- selecting a second one of the temperature setting and the time value according to the first and second Larson-Miller parameters, according to the first Larson-Miller relationship, and according to the first one of the temperature setting and the time value.
6. The method of claim 5, further comprising determining a third Larson-Miller parameter according to the first and second Larson-Miller parameters, wherein the second one of the temperature setting and the time value is selected according to the third Larson-Miller parameter, according to the first Larson-Miller relationship, and according to the first one of the temperature setting and the time value.
7. The method of claim 6, wherein determining the third Larson-Miller parameter comprises subtracting the second Larson-Miller parameter from the first Larson-Miller parameter.
8. The method of claim 7, wherein selecting the second one of the temperature setting and the time value comprises evaluating the first Larson-Miller relationship using the third Larson-Miller parameter and the first one of the temperature setting and the time value to obtain the second one of the temperature setting and the time value.
9. The method of claim 4, wherein the physical property is internal stress, and wherein the desired physical property value is one of a remaining internal stress value and an internal stress reduction value.
10. The method of claim 1, wherein the physical property is internal stress, and wherein the desired physical property value is one of a remaining internal stress value and an internal stress reduction value.
11. The method of claim 1, wherein the first order rate relationship for the first energy process is a first Larson-Miller relationship that relates application of the first energy type to the structure and the physical property, and wherein the first order rate relationship for the second energy process is a second Larson-Miller relationship that relates application of the second energy type to the structure and the physical property.
12. The method of claim 11, further comprising:
- determining a first Larson-Miller parameter according the first Larson-Miller relationship, the first Larson-Miller parameter corresponding to the desired physical property value;
- determining a second Larson-Miller parameter according to the second Larson-Miller relationship, the second Larson-Miller parameter corresponding to the desired physical property value;
- selecting a first one of the operational setting and the time value;
- selecting a second one of the operational setting and the time value according to the first and second Larson-Miller parameters, according to the first Larson-Miller relationship, and according to the first one of the operational setting and the time value.
13. The method of claim 12, further comprising determining a third Larson-Miller parameter by subtracting the second Larson-Miller parameter from the first Larson-Miller parameter, wherein the second one of the operational setting and the time value is selected according to the third Larson-Miller parameter, according to the first Larson-Miller relationship, and according to the first one of the operational setting and the time value.
14. The method of claim 13, wherein selecting the second one of the operational setting and the time value comprises evaluating the first Larson-Miller relationship using the third Larson-Miller parameter and the first one of the operational setting and the time value to obtain the second one of the operational setting and the time value.
15. The method of claim 1, wherein the second energy type is oscillatory, wherein the second energy type is provided to the structure at a frequency selected according to a resonant frequency of a system in which the structure is mounted while performing the first and second energy processes.
16. The method of claim 15, wherein the second energy type is provided to the structure at a frequency at or near the resonant frequency of the system.
17. The method of claim 1, wherein the second energy type is selected from the group consisting of sonic, laser, electrical, magnetic, mechanical vibration, and microwave.
18. A method of changing a physical property of a structure, comprising:
- providing energy of a first energy type to a structure by performing a first energy process according to an operational setting; and
- providing energy of a second energy type to the structure at an energy level above an activation energy for the structure by performing a second energy process;
- wherein the first and second energy processes are performed concurrently for at least a time value; and
- wherein one of the operational setting and the time value are selected according to a desired physical property value and according to a first order rate relationship that relates concurrent application of the first and second energy types to the structure and a physical property of the structure.
19. The method of claim 18, further comprising determining the Larson-Miller relationship that relates concurrent application of the first and second energy types to the structure and the physical property of the structure.
20. A method of stress-relieving a structure, comprising:
- determining a first Larson-Miller relationship that relates application of thermal energy to the structure and internal stress in the structure;
- determining a second Larson-Miller relationship that relates application of oscillatory energy to the structure and the internal stress in the structure;
- determining a first Larson-Miller parameter according the first Larson-Miller relationship and according to a desired internal stress value for the structure;
- determining a second Larson-Miller parameter according to the second Larson-Miller relationship and according to the desired internal stress value;
- determining a third Larson-Miller parameter according to the first and second Larson-Miller parameters by subtracting the second Larson-Miller parameter from the first Larson-Miller parameter;
- selecting a first one of a temperature setting and a time value;
- selecting a second one of the temperature setting and the time value according to the third Larson-Miller parameter, according to the first Larson-Miller relationship, and according to the first one of the temperature setting and the time value;
- selecting one or more oscillatory operational settings according to a resonant frequency of a system in which the structure is mounted;
- providing thermal energy to the structure according the thermal operational settings; and
- concurrently providing oscillatory energy to the structure according to the oscillatory operational settings for a time greater than or equal to the time value.
21. The method of claim 20, wherein selecting the second one of the temperature setting and the time value comprises solving a first Larson-Miller equation for the second one of the temperature setting and the time value first one of the temperature setting and the time value and the third Larson-Miller parameter, wherein the first Larson-Miller equation represents the first Larson-Miller relationship.
22. A method of determining operational settings and time values for concurrent application of multiple energy types to a structure to change a physical property of the structure, the method comprising:
- determining a first parameter according to a desired physical property value for the structure and according to a first order rate relationship for a first energy process that relates application of a first energy type to the structure and the physical property;
- determining a second parameter according the desired physical property value and according to a first order rate relationship for a second energy process that relates application of a second energy type to the structure and the physical property;
- selecting a first one of a time value and an operational setting for the first energy process;
- selecting a second one of the time value and the operational setting according to the first and second parameters, according to the first order rate relationship for the first energy process, and according to the first one of the time value and the operational setting.
23. The method of claim 22, further comprising:
- determining the first order rate relationship for the first energy process; and
- determining the first order rate relationship for the second energy process.
24. The method of claim 22, wherein the first order rate relationship for the first energy process is a first Larson-Miller relationship that relates application of the first energy type to the structure and the physical property, and wherein the first order rate relationship for the second energy process is a second Larson-Miller relationship that relates application of the second energy type to the structure and the physical property.
25. The method of claim 22, further comprising determining a third parameter according to the first and second, wherein the second one of the time value and the operational setting is selected according to the third parameter, according to the first order rate relationship for the first energy process, and according to the first one of the time value and the operational setting.
26. The method of claim 25, wherein determining the third parameter comprises subtracting the second parameter from the first parameter.
27. The method of claim 25, wherein selecting the second one of the time value and the operational setting comprises evaluating the first order rate relationship for the first energy process using the third parameter and the first one of the time value and the operational setting to obtain the second one of the time value and the operational setting.
28. The method of claim 22, wherein the physical property is internal stress, and wherein the desired physical property value is one of a remaining internal stress value and an internal stress reduction value.
29. A method of determining operational settings for concurrent application of multiple energy types to a structure to change a physical property of a structure, the method comprising:
- determining a first order rate relationship that relates concurrent application of first and second energy types to the structure and a physical property of the structure;
- determining a first order rate parameter according to the first order rate relationship, the first order rate parameter corresponding to a desired physical property value for the structure;
- selecting a first one of an operational setting for the first energy process and a time value; and
- selecting a second one of the operational setting and the time value according to the first order rate parameter, according to the first order rate relationship, and according to the first one of the operational setting and the time value.
30. The method of claim 29, further comprising determining the first order rate relationship that relates concurrent application of first and second energy types to the structure and a physical property of the structure.
31. A system for changing a property of a structure, comprising:
- a thermal energy source;
- an oscillatory energy source; and
- a control system that provides control signals to the thermal and oscillatory energy sources to control concurrent delivery of thermal and oscillatory energy from the thermal energy source and the oscillatory energy source to a structure.
32. The system of claim 31, further comprising transducers operatively coupled with the structure to provide feedback signals to the control system 180.
Type: Application
Filed: Jan 5, 2007
Publication Date: May 8, 2008
Inventor: Donna Murray Walker (Novi, MI)
Application Number: 11/620,047
International Classification: C21D 10/00 (20060101);