Abstract: A crack length sensor is fabricated in a rectangular or other geometrical form from a conductive powder impregnated polymer material. The long edges of the sensor are silver painted on both sides and the sensor is then bonded to a test specimen via an adhesive having sufficient thickness to also serve as an insulator. A lead wire is connected to each of the two outwardly facing silver painted edges. The resistance across the sensor changes continuously as a function of the crack length in the specimen and sensor.

Abstract: An element (e.g., a sensor) has a fine-line thin film of a conductor formed on a non-conductive substrate, and a change of physical properties (e.g., deformation) of the substrate or the ambient environment is detected through a change in physical properties of the conductor. The element is manufactured by forming a layered film, composed of a semiconductor and a conductor, on the substrate, and forcibly diffusing part of this film, e.g., by selective irradiation with high-energy ions, to form this part into an alloy semi-conductor, thereby providing a two-dimensional pattern of the fine lines of the conductor and the semiconductor. By arranging a plurality of fine lines of a conductor transversely to a direction of growth of a crack in the substrate, crack in the substrate is detected through a change in electrical resistance of the fine lines. A dissolved oxygen sensor, a hydrogen sensor, and an electrical conductivity sensor (of an ambient medium) can also be provided.

Abstract: A strain, crack and acoustic emission conformal structural health monitoring circuit with integral preprocessor and provisions for connectorization to a central processing system includes a strain gauge (11) having crack sensing traces (21), (23), and (25) sandwiched between a bottom layer (13) and a top layer (39). Strain gauge (11) is attached to an aircraft structural surface (51) to be monitored. Successive alternating layers of interconnecting sheet layers (61) and dielectric layers (63) joined by successive layers of non-structural adhesive (65) are added sufficient to effectively attenuate any stress forces, and forces directly from the strain and cracks, from traveling upward from the aircraft structural surface (51).

Abstract: A method and apparatus for inspecting a rupture initiation in an article. While a load is applied to the article repetitively, an elastic wave is monitored by an elastic wave sensor which converts it into an electric signal. The electric signal is fed to a signal transmission device having a capacity of transmitting low-frequency components of the electric signal. The transmitted electric signal is divided into successive signal segments. The successive signal segments are averaged to produce an averaged signal waveform informing the presence of a rupture initiation in the article.

Abstract: A fatigue testing system subjects a test specimen to a rotary stress applied about an axis at one or both ends which is perpendicular to the axis of the test specimen. The stress applied may be selected from sinusoidal, random, impulse or a signal generated by the stresses applied to an actual in service specimen. A servo applies the stress to the test specimen through a coupler and the changes in the electrical resistance of a portion of the test specimen is sensed to detect the initiation and propagation of a stress failure.

Abstract: A method for measuring fracture toughness of a brittle material is described which comprises the steps of impacting a sample of the material of preselected thickness and predetermined density and characteristic ultrasonic wave velocity C.sub.i at preselected velocity with a projectile of material having a known density and characteristic shock impedence corresponding to a predetermined characteristic ultrasonic wave velocity, determining the stress .sigma. at which the sample fractures upon impact of the projectile, and determining the fracture toughness of the sample as equal to 2.sigma.(c.sub.i t/.pi.)1/2, where t is the calculated time duration of a tensile pulse traveling the thickness of the sample.

Abstract: A fatigue crack growth rate measuring instrument serves to screen specimens of materials by cycling of load at a constant displacement and recording the load .upsilon. cycle characteristics and calculating the da/dN v. .DELTA. K for ascertaining if the specimen falls within or without the range of acceptability.

Abstract: A method and apparatus for determining the environmental stress crack resistance of plastic articles, such as polyethylene terephthalate containers, are provided. In accordance with the method of the invention, the internal chamber of a hollow plastic article is pressurized, the exterior of the base is then exposed to an environmental stress cracking agent, and it is then determined if crazing and/or changes in the base clearance of the plastic article have occurred. Subsequent increases in pressure and subsequent exposures and determinations yield information on the environmental stress cracking characteristics of the container.

Abstract: A method is provided for measuring crack growth in a solid comprising a sensor utilizing potential or voltage drop measurements across a preformed and propagating crack. Preferably the sensor is representative of a structural component and is exposed to an aggressive environment like that in which the structural component operates. Measured voltage values are plotted versus a distance at which the voltages are measured by a plurality of pairs of probes, and intercept values are obtained and used in combination with previously measured crack lengths in calculating subsequent crack lengths of a propagating crack.

Abstract: Apparatus is provided for obtaining a single crack in fatigue loading which emanates from a predetermined starting notch in a test specimen. This crack propagates in a direction in line with that of the applied Mode II load. The loading may be performed either monotonically or in a cyclic fatigue.

Abstract: A crack shear displacement gage for use in determining the critical load of a composite laminate by providing the laminate with a crack at one end, applying a load to near the center of the laminate, and measuring the shift in the longitudinal direction between the end portions of the laminate above and below the crack. The gage comprises a frame, a fixing member mounted on the frame and having a head for clamping the end portion of the laminate above the crack, a contact for contacting the end face of the end portion below the crack, a spring member for urging the contact against the end face, and a strain gage mounted on the spring member for detecting the strain of the spring member.

Abstract: A sample (16) with a cut (18) is mounted by clamps (14) between a stationary bar (10) and a movable bar (12). A motor driven cam (22) reciprocates the movable bar causing the samples to undergo cyclic deformation. A camera (C) is selectively positionable (B) to view each of the plurality of samples. A computer control (D) determines a cut length (60, 62, 64, 66) from each two dimensional electronic video image representation and stores it in a cut data memory (68). The next sampling time for each sample is calculated (72) generally in proportion to an inverse of the cut growth rate. The sampling order is re-ordered after each measurement and stored in a queuing table (78). A driver circuit (86) causes a motor (40) to position the camera in the appropriate positions to image the samples in the order indicated by the queuing table.

Abstract: A fixture capable of a brittle pre-crack introduction of prescribed shape and size in a ceramic specimen with high reproducibility comprises an anvil provided on the upper side thereof with a central groove perpendicularly intersecting a specimen to be mounted thereon for pre-crack introduction and a groove for positioning the specimen and a platelike pusher possessing a smooth and flat lower surface. To ensure stability of the brittle pre-crack introduction, the positioning groove in the anvil is so formed as to rise rectangularly in an equal length on either side of the central groove and the overall length of the positioning groove, i.e. the sum of the lengths of the raised portions plus the width of the central groove, is kept from exceeding the length of the specimen. To enhance the results of the introduction, the lower surface of the pusher is finished with roughness of not more than 0.8S and flatness of not more than 0.01 mm.

Abstract: A method of determining the mechanical behavior of solid materials by using stress field modified miniature specimens. The method is an improvement in the method of determining mechanical behavior information from specimens only so large as to have at least a volume or smallest dimension sufficient to satisfy continuum behavior in all directions. Mechanical behavior of the material is determined from the measurements taken during the loading of the specimen resulting in the formation of cracks and/or the further propagation of cracks in the miniature specimen. The specimens include construction features for applying additional stress field modifying loads upon the specimens during the test. These additional loads result in a desired stress state in the specimen which could not be achieved otherwise. A particular example is the introduction of a transverse tensile load during a bend test to increase the transverse stress field to achieve plane strain conditions in a thin specimen.

Abstract: A carbon composite tensile test specimen for high temperature testing and a method of fabricating the same are disclosed. A plurality of holes are drilled in first and second end sections of the specimen and then the end sections are electroplated with nickel. The nickel plating of the end sections prevents breakage of the ends in the jaws of a tensile testing apparatus. For high-temperature testing, a standard-sized specimen may be used with the jaws in the hot zone.

Abstract: A method of determining fracture mode transition behavior (FMTB) of solid materials by using stress field modified miniature specimens. The method is an improvement in the method of determining mechanical behavior information from specimens only so large as to have at least a volume or smallest dimension sufficient to satisfy continuum behavior in all directions. FMTB of the material is determined from the measurements taken during the loading of the specimen resulting in the formation of cracks and/or the further propagation of cracks in the miniature specimen and/or fracture. The specimens are provided with grooves that induce additinal stress field modifying stress components in the specimens during the test. These additional stress components result in a desired stress state in the specimen which could not be achieved otherwise. The methods are useful in determining FMTB for the material, when the specimen thickness is smaller than previously thought necessary for valid FMTB determinations.

Abstract: The fracture energy of a material is determined by first measuring the length of a profile of a section through a fractured surface of the material taken on a plane perpendicular to the mean plane of that surface, then determining the fractal dimensionality of the surface. From this, the yield strength of the material, and the Young's Modulus of that material, the fracture energy is calculated.

Abstract: An apparatus for measuring the adhesion force of a thin film deposited on a substrate of a specimen. The apparatus comprises an inclining mechanism for mounting a sample dish with a specimen inclined by a predetermined angle with respect to the sample dish, an indentor disposed above the specimen for deforming the specimen by indentation, a driver for driving the indentor perpendicular to the sample dish, a load transducer for measuring a load applied to the specimen by the indentor, a sensor for sensing propagation of a crack produced in the specimen by the load, a displacement gage interlocked with the driver for measuring a penetration depth of the indentor, and a measuring mechanism for measuring the adhesion force of the thin film to the substrate.

Abstract: A method and apparatus for determining crack growth in an elastomer. A horizontally elongate elastomeric test specimen is cyclically stretched crosswise by upper and lower rigid plates contiguously attached to the long edges on both sides. The lengthwise growth of a crack induced by a small cut at one vertical edge of the specimen is determined by measuring the stretching force at each end. The lower plate is reciprocated by a hydraulic actuator relative to the upper plate. Two load cells measure the forces at each end of the specimen. With the use of a computer program and the relative forces measured by the load cells, the crack growth can be calculated.

Abstract: An ultrasonic apparatus determines crack opening load by placing a transmit transducer on one side of the crack and a receive transducer on the opposite side of the crack. An acoustic signal passing through a region of the crack is mechanically rectified to produce a second harmonic of an input signal. A harmonic output signal of the receive transducer is converted into an electrical signal and the peak harmonic amplitude is determined while increasing a tension load on the specimen. The peak harmonic amplitude indicates crack opening load.

Abstract: A novel test specimen configuration and modified ring test method for determining the fracture toughness, K.sub.Ic, using rock core is disclosed. The use of a truncated hollow cylindrical specimen under compressive load avoids the development of a large process zone (microcracked region) during testing, thus allowing accurate fracture toughness measurements on subsized specimens. Results using soft sandstones and Indiana limestone validate the procedure.

Abstract: An impact testing apparatus and process are provided. The apparatus comprises a thickness verifier to measure the thickness of each specimen. The apparatus further comprises a notcher and a notch verifier which are operative to first cut notches in a test group of specimens and to subsequently verify the accuracy of the notches. The apparatus further comprises a robotic gripper to sequentially deliver specimens to a vise for impact testing. The impact tester of the apparatus is operative to automatically assess the impact on each specimen. Additionally, the impact tester comprises optical sensors to assess the type of break of each specimen subjected to the impact test. A control unit receives input data from the various components of the apparatus, analyzes the data and prepares test reports.

Abstract: A method system for assessing the safety of a rotor of a shrinkage fitted type wherein an opening displacement of a crack is determined an elastic-plastic fracture method and a reduction in shrinkage fitting force is calculated based on the crack opening displacement. The safety of the rotor is assessed based on the reduction in shrinkage fitting force caused to occur by the opening of the crack.

Abstract: The device concerns a method for detecting the position of at least one point of the crack front within a part (4) subjected to fatique stresses or to a ductile rupture. An ultrasonic beam is used focused in the plane P of the crack growth; the axis of this beam forms an angle comprised between 50.degree. and 80.degree. with P. The beam is displaced until the echo passes through a maximum, in which case the focusing is situated at the tip of the crack in the plane of displacement. The invention also concerns a device for the implementation of the method.

Abstract: A method of ultrasonic flaw detection in cast stainless steel components incorporating the steps of determining the nature of the microstructure of the cast stainless steel at the site of the flaw detection measurements by ultrasonic elements independent of the component thickness at the site; choosing from a plurality of flaw detection techniques, one such technique appropriate to the nature of the microstructure as determined and detecting flaws by use of the chosen technique.

Abstract: The disclosed method introduces a pressure effectivity factor h, so as to continuously determine fracture toughness K.sub.IC of rock during core boring by using the equation ofK.sub.IC =0.346.sqroot.N/.epsilon.L.multidot.hQ/B; andhere, N is the revolving speed of a coring bit, Q is the pressure supplied to it, L is its drilling speed, B is the width of its bit face, and .epsilon. is the number of rows of its face stones. The pressure effectivity factor h is predetermined by using both a core whose fracture toughness is measured by the ISRM (International Society for Rock Mechanics) method and the above constants which are used in boring the core.

Abstract: Method and system for monitoring cracks liable to appear and/or to grow in one point of a loaded structure. According to the invention, a theoretical increase of the length of the crack is cumulatively calculated, as and when the stresses are exerted, from said initial length, so as to determine an instant theoretical crack length; said instant theoretical length is permanently compared to said maximum acceptable length, and said point is inspected as soon as said instant theoretical length reaches said maximum acceptable length.

Abstract: A method and device are disclosed for the determination of the environmental stress crack resistance (ESCR) of polymer articles made from polymers such as acrylonitrile-butadiene-styrene copolymers, polycarbonate, polystyrene and blends thereof. The method and device involve the external application of stress to an unstressed test article which has been exposed to a stress cracking agent. The stress is induced by means of a weight located below the horizontal plane of the plastic article. The time between the application of stress and the cracking of the test article is measured to compute a characteristic ESCR parameter and thereby evaluate the environmental stress crack resistance of the article.

Abstract: A fatigue test apparatus in which a specimen to be tested is attached at its ends to a pair of opposing pistons positioned within a pair of opposing cylinders. The cylinders are attached to a support frame such that the specimen is oriented substantially vertically. In a preferred embodiment, the specimen is enclosed in a heat chamber to test at high temperatures. Each of the pistons is attached to a shaft having a weight at its end and the weights are drivingly connected to a pair of shakers which are actuated to vibrate 180.degree. out of phase with each other. The cylinders are pressurized to exert a static tensile load on the specimen, and the shakers are actuated to exert a dynamic tensile load which is superimposed on the static load and travels through the weights, shafts and pistons to the specimen.

Abstract: A distance between a distal end of a crack formed in a fatigue test piece on which a reference line is scribed, and the reference line, is monitored. The reference line and the crack are scanned with an ITV camera to prepare the fatigue test piece having the crack of a predetermined length. Luminance levels are integrated from a video signal obtained by scanning each raster in the same direction as that of the reference line to obtain a maximum luminance level, and the reference line position is detected from the maximum luminance level. At the same time, continuity of a high-level value is discriminated from the video signal, and a crack distal end position is detected from the discrimination result. A difference between both the detected positions is calculated, and the test piece is machined so that the difference corresponds to the predetermined length.

Abstract: A method and apparatus for determining crack initiation and propagation in metals subjected to environmental conditions encountered in drilling deep wells wherein strain sensors are used to measure crack initiation and propagation so that a prediction can be made about the life expectancy of the metal in actual operating conditions.

Abstract: A method is provided for measuring crack growth within a material utilizing reversing d.c. potential measurements across a preformed crack. Preferably, the material is representative of structural components of interest and the material is located within the aggressive environment of such components. The measured values are plotted versus distance to obtain intercept values. These intercept values correspond to the depth of the crack at the time the measured values were obtained.

Abstract: A sensor (10) responding to the action a force comprises a base body (12) and a force takeup element (14) which is connected to the base body (12) via at least one support element (16, 18, 20, 22). The support element deforms under the influence of a force acting on the takeup element (14). In the deformation region between each support element (16, 18, 20, 22) and the force takeup element (14) a measuring member (32, 34, 36, 38) is disposed which reacts to the deformation with a change in a physical parameter. An uninterrupted conductor path (44) is provided which extends from a first terminal land (46) on the base body (12) via each support element (16, 18, 20, 22) and the force takeup element (14) to a second terminal land (48) on the base body (12).

Abstract: A test specimen has a carefully controlled series of cracks on its surface and is useful for evaluating surface penetrants employed in non-destructive inspection. A flat brass substrate has a nickel electroplating on one surface, which plating varies in thickness along the length of the panel. The opposing side of the panel has a multiplicity of grooves which locally concentrate strain in the plating when the panel is bent during manufacture, thus providing a crack associated with each groove. In a preferred embodiment, the texture of the cracked surface varies across the panel in the same direction in which the cracks run, thus enabling evaluation of the usefulness of penetrants in finding different size cracks under different surface finish conditions.

Abstract: A device for monitoring the fatigue life of a structural member is comprised of at least one and preferably a plurality of substantially flat, elongated coupons which are fabricated of the same material as that of the member being monitored. The coupons are secured in parallel to the member so that they all experience the same strain history as the member. Each of the coupons includes a different stress concentrating notch pattern so that the application of the same strain to all of the coupons results in the development of different stress concentrations within the coupons. The development of different stress concentrations within the coupons causes each coupon to have a different fatigue life, the fatigue life of each coupon being a predetermined percentage of the fatigue life of the structural member being monitored.

Abstract: The moment of beginning of fracture in breaking strength tests of ferromatic samples (7) is detected by the spreading of a magnetic field out of the incipient crack in the magnetized sample by means of a magnetic probe (23). Until the beginning of the crack, the magnetic field runs through the magnetized sample. The voltage induced in the magnetic probe at the moment the crack starts is used to stop a time measuring counter which was reset and turned on at the beginning of the stressing of the sample.

Abstract: Apparatus for monitoring and measuring the growth of a crack in an elastic specimen. The specimen is repeatedly flexed by a piston at a set frequency and periodically slowed to a substantially lower frequency during which time a line scan camera monitors the length of the crack. The camera is positioned such that the specimen is drawn through the scan line thereof. The camera is calibrated such that the output signal from the camera correlates directly to the cracklength. This output signal is digitized, received, and stored by a digital processor for use in determining the crack growth rate.

Abstract: Structural failures, as in metal aircraft structures, are rapidly detected and measured by use of a new detection system comprising a thin film adhesively bonded to the metal structural surface to be monitored, said film containing a plurality of thin continuous strips which are adapted to be broken when a crack appears under the strips, said strips being substantially parallel but insulated from each other and the metal structural surface and arranged in a pattern such that there is frequent change in direction of the strips as in a zig-zag or rectangular pattern, each of said strips constituting a separate circuit joined to an electric power source and a sensing and recording means capable of detecting and recording any circuit failure caused by disruption of the metal strip, said disruption being caused by the formation of a crack under the said strip.

Abstract: An acoustic crack detection method and device in which an impact is produced between an actually tested metal piece and an anvil. This impact generates an acoustic wave formed of a plurality of components, one of these wave components being produced by vibrations of the metal piece and having a frequency indicating a cracked or uncracked state of this piece. A microphone senses the acoustic wave generated by the impact and a measuring circuit receives the signal from the microphone for measuring the energy, within a predetermined time gate and within a predetermined frequency bandwidth, of the wave component of interest. The measured energy is compared with a reference level in order to determine if the actually tested metal piece is cracked or not.

Abstract: Aluminum alloy armor weld joints are ballistic shock tested by first sepaely determining the ballistic impact capability of the components to be joined by the weldment by firing a plate proofing projectile at 0.degree. obliquity at each of said components at different striking velocities. The welded joint designs and welding procedures are then tested by firing the same projectile at the same angle at each of the components of the weldment so that the projectile impacts each component in the vicinity of the weld at a velocity comparable to the critical velocity of the component being impacted.

Abstract: Apparatus for automatically inspecting brittle articles such as containers of glass and the like has element (50) which applies a force to each article in turn, so as to propagate any cracks in the glass. Ultrasonic vibrations created during the propagation of a crack is transmitted via a constant laminar stream of liquid (76) from which the vibrations are received by a transducer head (94) of the crack detection equipment, which triggers an alarm, a visual display and/or an automatic marking or rejection device.

Abstract: Early detection of cracks in structural members subject to stress is accomplished before cracks traverse the member by(a) affixing multiple liquid impermeable enclosures to the material to be monitored such that a crack forming in the monitored material will provide passage for liquid to enter the enclosures either through the monitored materials or by destroying the integrity of said liquid impermeable enclosures;(b) sealing a resistor having a known value onto each of the enclosures, each of the resistors having one lead capable of liquid contact within the enclosure, said lead electrically isolated from the material being monitored and/or a second wire in the enclosures;(c) forming a circuit connecting the multiple enclosures wherein the opposite resistor leads in each enclosure are connected by insulated wire to means for measuring resistance and/or conductance wherein each resistor alone or together with any combination of other resistors in said enclosures within the circuit provides a unique total resi

Abstract: Expandable jaws comprise lever arms pivoted together at their base and forming a bifurcated Y-shaped assembly which acts by force application to fracture a specimen. The force is applied through and measured by deflection of a force gauge U-spring having one side fixed to one of the lever arms remote from the specimen and the other cable connected via a threaded shaft and knob to the other lever arm. A dial reads directly the force required to effect fracture toughness, fatigue crack, growth resistance or stress corrosion crack growth resistance of slotted short rod/bar specimens.

Abstract: The present invention relates to a process for producing a crack in a tube.The tube is placed in a groove made in a support, a load is applied by means of a plate disposed along a generatrix of the tube in order to start a crack and permit the propagation thereof. Load application is stopped when the crack has reached the desired dimensions.Application is to the production of faults having a controlled size in a tubular member.

Abstract: A method and apparatus for generating a measurable natural crack includes forming a primary notch in the surface of a solid material. A non-sustained single pressure pulse is then generated in the vicinity of the primary notch, resulting in the formation of a shock wave which travels through the material. The shock wave creates a measurable natural crack within the material which extends from the primary notch. The natural crack formed possesses predictable geometry, location and orientation.

Abstract: For the purpose of monitoring the formation and propagation of cracks in machine parts and components, especially in the rotating shafts of prime movers and mechanical equipment, at least one hole is drilled in the uncracked section of the component, this drilled hole intersecting the plane of the crack which is to be expected and being filled with a gas or a liquid, the gas or liquid being adjusted to a pressure above the ambient pressure, and the drilled hole being provided with a closure with respect to the environment and being connected, via a line, to an instrument for indicating a fall in the pressure of the medium present in the drilled hole.

Abstract: A damping device for use with acoustic information generation machines for isolating a generation portion of the generation device from contamination by extraneous acoustic emissions. A metal isolation piece consisting of a shape-memory alloy is disposed between an extraneous noise source and the generation portion of the device. Acoustic information generation devices in accordance with the present invention include phonograph record playing devices and testing devices for recording acoustic signals generated upon stressing a test piece. Thus, the present invention provides improved phonograph record playing devices and an improved testing device.

Abstract: A method of determining the impact fracture toughness K.sub.id of construction materials, for example structural steels or plastic materials, without the need of performing a load measurement at the striking hammer is provided. The elastic response of the specimen to the impact process, i.e. the dynamic stress intensity factor versus time curve, K.sub.I.sup.dyn (t), is determined in pre-experiments. The shadow optical method of caustics in reflection with an appropriate high strength steel is utilized for establishing this impact response curve. The dynamic fracture toughness for a given constructional material is then determined by performing an impact experiment and measuring the time to fracture t.sub.f. K.sub.Id is obtained from the measured t.sub.f -value and the pre-established impact response curve which corresponds to the experimental test conditions. The presented measuring procedure is used for determining the dynamic fracture toughness of two different steels at different test temperatures.

Abstract: A fatigue damage indicator includes a thin plate mounted between or integral with two members to which a stress is to be applied, the disposition of the two members being such that the thin plate is stressed in shear.Slots extending in the direction of the applied stress may be provided to ensure that cracks formed by fatigue stress propagate in a desired direction and the crack propagation is designed to ensure that a part of the plate becomes detached or is bent substantially away.

Abstract: A closed system, impact-fatigue test machine for grinding balls comprised of a vertically extending guide member and a lift conveyor wherein the guide member lies above a recessed anvil and defines in its center a longitudinal opening. Each grinding ball is carried upwardly by the conveyor to an opening in the upper portion of the guide member and then is dropped into the guide member to land laterally supported, upon an earlier dropped grinding ball which rests on the anvil below. The earlier dropped ball is then pushed from the anvil toward the conveyor causing the dropped ball to impact the anvil below. The number of dropping cycles that each ball can tolerate without fracture is counted by a counter. Fracture of the balls is detected by a fracture detector.