Abstract: A drive assembly for conveyor belt comprises a pair of opposing end plates for mounting a conveyor drive and mounting assemblies for mounting at least one of a position limiter assembly, a scraper assembly, a combined limiter-scraper assembly and side guards. The scraper assembly and combined limiter-scraper assembly include a leaf spring that is selectively tensioned by a tensioning element on an end plate to bias the scraper blade of the scraper assembly into an operational position.

Abstract: Current busbars may be made of copper and have at least one nominal bending point which has been locally heated and thereby softened prior to being installed. Such components may be used in power electronic circuits, especially an inverter, in fully electrical and partially electrical (hybrid) vehicles.

Abstract: A method for forming a piece of a sheet metal is performed by positioning a consumable body, made of metal, proximate to the piece of the sheet metal. The consumable body is rapidly vaporized, and the gas pressure generated thereby is directed into the piece of the sheet metal. This results in acceleration of the piece of sheet metal, and it is collided into a stationary body at a velocity, generally in excess of 200 m/s. Depending upon the type of stationary body, the piece of sheet metal is deformed into a predetermined shape or is welded onto the stationary body. The vaporization is accomplished by passing a high current of electricity into the consumable body. The effect of the vaporized metal may be augmented by additional components in the consumable body.

Abstract: A method of reinforcing a part formed from a sheet metal panel that has a predetermined area that requires reinforcement by forming a grid pattern of V-shaped channels in the predetermined area. The grid pattern may be formed by wire electrodes in an electro-hydraulic forming tool having a one-sided die. Alternatively, the grid pattern may be formed by a plurality of electrodes that are arranged in an array that is aligned in at least two directions on the opposite side of the part from the one-sided die.

Abstract: A forming method includes using at least one forming tool to form a material of a workpiece and using a lubricant between the material and the at least one forming tool. The lubricant has a viscosity that is modifiable by applying or varying a field.

Abstract: A method of welding two workpieces together is described. A conductor in electrical communication with a pulse circuit is provided. A portion of the second workpiece is located adjacent the conductor. The two workpieces are also located together. A portion, or all, of one workpiece is welded to the other by applying a pulse current to one of the workpieces. A method of forming a workpiece is disclosed using a pulse current to move the workpiece into a desired shape.

Abstract: A tool for modifying a workpiece by either trimming or joining the workpiece. The tool is an electro-hydraulic tool that uses a pulse transmitted through a liquid to trim a workpiece or to join two thicknesses of metal together. A method of trimming the workpiece includes the steps of providing a high voltage discharge in a liquid that drives a workpiece into engagement with a cutting edge of a tool steel insert. A method of joining two or more thicknesses of metal together includes the step of creating a high voltage discharge through an electrode that accelerates one panel or thickness of metal into a second panel that is held stationary by a backing plate while the first thickness of metal is accelerated into the second thickness of metal.

Abstract: A magnetic pulse forming device for a roll forming system includes forward and rearward guide rolling means, a guiding means including guiding rails disposed on the base between the forward and rearward guide rolling means and guide frames movably disposed on the guiding rails, a magnetic forming means including an upper plate connecting the guide frames corresponding to an upper surface of the forming beam, a coil housing assembled to the upper plate and a coil disposed within the coil housing and electrically connected to a pulse generator to generate a magnetic pulse by input current, a movement detector, a synchronizing motor connected to the lead screw to rotate the lead screw and a screw housing engaged with the lead screw and moving the guide frames with the forming beam in the process direction by rotation of the lead screw, and a forming mold.

Abstract: In an arrangement for bending tubular workpieces, in which a workpiece is supplied to a bending head for bending and is supported from the inside during the bending process in the bending region by means of a mandrel introduced into the workpiece, with the mandrel comprising a mandrel element and a traveler, sitting movably in the workpiece and the traveler being longitudinally displaceable in the workpiece by means of a feed device (14), the traveler is produced from a magnetizable material and the feed device comprises a magnetic device which is applied to a position corresponding to the position of the traveler outside of the workpiece, with a positive magnetic engagement being formed between the magnetic device and the traveler, with the traveler being displaceable in the workpiece via the magnetic device.

Abstract: A can manufacturing device in which a tool supporting base has: a plurality of working tool units that support a plurality of working tools; a supporting member that supports a plurality of working tool units; and a linear driving mechanism that reciprocates the working tool units with respect to the supporting member in the axial direction of a workpiece. The linear driving mechanism has: a guide section that is fixed on the supporting member with a base plate therebetween; a slide rail that is fixed on the working tool unit and slides along the guide section; an electromagnetic coil provided on the base plate; a magnet plate that is provided on the working tool unit and generates, between the electromagnetic coil and itself, a thrust force for the guide section; and a supply pipe that is provided at the electromagnetic coil and supplies coolant to the inside of the electromagnetic coil.

Abstract: A method for improving mechanical properties of a magnetically activatable material for reducing ripples in the magnetically activatable material. The method includes conveying the magnetically activatable material using at least one conveying device through a processing region, and applying a force on the magnetically activatable material in the processing region to deform the magnetically activatable material. The force is contactlessly applied by a plurality of magnet groups that form a plurality of magnetic fields, and which are arranged in a material flow direction side by side or one behind another. The plurality of magnetic fields are applied in or opposite to the material flow direction, and travel along one of the plurality of magnet groups or between two of the plurality of magnet groups.

Abstract: Electromagnetic forming methods suitable for creating surface features on a shape memory alloy are described. Features may be created over a range of scales, including those suitable for the generation of holographic images. Features, images, or patterns may be made capable of reversibly appearing and disappearing as a result of changes in temperature and may include temperature sensitive displays for automotive and other applications.

Abstract: An apparatus for applying labels to products includes a label application station at which the labels are applied to a product and an application head movably mounted relative to a base for movement between a first operative loading position spaced from the label application station and a second operative application position at which the application head applies at least one label to a product positioned at the label application station. An electrically actuated solenoid is operatively connected to the application head to move the application head between the first and second operative positions.

Abstract: Methods and devices provide for high velocity forming of medical device casings. The high velocity forming may be produced by creating a pressure wave within a liquid contained by an enclosure. A die and a workpiece adjacent to the die are in the path of the pressure wave within the enclosure and the pressure wave forces the workpiece to conform to the contours of the die. Objects may be adhered to the die to provide for customized contours. Trimming features may be included within the enclosure to trim excess material from a formed workpiece as an integral part of the forming process. Various other features may also be provided within the enclosure including a diffuser to disperse the pressure wave. The workpiece may be of various forms including flat sheet stock.

Abstract: An electronic casing and a method of manufacturing the same are provided. The method includes the following steps. Step (a): a metal laminate and a die of a predetermined shape are provided. The metal laminate comprises a metal top layer and a metal bottom layer that are bonded by interface atom diffusion. Step (b): the metal laminate is processed to form a casing blank by using the die, and the casing blank has at least one turning portion. Step (c): a profiler of a predetermined shape and an electromagnetic forming device are provided. Step (d): the casing blank is attached to the profiler, and the electromagnetic forming device is disposed at a position corresponding to the turning portion. Step (e): the electromagnetic forming device is activated, so that the casing blank has a shape corresponding to the predetermined shape of the profiler.

Abstract: Electromagnetic forming can lead to better formability along with additional benefits. The spatial distribution of forming pressure in electromagnetic forming can be controlled by the configuration of the actuator. A type of actuator is discussed which gives a uniform pressure distribution in forming. It also provides a mechanically robust design and has a high efficiency for flat sheet forming.

Abstract: The invention relates to a method of providing an armature housing having the steps of providing a solid cylinder of malleable material having a first part and a second part; raising at least a part of a perimeter of the first part in a direction away from the second part for defining a raised wall; compressing the second part in an axial direction toward the first part, resulting in a flattened disc generally perpendicular to the first part; and wherein the first part, second part, and at least part of the perimeter are all integrally connected as a single piece.

Abstract: A method of using an electromagnetic forming machine to hem a panel assembly includes providing an inner panel and an outer panel. The outer panel has a plurality of flanges and a plurality of relief areas. An electric forming machine is provided having a coil for discharging electric energy to generate a magnetic field. The inner panel is positioned such that portions of the outer edge of the inner panel are aligned with the flanges of the outer panel to form a loose assembly of panels. The loose assembly of panels is positioned proximate the electromagnetic forming machine such that the coil surrounds the flanges and is disposed substantially coplanar with a plane formed by the relief areas. The electromagnetic forming machine is activated to generate a magnetic field causing the flanges to bend over.

Abstract: Apparatus for forming an article from a blank of sheet metal including electromagnet field producing means disposed adjacent a die cavity for selectively energizing the field producing means for restraining movement of the blank during the forming thereof.

Abstract: A tooling method for calibrating a partially formed metal part in an electro-hydraulic forming tool. The method includes loading a partially formed metal part onto a forming surface of a die. The part is then clamped onto the forming surface and the part is pulsed with a high rate energy pulse to overcome a spring-back effect in the part. The EHF calibration tool includes a punch to which a part is held by clamps while a capacitive discharge circuit is discharged through electrodes provided in the tool. Upon discharge of the capacitive discharge circuit through the electrodes, a high rate energy pulse is applied through a liquid to calibrate the part.

Abstract: The present invention provides a linear motor mounted press machine that generate an optimum thrust for a press tonnage to perform different machining operations including one requiring a greater press tonnage and one requiring a high speed and a smaller press tonnage in an energy efficient manner. A linear motor mounted press machine includes a first linear motor 11, a second linear motor 12 that produces a thrust lower than or equivalent to that of the first linear motor 11, and a coupling switching mechanism 13 that releasably couples output shafts 30, 34 of the first and second linear motor 11, 12 together. A press tool 6 is driven forward and backward by the output shaft 34 of the second linear motor 12. Each of first and second linear motors 11, 12 is a unit linear motor assembly having a plurality of unit linear motors 15 arranged around a press working axis center P. The number of the unit linear motors 15 of the second linear motor 12 is the same as or smaller than that of the first linear motor 11.

Abstract: Shot for use in a peening installation, the shot having: hardness greater than or equal to 800 HV; density greater than or equal to 8 g/cm3; and pieces having a maximum dimension less than or equal to 1.5 mm.

Abstract: A system for ultrasonically peeing surfaces includes a sonotrode comprising a body material and a vibrating surface, the vibrating surface coated with a coating material having a hardness greater than the body material, a treatment chamber defined at least in part by the vibrating surface, and at least one piece of shot within the treatment chamber to be excited by the vibrating surface of the sonotrode, the at least one piece of shot having a hardness greater than or equal to 800 HV.

Abstract: An electrohydraulic forming (EHF) tool having a pair of electrodes that can be used to generate a shockwave to facilitate forming a sheet metal blank against a forming die. The electrodes may be adjusted during the course of operation. This may be useful should continued use cause their efficiency to drop below a desired threshold.

Abstract: The present invention is related to a stamping machine for stamping an item at a high speed. The stamping machine comprises a case having an opening, at least one guide shaft formed in an interior of the case and extending in a first direction, a pedestal movable along the at least one guide shaft in the first direction for holding the worked item, and a stamping part for pressing the working tool against the worked item held on the pedestal. The stamping part comprises at least one guide shaft formed in an interior of the stamping part and extending in a second direction, a head driver formed in the interior of the stamping part and extending in the second direction, and a stamping head movable along the at least one guide shaft and the head driver in the second direction, wherein the stamping head is proximal to the pedestal.

Abstract: A metal mold for electromagnetic forming, with the inner peripheral face thereof, serving as a forming face, is disposed on the outer peripheral side of a columnar workpiece, and a coil for electromagnetic forming is disposed on the inner peripheral side of the columnar workpiece. In a state of a configuration as described, electric energy is thrown into the coil for the electromagnetic forming, and the columnar workpiece is caused to undergo flaring to be thereby pressed against the forming face of the metal mold for the electromagnetic forming, so as to be turned into a shape corresponding to the forming face by means of the electromagnetic forming, thus obtaining a wheel rim. A disc is welded to the wheel rim obtained, and curling is applied to outer edges of the wheel rim. With the adoption of a method of manufacturing an automotive wheel, a manufacturing process as a whole is enhanced in efficiency.

Abstract: An electromagnetic forming device for a sheet of material is provided. The electromagnetic forming device includes a fixing base, a magnetic concentration block, an electromagnetic actuator, and a die. The fixing base has a groove. The magnetic concentration block is disposed in the groove of the fixing base, and has an accommodating space therein, which is in communication with a surface of the magnetic concentration block via a slit. The electromagnetic actuator, used to generate a magnetic field, is disposed in the accommodating space of the magnetic concentration block, but does not contact the magnetic concentration block. The die and the magnetic concentration block are separated by a gap, and a sheet of material can be disposed in the gap. As the magnetic concentration block is a block, eddy currents in the magnetic concentration block are distributed uniformly, so the generated magnetic field is also distributed uniformly, thus exerting a uniform forming force on the sheet of material.

Abstract: A device for electromagnetic high energy pulse deformation of workpieces of an electrically conductive material has a deformation tool including a coil carrier and at least two partial coils arranged on the coil carrier, at least one surge current generator to which the partial coils are connected so that magnetic fields of the partial coils superpose to form a resulting magnetic field which acts on the workpiece, the partial coils being formed as spiral coils which are formed identically with respect to inductivity, electrical resistance, winding number and forming, and each of the partial coils extending on the coil carrier from an inner starting point in an identical form and with a corresponding identical distance to a neighboring one of the partial coils in a spiral-shaped manner outwardly; and a method of electromagnetic high energy pulse deformation is proposed as well.

Abstract: A system for removing dents from metal or other materials comprising (i) a device which includes at least one magnet having a handle detachably held to a portion of the magnet by magnetic attraction and a roller detachably held to a portion of the magnet opposite the handle by the magnetic forces of the magnet; and (ii) a method which includes the steps of attaching the magnet to the handle, placing the roller inside the tubing of a dented instrument, placing the portion of the magnet opposite the handle against the exterior of the instrument, catching or acquiring the roller with the magnet such that the magnet and the roller form a magnetic assembly, wherein the roller is on the interior of the instrument and the magnet is on the exterior of the instrument, and moving, sliding, or rocking the magnetic assembly across the dents until the dents are removed from the metal.

Abstract: A scheme for deforming a sheet of material is provided. In accordance with one embodiment of the present invention, an apparatus for deforming a sheet of material is provided. The apparatus comprises a die portion, an electromagnetic actuator, and a conductive frame. The die portion defines a profiled surface. The electromagnetic actuator is arranged opposite the profiled surface of the die portion. The conductive frame is configured to (i) secure the sheet of material in electrical contact with the conductive frame in a position between the electromagnetic actuator and the profiled die surface, (ii) permit deformation of the sheet of material against the profiled die surface upon activation of the electromagnetic actuator, and (iii) define a return path for eddy currents induced in the sheet of material upon activation of the electromagnetic actuator.

Abstract: A mechanical transducer induces liquid cavitation, causing pressure waves in a liquid which are applied against a metal surface to afford localized elastic and plastic tensile microstrain. The pressure waves alter the surface tensile stresses in the treated metal by reducing the tensile stresses or forming surface compressive stresses. A boot is provided about the operating face of the transducer for confining a liquid through which compression waves are generated and applied to the metal surface, the boot sealing about the transducer and the surface undergoing treatment.

Abstract: A method for electromagnetically forming a metallic member includes deforming an end of a metallic member by electromagnetic forming, pressing the outer surface of the deformed end on the surface of a mold to form a flange having a predetermined shape at the end of the metallic member and, at the same time, work-harden the flange. The method is capable of forming a flange having a shape corresponding to the shape of the outer surface of another member to be joined to the metallic member at an end of the metallic member with high dimensional accuracy and shape accuracy and secured joint strength.

Abstract: A system for removing dents from metal or other materials comprising (i) a device which includes at least one magnet having a handle detachably held to a portion of the magnet by magnetic attraction and a roller detachably held to a portion of the magnet opposite the handle by the magnetic forces of the magnet; and (ii) a method which includes the steps of attaching the magnet to the handle, placing the roller inside the tubing of a dented instrument, placing the portion of the magnet opposite the handle against the exterior of the instrument, catching or acquiring the roller with the magnet such that the magnet and the roller form a magnetic assembly, wherein the roller is on the interior of the instrument and the magnet is on the exterior of the instrument, and moving, sliding, or rocking the magnetic assembly across the dents until the dents are removed from the metal.

Abstract: A method of forming a structural member includes hydroforming the blank to form a hydroformed member and finishing the hydroformed member by positioning the wall of the hydroformed member between a die surface and an electromagnetic discharging element having a non-circular cross-section, and actuating the electromagnetic discharging element so that the metallic wall of the hydroformed member presses against the die surface.

Abstract: A metal plate is formed in a process comprising cutting, perforating or both, by forcing the plate, by means of an abrupt and intense force towards a mold having openings or boundaries defined by wall sections which extend essentially normal to the forming plane of the mold. Consequently, the plate is cut along the edges of the openings or boundaries. The force may be a pulsed magnetic force or may be a force generated as a result of the discharge of electric current through a fluid.

Abstract: An electromagnetic forming apparatus for forming an essentially planar metal plate into a dish having a three-dimensional pattern, is provided. The apparatus comprises a mould having a forming surface with a contour corresponding to said three-dimensional pattern; a forming coil device; and an electric discharge circuitry for discharging a short and intense electric current pulse through the forming coil device to yield a pulsed magnetic forming (PMF) force for deforming said plate.

Abstract: A process for forming closed sections using electromagnetic force. A sheet metal stock is folded into a generally closed section having flanges. The folded section is placed in a die and the die is closed. An electromagnetic force is applied to the die to expand the sheet metal towards interior walls of the die, thereby forming the closed section to a predetermined shape. During expansion, the flanges are drawn inward toward the die. After removed from the die, excess flanges are trimmed from the section if needed, the sections welded closed.

Abstract: A press (10) for operating a tooling unit in the performance of a manufacturing operation, such as crimping terminals onto a conductor. The press is adapted for attachment to the frame of a host machine (12), such as a lead maker, and for receiving a tooling unit, such as a terminal applicator (52). The press (10) includes a frame (13), a carriage (20) arranged for reciprocating motion with respect to the frame (13) and a ram (110) in sliding engagement with and carried by the carriage (20). A relatively low powered actuator (22) causes the ram (100) to move through a first incremental amount of movement during the first portion of the crimp cycle and a second, more powerful, actuator (80) causes the carriage (20) and ream (110) assembly to move through a second incremental amount of movement to complete the crimp cycle.

Abstract: The rate of impact between the peening elements and an internal surface of a hollow part is a function of the vibration frequency, and there is a cut-off frequency at which a hollow part can vibrate and induce repeated impact between its internal surface and the peening elements because the rate of impact becomes erratic and loses its cyclical nature as the vibration frequency deviates from the cut-off frequency. The present invention provides a method for determining the cut-off frequency at which a hollow part can vibrate and maintain the repetitive nature of the impact between its internal surface and the peening elements. Such a method requires a peening element speed limit ratio, which is the ratio of the velocity of the hollow part compared to the velocity of the peening element above which the rate of impact begins to become erratic and lose its cyclical nature.

Abstract: A method for manufacturing a vehicle wheel includes the steps of providing a wheel rim and a spider and positioning the wheel rim and the spider adjacent each other. The wheel rim and the spider are then friction welded to each other. Subsequently, a portion of the spider is locked down onto the wheel rim by electromagnetic forming. Preferably, one end of the rim is positioned in a cavity formed in the spider. During friction welding, the upset material of the rim fills the cavity of the spider. Subsequently, while the metal is still relatively fluid, a flange of the spider is locked down onto the wheel rim by electromagnetic forming to secure the wheel rim and spider together.

Abstract: The present invention includes an apparatus for forming a metal work piece into a target shape, the apparatus comprising: (a) an male mold portion having a mold side and a back side; (b) a female mold portion having a mold side and a back side; the mold side of male mold portion and the mold side of female mold portion adapted to mate incompletely so as to deform a work piece disposed therebetween into a precursor shape, so as to leave at least one precursor area of the work piece to be further or finally formed; (c) at least one of the mold portions comprising at least one electromagnetic actuator so as to be capable of further forming the at least one precursor area. The invention additionally may comprise: (d) a current power source adapted to produce a current pulse through the at least one electromagnetic actuator, so as to produce a magnetic field in the at least one precursor area so as to deform the at least one precursor area into a target shape.

Abstract: A method for manufacturing a vehicle wheel includes the steps of providing a wheel rim and a spider and holding the spider inside the wheel rim. The wheel rim and the spider are positioned in a high capacity forming machine. At least one of a portion of the wheel rim located adjacent an outer periphery of the spider and a portion of the outer periphery of the spider is permanently deformed towards the other of the wheel rim and the spider thereby securing the wheel rim to the spider. An apparatus for securing the wheel rim to the spider includes a bottom die, a bottom inside rim stabilizer supported on the bottom die, a spider supported on the bottom inside rim stabilizer, a top inside rim stabilizer and a wheel rim supported by the bottom rim stabilizer and the top inside rim stabilizer. A high capacity forming machine encircles the wheel rim. The high capacity forming machine includes a workpiece which at least sometimes contacts the wheel rim and an electric circuit located adjacent the workpiece.

Abstract: The present invention relates to several hybrid methods of metal forming including: (1) a method involving a partial mechanical forming followed by electromagnetic forming; (2) a method involving the initial mechanical forming, followed by further mechanical and electromagnetic forming; and a method involving the initial partial mechanical forming and electromagnetic forming, followed by further mechanical and electromagnetic forming.

Abstract: The present invention relates to molds and mold portions that comprise or have integrated therewith a resinous material and comprise at least one electromagnetic actuator imbedded in the resinous material, so as to be capable of further forming the at least one precursor area of the work piece. The resin is used to locate the coil, and clamps or other restraints preferably are used to keep the weaker electrically insulating resin out of a state of large tensile stress or strain, which may cause it to fracture. Preferably, the resinous material comprises metallic flakes imbedded therein.

Abstract: The present invention includes a method of forming a metal work piece into a target shape, said method comprising the steps: (a) obtaining a metal work piece, said work piece having an original shape; and (b)forming said metal work piece by mechanical action while simultaneously subjecting said work piece to electromagnetic forming, so as to deform said metal work piece from said original shape to said target shape.

Abstract: The present invention is an apparatus for formimg a metal work piece into a target shape, the apparatus comprising: (a) a male mold portion having a mold side and a back side; (b) a female mold portion having a mold side and a back side; at least one of the mold side of male mold portion and the mold side of female mold portion comprising a removable portion and adapted to mate incompletely so as to deform a work piece disposed therebetween into a precursor shape, so as to leave at least one precursor area of the work piece to be finally formed; (c) the removable portion comprising at least one electromagnetic actuator, the removable portion disposed so as to be capable of further forming the at least one precursor area. The invention additionally may comprise: (d) a current power source adapted to produce a current pulse through the at least one electromagnetic actuator, so as to produce a magnetic field in the at least one precursor area so as to deform the at least one precursor area into a target shape.

Abstract: A magnetic press (10) for performing a manufacturing operation includes tooling (60) operatively connected to reciprocating parts comprising rods (22), and a magnet (41) connected to the rods (22) through a stationary plate (31). A control circuit (200) electrically operates a reciprocating magnet (41) and a stationary magnet (51) for inducing flux fields of attraction in the magnets (41,51), and for reversing the polarity of the flux fields to eliminate residual magnetism and for cushioning the landing of magnet (41) on a return stroke.

Abstract: The present invention is a method and apparatus for peening the internal surface of non-ferromagnetic hollow parts. Ferromagnetic peening elements are inserted into the non-ferromagnetic hollow part, and a magnetic dipole creates a magnetic field through the non-ferromagnetic hollow part attracting the peening elements which contact a portion of the internal surface of the non-ferromagnetic hollow part. The magnetic field is disengaged and a second magnetic dipole creates a second magnetic field, thereby causing the peening elements to contact a second portion of the internal surface. The magnetic dipoles are repeatedly turned on and off, thereby causing repeated impact within the interior of the hollow part until the internal surface attains a predetermined stress level.

Abstract: One of the key features of the present invention is the use of a electrical conduit arrangement that allows for the tailoring of the magnetic field so as to provide for the greater amount of force to be brought to bear generally in the center of the work force area. The present invention provides for such capability by providing for a single central current conduit for forming longitudinally extending work pieces. The present invention also provides for the splitting, and/or direction (or curvature) reversal, of the electrical current pulse one or more times to likewise tailor the magnetic field of the work-coil or forming actuator.

Abstract: An electromagnetic peening apparatus includes a first electromagnetic coil having a first face configured to conform to a first surface of a workpiece, and a second electromagnetic coil having a second face configured to conform to a second surface of the workpiece. A carriage positions the first and second coils in abutting contact with the workpiece at respective first and second faces and surfaces. A power supply powers the coils to produce electromagnetic force therein to plastically deform the workpiece at the first and second surfaces to effect a compressive layer therein.