A method for manufacturing a press formed part, the method including specifying stretch flange limit strain in a metal sheet by using strain gradient in a radial direction and strain gradient in a sheet thickness direction. The strain gradient in the radial direction being directed from an end portion of the metal sheet at a time a press load is applied. The strain gradient in the sheet thickness direction being a direction of the metal sheet that intersects a loading direction. Additionally, the stretch flange limit strain satisfies the formula .sub.lim=A[a.Math..sub./r+b.Math..sub./t]+c, where .sub.lim represents the stretch flange limit strain in a tangential direction of the sheet edge, .sub./r represents the strain gradient in the radial direction, .sub./t represents the strain gradient in the sheet thickness direction, A, a, and b represent influence coefficients, and c represents the limit strain at a time the strain gradient is zero.

A test rig combining high-frequency tribological stress and low-cycle fatigue. The test rig includes a first test piece which is fixed to a frame and defines at least one bearing surface, a second test piece which is connected to an actuator for loading the second test piece so that it bears against the at least one bearing surface of the first test piece, a heater configured for heating the test pieces and a vibration generator, such as a shaker, for loading the test pieces in a vibratory manner so as to carry out a fretting fatigue and low-cycle and high-cycle fatigue test. One of the test pieces includes a portion in the shape of a turbine engine rotor blade root and which is inserted in a groove having a shape that is substantially complementary to the other test piece so as to reproduce a turbine engine blade-disc attachment.

One example of the present disclosure relates to a coupon. The coupon includes a first surface with a first circular channel and a second surface opposite and parallel to the first surface. The second surface is spaced a distance D0 from the first surface and includes a second circular channel concentric with the first circular channel. The coupon also includes a toroidal portion between the first circular channel and the second circular channel. The toroidal portion includes a rectangular sectional portion.

A hardness test block wherein the number of test sites is optimized for a given test block size and a hardness being tested. The hardness test block has an alignment template that enables an operator to be assured of having the test bock grid pattern aligned properly with the indenter of a hardness testing machine. Another means for aligning the test block with the hardness testing apparatus is a cradle for the test block so that the primary test surface as well as the opposite surface can both be used for testing purposes such that the cradle protects the test surface from being contacted by the anvil of the hardness testing machine during the test operation. Another alternative is having a plurality of legs or pins on the test surface of the test block to prevent the test surface from contacting the anvil when the opposite test surface is being used for testing. A formula is provided so that the optimum grid pattern for a test surface can be obtained for any test block, irrespective of size, shape, or expected indentation size in order to obtain the least amount of test block material needed for a given number of test sites.

A method for manufacturing a formed component includes: determining a stress margin with a strain amount as a variable based on results of a test including placing a metal sheet in a predetermined hydrogen entry environment in a state where a load stress is loaded to a sheared surface of the metal sheet and the metal sheet is restrained; performing forming analysis of forming the metal sheet into the formed component and determining a residual stress and the amount of strain in a sheared end surface of the formed component; determining a load stress to be loaded to the sheared end surface by assembling the formed component to another component; and assessing a margin of the delayed fracture in the formed component based on the stress margin corresponding to the determined amount of strain and a total stress of the determined residual stress and the determined load stress.

The device for preparing sheet specimens comprises a base (1) for placing on it a sheet specimen (2) and a cutting punch (3) for cutting sheared cracks or sharp notches in said sheet specimen (2). Preferably, said cutting punch (3) comprises a beveled lower end (31) and/or a central vertical groove (32). Permits the cracks to be formed cutting directly the sheet, and not by cyclic loading, so that the preparation of the sheet specimen takes a reduced time in comparison with the conventional devices.