A method for defining a threshold stress curve utilized in fatigue and/or damage tolerance analysis, the method including conducting a direct test method on a plurality of specimens with a notch to generate raw data, the notch in each of the specimens having a notch dimension; determining a plurality of analyzed data points based upon the raw data; determining a regression line based upon the plurality of data points, the regression line including an exponential portion and a power law portion; and connecting the exponential portion and the power law portion of the regression line to form a threshold stress curve based on the regression line.

A method of testing a material sample of a type used in a wall of a structure in a standard test for in-plane fracture toughness evaluation. The method comprises obtaining a sample having a lateral length no larger than a thickness of the wall of the structure, shaping the sample to have (a) a bottom surface, (b) a profiled top surface having a central notch, (c) a first coupling feature on a first side of the central notch, and (d) a second coupling feature on a second side of the central notch, assembling a test specimen which increases the width of the sample beyond the lateral width by coupling a first lateral extension to the first coupling feature and a second lateral extension to the second coupling feature, and applying a standard fracture toughness test to the so-assembled test specimen and sample to evaluate the fracture toughness of the sample.

A method according to the present invention, it is possible to accurately measure the stretch-flangeability of sheet metal materials without size effects even when a small amount of specimen is used, compared with the stretch-flangeability established as an international standard, and to measure the stretch-flangeability in the local region. The method according to the present invention includes (a) performing a computer simulation of a small-scale specimen having a predetermined size by using finite element analysis to determine a size of the small-scale specimen; (b) using a standard-scale specimen having the same material as the small-scale specimen specified in the step (a) to perform a punching process specified in the standard testing method; (c) observing a distribution pattern of shearing defects in a hole-edge region of the specimen having performed the punching process, and evaluating a hole expansion ratio; (d) comparing the hole expansion ratio and the distribution pattern of shearing defects between the small-scale specimen and the standard-scale specimen to verify measurement reliability for the stretch-flangeability of the small-scale specimen; and (e) using the size of the small-scale specimen having verified the measurement reliability to evaluate stretch-flangeability.

A device to test the peeling resistance of coupons, each formed of a support and an adhesive, includes: (i) a frame including rollers with parallel axes designed to maintain the coupon supported while guiding movement of the latter, (ii) a traction device including a vertical jack linked to an attachment element including a loop configured in order to cause detachment of the adhesive from the surface of the support, (iii) a device for measuring the force exerted by the jack in order to pull the loop during peeling, and (iv) a coupon, complex in shape, such as one derived from a reinforced vane. At least one roller is translationally adjustable in relation to other rollers and the coupon is specially prepared in order to facilitate carrying out the tests.

There is a method of making a tubular specimen with a predetermined wrinkle defect including providing a layup tool with a cavity forming member having a cavity which resembles a desired shape of the at least one wrinkle; orienting a composite material around the mandrel at a wrap angle to form a closed loop; positioning a wrinkle tool on the closed loop; and/or generating at least one wrinkle with a predetermined characteristic in a portion of the closed loop to form a tubular specimen. The predetermined characteristic is at least one of the following: wrinkle location, an outward wrinkle, an inward wrinkle, a wrinkle width, a wrinkle height, and a wrinkle length. In another aspect, there is a method of offset load testing a tubular composite specimen. In a third aspect, there is a method of determining allowable defects for a composite component.

In a first aspect, there is a method of making a specimen with a predetermined wrinkle defect, the steps including orienting a composite material around a layup tool at a wrap angle to form a closed loop; and generating at least one wrinkle with a predetermined characteristic in a portion of the closed loop to form a specimen. The predetermined characteristic is at least one of the following: wrinkle location, an outward wrinkle, an inward wrinkle, a wrinkle width, a wrinkle height, and a wrinkle length. In another aspect, there is a method of determining allowable defects for a composite component.

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.

Test fixture grips for testing quasibrittle materials, such as fiber-polymer composites are provided having increased mass and stiffness relative to standard test grips to provide for obtaining postpeak measurements. The design is based on static analysis (using the second law of thermodynamics), confirmed by dynamic analysis of the test setup as an open system. Dynamic analysis of the test setup as a closed system with PID controlled input further indicates that the controllability of postpeak softening under CMOD control is improved not only by increasing the grip stiffness but also by increasing the grip mass.

A method for testing for hydrogen embrittlement, including mounting a container around a steel alloy test specimen, the container having a closed bottom below a notched area on the test specimen and an open upper end above the notched area; applying a tensile load to the test specimen and sustaining the load for a selected duration to incubate potential hydrogen embrittlement cracks with a sub-critical flaw size if sufficient hydrogen in dangerous levels is present in the test specimen; then, while sustaining the load, dispensing a cryogenic fluid into the container, immersing and chilling the notched area, reducing the sub-critical flaw size for any hydrogen embrittlement cracks incubated; and with the sustained load, fracturing the notched area if the sub-critical flaw size of any hydrogen embrittlement cracks incubated reaches a critical flaw size.

An apparatus for preparing notches in material samples for fracture mechanics testing is disclosed. The apparatus includes a base and a sample holder for gripping a sample. A linear rail is inclined at an angle relative to the sample holder, and may be attached to an attachment column extending upward from the base. A carriage assembly attached to the linear rail includes: a carriage capable of sliding up and down along the linear rail and a blade holder attached to the carriage. The blade holder slides up and down the linear rail to initiate a notch in the sample.