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In the scan images, the good weld appeared as a uniform line. The defective welds exhibited various discontinuities and a non-uniform appearance. Mechanical testing of the welds showed a marked decrease in properties, with reductions in the yield stress of one-third to one-half the value of the good weld.
The two plastic limit theorems apply to any elastic-perfectly plastic body or assemblage of bodies. Lower limit theorem: If an equilibrium distribution of stress can be found which balances the applied load and nowhere violates the yield criterion, the body (or bodies) will not fail, or will be just at the point of failure. [2] Upper limit theorem:
Figure 1: The yield stress of an ordered material depends on the square root of the number of dislocations present. Increase in the number of dislocations is a quantification of work hardening. Plastic deformation occurs as a consequence of work being done on a material; energy is added to the material.
The yield strength or yield stress is a material property and is the stress corresponding to the yield point at which the material begins to deform plastically. The yield strength is often used to determine the maximum allowable load in a mechanical component, since it represents the upper limit to forces that can be applied without producing ...
The stress in the aligned fibrils will carry majority of the stress as the covalent bonds are significantly stronger than the van der Waals bonds. The plastic like behavior of polymers leads to a greater assumed plastic deformation zone in front of the crack tip altering the failure process. [6]
The Hill yield criterion developed by Rodney Hill, is one of several yield criteria for describing anisotropic plastic deformations.The earliest version was a straightforward extension of the von Mises yield criterion and had a quadratic form.
Polycarbonate has a glass transition temperature of about 147 °C (297 °F), [8] so it softens gradually above this point and flows above about 155 °C (311 °F). [9] Tools must be held at high temperatures, generally above 80 °C (176 °F) to make strain-free and stress-free products.
Yield strength is the lowest stress that produces a permanent deformation in a material. In some materials, like aluminium alloys, the point of yielding is difficult to identify, thus it is usually defined as the stress required to cause 0.2% plastic strain. This is called a 0.2% proof stress.