A simulation of the effects of high strain energy storage in large plastic structures

Abstract

AbstractBrittle failures of large plastic structures observed in the field may have occurred at much higher loads than implied from the fracture surfaces, indeed, as if very ductile failures had occurred. It has been demonstrated that these brittle failures may be a direct result of high energy storage upon impact in large compliant systems. A rubber‐toughened blend of polybutylene terephthalate (PBT) and polycarbonate (PC) was highlighted in this study. Soft steel springs were used in series with compact tension samples to simulate the high energy‐storing capability of large compliant structures, Ductile and stable fractures of compact tension samples of the blend were observed at all of the temperatures tested down through −30°C. With the insertion of springs to simulate large compliant structures, however, unstable failures resulted. At 25°C, initial ductile crack growth was followed by ductile but unstable failure. At −30°C, initial ductile crack growth was followed by brittle unstable failure. These instabilities resulted from the excessive amount of stored energy released by the system during initial crack growth. A higher rubber variant of the PBT/PC blend as well as acrylonitrile‐butadiene‐styrene (ABS) and polycarbonate exhibited similar behavior.