Necking

About: Necking is a research topic. Over the lifetime, 5280 publications have been published within this topic receiving 113945 citations.

Effects of injection molding–induced morphology on the work of fracture parameters in rubber‐toughened polypropylenes

Abstract: The effects of the injection-molding induced skin-core morphology on the fracture behavior of rubber-toughened polypropylene (RTPP) systems were studied by employing the essential work of fracture (EWF) method. RTPP with 31 wt% ethylene/ propylene rubber (EPR) showed no skin-core structure after molding and the EWF approach worked well in this case. In contrast, RTPP with 10 wt% EPR exhibited a pronounced skin-core morphology: EPR depletion and enrichment was observed in the skin and core region, respectively. This morphology caused necking instead of crack growth in deeply double edge-notched (DDENT) specimens under tensile loading along the mold filling direction (MFD). The necking process not only was accompanied by a large scatter but also yielded highly unrealistic specific essential work of fracture (w e ) values. This skin-core structure was also the reason for an anistropic EWF response of this system observed by loading the specimens both in longitudinal (L) and transverse (T) directions to the MFD. The failure sequence and its characteristics were studied by light microscopy (LM) and infared thermography (IT). It was concluded that the EWF approach cannot be applied for RTPP with a prominent skin-core structure. Since yielding preceded the limited crack growth prior to necking in the loading direction for the DDEN-T specimen of RTPP with 10 wt% EPR, the yielding-related specific essential work (w e,y ) was used for toughness comparison. In case of RTPP with 31 wt% EPR, where yielding was less pronounced prior to the crack growth, the work of fracture until the maximum load was assigned to the yielding-related work of fracture (w f,y ) used for computing w e,y . The latter value seems to be closely matched to the plane-strain essential work of fracture value.

Effect of microalloying (Ca, Sr, and Ce) on elevated temperature tensile behavior of AZ31 magnesium sheet alloy

Abstract: The effect of microalloying with calcium, strontium, and cerium on the microstructure and the elevated temperature deformation behavior of magnesium sheet alloy AZ31 was investigated. Base composition and microalloyed AZ31 materials were cast and rolled into wrought sheet by an identical thermo-mechanical process. A series of hot tensile tests (temperatures of 300 °C, 400 °C, and 450 °C; constant true strain rates of 0.1 s−1, 0.01 s−1, 0.001 s−1, and 0.0003 s−1) were performed to characterize the deformation behavior of the sheet alloys. Interrupted tensile tests were used to study microstructural evolution with strain. A well-dispersed and thermally stable second phase produced by microalloying refines, stabilizes the grain structure, and significantly enhances hot formability of AZ31 sheet. The enhancement is most pronounced under deformation conditions of 450 °C and; 0.0003 s−1 strain rate, with tensile elongation increasing from 347% for the base alloy, to 406% with Ca only, 437% with Ca and Ce, and 552% with Ca, Sr and Ce for microalloyed AZ31 alloys. The second phase particles resist grain coarsening, promote grain boundary sliding, retard strain localization or necking, and postpone cavitation to higher strain levels to achieve this improvement in formability.