Effect of Scratch on the Mechanical Property of Injection Moldings

As well known that material’s scratch behavior/resistance is considering as a kind of surface toughness parameter, which can affect product’s appearance quality and mechanical property reduction. Material’s surface scratch damage may also accelerate critical fracture existence in following mechanical test process. In this paper, dumbbell and plate samples of neat polycarbonate (PC) and 20wt% of glass fiber (GF) additive corresponding GF/PC composite were fabricated by injection molding technology. Basically, scratch damage performance was investigated by applying various scratch depths in dumbbell sample thickness direction following with tensile property change discussion. Initially, cross-section of scratch path in samples was observed to investigate various scratch parameters’ effect on scratch damage. Afterwards, dumbbell tension, plate’s drop weight impact test and bending test were conducted. Finally, dumbbell sample tension’s brittle fracture and plate’s impact damage tolerance were discussed based on tension strain, impact energy absorption and fractural appearance. The results indicates that material’s critical scratch depth could make sample’s tension fracture change from ductile to brittle, affecting material’s failure early-warming. Additionally, PC material with surface damage would decrease the energy absorption during plate bending process bearing smaller maximum load and deflection.

Microstructure and Properties of Powder-Forged Steel

Sintered and forged powder metallurgy (P/M) steels were subjected to tensile, hardness and impact test, in order to understand the influence of the microstructure on the mechanical properties and fracture behavior. Ultimate tensile strength, yield strength, elongation, reduction in area, hardness and impact toughness all increase with a decrease in porosity. With the increase of density, the mode of fracture change from pure ductile in sintered necks of the material to complete brittle from fully dense pearlitic grains.

Small-Scale Simulations Of Lattice Fracture

Many properties of rapid fracture may profitably be studied in atomic scale computer simulations involving relatively small numbers of atoms. A first result of such a study is that qualitative properties of Mode III fracture change little when one explores various shapes of the interparticle potential, introduction of randomness, and elevated temperatures. A second result is that Mode I fracture is considerably more susceptible to instability than had previously been understood, and that to obtain stable Mode I fracture may require non-central forces between atoms.