Analysis of Percent Elongation for Ductile Metal in Uniaxial Tension

Percent elongation of ductile metal in uniaxial tension due to non-homogeneity was analyzed based on gradient-dependent plasticity. Three assumptions are used to get the analytical solution of percent elongation: one is static equilibrium condition in axial direction; another is that plastic volumetric strain is zero in necking zone; the other is that the diameter in unloading zone remains constant after strain localization is initiated. The strain gradient term was introduced into the yield function of classical plastic mechanics to obtain the analytical solution of distributed plastic strain. Integrating the plastic strain and considering the influence of necking on plastic elongation, a one-dimensional analytical solution of percent elongation was proposed. The analytical solution shows that the percent elongation is inversely proportional to the gauge length, and the solution is formally similar to earlier empirical formula proposed by Barba. Comparisons of existing experimental results and present analytical solutions for relation between load and total elongation and for relation between percent elongation and gauge length were carried out and the new mechanical model for percent elongation was verified. Moreover, higher ductility, toughness and heterogeneity can cause much larger percentage elongation, which coincides with usual viewpoints.

Tearing Toughness of Ductile Metals

A new parameter, i.e., tearing toughness, was employed to characterize the mechanical properties of some ductile metals （Cu, Cu-2 wt% Be, Cu-Al alloys, and some steels） by using three-leg trousers tearing tests. The experi- mental results demonstrate that their tearing toughness is not a physical constant and shows a close relationship with the materials＇ types and microstructures. It can be inferred that the tearing toughness of different ductile metals has their respective variation range, expectantly, and may be represented by the comprehensive mechanical properties of strength and ductility for various ductile materials.

Optimization of Abrasive Water Jet Cutting of Ductile Materials

Full factorial design of experiments was developed in order to investigate the effects of jet pressure, abrasive mixing rate, cutting feed, and plate thickness upon three response variables, surface finish of cutting wear zone, percentage proportion of striation free area, and maximum width of cut. The set of sixteen experiments was performed on each of the following two ductile materials： AISI 4340 （high strength low alloy steel, hardened to 49HRc） and Aluminum 2219. Analysis of Variance （ANOVA） was performed on experimental data in order to determine the significance of effects of different parameters on the performance measures. It was found that cutting feed and thickness were highly influential parameters, while abrasive mixing rate is influential upon surface roughness only. Strong interaction was found between jet pressure and workpiece material. Multi-criteria numerical optimization was performed in order to simultaneously maximize/minimize different combinations of performance measures.

Effects of Cu， Ni， Mn and Mo on the austemperability， microstructures and mechanical properties of ADI weld metal

Effect of Cu. ni. Mn and,mo on the austemperability, Inicroslruclures and Inechanlcal properlies of auslempered duclile iron(ADI) weld metal have been investigated it has been demonslrated foal Mn and.Mo obviously enhance the austemperablity of weld metal. but a exdcess of Mn or Mo impairs the mechanical properties of ADI weld metal because of the formation or carbide at cell boundaries. Cu and Ni can improve the plasticity of ADI weld metal by suppressing the formation of carbide and by increaxsing the amount of austemite,.in order to obtain the weld having both the high austemperability and exceptional combination of mechanical properties. it is advantageous that welds is alloyed withe tWo Or more elements in relalivelv.small amounts.

Competing failure mechanisms of thin metal films on polymer substrates under tension

The ductility of thin metal films on polymer substrates reported in recent experiments has a huge disparity,ranging from less than 1 % up to more than 50 %.To reveal the underpinning origins for such a large variation,this paper reports a systematic computational study of two competing failure mechanisms:metal film necking and grain boundary cracking.The quantitative results suggest that strong grain boundaries and metal/polymer interfacial adhesion are keys to achieve high ductility of polymer-supported metal films.

Rate Dependence of Serrated Flow and Its Effect on Shear Stability of Bulk Metallic Glasses

The rate dependence of serrated flow and its effects on the stability of shear banding were systematically investigated in a prototypic bulk metallic glass.It was found that with the increase of external strain rate,the serrated flow is gradually suppressed and could completely disappear at a critical strain rate.The serration size,characterized by the mean stress drop amplitude,decreases inversely with the strain rate,while the waiting time for serration decreases with the strain rate in a power-law manner.The rate dependence of the serrated flow has important effects on the dynamics and stability of shear banding process,and leads to an optimal plasticity achieved around the critical strain rate for the disappearance of serrated flow.These results are discussed and interpreted in terms of the microscopic deformation theory and the stick-slip dynamics of shear banding for bulk metallic glasses.

Effect of pre-existing shear bands on mechanical properties and serration behaviors in bulk metallic glasses

Pre-existing（multiple）shear bands were introduced into the ductile Zr56Co28Al16 and Zr65Ni10Cu15Al10bulk metallic glasses（BMGs）through the lateral-deformation,respectively.It was found that the pre-exiting shear bands can further enhance the compressive plasticity of ductile BMGs.According to the serration analysis on the plastic deformation of the as-cast and the pre-deformed samples,the serration events in the stress-strain curves during deformation display a self-organized critical（SOC）behavior.Compared with the as-cast BMGs,a larger power-law scaling exponent calculated based on serrated flow behaviors becomes larger for the pre-deformed BMGs,implying that the shear banding stability of BMGs is effectively enhanced.This should be caused by the pronounced interactions of shear bands during plastic deformation for the pre-deformed BMGs.However,by introducing a large amount of multiple shear bands into the glassy matrix,it also becomes easier for shear bands to propagate along the pre-existing shear bands,leading to a lower cut-off elastic energy density for the pre-deformed BMGs.More multiple shear bands with stronger interactions for the pre-deformed BMGs could provide a larger chance to activate the shear-band cracking but less local elastic energies are remained for the subsequent crack-linking.