Advanced Materials Research Vols. 97-101

Abstract: Taking into account the nonlinear constitutive relationship and transverse Poisson effects, the propagation characteristic of nonlinear wave for one-dimension elastic thin rod is studied. With the help of Mathematic, two traveling wave solutions for this nonlinear wave equation are obtained by sine-cosine function method, which include the shock wave solution and the solitary wave solution. The necessary condition of these solutions is given also.

Abstract: The space morphology of martensite in 15, 45 and T9 steels quenched from high temperatures had been observed under a scanning electron microscope using a thin-foil specimen which were deeply etched. The results show that the space appearance of packet martensite is not lath-like in shape, but sheet-like in low carbon steel, and thin plate-like in medium and high carbon steels. The stereoscopic models of two kinds of packet martensite, named sheet-like and thin plate-like martensite by authors, were proposed.

Abstract: Fatigue test is carried out for 16MnR steel weldment. The compact tension (CT) samples with 3.8mm thickness are used, and comparisons of fatigue crack growth between base metal and fusion zone in the weldment are considered in Paris region. It is shown that fatigue crack growth rate in the base metal is not sensitive to R-ratio, but the crack growth rate in the fusion zone increases with R-ratio increasing. To the low R-ratio, the crack growth rate in the fusion zone is smaller than that in the base metal, but they approximate the same under the high R-ratio. The mechanism of fatigue crack growth is analyzed through crack growth path in the microstructure, the different of fatigue crack growth behavior is studied for the base metal and the fusion zone.

Abstract: The objective of this study is to explore the influence of the steel’s material properties on the distribution of welding residual stresses of the butt-welded steel plate. First, S15C carbon steel’s material properties are varied in this study to calculate the corresponding welding residual stress by carrying out 3D finite element analyses. Results show the maximum longitudinal tensile residual stresses increase linearly with increasing thermal expansion coefficient and increasing yield stress. The length of the tensile residual stress zone decreases linearly with increasing thermal conductivity. Finally, based on the relationship between material properties and welding residual stresses, a useful prediction equation is developed and verified in this study.

Abstract: Initial Discontinuity State is the characteristic of aluminum alloy, it is a random parameter. According to an advanced aluminum alloy rolling alclad sheet, the coupons were carried out tension and fatigue test, stress ratio R=0.06, 0.2, 0.5 and the maximum stress level σmax=403, 370, 330, 310, 280, 260, 240, 220MPa through Material Test System 810. By use of scanning electron microscope, the tension and fatigue fracture surface was analyzed and the flaw size was obtained. The metallographic coupons were prepared, the constituent particles were surveyed using KH-7700 optical microscope and particulate size was gained. Based on measuring data, different distributions (Normal, Lognormal, Weibull, Logistic, Gumbel) were verified, the best-fit distributions of tension and fatigue facture flaw size is Lognormal distribution, as same as that of θ phase. However, that of S phase size is Weibull distribution.

Abstract: Material constitutive model for metal machining is very difficult to obtain and establish accurately by conventional tension and compression tests. The dynamic mechanical properties and material model during machining aluminum 7050-T7451 are studied by means of orthogonal machining experiments (including quick-stop experiment, cutting force and cutting temperature measurements). Compare with compression tests (SHPB), the established material model with large strain (0.8~1.9) and high strain rate (0.45×105~1.89×105) in this paper is more valid and reliability in simulation and analyzing machining process.

Abstract: The nano-Al2O3p/Cu composite performed in this paper was prepared by internal oxidation. The nano-Al2O3p/Cu composite wire and the Cu-Ag alloy wire were slid against a copper-based powder metallurgy strip under unlubricated conditions. The wear behavior of nano-Al2O3p/Cu composite and Cu-Ag alloy were researched under different currents from 0~50A and sliding distance from 0~72Km. Worn surfaces of the nano-Al2O3p/Cu composite were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). The results indicate that the nano-Al2O3p/Cu composite surface is dispersed with Al2O3 particles having a size of 10~20nm; the wear rate of both 0.60Al2O3p/Cu (containing 0.60wt.% Al2O3) composite and Cu-Ag alloy increases with the increasing electrical current and sliding distance, which increases abruptly at the beginning and smoothly subsequently; The wear rate of Cu-Ag alloy is 2-5 times that of 0.60Al2O3p/Cu composite without electrical current; The wear rate of Cu-Ag alloy is 5-10 times that of 0.60Al2O3p/Cu composite with electrical current of 30A-50A; The sensitivity of electrical current on the Cu-Ag alloy is more apparently than that on 0.60Al2O3p/Cu composite. Adhesive, abrasive, and electrical erosion wear are the dominant mechanisms during the electrical sliding processes.

Abstract: Dynamic shear test and creep shear test were employed to investigate the dynamic properties of various fiber modified asphalt binders with the fiber content of 1.0%. The test results indicate that complex shear modulus of asphalt binders containing fibers are increased while the phase angles are decreased greatly, which implies that the asphalt binder is reinforced by the addition of fibers and the elastic property of asphalt binder is improved significantly, especially at high frequency levels. The total strain during loading period and the residual strain after the creep shear test of asphalt binders are reduced greatly by the addition of fibers. Furthermore, the creep modulus of fiber modified asphalt binders is increased and the development rate versus loading time of creep modulus is decreased.

Abstract: An ultrahigh strength dual-phase (DP) steel with low ratio of yield strength/ultimate tensile strength (YS/UTS) was designed based on the simulation using JmatPro software so as to improve formability as well as to extend its application in automobile industry. Results show the DP steel suffered from water quenching (WQ) technology exhibits high ratio, 0.872, of YS/UTS, which loses the advantage of formability of DP steels and restricts its application in automobile industry. Therefore, the controlled slow-cooling rate (CSCR) technology is employed to this DP steel, and the low ratio, 0.458, of YS/UTS is obtained. Although the tensile strengths of the DP steel suffered from two kinds of technologies are over 1000 MPa, The YS of the DP steel with CSCR technology is 480 MPa and is much lower than 983MPa of the DP steel with WQ technology, which are attributed to relative large grains and small volume fraction of martensite in the former based on the characterization of microstructure by optical microscope, scanning electron microscope, transmission electron microscope and electron backscattering diffraction.

Abstract: Charpy V-Notch impact tests of N1, N2 and N3 steels from 77K to 293K are possessed in this paper. With increasing the nitrogen concentration, the ductile to brittle transition temperature (DBTT) increases. The toughness of the tested steels decreases rapidly with decreasing the temperature. The change of fracture patterns of high nitrogen austenitic stainless steels is dimple → shallow dimple → mixture of quasi-cleavage facet and dimple → cleavage facet. Fracture facets with river patterns, with tear ridges, along annealing twin boundary and cross the annealing twin plane are observed in this investigation. Critical dislocation density of crack tips ρc=[6π(τp)2/(KIc)2]2 can affect ductile to brittle transition (DBT) behavior at cryogenic temperature. Deformation twinning is also frequently observed at cryogenic temperature. Crack forms along the coherent twin boundary between one twin and the matrix.