Advanced Materials Research Vols. 97-101

Abstract: A theoretical study is presented herein on the penetration of the laminated composite aluminum alloy foam target struck normally by conical-nosed projectiles. Two layers were arranged according to the density of the respective foam; configuration 1 consisted of 10mm/semi-infinite continuous foams and configuration 2 consisted of 20mm/ semi-infinite continuous foams. The dynamic cavity expansion theory is applied to formulate analytical model. The penetrating process can be divided into 6 stages. The resistance equations during every stage are derived. Penetrating depth of projectile are analyzed. The effect of initial velocity, mass density of foam material and the thickness of the upper layered foam on the penetration resistance are investigated. It is found that composite target have a higher penetrating resistance than the monolithic foam material target of equal mass. The analytical results show that configuration 1 outperformed configuration 2 in regards to their penetrating resistance. The thickness of the upper layered foam within 5-20mm has significant influence on penetrating depth. The energy absorption capacity of the composite target material is evaluated.

Abstract: Invar 36 alloy is widely used in the field of precision manufacturing owing to its minimal thermal expansion coefficient. Grinding is very important in Invar surface processing, and the thermal characteristics is a key factor to affect the residual stress and deformation of grinding. In this paper, the thermal characteristics of Invar 36 alloy during plane grinding was tested. The thermal characteristics of Invar 36 alloy was found to be between carbon steel and nickel-based superalloy. The lower grinding temperature and better ground surface with lower residual stress can be obtained by using the reasonable grinding parameters.

Abstract: The failure assessment for thick wall CrMoV steel pipes circumferentially welded at 640°C was studied using the Finite Element (FE) method under close-ended, open-ended and axial compression conditions, respectively. The life and position of failure, redistribution of stress on the welds and damage variations were obtained using damage modeling. Since there is a distinct mismatch of mechanical properties in parent material, weld material and heat affect zone, variations of damage with time, stress redistribution and failure life in each zone are different. The FEM results show that the weakness of the welds is the heat-affected zone (HAZ) where the hoop stresses increase sharply in the tertiary stage of creep. The maximum of damage of the welds lies on the inner surface of in the weld zone when failure occurs. The information is useful for assessing the performance of practical service welds in power plants pipe work.

Abstract: The moving crack problem in an infinite plate of orthotropic anisotropy functionally graded materials (FGMs) subjected to an anti-plane shear loading is studied by making use of non- local theory. The shear modulus and mass density of FGMs are assumed to be of exponential form. Fourier transform is employed to solve the partial differential equation. The mixed boundary value problem is reduced to a pair dual integral equations which is solved by using Schmidt’s method. The semi-analytic solution of crack-tip stress is obtained, contrary to the classical elasticity solution, the crack-tip stress fields does not retains the stress singularity. The influences of the characteristic length, graded parameter, orthotropic coefficient and crack velocity on the crack-tip stress are analyzed. The numerical results show that the stress at the crack tip decrease as the characteristic length, crack velocity, graded parameter are increased and increase as the orthotropic coefficient is increased.

Abstract: In the present paper, the effects of different die temperatures on microstructures and mechanical properties of aluminum alloy ADC12 at Super Slow Speed (SSS) die casting have been investigated, in order to optimize the die-casting process and its parameters. The results show that under SSS experimental condition, the density of castings is higher than that of general die castings. Die temperature has the best value, when the die temperature is 150 °C, smaller dendrites are distributed in the hardened surface layer, and the eutectics structure of and Si changes from needle-like structure into herringbone structure. The properties of the die casting are significantly influenced by the die temperature, the optimum die temperature is 150 °C.

Abstract: An investigation on low frequency strain amplitude dependence damping characteristic of as-cast high damping Mg-based alloys continuously extending to microplastic strain was carried out. Two-stage damping behavior via strain amplitude was particularly reported. The first is the strain amplitude strongly dependent part due to breakaway loss and the second is the strain amplitude weakly dependent part due to microplastic deformation loss, which is also frequency dependent. The damping mechanism is discussed in detail.

Abstract: To reduce the internal stress and obtain thicker DLC film, a multilayer structure DLC comprised of Ti-doped nanolayer were deposited on Titanium alloy substrate by pulse cathodic arc technology, the Ti content is decreased from bottom to top layer. And the surface layer is carbon deposited with ion–assist deposition. The chemical composition of the films was determined using X-ray photoelectron spectroscopy (XPS). The film structure was characterized by Raman spectroscopy. Other properties of the films are evaluated by Dektak 8 Stylus Profilometer, nano-hardness tester and reciprocating sliding wear tester. And the thickness, hardness, and friction coefficient of two samples are 2.2μm, 1.5μm, 5200Hv, 5500Hv, and 0.09, respectively. The internal stress, calculated by Stoney’s equation, is 2.2GPa, 2.1GPa. And the adhesion strength is 40N/mm2, 35N/mm2.

Abstract: The paper explores in depth a new annealing technology -electric pulse annealing treatment. To improve the disadvantage of the traditional annealing, such as, low efficiency, high energy consuming, polluting the environment, badly oxidation of the product surface, and so on, a new technique that carrying through the annealing and soften treatment with pulse electric current on the Q235 steels was put forward in the text. The experimental device was designed and the parameter was optimized in this assay. And also, the annealing mechanism was explored according to the analyzing of the metallurgical structure and the changing of the property of the steel wires. It is found through the analysis that the pull-out resistance of the wire is significantly decreased and the elongation is improved significantly after electric pulse treatment, and the effect of using high-strength pulse current treatment about 25 seconds (temperature up to 390°C) is similar to the effect with traditional annealing or even reduce the initial temperature.

Abstract: The effect of recessing on the stresses distributed along the mid-bondline in both standard single lap joints and co-axial ones were analyzed using elasto-plastic finite element method (FEM). The results obtained show that the values of the peak stresses of all the stresses distributed in the mid-bondline were changed greatly as the preformed angle in over lap zone was about 10 0 when the high elastic modulus adhesive is used. The effect of the elastic modulus level on the stress distribution (especially the peak stresses) is small in the middle part of the lap zone. When taken the stress distributed in the middle part of the lap zone into account, there is nearly no significant difference between the peel stress distributed in the standard joint and co-axial single lap joint when the adhesives with lower elastic modulus was used. It is recommended that a co-axial joint is suitable for the recessing joint made by aluminum alloy and a higher elastic modulus adhesive.

Abstract: A two-dimensional electro-elastic analysis is performed on a transversely isotropic piezoelectric material with an elliptical hole, which is subjected to remote uniform shear forces, and remote electric field. Based on the impermeable electric boundary conditions, close form solutions are obtained by using the complex potentials method. Taking PZT-4 ceramic into consideration, the stress distributions around the neighborhood of the elliptical hole are given. It is shown that the hole geometry and the electric field are responsible for the shielding effect, there are sharp stress concentration near the hole.