Advances in Fracture and Materials Behavior

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Authors: Mutellip Ahmat, Wei Cheng, Li Zheng
Abstract: In this study, the chief heat sources of the spindle system for the TH6350 Machining Center are analyzed, and an experimental system based on the virtual instruments technology is presented, thirty-two thermocouple sensors are set at the spindle system of the machining center to measure the thermal field, and five electric vortex sensors are used to measure the thermal error of the spindle by five-point method. The FEM modeling of the thermal deformation of the spindle system is built up by based of I-DEAS, the temperature field and the thermal deformation of it are calculated, and the calculated values of the model tallies with the experimental values.The researching results provide a theoretical foundation for the improving design􀋈temperature controlling and the error compensation to the machining center.
Authors: Jian Ping Zhou, Chu Hua Liang, Wen Jing Teng, Yan Xu, Bi Sheng Zhou
Abstract: Short electric arc machining (SEAM) is a non-conventional machining process that utilizes an arc to melt and vaporize workpiece material. A low voltage, high current supply is employed to produce a continuous arc in either a water-air mixed medium or in air. This paper describes an investigation into the optimization of the SEAM machining efficiency based on experimental design which considers both electrical parameters and machine parameters. The work uses the orthogonal experiment processes to research the influence of the process indicators on machining efficiency.
Authors: Meng Ju Lin, Jen Cheh Lee, Chung Li Hwan, Jung Nan Liao
Abstract: Pulse heated reflow soldering is widely used as junction methods of electronic devices such as ACF, HSC, FPC, PCB, TCP, and FFC. Hot bars are the devices used in pulsed heated reflow method to heat and melt the solder materials between devices and wire becoming a junction. Therefore the performance is determined by the welding properties. The welding time, temperature and induced pressure are important factors affecting welding property. And the temperature has the significant effect due to electricity and mechanical property of solder being determined by welding temperature. However, the consistency of temperature is hard to achieve due to complex coupling of driving current, materials property, heat generation, heat conduction and hot bar shape. In this work, different shapes of hot bat are designed to obtain the temperature consistency. Due to the welding requirement, the heating process is a two steps process. And the hot bar is heated by electric current from power supply with feedback control. For assembly purpose, the hot bar is designed as a rectangular plate with circular holes near the other side respect to the heating edge to fasten the hot bar on the welding machine. And the hot bar with polygon hole in the center part would induce the uniform temperature distribution. Four dimensions of the hot bar determine the shape and investigate the temperature consistency: polygon’s sizes and its positions. Some experiments are made to measure the temperature distribution. The results show the shape has significant effect on temperature consistency. Changing the polygon hole positions will alter the temperature distribution. The central part of heating edge will hotter than both ending part initially. And in some cases, during the heating process, the both ending part will have cooler, hotter, and cooler temperature that central part with respect to heating time. The polygon hole sizes have also significant effect on the temperature distribution. They have the similar temperature distribution phenomena as positions effect. Therefore, from the experiments and analysis, the hot bar could have more uniform temperature distribution by shape design. And it is also found the temperature distribution would induce thermal residual stress and deform the hot bar.
Authors: Chia Lung Chang, Chia Huei Chiou
Abstract: The assembly of plastic electronic package requires a sequence of process steps. Every process step induces thermal residual deformation and stresses on the assembled components, which cause mechanical effects on the subsequent process step. In this study, both processing and non-processing models with and without considering the effect of chemical shrinkage on molding compound are built to simulate the package warpage and stresses in assembly. The processing model, a nonlinear model with element birth and death used to activate and deactivate the processing materials, can more realistically simulate a series of assembly processes in a plastic package. Due to negligence of the intermediate step, the package warpage and stresses predicted by non-processing model are in significant error.
Authors: Yi Liang Zhang, Zhen Hai Zhang, Xue Dong Xu
Abstract: Comprehensive residual stress of a 1500m3 liquefied petroleum gas spherical vessel was measured and analyzed after many cracks arised. The results show that the general residual stress was at a high level in the field with cracks as well as the field without cracks. Furthermore, the measurements were taken at the same place to evaluate the effect of the heat treatment after this spherical vessel was re-welded and the integral heat treatment was performed. Meanwhile, the measurement to the stress in the vertical direction with X-Ray was finished after a set of special treatments in the outfield.
Authors: Yi Qi Wang, W.K. Joo, Chae Sil Kim, Jung Il Song
Abstract: High-temperature oxidation resistance of 7 wt.%Y2O3-ZrO2 thermal barrier coatings (TBCs) irradiated by high-intensity pulsed ion beam (HIPIB) has been investigated in a cyclic oxidation condition at 1050 °C ×1 h. The ceramic coating of a tetragonal ZrO2 phase structure was prepared on GH33 superalloy substrates with a NiCoCrAlY bond coat by using electron-beam physical-vapor deposition (EB-PVD). The ceramic coating is composed of columnar grains forming dense clusters spacing with several-μm gaps among grain clusters. The characteristics of the columnar grains disappeared after HIPIB irradiation at the ion current densities of 100-200 A/cm2, and the irradiated surface presented a smoothed, densified feature after the remelting and ablation due to the HIPIB irradiation. The thickness of the densified layer is about 1 μm. After oxidation with 15 cycles at 1050 °C ×1 h, the oxidation kinetics curves of the as-deposited and irradiated TBCs showed a parabolic shape. The weight gain of original sample is about 0.8-0.9 mg/cm2, while the values of the HIPIB-irradiated TBCs decreased to some extent. The lowest weight gain is obtained for the irradiated TBCs at 200 A/cm2 with one shot, being 0.3-0.4 mg/cm2, and those at 100 A/cm2 have a medium weight gain of 0.6-0.7 mg/cm2. The cross-sectional morphologies of HIPIB-irradiated TBCs show less oxidation of the NiCoCrAlY bonding layer, with a thinner thermally grown oxide (TGO) layer. The morphology observation is consistent with the results of cyclic oxidation test. It is found that the inward diffusion of oxygen through TBCs can be significantly impeded by the densified top layer by the HIPIB irradiation, thus limiting the oxidation of the bonding layer, improving the overall oxidation resistance of the irradiated TBCs.
Authors: W.K. Joo, Yi Qi Wang, H.T. Yang, W.C. Lee, C.Y. Sim, Jung Il Song
Abstract: The microstructures and mechanical properties of OFHC copper/STKM 11A for D-tube joints brazed using BAg filler metal at 870 °C for 20 minutes in NH3 atmospheres were performed. Interfacial microstructures were observed in reaction layer. A brazing strength causes of decline with defects of pin hole and base metal by lack of penetration. In tensile test, the properties of joints clearance of 0.01mm are better than other joints clearance that has yield strength of elasticity area with the brazing length of 2.5mm, and also suitable for the case of brazing length of 5.0mm. According to the results of FEA (finite element analysis) on the tensile test, the maximum stress and strain were generated apart from the interface in large deformation. Diffused layer was formed by counter diffusion action of base metal and filler metal layer, and crack between two base metals was not discovered. This is the main reason that fracture of test piece does not appear in copper base metal, and brazing department forms good junctures.
Authors: Tatsuo Inoue
Abstract: Phenomenological mechanism of transformation plasticity is proposed in the first part of the paper by use of simple model why stress in mother phase increases to reach yielding due to progressing new phase and to induce plastic deformation even under small applied stress. Based on the discussion, a unified constitutive model including transformation-induced and ordinal thermomechanical plastic strain rates by introducing an effect of varying phases during phase transformation into yield function. Thus derived constitutive equation is applied to describe strain response under varying temperature and stress with some discussions as well as metallo-thermo-mechanical simulation of quenching.
Authors: Qiao Yu Xu, Kalbinur Ahmat, Xiang Liu
Abstract: Fine martensite could be gained in 70Mn2Mo cast steel roller after solidification by laser treatment. The hardness and depth of hardened zone reached 920 HV (about 65HRC) and 0.6mm respectively. After tempered in high temperature, the depth of hardened zone whose hardness was maintained above 430HV was 0.4mm. These results showed the better anti-tempering property and the higher hardness and hardened depth compared with water quenching and implied the greater applied potentiality of laser strengthening.
Authors: Yu Sup Nijat, Mamatjan Tursun, Gulbahar Tohti, Jurat Matruzi, Mamtimin Gheni
Abstract: Finite Element Method pre and post processing tool FAST and a self-programmed software optim3.f are used for structural optimization analysis for main parts of a railway locomotive support vehicle. For best structure optimization, a program code which has considered 3D structure optimization was added to original program to automatically erase nodes whose effective stress was smaller than a given value. Detailed analysis are undertaken to main causes of stress concentration, and using optimized design methods, effective measure for reforming stress concentration and a new structure were proposed.

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