Showing papers in "International Journal of Materials and Structural Integrity in 2014"
TL;DR: In this article, the effect of deep cryogenic treatment on properties of different types of steels was extensively studied, and the mechanism of DCT with respect to different materials, pretreatment conditions and properties of the steels for practical application was revealed.
Abstract: The effect of deep cryogenic treatment on properties of different types of steels was extensively studied. Cryogenic treatment can convert the retained austenite into martensite along with the carbide precipitation and hence enhances the wear resistance when compared to the conventional heat treatment of steels. It also increases the compressive residual stresses in the component, which leads to better fatigue life. However, this study is carried out to reveal the mechanism of deep cryogenic treatment with respect to different materials, pretreatment conditions and properties of steels for the practical application.
16 citations
TL;DR: In this article, an investigation is made on the possible reduction of structural vibration effect due to underground blast by using the fluid viscous damper (FVD), which is modelled by an exponentially decaying function representative of typical rock blast.
Abstract: Blast induced ground vibration, caused by underground explosions, can result in substantial damage to nearby structures. In the present study, an investigation is made on the possible reduction of structural vibration effect due to underground blast by using the fluid viscous damper (FVD). The blast load is modelled by an exponentially decaying function representative of a typical rock blast. The cylindrical pot FVD is considered for which the fractional-derivative Maxwell model is adopted. The dynamic response analysis of the structure-FVD system is performed in the time domain by an equivalent single degree of freedom (SDOF) viscous oscillator approach which is also compared with the response obtained by the discrete Fourier transform (DFT) approach. It is generally observed that the peak structural displacement due to underground blast can be effectively reduced by the FVD while a limited amount of reduction in the peak absolute acceleration of the structure is obtained.
5 citations
TL;DR: In this article, the symmetric character of the conductivity tensor for linear heterogeneous anisotropic material is established as the result of arguments from tensor analysis and linear algebra for Fourier's heat conduction.
Abstract: In this paper, the symmetric character of the conductivity tensor for linear heterogeneous anisotropic material is established as the result of arguments from tensor analysis and linear algebra for Fourier’s heat conduction. The non-singular nature of the conductivity tensor plays the fundamental role in establishing this statement.
5 citations
TL;DR: In this article, the dominant structural factors of the local residual stress in a silicon chip are investigated quantitatively based on the measurement of a chip using stress sensor chips, where piezoresistive strain gauges were embedded in the sensor chips.
Abstract: The local thermal deformation of the chips mounted by area-arrayed fine bumps has increased drastically because of the decrease of the flexural rigidity of the thinned chips. In this paper, the dominant structural factors of the local residual stress in a silicon chip are investigated quantitatively based on the measurement of the local residual stress in a chip using stress sensor chips. The piezoresistive strain gauges were embedded in the sensor chips. The length of each gauge was 2 µm and a unit cell consisted of four gauges with different crystallographic directions. This alignment of strain gauges enables to measure the tensor component of three-dimensional stress fields separately. Test flip chip substrates were made by silicon chip on which the area-arrayed tin/copper bumps were electroplated. The width of a bump was fixed at 200 µm and the bump pitch was varied from 400 µm to 1,000 µm. The measured amplitude of the residual stress increased from about 30 MPa to 250 MPa. It was confirmed that both the material constant of underfill and the alignment structure of fine bumps are the dominant factors of the local deformation and stress of a silicon chip mounted on area-arrayed metallic bumps.
5 citations
TL;DR: In this paper, a cylindrical steel shell was simulated numerically by using nonlinear dynamic finite element analysis code LS-DYNA and the fracture mode and mechanism of a cylinrical shell were specially studied by means of the analysis of deformation, macrographs and meso-graphs of fracture surface and elastic-plastic response.
Abstract: Dynamic fracture characteristics are the foundation for conducting safety assessment and failure analysis of explosion containment vessels (ECVs) subjected to internal blast loading. The experiment was conducted to investigate dynamic fracture characteristics of cylindrical steel shells subjected to internal blast loading at the centre. The elastic-plastic response of cylindrical steel shells was simulated numerically by using nonlinear dynamic finite element analysis code LS-DYNA. The fracture mode and mechanism of a cylindrical shell were specially studied by means of the analysis of deformation, macrographs and meso-graphs of fracture surface and elastic-plastic response. The results show that the axial direction fracture surface of the cylindrical steel shell exhibits a mixed ductile fracture mode with shearing dimple by micro-voids coalescence. Dynamical ductility deformations appear and the shear bands form when the cylindrical steel shell expands under internal blast loading. The fracture mechanism is that the shear bands destroyed the initiation and growth of the micro-voids and micro-cracks along the shear bands due to its softening effect under tensile circumferential stress. The shear bands and the tensile circumferential stress dominate the final fracture mode. The fracture mode is the ductile fracture.
4 citations
TL;DR: In this article, a defective model of graphene-carbon nanotube composite has been established, for exploring the field emission properties of this composite, some efforts have been set on calculating binding energy, then energy level, local electron density distributions, and the Mulliken charge of the defective graphene carbon nanotubes composite have been analyzed, work functions and ionisation potentials are calculated by first principles based on density functional theory (DFT) calculations.
Abstract: To improve the field emission properties of graphene-carbon nanotube composite, a defective model of graphene-carbon nanotube composite has been established in this study, for exploring the field emission properties of this composite, some efforts have been set on calculating binding energy, then energy level, local electron density distributions, Mulliken charge of the defective graphene-carbon nanotube composite have been analysed, work functions and ionisation potentials are calculated by first principles based on density functional theory (DFT) calculations. When the electric field is applied, the numerical value of band gap keeps in a limited scope, local electron density distribution also shows positive changes, Mulliken charge moves regularly and effectively, work functions and ionisation potentials descend significantly, all of these results we obtained show that the defective graphene-carbon nanotube composite can be used as a good candidate for field emission electron sources.
4 citations
TL;DR: In this article, the authors studied the tensile fracture mechanism of the composite structure and found tensile failures in this composite structure always start from the silicon and showed that interactions between graphene and silicon have a profound impact on damages in the silicon thin film.
Abstract: Molecular dynamics simulation is used to study mechanical properties of the graphene/silicon bi-layer film structure. We studied the tensile fracture mechanism of the composite structure and found tensile failures in this composite structure always start from the silicon. The results also indicate that interactions between graphene and silicon have a profound impact on damages in the silicon thin film. Owing to the interlayer interaction, the ultimate strain of silicon film is improved; also a phase transition appears in the fracture process, which makes the film more ductile, quite unlike the monocrystalline silicon. The comparison between uniaxial tensile stress-strain curves at different temperatures shows tensile strength of the structure decreases with the increase of temperature.
3 citations
TL;DR: In this article, the high temperature vibration reliability was evaluated for Sn-3.5Ag and Sn-0.7Cu solders, and the reliability of solder joint was determined by electrical resistance and shear strength.
Abstract: Lead-free solders have been recently applied to automotive electronics under harsh, high temperature environments. In this study, the high temperature vibration reliability was evaluated for Sn-3.5Ag and Sn-0.7Cu solders. The lead-free solder balls with diameters of 450 µm were mounted on ENIG-finished Cu pads of a BGA test chip. The solder-ball-mounted BGA test chips were then assembled on an OSP finished Cu pads of a daisy-chained PCB. The vibration test was performed with the acceleration of 27.8 m/s2, a frequency of 10~1,000 Hz, and test temperatures of 85 and 150°C. The reliability of solder joint was determined by electrical resistance and shear strength. The resistance increased gradually and shear strength were decreased as the test time increased. After a 120-hour test, the resistance of Sn-3.5Ag increased by 71% for the 150°C test condition. In addition, shear strength degradation was observed in Sn-3.5Ag solders under high temperature. The Sn-0.7Cu solder was much more stable as compared with the Sn-3.5Ag solders.
3 citations
TL;DR: In this article, the fatigue life of solder joints of plastic ball grid array packages (PBGA) under thermal cycling condition is evaluated using the finite element method, where a unified, viscoplastic constitutive model is employed to improve accuracy of reliability prediction.
Abstract: In the present study, the fatigue life of solder joints of plastic ball grid array packages (PBGA) under thermal cycling condition is evaluated using the finite element method. A unified, viscoplastic constitutive model for solder joints of plastic ball grid array packages is employed to improve accuracy of reliability prediction. The constitutive model is then implemented into the commercial finite element analysis software, ABAQUS, to predict the thermo-mechanical behaviour of solder balls in PBGA package subjected to thermal cycling. Damage parameters are obtained from the FEA results and are used to estimate the thermal fatigue life of solder balls. The Coffin-Manson equation is employed. The predicted thermal fatigue lives are discussed in detail.
3 citations
TL;DR: In this article, the thermal-structural coupling field analysis model of spindle system is established, and the numerical simulation which accounts for the spindle component system's structure, actual working condition, the influence of heat source and lubrication system condition factors, etc., is conducted.
Abstract: In this paper, the thermal-structural coupling field analysis model of spindle system is established, and the numerical simulation which accounts for the spindle component system’s structure, the actual working condition, the influence of heat source and lubrication system condition factors, etc. which are from a machine tool factory, such as ambient temperature, flow velocity of coolant, and the rotating speed of spindle motor, etc., is conducted. It is found that the maximum temperature up to about 38.8°C appears in the spindle where the double row cylinder roller bearing is installed, while the maximum comprehensive deformation of the spindle’s front-end reaches 0.93 × 10 –5 m. And the spindle system needs nearly 1 hour to reach thermal equilibrium state when the system uses the L-HM32 lubricant. However, temperature rise, heat deformation and the thermal equilibrium time are reduced by 11.1%, 22.6% and 12%, respectively, when the lubricant of the lubrication system is replaced by Shell-tellus22, and the maximum Von-Mises stress value is 125.6 MPa. The results are beneficial for providing a basis for the requirements of practical manufacture, especially the optimisation of structure, cooling system and compensation system design.
2 citations
TL;DR: In this paper, the drop/shock reliability of new quaternary Sn-Ag-Cu-In Pb-free solder alloy with increasing amounts of copper was investigated on the basis of their mechanical properties and microstructures.
Abstract: The drop/shock reliability of new quaternary Sn-Ag-Cu-In Pb-free solder alloy with increasing amounts of copper was investigated on the basis of their mechanical properties and microstructures in comparison with ternary Sn-1.2Ag-0.5Cu Pb-free solder alloy and quaternary Sn-1.2Ag-0.5Cu-0.4In Pb-free solder alloy as suggested in a previous work. The results showed that Sn-1.2Ag-0.7Cu-0.4In solder alloy has excellent drop/shock reliability compared to Sn-1.2Ag-0.5Cu and Sn-1.2Ag-0.5Cu-0.4In solder alloys owing to the thin IMC thickness and the increased mechanical strength. It was considered that indium addition restrained the IMC growth and increasing the amount of copper promoted the formation of Cu6Sn5 and Ag3Sn phase, which resulted in an increase in the alloy strength.
TL;DR: In this article, the reflow of lead-free solder by microwave heating was studied, and the microwave heating system worked at 2.45 GHz frequency on TE10 mode on a printed substrate and electric packages.
Abstract: Recently, the use of solder containing lead in the interconnection between printed substrate and electric packages has been prohibited since lead may have a bad influence on humans and the environment. Today Sn-Ag-Cu alloys (SnAgCu) are used in general as a substitute of Sn-Pb alloys (SnPb). However, the melting point of SnAgCu is higher than that for SnPb which may induce damages in the substrate and packages. To solve this problem, the reflow of lead-free solder by microwave heating was studied. The microwave heating system worked at 2.45 GHz frequency on TE10 mode. The most suitable heating location in the waveguide and the most suitable microwave power were investigated by measuring the temperature of the substrate and the solder simultaneously. After the solder was heated up to the melting point of 493 K, solder-mounted was achieved. The intermetallic chemical compound between the solder and Cu was observed by SEM and it was also analysed by the cross-section of the solder using EDX.
TL;DR: The reduction algorithm of tri-state and bi-direction interconnect is proposed with the properties and principles above, and simulation results show the effectiveness of this method.
Abstract: Signal integrity testing for inter-cores in SoC has become an important issue within DSM manufacturing technology and GHz working frequency of VLSI. A new testing method for SoC inter-core interconnects is presented in this paper. Properties and principles are obtained based on analysis of crosstalk characteristics for tri-state and bi-directional interconnects. The reduction algorithm of tri-state and bi-direction interconnect is proposed with the properties and principles above. Primary and secondary factors of crosstalk are analysed based on orthogonal design, and then test vectors for interconnects are generated gradually. Finally experiments are implemented, and simulation results show the effectiveness of this method.
TL;DR: In this paper, a two-stage approach is proposed to solve the problem of sequential pick-and-place assembly on the semiconductor manufacturing industry, which is a typical NP-hard combinatorial optimization problem.
Abstract: PCB assembly on the sequential pick-and-place machine is a typical NP-hard combinatorial optimisation problem which is a critical bottleneck in electronic product manufacturing industry. In this paper, a two-stage approach is proposed. In the first stage, the distance score with weights selection (DSWS) method is proposed to select a suited set of slots to load feeders. In the second stage, a novel swarm intelligence approach, called the elimination with decay-based swarm intelligence approach (EDSIA) is proposed to solve the problems of assignment of feeders to the selected slots and the placement sequence of the components. In EDSIA, a new population evolution mechanism, based on proposed elimination coefficient and decay factor is proposed to propel the population forwards the global optimum. The numerical results and comparisons illustrate the effectiveness and efficiency of the proposed two-stage approach.
TL;DR: In this paper, the ball shear strength of CBGA and plastic ball grid array (PBGA) packages with lead-free solder pastes was analyzed using the energy dispersive X-ray (EDX) machine.
Abstract: The present study is carried out to characterise the ball shear strengths of ceramic ball grid array (CBGA) and plastic ball grid array (PBGA) packages with lead-free solder pastes. Three commercially available Sn/Ag/Cu (SAC) solder pastes such as Sn 96.5/Ag3.0/Cu0.5 and 95.5/Ag3.8/Cu0.7 with a no-clean flux are employed. The effects of temperature profiles during reflow on the strength of solder joints are studied. Their printing abilities are also observed. Of particular concern for ceramic ball grid array packages is the interaction between 90/10 Pb/Sn compound solder balls and SAC solder pastes. The composition of the solder paste region between the I/O pad and the solder ball is analysed using the energy dispersive X-ray (EDX) machine.
TL;DR: In this paper, a model considering thermo-mechanical coupled effect is presented to construct a precise model of the whole machine tools, which can be used to construct the joint interface property of a high speed motorized spindle.
Abstract: Joint interface property is of great importance to the whole machine tool behaviour, especially for mechanical and thermal behaviour. Traditionally, studies of mechanical joint interface focus on mechanical behaviour or thermal behaviour separately, while in fact they couple tightly. By studying thermal contact resistance and thermo-mechanical coupled mechanism on fixed joint interface, a model considering thermo-mechanical coupled effect is presented in this paper. Compared with experimental data in specimens and high-speed motorised spindle, accuracy is verified on this modelling method. This would be useful to construct a precise model of the whole machine tools.
TL;DR: In this paper, a rigid-flexible-coupling virtual prototype of roll system is established for KOCKS mill, and dynamic characteristics of the roll system are analyzed under the limit condition of rolling 25 mm-40Cr bar.
Abstract: For KOCKS mill, dynamic characteristics of roll system are the main factors influencing the quality of rolled products. In this paper, the rigid-flexible-coupling virtual prototype of roll system is established. Under the limit condition of rolling 25 mm-40Cr bar, dynamic analysis on whole rolling process including idling, biting steel, steady rolling state and throwing steel is executed to obtain the time-domain dynamic characteristic curves of roll system based on rigid-flexible-coupling virtual prototype. In addition, free modal analysis on the roll system is also carried out under pre-stressing force. The research verifies the rationality of the prototype and provides a data platform for manufacturing of physical prototype.
TL;DR: In this paper, a comparison of results obtained from conventional and ultrasonic tests, in the high cycle fatigue region, from two viewpoints was made, with a short direct comparison of fatigue data, with similar conditions, has been undertaken.
Abstract: Ultrasonic fatigue testing is a convenient method to examine the S-N property in long life region, within a definite period. However, a distinct gap of the loading stressing frequency between conventional and ultrasonic testing methods (100–1,000 times larger) urges us to study a potential effect of the loading frequency. The present paper deals with a comparison of results obtained from conventional and ultrasonic tests, in the high cycle fatigue region, from two viewpoints. Firstly, a short direct comparison of fatigue data from conventional and ultrasonic tests, with similar conditions, has been undertaken. Secondly, overview analyses based on a far larger amount of data have been carried out for structural steels and aluminium alloys. Results obtained from this work give us some idea of the extent of differences between fatigue test results obtained at usual and ultrasonic frequencies in the fatigue regime of N f < 10 7 cycles. Particularly, the second study gives a potential 18% difference of fatigue strength for steels, whereas it reveals only a slight difference of fatigue behaviours for aluminium alloys.
TL;DR: In this article, a multiscale analysis method is put forward to evaluate the interfacial properties of the Al-Cu interface structure in the macro-scale, and the non-equilibrium molecular dynamics method is used to investigate interfacial heat transfer in the nanoscale.
Abstract: A multiscale analysis method is put forward to evaluate the interfacial properties. The finite element method is used to estimate the thermodynamics properties of the Al-Cu interface structure in the macroscale, and the non-equilibrium molecular dynamics method is used to investigate the interfacial heat transfer in the nanoscale. The deformation and nanocracks always appear at the outside edge of interface owing to the dissimilar thermal expansion coefficients. The diffusion thickness of different atoms increases with the increase of temperature. The diffusion enhances the heat transfer with the increase of temperature in the nanoscale. The results reveal the mechanism of the interfacial heat transfer, which is helpful in the design and manufacture of IC assembly.