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2011 Vol. 32, No. 1
Published:
论文
1
DUCTILITY OF POLYMER-SUPPORTED METAL FILMS WITH CURVED INTERFACES
Electronic components in modern flexible electronics are connected by interconnects, having typically the form of metal films on polymer substrates. Since the film/substrate system may sustain large deformation in practice, how to improve the ductility of polymer-supported metal films is a key issue for flexible electronics technology. Previous researches demonstrate that the interfacial bond strength can be improved by surface treatments of the substrate (such as acid/alkali soaking and sandblasting), but few consider how this would affect the ductility of the film/substrate system. We study experimentally the ductility of a polyimide-supported Cu film with rough interface (due to sandblasting) and show that, upon tensile loading along the direction of film surface, the crack density can be reduced by increasing substrate surface roughness. The distribution of tensile stresses in the film and their effects on film cracking (initiation and propagation) are subsequently studied using the method of finite elements. The rough interface is idealized as a perfect curved interface of sine wave form and two different films, one with flat surface and the other having curved surface (identical to that of the interface) are modeled. Obtained results show that a rough (curved) interface can reduce the tensile stresses along the film surface so as to restrain the cracking of the film. Finally, we employ the cohesive zone model to study the initiation and spreading of damage in the film and interfacial cracking of the curved interface. It is demonstrated that both the damage and length of interfacial crack are reduced due to interface roughening. Interface roughening provides a new route for improving the ductility of polymer-supported metal films.
2011 Vol. 32 (1): 1-9 [
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1393
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10
Elasto-plastic cohesive zone modeling of delamination of Si/Cu interface in a nano-cantilever
Previous experimental tests [Thin Solid Films 516: 1925-1930] have shown that nano-cantilever Si/Cu/SiN/Pt/C tend to delaminate along the interface between Cu and Si layers when subject to monotonically bending load, the measured load-displacement curve shows a clear nonlinear behavior. Based on the continuum mechanics model, this study carries out numerical simulation and analysis of the crack initiation and propagation along the interface Si/Cu, which was observed in the above tests. Exponential type cohesive zone model (CZM) using finite element method was adopted to characterize the constitutive relationship of the interface Si/Cu, Cu layer obeys either linear elastic or Ramberg-Osgood elasto-plastic constitutive relationship. The characteristic parameters of interface bonding strength are extracted through calibration via experimental results. The simulation results show that (i) cohesive strength and cohesive energy are the dominating CZM parameters, exponential CZM is suitable to describe the interfacial delamination between Cu and Si layers when Cu layer is linear elastic; (ii) comparing to bulk Cu, nano-scale Cu has a much higher yield stress and hardening rate, which leads to little plastic deformation of the nano-cantilever specimen during the whole delamination process. These predictions are in accordance with the experimental results.
2011 Vol. 32 (1): 10-20 [
Abstract
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858
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845
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29
A multi-scale coupling theory for
2011 Vol. 32 (1): 29-36 [
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643
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735
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37
Notched fatigue life prediction under multiaxial loading
Based on the critical plane approach and the analysis of the proposed fatigue life prediction model applied to the smoothing tubular specimen, the recently proposed multiaxial fatigue life prediction model is extended to assess multiaxial fatigue life for notched specimens. In addition, with the aid of finite element method (FEM), the orientation of the critical plane and the effective cyclic parameter are determined by using the coordinate transformation principle. In the meantime, the proposed model is modified when the mean stress is existence.
2011 Vol. 32 (1): 37-42 [
Abstract
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662
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43
Studies on Low-velocity Impact Damage of Stitched Composite Laminates
A 3D dynamic finite element model with stitching threads is described as the spatial truss element is proposed to predict the progressive damage of stitched laminates. Combined with the user-defined material constitutive program of ABAQUS/Explicit, the typical failure modes, such as fiber break, matrix crushing, matrix cracking and delamination are simulated by employing the strain-based Hashin and Yeh failure criterion The dynamic response and damage propagation of stitched/unstitched laminates were simulated with this method. The numerical results are well agreed with the measured results and verify the effectiveness of the model. The effects of the impact velocity, the component material systems and the main stitching parameters on the dynamic response and damage evolution of stitched composites were discussed in detail, and some valuable conclusions are drawn herein. The results indicate that the stitched threads are not broken during the low velocity impact. The failure modes and damage evolution of stitched laminates are similar to the unstitched laminates, but the former has smaller damage areas. With the stitching density and strength of threads increasing, the stitching threads restrain damage evolution more effectively.
2011 Vol. 32 (1): 43-56 [
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685
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57
The optimization of a tensile split Hopkinson bar and the determination of the dynamic constitutive models for Oxygen-free high conductivity copper
A optimizing analysis of a tensile split Hopkinson bar (TSHB) is presented to make effective measure for the stress, strain and strain rate in the specimen. The numerical simulation of the TSHB test is performed including the effects of interconnecting linkage on the experimental data. Gauge length and geometry of the TSHB specimen are required to reduce ring-up time, inertial effects, and to result in uniaxial stress and uniform stress and strain state in the specimen. The stress-strain curves of quasi-stratic tension tests and the optimized TSHB tests of different strain rates and temperatures are obtained and fitted to determine the J-C and Z-A type dynamic constitutive models for a oxygen-free high conductivity (OFHC) copper. The reflected and transmitted pulses computed with the determined constitutive models for OFHC copper can be consistent with the experimental data to a certain extent. It is indicated that TSHB tests should be optimized and the determined constitutive models of the specimen should be checked by using the numerical simulations of TSHB tests.
2011 Vol. 32 (1): 57-63 [
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1497
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64
Experimental Study on Three-Dimensional (3-D) Propagation from a Pre-existing Ellipse Flaw under Compression-Shearing
Some testing samples containing a pre-existing ellipse flaw (b/a=0.5) made from non-transparent mortar and transparent resin material are built. Under uniaxial compression, a series of observation experiments on the 3-D fracture process of the flaw are carried out. The experimental results show that the primary crack shapes are basically similar in the two different materials, are a pairs of antisymmetric wrapping wing cracks. But, their initial fractured places are different. Some new cracks initiated almost simultaneously near the long-axis tips of the ellipse flaw, yet not on its long-axis tips in transparent resin. but, cracks started to extend near short-axis tips, yet not on its tips in mortar samples. And, the finally fractured patterns from the samples from the two materials are greatly different under the same loading. The samples are cleaved by macroscopically tensile fracture planes in resin samples, cut by compression-shearing fracture faces in mortar ones. It may be resulted from material behavior and initial fractured place. The results from 3-D fracture analysis agree with the observed phenomena in experiments. The result from the 2-D simplified mode only is the characteristic solution in the normal plane cross ellipse long-axis, and the fractured effect from Mode III is omitted. It need further investigate the 3-D fracture mechanism of pre-existing flaws with mode III fracture.
2011 Vol. 32 (1): 64-73 [
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697
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553
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简报
82
Numerical validation of operating point for cumulative second-harmonic longitudinal guided wave generation in pipe
The potential advantage of using nonlinear guided waves to track early damage is that they are sensitive to micro-cracks or degradation that manifest in the form of micro-structural changes. The capable of propagating long distance makes the cumulative nonlinear second-harmonic longitudinal guided wave an ideal candidate to interrogate pipes. A scheme to generating axisymmetric second-harmonic longitudinal guided waves that is mono-frequency zero order longitudinal waves in a homogeneous, isotropic, stress-free elastic solid pipe is presented in this paper. The possible pairs corresponding to the scheme are obtained according to the condition of phase matching. Then they are validated numerically based on the other condition, i.e., non-zero power flux. At last the operating points to generate second-harmonic longitudinal guided waves in pipes are determined.
2011 Vol. 32 (1): 82-87 [
Abstract
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620
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539
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88
PARALLEL SIMULATION OF FRP-CONCRETE DEBONDING FAILURE PROCESS
The interfacial bonding and anti-tensile behavior between FRP and concrete is the key problem for the application of FRP to strengthen concrete structures. In this paper, the 3D Parallel Realistic Failure Process Analysis (RFPA3D-parallel) is employed to investigate the bonding behavior in FRP-concrete interface based on the single shear testing results on FRP-concrete in laboratory. Numerical simulations visually reproduce the complete three-dimensional debonding process and characteristics of FRP bonded to concrete, which is a progressive process induced by meso-scopic cracks initiation and growth and macroscopic fractures form. The damage of FRP-concrete structures under external loading can be founded by monitoring the acoustic emission induced by microcracking in FRP-concrete. Based on the simulated stress evolution and deformation distribution along the length FRP sheet, the deformation and debonding failure can thus be divided into four stages, i.e., elastic, elastic-softening, elastic-softening-debonded and softening-debonded stage. The numerical approach in this study provides a useful tool for enhancing our understanding of cracking and debonding failure process and mechanism of FRP-concrete and our ability to predict mechanical performance and reliability of these FRP sheet bonded to concrete structures.
2011 Vol. 32 (1): 88-94 [
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711
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571
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95
基于Green函数的动态载荷区间识别方法研究
基于位移响应时间序列，提出了对结构动态载荷时间历程进行识别的区间方法。载荷在时域内可用一系列脉冲响应函数来表示，系统的响应是载荷与单位脉冲响应函数(Green函数)的卷积分。采用区间向量定量化不确定但有界的位移响应时间序列，并将Green函数离散，构造区间线性方程组。将载荷识别反问题转换为正问题，采用区间摄动法求解区间方程，从而得到待识别载荷时间历程的区间估计。通过不同测点下识别得到的载荷区间进行求交运算，改进识别结果。通过一个十杆桁架系统的载荷识别问题，说明了本文方法的可行性和有效性。
2011 Vol. 32 (1): 95-101 [
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704
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102
Nonlinear Calculation on the Pressure-filled Telescopic Water Seal Based on the Three Ogden Formula
DOI:
Abstract: Considering the importance of the mechanical properties for the rubber-like material on the water-seal design, Mooney-Rivlin formula and Three Ogden formula has been applied in the processing experimental data of uniaxial tension test, uniaxial compression test and pure shear test. The nonlinear calculation for the free extension of pressure-filled telescopic water seal has been done by using the fitting parameters from the both formulas. Then the comparative study between the calculated results and test results has been carried. The results show that Three Ogden formula is better than Mooney-Rivlin formula on describing the mechanics properties of rubber-like material. It is more precise to use Three Ogden formula in nonlinear finite element calculation, which provides a good reference for the design and calculation of gate water seal structure.
2011 Vol. 32 (1): 102-107 [
Abstract
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711
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600
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