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1.
工程实际中,建筑用钢不可避免地会接触空气而遭受氧化腐蚀。本文开展了地震区域大力推广应用的HRB400EIII级钢筋氧化前、后的低周疲劳行为研究。采用轴向应变控制方法,在MTS809拉扭复合疲劳试验机上开展了大量的低周疲劳试验,获得了氧化前、后HRB400EIII级钢筋低周疲劳性能,如循环应力响应特征、循环应力-应变关系以及寿命预测公式等。通过断口电镜扫描发现,氧化后HRB400EIII级钢筋的裂纹均萌生于试件表面,且存在多处裂纹源。研究结果表明,氧化腐蚀对低周疲劳寿命及微观断裂机理方面均存在明显影响,并从力学性能变化的角度对引起差异的原因进行了解释。 相似文献
2.
SMT solder joint's semi-experimental fatigue model 总被引:6,自引:0,他引:6
The low-cycle fatigue induced by thermal cycling is the major concern in the reliability of surface mounted technology (SMT) for electronic packaging; however, dynamic loading effects to solder joint fatigue life have not been thoroughly investigated. In fact, the high-cycling fatigue induced by vibration can also contribute a significant effect. In certain circumstances it can become the dominant failure case when semiconductor devices are used in a vibration environment. In this paper, according to random vibration theory, a random fatigue semi-experimental model of SMT solder joint in random vibration condition is created and a series of vibration fatigue experimental vehicles including PBGA256 assembly were conducted. Compared with random vibration test results, its results are good enough to predict solder joints' fatigue. 相似文献
3.
Xishu Wang ;Huaihui Ren ;Bisheng Wu ;Su Ja ;Norio Kawagoishi 《Acta Mechanica Solida Sinica》2014,27(3):245-258
Fatigue cracking tests of a solder joint were carried out using in-situ scanning electron microscopy (SEM) technology under tensile and bending cyclic loadings. The method for predicting the fatigue life is provided based on the fatigue crack growth rate of the solder joint. The results show that the effect of the loading type on the fatigue crack growth behavior of a solder joint cannot be ignored. In addition, the finite element analysis results help quantitatively estimate the response relationship between solder joint structures. The fatigue crack initiation life of a solder joint is in good agreement with the fatigue life (N50%) of a totally electronic board with 36 solder joints. 相似文献
4.
Few studies have been made on the fracture mechanics of polymers, their resistance to plastic failure, fatique rupture, and the adverse effects of environmental conditions, in contrast to the numerous studies conducted on metallic materials. Since fatigue is characterized by very local and cyclic fractures, in the present study a real-time fine-grid method was applied to study the fatigue rupture of polymers: to examine changes in local strain at the root of the notch during the process of crack initiation, the local strain at the tip of the crack during crack propagation and the relation between the plastic zone formed in front of the crack tip and the rate of crack propagation. As a result, strong correlation between three proposed parameters of the local crack-tip strain, the crack initiation and the propagation rate was obtained, and the mechanism of low-cycle fatigue rupture of polymers could be discussed.Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Portland, OR on June 5–10. 相似文献
5.
《International Journal of Solids and Structures》2007,44(17):5680-5694
In ball grid array (BGA) packages, solder balls are exposed to cyclic thermo-mechanical strains arising from the thermal mismatch between package components. Thermo-mechanical fatigue crack propagation in solder balls is almost always observed at the chip side of the bump/pad junction. The objective of the experimental part of this study is to characterize the bump/pad interface under fatigue loading. Fatigue specimens are prepared by reflowing Sn3.8Ag0.5Cu lead-free solder alloy on Ni/Au substrates. Obtained results show that fatigue damage evolution strongly depends on the microstructure. Applied strain and solder volume both have an influence on the fatigue damage mechanism. In the numerical part of the study, fatigue experiments are modeled using the finite element technique. A cohesive zone approach is used to predict the fatigue damage evolution in soldered connections. Crack propagation is simulated by an irreversible linear traction–separation cohesive zone law accompanied by a non-linear damage parameter. Cohesive zone elements are placed where failure is experimentally observed. Damage evolution parameters for normal and tangential interaction are scrutinized through dedicated fatigue tests in pure tensile and shear directions. The proposed cohesive zone model is quantitatively capable of describing fatigue failure in soldered joints, which can be further extended to a numerical life-time prediction tool in microelectronic packages. 相似文献
6.
《International Journal of Solids and Structures》2006,43(7-8):1928-1945
Ball shear tests were investigated in terms of the effects of test parameters, i.e., shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. Two representative Pb-free solders were examined in this work: Sn–3.5Ag and Sn–3.5Ag–0.75Cu. The substrate was a common solder mask defined (SMD) type with solder bond pad openings of 460 μm in diameter. The microstructural investigations were carried out using scanning electron microscopy (SEM), and the intermetallic compounds (IMCs) were identified with energy dispersive spectrometry (EDS). Shear tests were conducted with the two varying test parameters. It was observed that increasing shear height at a fixed shear speed has the effect of decreasing shear force for both Sn–3.5Ag and Sn–3.5Ag–0.75Cu solder joints, while the shear force increased with increasing shear speed at fixed shear height. Shear heights that were too high had some negative effects on the test results such as unexpectedly high standard deviation values or shear tip sliding from the solder ball. Low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces. 相似文献
7.
Milton M. Leven 《Experimental Mechanics》1973,13(9):353-372
Twenty tests were performed on a 1 Cr?1 Mo?1/4 V rotor steel at 1000° F (538°C) to determine the interaction of creep and low-cycle fatigue. These tests involved five different types of strain-controlled cycling: creep at constant tensile stress; linearly varying strain at different frequencies; and hold periods at maximum compressive strain, maximum tensile strain, or both. The experimental data were then used to characterize the interaction of creep and fatigue by the:
- Frequency-modified strain-range approach of Coffin;
- Total time to fracture vs. the time of one cycle relation as proposed by Conway and Berling;
- Total time to fracture vs. the number of cycles to fracture characterization of Ellis and Esztergar;
- Summation of damage fractions obtained from tests using interspersed creep and fatigue as proposed by the Metal Properties Council;
- Strain-range-partitioning method of Manson, Halford, and Hirschberg.
8.
Uniaxial ratcheting and fatigue failure of tempered 42CrMo steel were observed by the tests under the uniaxial stress-controlled cyclic loading with non-zero mean stress [G.Z. Kang, Y.J. Liu, Mater. Sci. Eng. A 472 (2008) 258–268]. Based on the obtained experimental results, the evolution features of whole-life ratcheting behavior and low-cycle fatigue (LCF) damage of the material were discussed first. Then, in the framework of unified visco-plasticity and continuum damage mechanics, a damage-coupled visco-plastic cyclic constitutive model was proposed to simulate the whole-life ratcheting and predict the fatigue failure life of the material presented in the uniaxial stress cycling with non-zero mean stress. In the proposed model, the damage was divided into two parts, i.e., elastic damage and plastic damage, which were described by the evolution equations with the same form but different constants, since the maximum applied stresses in most of loading cases were lower than the nominal yielding strength of the material. The ratcheting of the material was still described by employing a nonlinear kinematic hardening rule based on the Abdel-Karim–Ohno combined kinematic hardening model [M. Abdel Karim, N. Ohno, Int. J. Plast. 16 (2000) 225–240] but extended by considering the effect of damage. The maximum strain criterion combined with an elastic damage threshold was employed to determine the failure life of the material caused by two different failure modes, i.e., fatigue failure (caused by low-cycle fatigue due to plastic shakedown) and ductile failure (caused by large ratcheting strain). The simulated whole-life ratcheting behavior and predicted failure life of tempered 42CrMo steel are in a fairly good agreement with the experimental ones. 相似文献
9.
Very high cycle fatigue (VHCF) behaviors of bridge steel (Q345) welded joints were investigated using an ultrasonic fatigue test system at room temperature with a stress ratio R = ?1. The results show that the fatigue strength of welded joints is dropped by an average of 60% comparing to the base metal and the fatigue failure still occurred beyond 107 cycles. The fatigue fracture of welded joints in the low cycle regime generally occurred at the solder while at the heat-affected zone (HAZ) in the very high cycle regime. The fatigue fracture surface was analyzed with scanning electron microscopy (SEM), showing welding defects such as pore, micro-crack and inclusion were the main factors on decreasing the fatigue properties of welded joints. The effect of welding defects on the fatigue behaviors of welded joints was discussed in terms of experimental results and finite element simulations. 相似文献
10.
An investigation about interference fit effect on improving fatigue life of a holed single plate in joints 总被引:1,自引:0,他引:1
T.N. Chakherlou M. Mirzajanzadeh B. Abazadeh K. Saeedi 《European Journal of Mechanics - A/Solids》2010,29(4):675-682
In this article, the effect of interference fit on fatigue life of holed plate of mechanical joints was investigated both experimentally and numerically. In the experimental part, fatigue tests were carried out on the holed specimens of Al 7075-T6 alloy in which oversized steel pins were force fitted to them. These fatigue tests were conducted on open hole specimen and specimens with 1, 1.5, 2 and 4% nominal interference fit sizes at different cyclic longitudinal loads. From these tests the stress-life (S–N) data for different interference fit sizes were obtained. The results show that interference fit increases fatigue life compared to open hole specimens. In the numerical part of the investigation, 3D finite element simulations have been performed to obtain stress (or strain) histories and distributions around the hole due to interference fit and subsequent cyclic longitudinal loading using FEM package. The stress history from finite element (FE) simulation was used to explain the reason for fatigue life improvement in the interference fitted specimens. 相似文献
11.
Low-cycle flexural fatigue tests on an epoxyglass-fabric composite were performed at large constant-deflection amplitudes using a modified Tatnall-Krouse plate-bending fatigue-testing machine. Strain vs. cyclesto-failure data were obtained for cyclic speeds of 25, 150 and 425 cpm. The rate of cycling was found to have a strong effect on the low-cycle fatigue life of this composite, but the effect was less pronounced at higher numbers of cycles. 相似文献
12.
A crystallographic model for the orientation dependence of low cyclic fatigue property of a nickel-base single crystal superalloy 总被引:3,自引:0,他引:3
IntroductionMuchworkhasbeencarriedouttoinvestigatetheinfluenceoforientationandstrainrateonthemechanicalpropertyofnickel_basesinglecrystalsuperalloys .Inparticular,theanomalousyieldingbehavior,tension/compressionasymmetryandorientationdependencehavebeen… 相似文献
13.
Methods of achieving biaxial-stress states in fatigue tests are reviewed. A new design of equipment that produces five distinct biaxial-stress states by simultaneous direct pressurization and axial loading of thinwalled cylindrical specimens is described. Four variations of stress state are obtained by the use of two sizes of specimen and by reversal of the pressurizing connections. The fifth state is obtained by direct pressurization without axial load. The actual magnitudes of stress in the specimen are computed from the output of the load cell in the reaction frame in which the biaxial-testing device is mounted. Additional stress ratios are obtained using standard uniaxial and torsional cyclic-testing arrangements. The initial program using this equipment was to investigate the effects of biaxiality on the cyclic properties and low-cycle fatigue behavior of normalized 1018 mild steel, under fully reversed constant-amplitude strain control. Control was achieved using a servo-controlled, electrohydraulic testing system with one of the two clipon strain transducers, that were mounted on the specimen, providing the controlling electrical signal. The system allowed direct recording of the stress-strain hysteresis loops in both principal directions. The behavior of the equipment and the modes of failure of the specimens are described and some test data are presented. The range of application and limitations of the equipment for further cyclic biaxial testing are discussed. 相似文献
14.
To investigate whether the two fatigue processes of crack initiation and propagation can be combined, the change of local notch root strain and its history, as well as the change of local crack tip strain and the local strain history, of a fatigued element ahead of the propagating crack tip up to failure in a polycarbonate subjected to low-cycle fatigue tests are measured by the fine grid method. As a result, the existence of a unified local strain field in which the two fatigue processes can be substantially combined is experimentally confirmed. Therefore, the local crack tip strain may be examined by a simpler, one-parameter approach for fatigue life estimation. 相似文献
15.
The effects of out-of-phase or nonsynchronous straining on low-cycle fatigue was investigated. Biaxial strains were imposed on thin-walled tubular 7075-T6 aluminum specimens by tension—compression and torsion. Phase angles of 0 deg, 30 deg, 45 deg, 60 deg and 90 deg were applied between two strains. It was found that out-of-phase cycling has an effect on the failure mode in the low-cycle-fatigue range. An analysis based on the maximum total strain in three-dimensional strain is proposed for treating “out-of-phase” straining conditions in low-cycle fatigue. 相似文献
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18.
Despite extensive research on the mechanical properties of one-dimensional (1-D) nanomaterials such as nanowires and nanotubes in the past two decades, experimental data on the fatigue behavior of 1-D building blocks are still very limited. Here, we demonstrate the first quantitative in situ tensile fatigue testing of individual nanowires inside a high-resolution scanning electron microscope (SEM), based on the nanoindenter-assisted “push-to-pull” dynamic tensile straining mechanism. With the robust micro-mechanical devices and independent quantitative nanoindenter for actuation and force sensing, we achieved both stress- and strain-controlled cyclic tensile loading on nanowire samples with variable loading frequencies up to 10 Hz, and demonstrated the low-cycle fatigue behavior of pristine single crystalline nickel (Ni) nanowires. 相似文献
19.
The Chaboche nonlinear kinematic hardening model: calibration methodology and validation 总被引:2,自引:0,他引:2
This work studies how a nonlinear kinematic model aimed for cyclic plasticity could be put into effect and used within a FEM code. A correct modeling of cyclic elasto-plastic behavior can be exploited in low-cycle fatigue life investigation as well as in manufacturing problems related to springback prediction. The chosen formulation has been proposed by Chaboche, and it is implemented in most of the commercial codes used for nonlinear FEM simulations. At first, a procedure for the proper identification of unknown material model parameters has been put forward. This calibration, based on the data collected from experimental low-cycle fatigue tests, has been performed by means of an inverse method. Laboratory tests differ according to the type of material under investigation. A classification can be operated distinguishing between specimens obtained from bulk materials or from sheet metals. For the former, standard tension-compression tests have been performed, while for the latter, a dedicated testing equipment for three-point bend cyclic tests has been devised. Then, further experimental tests have been run to check model transferability: different strain per cycle amplitudes, asymmetric strain cycling and different stress triaxiality levels have been investigated. For each of these tests, experimental vs. FEM results have been analyzed to show the level of agreement that has been reached. 相似文献