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181.
A. Johansen D. Sornette 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):163-181
The fracture of materials is a catastrophic phenomenon of considerable technological and scientific importance. Here, we analysed
experiments designed for industrial applications in order to test the concept that, in heterogeneous materials such as fiber
composites, rocks, concrete under compression and materials with large distributed residual stresses, rupture is a genuine
critical point, i.e., the culmination of a self-organization of damage and cracking characterized by power law signatures. Specifically, we analyse
the acoustic emissions recorded during the pressurisation of spherical tanks of kevlar or carbon fibers pre-impregnated in
a resin matrix wrapped up around a thin metallic liner (steel or titanium) fabricated and instrumented by Aérospatiale-Matra
Inc. These experiments are performed as part of a routine industrial procedure which tests the quality of the tanks prior
to shipment. We find that the seven acoustic emission recordings of seven pressure tanks which was brought to rupture exhibit
clear acceleration in agreement with a power law “divergence” expected from the critical point theory. In addition, we find
strong evidence of log-periodic corrections that quantify the intermittent succession of accelerating bursts and quiescent
phases of the acoustic emissions on the approach to rupture. An improved model accounting for the cross-over from the non-critical
to the critical region close to the rupture point exhibits interesting predictive potential.
Received 6 July 2000 相似文献
182.
In this paper, a new finite element method for the flow analysis of the viscous incompressible power-law fluid is proposed by the use of penalty-hybrid/mixed finite element formulation and by the introduction of an alternative perturbation, which is weighted by viscosity, of the continuity equation. A numerical example is presented to exhibit the efficiency of the method.The Project Supported by the National Natural Science Foundation of China. 相似文献
183.
184.
欧洲近海结构用钢研究计划的进展 总被引:3,自引:0,他引:3
欧洲近海结构用钢研究计划在第一阶段(1975—80年)关于海洋焊接结构在疲劳载荷下工作性能的研究基础上,于1981—87年继续进行了第二阶段的研究工作。参加国家有欧洲经济共同体6国及挪威、加拿大等。本文综合报道第二阶段研究情况与主要成果,内容包括:板厚对疲劳强度的影响,焊后改进技术与腐蚀疲劳,疲劳载荷及变幅疲劳试验,疲劳分析的断裂力学方法,某些管节点的应力分析等;并对研究计划的背景及今后研究工作的方向作了介绍。 相似文献
185.
通过对PBGA焊点形态参数与焊点热疲劳寿命的正交试验,利用大型统计分析软件进行多元线性回归分析,建立起PBGA焊点高度固定,芯片在上焊点高度不固定及芯片在下焊 度不固定三种不同工作条件下形态参数与热疲劳寿命之间的回归多项表式,即PBGA焊点形参数与热疲劳寿命的关系表达式。 相似文献
186.
激光冲击处理工艺因素对铝合金疲劳寿命影响的研究 总被引:1,自引:0,他引:1
约束层和激光脉冲功能和密度是影响激光冲击处理强化效果的重要工艺因素,本文研究了不同的约束层和激光脉冲功率密度对铝合金疲劳寿命的影响。疲劳试验结果表明,约束层冲击阻抗越大,激光脉冲功率密度越高,铝合金激光冲击处理后疲劳寿命的提高越显著。 相似文献
187.
Yoshiharu Kariya Yasunori Hirata Masahisa Otsuka 《Journal of Electronic Materials》1999,28(11):1263-1269
Quad Flat Pack (QFP) Leads/Sn-3.5Ag-X (X=Bi and Cu) joint was thermally cycled between 243 K and 403 K or 273 K and 373 K,
and both metallographic examination and mechanical pull test were performed to evaluate thermal fatigue damage of the joint.
The addition of bismuth drastically degrades the thermal fatigue resistance of Sn-3.5Ag solder. On the other hand, the pull
strength of Sn-3.5Ag-Cu solder joints slightly decreased with increasing number of thermal cycles, though it still remains
higher in comparison to that for conventional Sn-37Pb or bismuth containing solder joint. The behavior observed here reflects
the isothermal fatigue properties of bulk solder, because thermal fatigue crack initiates at the surface of solder fillet
and propagates within the fillet in an early stage of fatigue damage. Furthermore, the lead phases lying at the interface
between lead-frame and bismuth containing solder joint may promote the crack propagation at the interface, resulting in the
extremely low thermal fatigue resistance of the joint. 相似文献
188.
Solder joint reliability under thermal cycling is a key problem in electronic packaging. Accelerated life testing (few cycles,
larger temperature excursions) is often a practical necessity in predicting fatigue life in field environments (many cycles,
smaller temperature excursions). Complex solder behavior with marked temperature dwell and cycle time influence at slower
frequencies makes this a difficult problem. A dynamic model is presented which couples the effect of instability of coarsened
grain shear band evolution in microstructure with the change in macroscopic constitutive behavior. Key features of the model
include effects of shear band thickness compared with total solder joint thickness, pertinent to small scale design, and frictional
resistance at slow deformation rates. Model correlation with test data is discussed and applied to the accelerated life test
design. 相似文献
189.
Degradation of the residual strength of a glass-fiber-reinforced polyester composite of a lay-up typical of the wind rotor
blade material is studied at low-cycle fatigue. A gradual reduction of the residual strength is observed as expected for GRP,
accompanied by an increasing scatter of strength. The residual strength model based on the strength-life equal rank assumption
yields an accurate approximation of experimental data. The strength reduction at a stress level corresponding to high-cycle
fatigue (N>10
6 cycles) appears to correlate well with the test results at higher stress levels, which indicates that the strength degradation
at the design stress level can be evaluated using low-cycle tests. Assuming that the parameters of the strength degradation
model do not depend on the applied stress level, the residual strength data obtained in low stress level tests of comparatively
short duration can be used to estimate the average fatigue life at the same stress thus reducing the total test time.
Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 5, pp. 595–604, September–October, 1999. 相似文献
190.
二级加载下疲劳可靠性分析 总被引:1,自引:0,他引:1
基于二维概率Miner准则,建立了在二级变幅加载下进行疲劳可靠性分析的系统方法并采用八组较大子样的二级低高和高低加载下的试验数据进行了验证、结果表明;本文方法初步实现了对第一级加载后的剩余疲劳寿命和二级加载下的疲劳总寿命进行较为准确的可靠性预测,预测值与试验值吻合良好 相似文献