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191.
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
192.
193.
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
194.
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
195.
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
196.
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
197.
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
198.
纤维金属层极疲劳寿命预测的研究进展 总被引:1,自引:0,他引:1
简要介绍了纤维金属展板的起源、性能特点、应用现状与前景,对其疲劳损伤机理作了简要分析.对影响层板疲劳寿命的两个关键因素──桥接应力与分层扩展从理论分析与测量技术两方面结合自己的研究成果作了系统评析.详细分析了层板在等幅疲劳下寿命预测的研究现状.介绍了层板在变幅载荷下的疲劳行为(包括裂纹扩展与分层扩展)与寿命预测的研究进展,指出了目前预测模型的有待改进的建议. 相似文献
199.
200.
提出疲劳裂纹尖端塑性核半径门榄值Rth的概念及计算方法,Rth是材料性质,在满足光塑性相似关系要求及模型与原型几何形状尺寸相同的前提下,模型与原型间的相似系数n为两种材料屈服极限之比。 相似文献