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目的 为了有效量化库尔勒香梨因冲击载荷造成的损伤,实现库尔勒香梨冲击损伤量化评价。方法 以不同成熟度库尔勒香梨为实验材料,探究不同成熟度下冲击高度与香梨损伤程度的关系,构建冲击高度与香梨损伤程度模型,依据电学特性检测系统构建不同测试频率下电学参数并联等效电容(Cp)与冲击损伤程度的量化模型。结果 在同一冲击高度下,香梨损伤程度与成熟度成正比关系。当成熟度为H1—H5,冲击高度为30 cm,与瓦楞纸板进行冲击时,香梨表面未发现损伤。当冲击高度达到150 cm时,不同成熟度香梨表皮均已破损,不同成熟度香梨冲击高度与损伤程度量化模型决定系数R2为0.984 9~0.9985,可有效量化评价不同成熟度香梨冲击高度与损伤程度的关系。在同一测试频率下,Cp值随着香梨损伤程度的增加而增大。随着测试频率的升高,电学参数Cp值逐渐减小,5种测试频率、不同成熟度下的量化模型决定系数R2的平均值由高到低为1 kHz、1 MHz、10 kHz、100 kHz、100 Hz。结论 在测试频率1 kHz下,所构建的电学参数Cp与冲击损伤面积的量化模型检测效果相对最优,能够有效量化评价香梨的损伤程度。该模型的构建为... 相似文献
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《振动与冲击》2019,(3)
针对复合材料低速冲击损伤模式复杂多样以及损伤评估时损伤表征参数选取和简化困难的问题,通过编写VUMAT子程序,采用三维Hashin准则和Cohesive界面单元建立了复合材料从低速冲击损伤发生到损伤后压缩破坏的全过程仿真分析模型,用于复合材料低速冲击损伤评估,考虑了复合材料损伤模式的多样性,规避了损伤表征参数的选取和简化问题。分别进行了复合材料低速冲击试验和冲击后压缩试验,从冲击响应、损伤情况和剩余强度三方面将试验结果和仿真结果进行了对比,对比效果良好,表明建立的模型适用于复合材料低速冲击损伤评估。采用该模型进一步对冲击能量和冲击角度对损伤的影响进行了探讨。 相似文献
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运用ABAQUS有限元软件建立了HT3/5222碳纤维环氧树脂复合材料层合板的湿热冲击有限元模型,计算了室温干燥环境下不同冲击能量的冲击损伤结果,损伤形状与文献实验结果吻合较好。采用该模型计算分析了温度和吸湿率对层合板冲击损伤的影响,结果表明:冲击损伤面积随着温度的升高而增大,且温度越高,增幅越大;温度的升高对低能冲击影响更为严重,20J的冲击能量下,120℃下的损伤面积较20℃扩大了16.3倍;吸湿率对层合板冲击损伤的影响与温度类似,但高湿较高温对冲击损伤的影响更大;温度及吸湿率对层合板初始损伤冲击能量及穿透能量影响显著,初始损伤冲击能量由20℃时的14.7J下降到120℃时的6.2J。 相似文献
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基于连续介质损伤力学(CDM)方法,建立了分析复合材料层合板低速冲击问题的三维数值模型。该模型考虑了层内损伤(纤维和基体损伤)、层间分层损伤和剪切非线性行为,采用最大应变失效准则预测纤维损伤的萌生,双线性损伤本构模型表征纤维损伤演化,基于物理失效机制的三维Puck准则判断基体损伤的起始,根据断裂面内等效应变建立混合模式下基体损伤扩展准则。横向基体拉伸强度和面内剪切强度采用基于断裂力学假设的就地强度(in-situ strength)。纤维和基体损伤本构关系中引入单元特征长度,有效降低模型对网格密度的依赖性。层间分层损伤情况由内聚力单元(cohesive element)预测,以二次应力准则为分层损伤的起始准则,B-K准则表征分层损伤演化。分别通过数值分析方法和试验研究方法对复合材料典型铺层层合板四级能量低速冲击下的冲击损伤和冲击响应规律进行分析,数值计算和试验测量的接触力-时间曲线、分层损伤的形状和面积较好吻合,表明该模型能够准确地预测层合板低速冲击损伤和冲击响应。 相似文献
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对T300/QY8911复合材料层合板进行了低速冲击试验研究及数值仿真模拟。通过自由落体装置对层板进行冲击,并使用超声C扫描技术检测了层板冲击后的损伤状态,获得了不同能量下层板内部的损伤面积。建立了用于预测复合材料层合板在低速冲击作用下损伤演化的3D有限元模型,模型包含了用于模拟分层损伤的界面元和用于模拟纤维断裂、纤维挤压、基体开裂、基体挤裂等面内损伤形式的3D实体单元。该模型考虑了面内基体损伤对层间强度的影响。本文中的数值仿真结果和试验结果的对比验证了模型的合理性和有效性,文中还分析了影响低速冲击后层板内部分层面积的主要因素。 相似文献
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进行了复合材料层合板低速冲击和冲击后压-压疲劳试验。在疲劳试验过程中详细测量了损伤扩展情况,获得了损伤扩展规律。将冲击损伤等效为一圆形开孔,应用含椭圆形夹杂的杂交应力单元分析含圆孔有限大板的应力分布,采用特征曲线和点应力判据相结合的方式并通过引入损伤扩展规律建立了含低速冲击损伤复合材料层板压-压疲劳寿命预测模型。通过与试验数据的对比,证明了该模型的有效性。同时,该模型还可预报在疲劳载荷下含冲击损伤层板的剩余压缩强度。 相似文献
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Bin Sun 《Fatigue & Fracture of Engineering Materials & Structures》2020,43(8):1837-1850
This paper addresses a novel continuum damage‐based method for simulating failure process of quasi‐brittle materials starting from local damage initiation to final fracture. In the developed method, the preset characteristic length field is used to evaluate damage instead of element, which is used to reduce the spurious sensitivity. In addition, damage is only updated in the most dangerous location at a time for considering stress redistribution due to damage evolution, which is used to simulate competitive fracture process. As cases study, representative numerical simulations of two benchmark tests are given to verify the performance of the developed continuum damage‐based method together with a used damage model. The simulation results of the crack paths for two concrete specimens obtained from the developed method matched well with the corresponding experimental results. The results show that the developed continuum damage‐based method is effective and can be used to simulate damage and fracture process of brittle or quasi‐brittle materials. And the simulation results based on the developed method depend only the preset characteristic length field and not grid mesh. 相似文献
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In this paper we review the peridynamic model for brittle fracture and use it to investigate crack branching in brittle homogeneous and isotropic materials. The peridynamic simulations offer a possible explanation for the generation of dynamic instabilities in dynamic brittle crack growth and crack branching. We focus on two systems, glass and homalite, often used in crack branching experiments. After a brief review of theoretical and computational models on crack branching, we discuss the peridynamic model for dynamic fracture in linear elastic–brittle materials. Three loading types are used to investigate the role of stress waves interactions on crack propagation and branching. We analyze the influence of sample geometry on branching. Simulation results are compared with experimental ones in terms of crack patterns, propagation speed at branching and branching angles. The peridynamic results indicate that as stress intensity around the crack tip increases, stress waves pile-up against the material directly in front of the crack tip that moves against the advancing crack; this process “deflects” the strain energy away from the symmetry line and into the crack surfaces creating damage away from the crack line. This damage “migration”, seen as roughness on the crack surface in experiments, modifies, in turn, the strain energy landscape around the crack tip and leads to preferential crack growth directions that branch from the original crack line. We argue that nonlocality of damage growth is one key feature in modeling of the crack branching phenomenon in brittle fracture. The results show that, at least to first order, no ingredients beyond linear elasticity and a capable damage model are necessary to explain/predict crack branching in brittle homogeneous and isotropic materials. 相似文献
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H. Jasarevic A. Chudnovsky J.W. Dudley G.K. Wong 《International Journal of Fracture》2009,158(1):73-80
Observations and characterization of brittle fracture initiation in a micro-heterogeneous material (sandstone) are conducted
using the standard indirect tensile strength test. Acoustic emissions, optical microscopy and scanning electron microscopy
(SEM) are employed for monitoring and characterizing the discrete micro-mechanical events preceding macroscopical fracture.
The observations suggest that brittle fracture initiation is the end result of a microscopic damage accumulation process.
A simple statistical model of micro damage accumulation leading to brittle fracture in a micro-heterogeneous material is also
proposed. The model is calibrated by matching the coefficient of variation of measured ultimate stress with that resulting
from the proposed model. 相似文献
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In this paper, we present a damage model and its numerical solution by means of Fast Fourier Transforms (FFT). The FFT-based
formulation initially proposed for linear and non-linear composite homogenization (Moulinec and Suquet in CR Acad Sci Paris
Ser II 318:1417–1423 1994; Comput Methods Appl Mech Eng 157:69–94 1998) was adapted to evaluate damage growth in brittle materials. A non-local damage model based on the maximal principal stress
criterion was proposed for brittle materials. This non-local model was then connected to the Griffith criterion with the aim
of predicting crack growth. By using the proposed model, we carried out several numerical simulations on different specimens
in order to assess the fracture process in brittle materials. From these studies, we can conclude that the present FFT-based
analysis is capable of dealing with crack initiation and crack growth in brittle materials with high accuracy and efficiency. 相似文献
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A constitutive ply model is developed to allow for the simulation of laminated structures made of fiber-reinforced polymers. The model accounts for stiffness degradation accompanied by strain hardening (i.e. distributed brittle damage), unrecoverable strain accumulation (i.e. multi-surface plasticity), and stiffness degradation accompanied by strain softening (i.e. localized brittle damage). Owing to the characteristics of such ply materials the model handles these effects and their evolutions in an anisotropic manner. 相似文献
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A mechanics based theory for surface degradation in brittle material systems is introduced. Surface degradation is directly related to damage progression. For this reason the mechanics of damage evolution is presented first. Subsequently, relations governing surface degradation mechanisms are derived and discussed in detail. It is shown that surface degradation can capture important properties of brittle materials such as scale (size) and shape effects, surface damage growth and subsequent bursting instabilities. Finally, the problem of transferring information from laboratory experiments to large scale problems is discussed; the need for further experimental and theoretical research is pointed out. 相似文献
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In order to understand the processes involved in the high-velocity rain erosion of brittle materials the impact damage produced in soda-lime-silica glass by single and multiple jet impact was studied. The damage was quantified by measuring the post-impact strength of specimens. It is shown that the impact damage depends on the impact velocity, the number of impacts and the specimen dimensions. A new analysis for calculating the velocity dependence of jet/drop impact damage in brittle materials is presented. The model is based on Hertzian contact analysis and dynamic fracture mechanics and takes into account the statistical nature of the flaws in the specimen. A good qualitative agreement with experimental results is obtained. 相似文献
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Demetriou MD Launey ME Garrett G Schramm JP Hofmann DC Johnson WL Ritchie RO 《Nature materials》2011,10(2):123-128
Owing to a lack of microstructure, glassy materials are inherently strong but brittle, and often demonstrate extreme sensitivity to flaws. Accordingly, their macroscopic failure is often not initiated by plastic yielding, and almost always terminated by brittle fracture. Unlike conventional brittle glasses, metallic glasses are generally capable of limited plastic yielding by shear-band sliding in the presence of a flaw, and thus exhibit toughness-strength relationships that lie between those of brittle ceramics and marginally tough metals. Here, a bulk glassy palladium alloy is introduced, demonstrating an unusual capacity for shielding an opening crack accommodated by an extensive shear-band sliding process, which promotes a fracture toughness comparable to those of the toughest materials known. This result demonstrates that the combination of toughness and strength (that is, damage tolerance) accessible to amorphous materials extends beyond the benchmark ranges established by the toughest and strongest materials known, thereby pushing the envelope of damage tolerance accessible to a structural metal. 相似文献