共查询到20条相似文献，搜索用时 265 毫秒
1.
推导了应力控制和应变控制模式下沥青混合料的热力学疲劳损伤模型.选取回弹模量作为损伤硬化参数,提取出一个与动态模量相关的损伤变量作为评估指标.所获得的2种控制模式下的损伤演化规律中保留了一个与加载水平有关的非负材料参数m,具有与Chaboche疲劳模型相似的形式.在每种控制模式下,采用4组加载水平所获得的疲劳损伤试验数据校核模型并确定参数.由此发现参数m与荷载水平呈指数关系.利用所获得的演化方程可阐述2种控制模式下的损伤演化差异,即在应变控制模式下,疲劳损伤演化由快变慢,在应力控制模式下情况则相反.通过利用损伤等效原理计算等效荷载循坏次数,该模型还解释了在多级加载条件下,2种控制模式的疲劳演化差异:在应变控制的疲劳模式下,所加荷载等级按照从低荷载到高荷载的顺序会加速损伤演化,而在应力控制的疲劳模式下,相反的荷载施加顺序可延长疲劳寿命. 相似文献
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《实验室研究与探索》2019,(9):38-41
采用两步实验法研究了加载历史对聚乙烯管道力学性能和损伤演化规律的影响。在第1步实验中,通过单轴拉伸、蠕变和疲劳3种加载模式将聚乙烯缺口管道环式样拉伸到预先设定的预应变值。2个月后,第2步实验采用加载速度为0. 001 mm/min的单轴拉伸实验表征管道环式样力学性能的变化。实验结果表明:聚乙烯管道的屈服应力和切线模量随着第1步实验预应变的增大而减小,但残余塑性应变随着预应变的增大而增大。基于实验测得的切线模量的变化建立了聚乙烯管道的损伤演化方程,实验发现力学性能的衰减程度和损伤演化与第1步实验的加载模式(单轴拉伸,蠕变或者疲劳加载)和加载速度有关。 相似文献
3.
基于ABAQUS有限元分析方法,对两种热处理工艺下的16 Mn钢中MnS夹杂物在同一拉伸载荷作用下的应力和应变分布进行了研究。结果表明,两种晶粒尺寸的材料在长条形MnS夹杂物附近存在着垂直于加载方向的X形状的Mi-ses应力和PEEQ集中区。但细晶的16Mn钢中MnS引起的应力和应变集中程度要明显大于粗晶的16Mn钢中MnS引起的应力和应变集中,其原因与细晶强化有关。 相似文献
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《浙江大学学报(A卷英文版)》2017,(11)
目的:钢框架焊接梁柱节点在地震作用下往往容易产生脆性裂纹,裂纹的发展和损伤累积将导致节点延性降低,发生脆性断裂。本文旨在探究节点在地震往复荷载作用下的损伤性能,分析其主要影响因素,提出有效的损伤评估模型,为后续节点损伤数值模拟提供基础,为钢框架的抗震设计提供参考。创新点:1.通过足尺节点试验,分析加载幅值、加载历程和荷载峰值对节点损伤性能的影响;2.基于试验结果,标定并验证3种经验损伤演化模型,提出基于疲劳断裂力学的节点损伤评估模型。方法:1.通过对9个足尺梁柱节点试件开展往复加载试验,包括5种变幅加载制度及4种常幅加载制度,分析加载幅值、加载历程和荷载峰值对节点损伤性能的影响;2.基于试验结果,根据节点损伤特点,在能量模型基础上,推导并拟合适用于节点循环加载的双参数损伤演化方程,并与其他模型进行比较,以验证其准确性;3.结合疲劳和延性断裂理论,依据损伤机理,定义"有效塑性应变"量化损伤过程,并以疲劳裂纹发展公式为基础,推导适用于计算在极低周循环荷载下节点损伤过程的损伤演化方程。结论:1.加载跨幅对节点性能影响较小;加载历程的影响与历程中峰值位移循环次数密切相关;突发性的强峰值对节点造成的损伤最大。2.节点损伤过程为幂函数形式;通过比较表明,在能量模型基础上推导出的适用于节点循环加载的双参数损伤演化方程,相对于单参数线性模型,能够更准确模拟节点在极低周循环下的损伤过程。3.基于疲劳断裂力学理论的损伤演化方程物理意义明确,能够描述节点循环损伤试验中所表现出的加速损伤及"损伤拐点"特征。 相似文献
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在霍普金森试验系统上进行了花岗岩破坏的动静组合加载实验,根据实验结果,分析了岩石在动静组合加载下损伤断裂机制与特征.结果表明,不同动静组合加载下岩石破碎的粒度分布具有明显的率变效应;采用张开位移法计算出了岩石破裂时裂纹的宽度. 相似文献
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对GH4169镍基高温合金制成的薄壁圆管试样的多轴循环相关特性进行了研究。试验在MTS809-250 kN/2000 Nm电液伺服拉-扭低周疲劳试验机上进行,采用恒幅总应变控制,对称加载,轴向应变与扭转应变的加载采用三种不同相位(0°、45°和90°),其加载频率分别为0.1 Hz和0.2 Hz,试验温度为650℃.通过对薄壁圆管高温多轴比例和非比例循环加载试验,研究了该材料在多轴循环载荷下的应力-应变响应和循环相关特性。试验结果表明,GH4169合金在试验温度下不通加载路径下均呈现为循环软化现象,其循环软化程度与等效应变和轴向与剪切方向之间的相位差密切相关。 相似文献
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研究目的:研究弱胶结软岩在应变软化变形阶段的强度参数演化规律。创新要点:针对弱胶结软岩在峰后应变软化变形阶段的刚度劣化和强度衰减的现象,建立考虑刚度损伤劣化的峰后强度参数演化模型。研究方法:首先依据实验结果建立弱胶结软岩的应变软化模型及刚度劣化模型,然后假设岩体后继屈服面均满足Mohr-Coulomb屈服准则,建立考虑峰后刚度劣化行为的强度参数演化规律方程,最后将模型嵌入软件进行数值验证。重要结论:峰后摩擦角演化规律主要由瞬时应力状态和损伤特性所主导,黏聚力除了与应力水平和损伤机制有关外,还与岩体的塑性变形机制有关。所建立的演化模型能较准确地描述弱胶结软岩体的应变软化行为。 相似文献
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为了研究沥青混凝土的疲劳特性,提出了基于双线性内聚力模型（CZM）的数值模拟方法．建立了疲劳损伤演化模型并将其与内聚力模型耦合,以反映沥青混凝土在循环荷栽作用下的软化行为．通过编制用户材料子程序。实现了疲劳损伤模型在有限元软件ABAQUS中的应用,并对劈裂疲劳试验进行了模拟．研究结果表明：模拟得到的疲劳寿命与实验室结果基本一致;疲劳损伤随加载次数的累积是非线性的,且损伤累积阶段是疲劳破坏的主要阶段;应力比增大时,损伤稳态发展阶段的寿命明显减小．可以发现提出的疲劳损伤数值模型是一种预估沥青混凝土疲劳损伤的有效方法． 相似文献
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Extensive research has shown that externally bonded carbon fiber reinforced polymer (CFRP) laminates are particularly suitable for improving the fatigue behavior of reinforced concrete (RC) beams. This paper presents the research on flexural rigidity evolvement laws by testing 14 simple-supported RC beams strengthened with carbon fiber laminates (CFL) under cyclic load, and 2 under monotone load as a reference. The cyclic load tests revealed the peak load applied onto the surface of a supported RC beam strengthened with CFL is linear to the logarithm of its fatigue life, and the flexural rigidity evolvement undergoes three distinct phases: a rapid decrease from the start to about 5% of the fatigue life; an even development from 5% to about 99% of the fatigue life; and a succedent rapid decrease to failure. When the ratio of fatigue cycles to the fatigue life is within 0.05 to 0.99, the flexural rigidity varies linearly with the ratio. The peak load does not affect the flexural rigidity evolvement if it is not high enough to make the main reinforcements yield. The dependences of the flexural rigidity of specimens formed in the same group upon their fatigue cycles normalized by fatigue life are almost coincident. This implies the flexural rigidity may be a material parameter independent of the stress level. These relationships of flexural rigidity to fatigue cycles, and fatigue life may be able to provide some hints for fatigue design and fatigue life evaluation of RC member strengthened with CFL; nevertheless the findings still need verifying by more experiments. 相似文献
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To study the bending strength of mass concrete under dynamic loading, the pure bending zone of three-graded concrete beam is considered as a three-phase composite composed of matrix, aggregate and interface between them on meso-level. Dynamic constitutive model considering strain-rate strengthening effect and damage softening effect is adopted to describe the cocrete and meso-element's damage. The failure mechanisms of beam under impact loading, triagle wave load, dynamic load coupling with initial static loading were simulated by using displacement-controlled FEM. Furthermore, stress-strain curve of the specimens and their dynamic bending strength were obtained. The results obtained from numerical simulation agreed well with experimental data. 相似文献
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Current practice in analysis and design of blast doors subjected to blast loading considers only simple boundary conditions and material properties. The boundary conditions and material properties, in fact, have considerable influence on the response of blast doors subjected to blast loading. In this paper, the dynamic responses of a reinforced concrete arched blast door under blast loading were analyzed by the finite element program ABAQUS, combined with a previously developed elasto-viscoplastic rate-sensitive material model. And the effect of the surrounding rock mass and contact effect of the doorframe were also taken into account in the simulation. It is demonstrated that the strain-rate effect has considerable influence on the response of reinforced concrete blast door subjected to blast loading and must be taken into account in the analysis. 相似文献
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钢桥面环氧沥青铺装的界面行为 总被引：2，自引：0，他引：2
通过引入一个新参数膜劲度,在部分共同作用原理的基础上,建立了描述钢桥面环氧沥青混凝土铺装复合梁在负弯矩作用下的界面行为模型,用以分析钢-环氧沥青混凝土之间的界面滑移与应变.推导了弹性工作状态下复合梁的界面滑移与应变的表达式,编制了数值计算程序并用2根复合梁进行了校核.然后采用该程序分析了界面滑移与应变沿复合梁纵向的分布特征,以及铺装层中的最大拉应力、层间剪应力对材料参数的敏感性.结果表明,界面效应削弱了钢桥面铺装复合梁的整体抗弯刚度;中低温条件下,采用劲度更大的粘结层材料有利于改善沥青铺装层的受力;粘结层的损伤累积将加剧沥青铺装层的破坏. 相似文献
15.
Numerical Derivation of Strain Rate Effects on Material Properties of Masonry with Solid Clay Bricks
In this paper, numerical method is used to study the strain rate effect on masonry materials. A typical unit of masonry is selected to serve as a representative volume element (RVE). Numerical model of RVE is established with detailed distinctive modeling of brick and mortar with their respective dynamic material properties obtained from laboratory tests. The behavior of brick and mortar are characterized by a dynamic damage model that accounts for rate-sensitive and pressuredependent properties of masonry materials. Dynamic loads of different loading rates are applied to RVE. The equivalent homogenized uniaxial compressive strength, threshold strain and elastic modulus in three directions of the masonry are derived from the simulated responses of the RVE. The strain rate effect on the masonry material with clay brick and mortar, such as the dynamic increase factor (DIF) of the ultimate strength and elastic modulus as a function of strain rate are derived from the numerical results. 相似文献
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对混凝土立方体试件施加竖向荷载,同步进行应力应变测量,结合实时法预估混凝土出现宏观裂纹的时间,运用损伤力学理论,给出一种预估混凝土试件工作寿命的试验方法. 相似文献
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对弹塑性大变形，由于外界栽荷的作用和材料自身性能的影响，损伤常常表现为各向异性。通过有效应力的概念，损伤对变形的影响可用一个四阶损伤影响张量来表示。对于弹塑性损伤变形，可以通过不同的极分解途径，而得到各种定义的变形梯度张量和相应的应变张量。分析结果表明：变形与材料的损伤有着较为密切的关系。 相似文献
18.
为获得路用水泥混凝土在高应力比作用下其疲劳可靠度的变化规律,首先推导了包括混凝土疲劳寿命在内的单调随机变量的概率密度,然后推导了 Miner 与 Chaboche-Zhao 疲劳损伤模型的概率密度. 借助室内疲劳试验结果,获得这 2 种模型的疲劳损伤概率密度函数. 最后,将荷载作用次数代入上述函数,从而获得水泥混凝土疲劳可靠度随荷载作用次数的变化规律. 结果表明: 随着荷载作用次数的增加,相同应力比下,疲劳可靠度从 100%逐渐衰减为 0%; 无论何种应力比,在荷载作用初期,疲劳可靠度均有一个较为稳定的阶段; 随着应力比的增加,该稳定阶段逐渐缩短,且可靠度为 0%时对应的荷载作用次数也减小; 在可靠度衰减阶段,对于相同荷载作用次数,应力比越高,则混凝土可靠度越低; 此外,Miner 疲劳损伤模型比Chaboche-Zhao 疲劳损伤模型偏安全. 相似文献
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一种新的可用于混凝土疲劳研究的非线性累积损伤模型 总被引：3，自引：0，他引：3
研究混凝土疲劳问题的主要困难之一，就是混凝土疲劳损伤的累积速度与不同强度循环荷载的作用次序有关，且是非线性的。但通常 的一些非线性损伤模型却不能反映荷载作用次序的影响，为了解决此问题和混凝土结构在长期不稳定循环荷载作用下的疲劳问题，我们在Miner线性累积损伤模型的基础上提出了一个新的非线性累积损伤模型，通过两个 疲劳损伤实例的计算证明了该模型不仅能够反映出不同强度应力水平先后作用次序对疲劳损伤演变情况的影响，而且保留了Miner模型概念明确，使用方便的优点，当通过试验得到一组有关曲线之后，不稳定循环荷载作用的混凝土疲劳累积损伤计算将变得异常简单，极便于在工程设计中采用。 相似文献
20.
Many engineering materials demonstrate dynamic enhancement of their compressive strength with the increase of strain-rate, which have been included in material models to improve the reliability of numerical simulations of the material and structural responses under impact and blast loads. The strain-rate effects on the dynamic compressive strength of a range of engineering materials which behave in hydrostatic-stress-sensitive manner were investigated. It is concluded that the dynamic enhancement of the compressive strength of a hydrostatic-stress-sensitive material may include inertia-induced lateral confinement effects, which, as a non-strain-rate factor, may greatly enhance the compressive strength of these materials. Some empirical formulae based on the dynamic stress-strain measurements over-predict the strain-rate effects on the compressive strength of these hydrostatic-stress-sensitive materials, and thus may over-estimate the structural resistance to impact and blast loads, leading to non-conservative design of protective structures. 相似文献