冲击载荷下玄武岩纤维增强混凝土的动态本构关系

为了研究玄武岩纤维增强混凝土的动态本构关系,利用Ф100mm分离式霍普金森压杆装置,对玄武岩纤维增强混凝土进行冲击压缩试验,得到了动态应力-应变曲线,对试验数据进行了分析,根据试验结果,通过叠加应变率强化效应和损伤软化效应,对混凝土静态Ottosen非线性弹性本构模型进行修正,建立了玄武岩纤维增强混凝土损伤型的动态本构模型,确定参数并将理论模型计算结果与试验结果进行了对比。研究表明,玄武岩纤维增强混凝土的动态性能存在明显的应变率强化效应,动态强度增长因子和峰值应变与应变率对数之间存在近似函数关系;建立模型的方法可行,理论模型计算结果与试验结果吻合较好,建立的本构模型可用来描述玄武岩纤维混凝土的动态力学行为,并能为玄武岩纤维增强混凝土的进一步研究和工程应用提供参考依据。     

温度、应变率对地质聚合物混凝土抗压强度的影响

采用自主研制的高温SHPB试验系统,对高温条件下地质聚合物混凝土的动态抗压强度进行了试验研究。结果表明:200℃时地质聚合物混凝土的动态抗压强度较常温时有所增长,800℃时强度则急剧下降;应变率随弹速近似线性增长;同一弹速水平下,200~600℃时的应变率与常温接近,800℃时较常温提高明显;高温条件下,由侧向约束引起的附加应力可以忽略不计,试验所测得的动态强度增长因子(DIF)的应变率增强效应反应了材料的本质属性;在30~130 s-1应变率范围内,高温下地质聚合物混凝土的DIF与应变率的对数呈线性关系,且温度越高,应变率效应越明显。     

氧化铝空心球复掺玄武岩纤维轻骨料混凝土动力学性能

采用直径100 mm分离式霍普金森压杆试验系统,研究不同应变率下素混凝土(PC)、玄武岩纤维混凝土(BC)、氧化铝空心球混凝土(AC)及玄武岩纤维-氧化铝空心球复合混凝土(BAC)动力学性能,构建动态本构模型。结果表明,应变率提高,4组试件动压强度、峰值应变、均值应变及破碎分形维数增大,应变率效应显著;掺入氧化铝空心球使试件强度及动弹性模量降低,峰值应变及均值应变增大,冲击变形性能增强。基于Sargin非线性弹性静态本构模型,引入率强化因子与骨料弱化因子构建材料的动态本构模型,所得拟合曲线与实测应力应变曲线吻合较好,特征强度与特征应变等基本相同。     

中低应变率加载下弱胶结软岩动力学特性

我国西部侏罗系煤层上覆巨厚白垩系富水软岩,为了解此类软岩在冲击荷载作用下的力学本构关系及损伤演化规律,利用Hopkinson压杆装置对干燥、饱和红砂软岩进行中低应变率下的冲击试验,结果表明:红砂软岩峰值应力、峰值应变均表现出明显的应变率效应,其中峰值应力与应变率呈指数关系;相同应变率下,干燥红砂软岩的强度大于饱和状态,对冲击荷载表现出更强的抵抗能力,但饱和红砂软岩的宏观破坏强度大于干燥状态;低应变率加载下,干燥红砂软岩出现负损伤;结合微观机理分析,低应变率下,水对红砂软岩的弱化作用占据主导地位,随着应变率的增大,在惯性效应和水的Stefan效应共同作用下,饱和红砂软岩的动态强度得到强化;基于Z-W-T模型和应变等效原理,建立了服从Weibull分布的损伤本构方程,经验证能很好的反映红砂软岩的动态本构关系,具有一定的工程实际意义。     

钢纤维地质聚合物混凝土冲击力学性能研究EI北大核心CSCD

通过控制粉煤灰、矿渣用量制备基准强度分别为C50、C60和C70的普通地质聚合物混凝土试件,再掺入不同体积量(0.3%, 0.6%, 0.9%和1.2%)的钢纤维制备出钢纤维地质聚合物混凝土试件。采用霍普金森压杆(split Hopkinson pressure bar, SHPB)对试件在不同冲击气压(对应不同应变率)下的抗冲击性能进行研究,探讨钢纤维掺量、应变率及混凝土基准强度对试件动态抗压强度和韧性指数的影响;采用ABAQUS软件进行数值模拟,对模拟与试验结果加以分析和验证;建立钢纤维地质聚合物混凝土动态应力-应变本构模型。结果表明:各组试件的动态抗压强度随着应变率、混凝土基准强度地提高逐渐增大,而钢纤维掺量仅对强度较低地质聚合物混凝土产生较大影响;应变率的提高使试件完整性逐渐变差,而随着钢纤维掺量与混凝土基准强度的提高,试件完整性逐渐变好,冲击耗能与韧性逐渐增加;数值分析与试验结果吻合较好,验证了结果的可靠性;钢纤维地质聚合物混凝土动态应力-应变本构模型计算结果与试验结果整体吻合较好,可用于预测冲击荷载下钢纤维地质聚合物混凝土的力学性能。     

陶瓷纤维混凝土冲击力学响应及统计损伤本构模型试验研究

采用Φ100mm分离式霍普金森压杆(SHPB)试验装置对陶瓷纤维混凝土的动态力学性能进行研究,并验证了试验结果的有效性;基于IPBS模型(修正平行杆模型),建立考虑应变率效应的混凝土单轴受压统计损伤本构模型,模拟陶瓷纤维混凝土的动态损伤破坏过程。结果表明：陶瓷纤维对普通硅酸盐混凝土的增强增韧效果明显,尤其是在高应变率范围内;SHPB试验过程中应力均匀性和恒应变率加载条件得到了较好地满足;动态损伤本构模型提供曲线与试验曲线吻合较好,能够较为准确地描述陶瓷纤维混凝土破坏前的应力应变关系。     

高温下混凝土SHPB动态力学性能试验研究

采用霍普金森压杆(Split Hopkinson pressure bar,SHPB)试验装置和高温炉进行了高温下普通混凝土的抗冲击性能试验研究,通过比较实测动态强度和应力-应变曲线,揭示了温度和应变率对高温下混凝土动态力学性能的影响规律.试验结果表明：除200℃~300℃范围外,高温下混凝土具有显著的应变率效应,且温度越高动态应变率效应越显著;温度和应变率对混凝土归一化应力-应变关系曲线上升段的形状影响很小,可采用统一的函数形式.200℃~300℃低温区混凝土不仅无明显动态效应,且存在静力强度衰减现象,此特性需引起注意并有待进一步研究.     

小变形条件下聚合物本构关系研究

通过两种工程塑料不同温度条件下的准静态和动态压缩试验,研究这两种工程塑料的应力应变特性。同时,为描述所研究聚合物在高温、高应变率下的应力-应变特性,基于Johnson-Cook本构模型,建立一种形式简洁、便于参数拟合的聚合物本构模型。分别利用聚甲醛和密胺树脂在准静态下和高应变率条件下的真应力-真应变曲线,对模型进行参数拟合和标定,结果表明:在高温、高应变率条件下,模型可以预测到5%应变以前的应力-应变关系,与聚合物力学性质符合率良好。     

TC4钛合金动态力学性能及本构模型研究

为研究TC4钛合金的动态力学性能及本构模型,利用电子万能试验机、高速液压伺服试验机和分离式Hopkinson压杆(SHPB)装置,对其进行常温下准静态、中应变率和高应变率动态力学性能试验,得到不同应变率下的应力应变曲线,拟合得到Johnson-Cook本构模型,并分析材料中应变率力学特性对本构模型参量的影响。结果表明:TC4钛合金在应变率10~(-4)~10~3s~(-1)范围内具有明显的应变率强化效应和一定的应变硬化效应,且应变率强化效应随应变的增大而减小,应变硬化效应随应变率的增大而减小;考虑材料中应变率力学特性可提高本构模型参量的准确性;通过数值方法和试验方法研究TC4钛合金平板撞击和高速拉伸过程的动态响应,两者结果具有很好的一致性,证明所得本构模型的准确性。     

高温效应对钢筋-混凝土动态黏结性能的影响：精细化模拟

为研究高温效应对钢筋-混凝土动态黏结性能的影响,建立了考虑带肋钢筋表面特征和混凝土材料非均质性的三维细观模型,与试验的破坏模式和黏结应力-滑移曲线进行对比,验证了细观模型的合理性。在此基础上,分析了高温下和冷却后钢筋-混凝土动态黏结应力-滑移行为的变化规律。结合数值模拟结果,建立了考虑高温效应的动态黏结强度预测公式。结果表明：细观模型能够反映变形钢筋与混凝土界面的开裂过程和黏结破坏机理;随着应变率的增加,高温下或冷却后的混凝土损伤区域逐渐减小;应变率相同时,高温下混凝土的损伤区域明显大于冷却后;随着温度的升高,高温下或冷却后试件的极限黏结强度均线性下降;相同温度环境下,应变率增加使得极限黏结强度非线性提高;预测结果与试验结果的良好吻合,说明本文提出的经验公式可以合理反映钢筋-混凝土动态极限黏结强度的高温效应。     

玄武岩纤维增强地质聚合物混凝土的动态本构模型

以矿渣与粉煤灰为原材料制备玄武岩纤维增强地质聚合物混凝土(BFRGC),采用φ100mm分离式霍普金森压杆(SHPB)装置对BFRGC进行了冲击压缩试验,并对SHPB试验过程中的波形整形技术展开了研究,以此来提高材料SHPB试验的精度。通过SHPB试验,获得了BFRGC在10s-1―102s-1应变率范围内的应力-应变曲线,分析了BFRGC的强度和变形性能,并建立了BFRGC的率型非线性粘弹性本构模型。通过试验对模型进行验证,模型曲线与试验曲线吻合良好,该文建立的率型本构模型可以较为准确地描述BFRGC的动态力学行为。     

弹射冲击载荷作用下沥青混凝土路面面层的损伤

沥青混凝土作为一种粘弹性材料一般只研究其疲劳损伤特性,冲击损伤研究较少。针对路面在弹射载荷作用下产生中低应变率响应的特点,采用Cauchy应变表达的三维简化ZWT(朱-王-唐)非线性粘弹本构模型以及应变率相关的损伤演化模型,建立了增量形式并将Kirchhoff应力转化为Cauchy应力,编写用户材料子程序嵌入有限元软件中。推导了恒应变率条件下含损伤的简化ZWT本构表达式,使用最小二乘法拟合出本构参数。分析了沥青混凝土场坪面层的冲击损伤,阐明了损伤变化规律、分布规律,为发射场坪的选择提供了一定参考。     

Multi-axial thermo-mechanical analysis of power plant components from 9–12% Cr steels at high temperature

The aim of this paper is to analyze local changes of stress and strain states in a power plant component under a transient thermal environment. A robust constitutive model is developed to describe inelastic behavior of advanced 9–12% Cr heat-resistant steels at high temperature and in a multi-axial stress state. The model includes the constitutive equation for the inelastic strain rate tensor, the evolution equation for a tensor-valued state variable to reflect hardening/recovery processes and two evolution equations for two scalar-valued variables that characterize softening and damage states. The model is calibrated against experimental creep curves and verified for inelastic responses under different isothermal and non-isothermal loading paths. Steam temperature and loading profiles that correspond to an idealized start-up, holding and shut-down sequence of a power plant component are assumed. To estimate the thermal fields, transient heat transfer analysis is performed. The results are applied in the subsequent structural analysis using the developed inelastic constitutive model. The outcome is a multi-axial thermo-mechanical fatigue loop which can be used for damage assessment.     

Modeling of Nonlinear Mechanical Behavior for 3D Needled C/C-SiC Composites Under Tensile Load

This paper established a macroscopic constitutive model to describe the nonlinear stress–strain behavior of 3D needled C/C-SiC composites under tensile load. Extensive on- and off-axis tensile tests were performed to investigate the macroscopic mechanical behavior and damage characteristics of the composites. The nonlinear mechanical behavior of the material was mainly induced by matrix tensile cracking and fiber/matrix debonding. Permanent deformations and secant modulus degradation were observed in cyclic loading-unloading tests. The nonlinear stress–strain relationship of the material could be described macroscopically by plasticity deformation and stiffness degradation. In the proposed model, we employed a plasticity theory with associated plastic flow rule to describe the evolution of plastic strains. A novel damage variable was also introduced to characterize the stiffness degradation of the material. The damage evolution law was derived from the statistical distribution of material strength. Parameters of the proposed model can be determined from off-axis tensile tests. Stress–strain curves predicted by this model showed reasonable agreement with experimental results.     

基于损伤演化的杆件断裂模拟方法及其应用

建立了钢材的弹塑性损伤本构模型,将其与有限单元法中分段纤维梁模型结合,实现了杆件不同位置损伤程度评估,根据评估结果实时修正杆件特性,建立了杆件断裂数值模拟方法。将所建立的杆件断裂模拟方法应用于单调递增荷载作用下的梁系结构和地震作用下的单层网壳结构,结果表明,所建立方法可有效地模拟杆件断裂;杆件断裂突然,与其相连的节点位移及杆件应变能突增,可能导致与其相连杆件破坏;强震作用下单层网壳结构可能发生杆件断裂,导致结构局部刚度降低,引起结构倒塌破坏。     

Asphalt material fatigue test under cyclic loading: the lengthening of samples as a way to characterize the material damage experiments and modelling

Fatigue tests of bituminous materials performed on trapezoidal specimens induce a loss of stiffness, combined with a significant extension of the specimens at the beginning of the test when applying high strain levels. This paper presents the development of a viscoelastic constitutive law with unilateral damage for asphalt materials, based on the observation of tensile failure tests on asphalt binder lenses between two metal spheres. The unilateral damage is defined as the opening of the micro-cracks in the bitumen during extension and their closing during contraction. When put into a semi-analytical structural model of the trapezoidal specimen, this constitutive law leads to results close to those highlighted at the beginning of fatigue experiments for various experimental conditions (temperature, load frequency and strain amplitude level). According to the used modelling, the damage evolution law describes the fast initial homogeneous creation of the micro-cracks and then their slow development. The modelling is also able to explain a given percentage of the loss of stiffness. These results show mainly that the bituminous material extension is due to the dissymetric behaviour induced by the unilateral damage coupled with viscoelasticity. Therefore the asphalt mix extension is a way to quantify the level of the material damage.     

Fatigue and ratcheting assessment of AISI H11 at 500°C using constitutive theory coupled with damage rule

Hot extrusion is one of the most commonly used manufacturing methods for metal plastic deformation, and the consumption of extrusion tooling is considerably high due to its fatigue damage under cyclic serving condition. Hot‐work tool steel AISI H11 is one of these typical materials employed in extrusion tooling. This work is dedicated to calculating the stress/strain state of AISI H11 and predicting its lifetime at high temperature 500°C by building a unified constitutive model coupled with Lemaitre's damage law. Tensile tests and strain/stress reversed cycling tests have been conducted at 500°C to investigate mechanical properties and damage evolution. A unified constitutive model with Armstrong‐Fredrick/Ohno‐Wang kinematic hardening rule and a new proposed isotropic hardening rule is built; Lemaitre's damage law is employed as well. Parameters are determined based on tests and are temperature dependent. Finite element simulation of the deformation behaviour and fatigue lifetime is implemented into commercial software ABAQUS Standard v6.14‐2 with user material subroutine to validate the proposed method. The comparison shows good agreement with experimental results, and this part of work is essential and crucial to subsequent structure analysis.     

复合固体推进剂黏弹性微裂纹损伤本构模型

为建立复合固体推进剂的损伤本构模型,在介观尺度上视其为微裂纹损伤,选取微裂纹密度为损伤内变量。在Abdel-Tawab本构方程的基础上,基于微裂纹均匀化理论,推导了损伤映射张量的一般形式。该张量通常具有非完全对称性,其物理意义是将真实应力空间中各向异性材料的多轴加载映射为等效应力空间中各向同性材料的更为复杂的多轴加载。其次,基于黏弹性动态裂纹扩展模型和裂纹扩展阻力曲线的概念,建立了损伤内变量的演化方程。该演化方程仅含4个物理意义明确的细观参数,并且参数的取值规律与宏观应力曲线的变化规律相一致。数值结果表明,建立的模型能够有效反映材料损伤的应变率、温度依赖性及各向异性特征,并且具有一定的蠕变损伤预测能力。     

Temperature and strain rate dependent constitutive model of TRIP steels for low-temperature applications

The aim of this study was to develop a constitutive model that takes into consideration the strain rate and temperature dependent characteristics of TRIP steels, in conjunction with a damage mechanics approach. The martensitic-transformation-induced strain hardening of type 300 series austenitic stainless steels at low temperature is a remarkable phenomenon. From a mechanical point of view, the temperature and strain rate play critical roles in such material nonlinearities. A series of tensile tests for 304L ASS, which is representative of TRIP steels and cryogenic materials, were conducted at various temperatures and strain rates. The experimental results revealed nonlinear material characteristics of TRIP at low temperature and were simulated by the proposed numerical model. A strain-induced martensitic transformation model was implemented in a unified viscoplastic constitutive equation. The damage evolution equation was also incorporated into the proposed constitutive model to simulate material degradation. Using a series of finite element analyses, quantitative verification of the proposed numerical technique was carried out by comparing the experimental and numerical results.