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。     

聚脲材料动态压缩力学行为的数值模拟研究

以聚脲材料动态压缩力学特性为研究对象,提出了考虑动态弹性模量、动态强度因子和动态切线模量的简化三直线弹塑性本构模型;基于ANSYS/LS-DYNA有限元分析软件,建立了低、中、高不同应变率下聚脲材料压缩有限元模型,并与实验结果进行对比分析。结果表明：动态弹性模量增大因子、动态强度因子和动态切线模量因子随应变率增加而有规律的增大,均和应变率的对数呈双线性关系。在中低应变率下,三者的线性关系斜率都比较平缓;在高应变率下,三者的线性关系斜率都比较陡,且弹性模量动态增大因子的斜率比动态强度因子的更大,而第二阶段动态切线模量因子的斜率与动态强度因子的基本一致,但第三阶段动态切线模量因子的斜率是动态强度因子的2.3倍左右,说明高应变率下聚脲材料的后期应力强化效应更加显著。聚脲材料的简化三直线弹塑性本构模型可以在ANSYS/LS-DYNA有限元软件中较好地实现。该文建立的有限元模型能较为准确地模拟聚脲材料压缩实验,进一步验证了简化弹塑性本构模型在不同应变率压缩加载下的有效性。该研究可以为聚脲涂覆加固防护结构有限元模型提供材料模型参数依据。     

基于不可逆热力学的Ni-Ti合金动态本构模型及其有限元实现

为了准确描述Ni-Ti形状记忆合金在高应变率下的动态压缩力学行为,基于不可逆热力学理论框架假定了两个内变量表征Ni-Ti合金应力诱发马氏体相变与塑性屈服的不可逆变形过程,分别推导了马氏体相变与塑性屈服演化规律的主控方程,构建了Ni-Ti合金的三维动态本构模型。根据材料单轴动态压缩实验的应力-应变曲线并采用最小二乘法对本构参数进行了优化识别,然后采用应力补偿更新算法,通过隐式用户子程序接口UMAT将动态本构模型嵌入ABAQUS有限元软件,实现了Ni-Ti合金在高应变率下动态压缩力学行为的数值模拟。通过比对发现,模拟结果与实验数据吻合良好,验证了动态本构模型与UMAT子程序的准确性。本工作为Ni-Ti合金在高速冲击、切削等极端条件下的工程应用奠定了基础。     

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。     

EPS混凝土的冲击力学行为及本构模型

采用大直径分离式霍普金森压杆(SHPB)试验装置研究了多种EPS体积掺量的EPS混凝土在不同应变率下的力学行为。分析了平均应变率以及EPS体积掺量对EPS混凝土的冲击力学性能的影响。采用朱-王-唐(ZWT)模型,在试验研究的基础上,建立了EPS混凝土非线性粘弹性本构模型。结果表明：在高应变率条件下,EPS混凝土的动态抗压强度与极限应变随平均应变率的提高近似线性增长,呈现出显著的应变率相关性。随着EPS体积掺量的增加,混凝土的动态抗压强度和弹性模量降低,变形能力得到改善。本构模型提供的理论曲线与试验曲线比较接近,ZWT模型可以较为准确地描述EPS混凝土的高应变率力学行为。     

高应变率下岩石动态本构关系试验研究现状

高应变率下材料动态本构关系，目前主要是通过Ｓ．Ｈ．Ｐ．Ｂ．装置和轻气炮装置来获得。研究［１］表明，平面波发生器加载更是一般爆破实验室适用的试验手段。Ｌａｇｒａｎｇｅ分析方法由于在材料动态性能实验分析中只有重要的指导和运用价值而越来越受到重视。本文主要评述这些方法在岩石介质材料中的应用和最新进展，对其历史和今后发展趋势也作了简要说明。     

高应变率下岩石动态本构关系试验研究现状

高应变率下材料动态本构关系，目前主要是通过Ｓ．Ｈ．Ｐ．Ｂ．装置和轻气炮装置来获得。研究［１］表明，平面波发生器加载更是一般爆破实验室适用的试验手段。Ｌａｇｒａｎｇｅ分析方法由于在材料动态性能实验分析中只有重要的指导和运用价值而越来越受到重视。本文主要评述这些方法在岩石介质材料中的应用和最新进展，对其历史和今后发展趋势也作了简要说明。     

高应变率下含水红砂岩爆破损伤演化模型研究

基于直径50 mm的Hopkinson压杆装置,从宏观与微观两方面探究含水红砂岩在应力波作用下的力学特性与损伤演化机理,并将弹性模量定义的含水损伤与微元破坏数量定义的荷载损伤视为宏观损伤与微观损伤,基于Weibull理论与Drucker-Prager准则,推导得到红砂岩在含水率与应变率耦合作用下的复合损伤变量与动态损伤本构方程。研究表明,岩石损伤在一定范围内随含水率的增加而逐渐扩大,随着试样饱和,含水损伤趋于稳定。复合损伤变量与荷载损伤在应变率的作用下变化趋势近似,可分为初始阶段、低速发展阶段与快速发展阶段,代表了岩石在爆破冲击作用下的损伤演化过程,与含水红砂岩动态压缩破坏过程中应力-应变曲线的各个阶段相对应。将理论应力-应变曲线与实测应力-应变曲线进行对比,对建立的动态损伤本构模型准确性进行验证,发现该模型与含水红砂岩在动态压缩过程中的各个阶段拟合度较好,证明了该模型的准确性。     

强动载下岩石动态本构关系试验研究

高应变率下材料动态本构关系，目前主要通过Ｓ．Ｈ．Ｐ．Ｂ装置和轻气炮装置来获得。研究表明，平面波发生器加载更是一般爆破实验室适用的试验手段。Ｌａｇｒａｎｇｅ分析方法由于在材料动态性能实验分析中具有重要的指导和实用价值而越来越受到重视。本文主要评述它们在岩石介质材料中的应用和最新进展，对它们的历史和今后的发展趋势也作了简要说明。     

隔振橡胶本构建模研究

提出适合描述隔振橡胶在宽频振动时力学行为的本构模型。本构模型包含超弹性和粘弹性两个部分，超弹性部分表征橡胶材料的静态特性；非线性粘弹性部分描述橡胶材料在振动、冲击载荷下的动态响应。基于该本构模型，对橡胶材料在宽应变率范围内进行试验，九个材料参数通过高、低应变率下的试验数据拟合确定。模型预测结果与试验结果是相当吻合的。     

随机多孔碳纤维纸的非线性面外压缩本构模型

多孔碳纤维纸由随机分布的碳纤维构成,常用于燃料电池、发热材料等先进结构,其主要服役状态为面外压缩。碳纤维纸的压缩应变对其力学、热学、电学性能均有显著影响,因此迫切需要揭示其面外压缩本构关系。该文针对碳纤维纸微结构随机多孔的特点,提出了2种非线性面外压缩本构模型,分别是考虑赫兹接触影响的对数型模型和考虑孔隙率和单胞尺寸的幂函数型模型。基于3种商品化碳纤维纸的应力-应变实验数据,将该文提出的两种模型与传统的线性模型进行分析对比,并讨论了有、无额外有机物对碳纤维纸力学性能的影响。结果表明：碳纤维纸中的额外有机物对其应力-应变关系有比较明显的影响,全面考虑接触变形、弯曲变形与孔隙率变化的对数型本构模型具有较好的鲁棒性,适用范围较广;幂函数型本构模型能够较准确地预测有机物含量较低的碳纤维纸的应力-应变关系;传统的线性本构模型对各种碳纤维纸的预测均有较大的误差,该文提出的两种非线性本构模型对碳纤维纸具有较好的适用性,可以反映碳纤维纸的非线性应力-应变关系。     

Fracture-induced Physical Phenomena and Memory Effects in Rocks: A Review

ABSTRACT: Fracture-induced physical phenomena allow a real-time monitoring of damage evolution in rocks induced by mechanical loading. Some of these phenomena, e.g. plastic deformation, changes in permeability and electric resistivity, provide an overall estimate of damage as a function of stress. Others, such as acoustic emission or electromagnetic emission, allow an exact location of cracks in space and time. Being nondestructive, monitoring techniques based on fracture-induced physical phenomena, are a basis for prediction of earthquakes and rockbursts in underground mines. They are also crucial for a fundamental understanding of rock fracture mechanisms and for developing constitutive models of rock behaviour. Memory effects take place in rocks subjected to cyclic loading with the peak stress (strain) value increasing from cycle to cycle. The effects are represented by certain characteristic changes in rock properties and parameters that are observed when the stress (strain) reaches its previous peak value. Potential applications of memory effects range from stress measurement techniques to earthquake prediction to damage surface scanning. Essential experimental and theoretical results on fracture-induced physical phenomena and memory effects in rocks are considered in the article. Possible applications as well as not-yet-clear points are discussed.     

超高性能混凝土单轴拉压本构关系研究

超高性能混凝土（UHPC）是一种具有超高强度、超高耐久性和超高韧性的新型水泥基复合材料,因其优越的性能而受到国内外土木工程领域的广泛关注,具有广阔的工程应用前景。单轴受拉和受压应力-应变本构模型是进行UHPC构件力学性能分析的前提和基础。为了进一步深入研究UHPC力学性能,本文归纳总结了国内外不同学者提出的UHPC本构模型,包括单轴受压应力-应变关系和单轴受拉应力-应变、应力-裂缝宽度关系,对其进行了分类和比较,发现了现有模型的共同点和存在的差异,并对这种差异进行了原因分析,最后将部分本构关系应用于ABAQUS有限元分析软件,对高强钢筋UHPC梁进行数值模拟,并与试验结果对比,验证了部分本构模型的合理性,最后提出了一些研究结论。本文研究成果将为UHPC的结构性能研究进行结构分析和结构设计提供依据。      

A thermovisco-hyperelastic constitutive model of HTPB propellant with damage at intermediate strain rates

The uniaxial compressive tests at different temperatures (223–298 K) and strain rates (\(0.40\mbox{--}63~\mbox{s}^{-1}\)) are reported to study the properties of hydroxyl-terminated polybutadiene (HTPB) propellant at intermediate strain rates, using a new INSTRON testing machine. The experimental results indicate that the compressive properties (mechanical properties and damage) of HTPB propellant are remarkably affected by temperature and strain rate and display significant nonlinear material behaviors at large strains under all the test conditions. Continuously decreasing temperature and increasing strain rate, the characteristics of stress-strain curves and damage for HTPB propellant are more complex and are significantly different from that at room temperature or at lower strain rates. A new constitutive model was developed to describe the compressive behaviors of HTPB propellant at room temperature and intermediate strain rates by simply coupling the effect of strain rate into the conventional hyperelastic model. Based on the compressive behaviors of HTPB propellant and the nonlinear viscoelastic constitutive theories, a new thermovisco-hyperelastic constitutive model with damage was proposed to predict the stress responses of the propellant at low temperatures and intermediate strain rates. In this new model, the damage is related to the viscoelastic properties of the propellant. Meanwhile, the effect of temperature on the hyperelastic properties, viscoelastic properties and damage are all considered by the macroscopical method. The constitutive parameters in the proposed constitutive models were identified by the genetic algorithm (GA)-based optimization method. By comparing the predicted and experimental results, it can be found that the developed constitutive models can correctly describe the uniaxial compressive behaviors of HTPB propellant at intermediate strain rates and different temperatures.     

丁羟包覆层的黏超弹本构模型

为了准确地描述丁羟（HTPB）包覆层在有限变形下的拉伸力学特性,研究了HTPB包覆层的黏超弹本构模型。分别构建了含率相关函数的本构模型和并联式本构模型,前者由超弹模型与率相关项相乘得到,后者由超弹模型与含损伤因子的黏弹模型并联而成。进行了HTPB包覆层的单步松弛、多步松弛和不同速率的单轴拉伸试验,并将试验数据用于拟合模型参数。结果表明,HTPB包覆层对应变率极其敏感,且具有很大的延伸率,表现出明显的黏超弹特性;两种模型均能很好地预测HTPB包覆层较大形变范围内的拉伸力学性能,其中含率相关函数的模型的描述更加准确,其研究具有重要的军事意义。     

Numerical integration on the sphere and its effect on the material symmetry of constitutive equations—A comparative study

In the present paper, we consider a class of constitutive models based on numerical integration on the unit sphere. The directional behaviour of the quadrature schemes and its effect on the symmetry properties of these constitutive models are studied by subjecting the set of integration points on the sphere to arbitrary rigid rotations. We investigate a number of recently proposed integration schemes in application to a full network model of rubber elasticity and to an exponential model for soft tissues. In order to assess and compare these schemes, statistical methods are presented and applied. The analysis discloses a number of integration schemes that offer a good compromise between the numerical error and the number of integration points. However, as a general result it turns out that numerical integration is prone to introduce strong anisotropy into originally isotropic constitutive equations, in particular, for highly non‐linear integrand functions. The consequences for application of the investigated class of constitutive models in finite element calculations are highlighted in a benchmark‐like numerical example. Copyright © 2009 John Wiley & Sons, Ltd.     

Piezocomposites of complex microstructure: theory and experimental assessment of the coupling between phases

A new theoretical framework is presented for the study of the elastic, dielectric, and piezoelectric properties of two-phase piezoelectric composite materials of complex microstructure. These kinds of materials are usually analyzed by means of averaging models. This paper begins with basic thermodynamic relations and obtains new general constitutive equations for a two-phase composite. These new constitutive equations consider in a general and novel way the dielectric and elastic interactions between the two components and provide a method of measuring or calculating these interactions, as well as their influence on the global behavior of the composite. Some measurements of the dielectric, mechanical, and piezoelectric properties of 3-3 and 0-3 composites are presented and compared with the results of both this new approach and an averaging model.     

粘弹性材料本构模型的研究

介绍了近年来建立粘弹性材料本构模型的方法。目前主要有两种方法:利用现有本构模型;对粘弹性材料进行试验研究,拟合实验曲线。     

Predictive constitutive modelling of arteries by deep learning

The constitutive modelling of soft biological tissues has rapidly gained attention over the last 20 years. Current constitutive models can describe the mechanical properties of arterial tissue. Predicting these properties from microstructural information, however, remains an elusive goal. To address this challenge, we are introducing a novel hybrid modelling framework that combines advanced theoretical concepts with deep learning. It uses data from mechanical tests, histological analysis and images from second-harmonic generation. In this first proof of concept study, our hybrid modelling framework is trained with data from 27 tissue samples only. Even such a small amount of data is sufficient to be able to predict the stress–stretch curves of tissue samples with a median coefficient of determination of R² = 0.97 from microstructural information, as long as one limits the scope to tissue samples whose mechanical properties remain in the range commonly encountered. This finding suggests that deep learning could have a transformative impact on the way we model the constitutive properties of soft biological tissues.