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1.
Summary A constitutive model is developed for the isothermal response of particle-reinforced elastomers at finite strains. An amorphous
rubbery polymer is treated as a network of long chains bridged to permanent junctions. A strand between two neighboring junctions
is thought of as a sequence of rigid segments connected by bonds. In the stress-free state, a bond may be in one of two stable
conformations: flexed and extended. The mechanical energy of a bond in the flexed conformation is treated as a quadratic function
of the local strain, whereas that of a bond in the extended conformation is neglected. An explicit expression is developed
for the free energy of a network. Stress–strain relations and kinetic equations for the concentrations of bonds in various
conformations are derived using the laws of thermodynamics. In the case of small strains, these relations are reduced to the
constitutive equation for the standard viscoelastic solid. At finite strains, the governing equations are determined by four
adjustable parameters which are found by fitting experimental data in uniaxial tensile, compressive and cyclic tests. Fair
agreement is demonstrated between the observations for several filled and unfilled rubbery polymers and the results of numerical
simulation. We discuss the effects of the straining state, filler content, crosslink density and temperature on the adjustable
constants.
Received 3 January 2001; accepted for publication 12 July 2001 相似文献
2.
采用Instron1342电液伺服试验机和改进的SHPB技术对以113材料为例的PP/PA共混高聚物进行了应变率在10-4~103 s-1宽广范围,温度为25、40、60、80 ℃下的一维应力力学性能试验。结果表明,这类共混高聚物的力学响应对温度和应变率都是敏感的。以朱-王-唐非线性粘弹性本构方程来描述这类PP/PA共混高聚物的力学响应,并拟合得到了其热粘弹性本构参数,理论预言与试验结果在应变小于7%时吻合良好。对113材料20~80 ℃温度范围内不同应变率下的试验结果进行分析,证明PP/PA共混高聚物存在率温等效关系,提高温度和增加作用时间(减小应变率)的效果相当,反之,降低温度与减少作用时间(提高应变率)的效果相当。通过引入量纲一参量Z,使应变率d/dt、温度T这2个参量归结为统一的Z参量,从而得到了体现时温等效性的统一曲线。 相似文献
3.
In order to predict the high-temperature deformation behavior of Al-Zn-Mg-Cu alloy, the hot compression tests were conducted
in the strain rate range of (0.001–0.1)s−1 and the forming temperature range of (573–723) K. Based on the experimental results, Johnson-Cook model was found inadequate
to describe the high-temperature deformation behavior of Al-Zn-Mg-Cu alloy. Therefore, a new phenomenological constitutive
model is proposed, considering the coupled effects of strain, strain rate and forming temperature on the material flow behavior
of Al-Zn-Mg-Cu alloy. In the proposed model, the material constants are presented as functions of strain rate. The proposed
constitutive model correlates well with the experimental results confirming that the proposed model can give an accurate and
precise estimate of flow stress for the Al-Zn-Mg-Cu alloy investigated in this study. 相似文献
4.
The mechanical behaviour of a material can be established by an analytic expression called the constitutive relation that
shows stress as a function of plastic strain, strain rate, temperature, and possibly other thermo-mechanical variables. The
constitutive relation usually includes such parameters as coefficients or exponents that must be determined. At a high strain
rate, the heat generated during the deformation process is directly related to the plastic deformation energy of the material.
This energy can be calculated from the plastic work, resulting in an expression that includes the constitutive relation parameters
as variables. The heat generated can also be estimated by measuring the temperature surface of the specimen during compressive
tests using the technique of infrared thermography. The objective of this paper is to present a procedure for determining
the constitutive relation parameters by measuring the temperature increase associated with plastic strain in compressive Hopkinson
tests. The procedure was applied to estimate the parameters of the Johnson–Cook constitutive relation of an aluminium alloy
(Al6082). 相似文献
5.
激光诱导变形条件下10#钢本构方程的建立 总被引:1,自引:0,他引:1
针对靶材在激光诱导不变形的热力学特点,设计了一套宏观力学性能实验方案,考虑温升率、温度、应变率及其历史效应对10#钢力学性能的影响,在此基础上,提出和发展了一组新的一维本构方程,它能描述文中实验所反映出的各种宏观力学规律。 相似文献
6.
Experimental analysis of dynamic mechanical properties for artificially frozen clay by the split Hopkinson pressure bar 总被引:2,自引:0,他引:2
Qin-Yong Ma 《Journal of Applied Mechanics and Technical Physics》2010,51(3):448-452
A device for impact compression experiments is the split Hopkinson pressure bar with a refrigerating attemperator. Data for
incident and reflected waves are obtained by the measuring technique with strain gauges, and data for transmitted waves are
obtained by the measuring technique with semiconductor gauges. Static compression tests of frozen clay are conducted at an
identical temperature and different strain rates of 0.001 and 0.01 sec
−1
. Dynamic stress-strain curves are obtained at strain rates of 360–1470 sec
−1
. The low and high temperatures correspond to high and low strain rates, respectively. It is shown that both the temperature
and strain rate affect the frozen soil deformation process. Different dynamic stress-strain curves obtained at the same temperature
but different strain rates are found to converge. The test results indicate that frozen soil has both temperature-brittleness
and impact-brittleness. 相似文献
7.
A.D. Drozdov J.deC. Christiansen 《International Journal of Solids and Structures》2008,45(14-15):4274-4288
Observations are reported on high-density polyethylene in uniaxial tensile tests with constant strain rates and relaxation tests at various temperatures ranging from 25 to 90 °C. A constitutive model is derived for the nonlinear viscoelastic and viscoplastic behavior of semi-crystalline polymers at three-dimensional deformations. Adjustable parameters in the stress–strain relations are found by fitting the experimental data. It is demonstrated that (i) the model correctly approximates the observations and (ii) material parameters are independent of strain rate and change consistently with temperature. 相似文献
8.
A method allowing the identification of parameters that govern constitutive equations of materials is proposed in this Note. These parameters are identified from heterogeneous strain fields. The method is direct so that iterative calculations based on finite element model updating are avoided. To cite this article: M. Grédiac et al., C. R. Mecanique 330 (2002) 107–112. 相似文献
9.
At high temperature rise rate, the mechanical properties of 10 # steel were determied experimentally in a very wide range
of temperature and strain rates. A new constitutive relationship was put forward, which can fit with the experimental results
and describe various phenomena observed in our experiments. Meanwhile, some interesting characteristics about the temperature
rise rate, strain and strain rate hardening and thermal softening are also shown in this paper. Finally, the reliability of
the constitutive law and the correctness of the constitutive parameters were verified by comparing the calculation results
with the experimental data.
This project is supported partly by The Lasers Technology Field of National High Technology Plan and partly by Key-Grant of
NNSF of China (No. 19891180-4). 相似文献
10.
Variation of the stress intensity factor along the front of a 3-D rectangular crack subjected to mixed-mode load 总被引:3,自引:0,他引:3
Summary The singular integral equation method is applied to the calculation of the stress intensity factor at the front of a rectangular
crack subjected to mixed-mode load. The stress field induced by a body force doublet is used as a fundamental solution. The
problem is formulated as a system of integral equations with r
−3-singularities. In solving the integral equations, unknown functions of body-force densities are approximated by the product
of polynomial and fundamental densities. The fundamental densities are chosen to express two-dimensional cracks in an infinite
body for the limiting cases of the aspect ratio of the rectangle. The present method yields rapidly converging numerical results
and satisfies boundary conditions all over the crack boundary. A smooth distribution of the stress intensity factor along
the crack front is presented for various crack shapes and different Poisson's ratio.
Received 5 March 2002; accepted for publication 2 July 2002 相似文献
11.
A constitutive modeling approach for shape memory alloy (SMA) wire by taking into account the microstructural phase inhomogeneity
and the associated solid–solid phase transformation kinetics is reported in this paper. The approach is applicable to general
thermomechanical loading. Characterization of various scales in the non-local rate sensitive kinetics is the main focus of
this paper. Design of SMA materials and actuators not only involve an optimal exploitation of the hysteresis loops during
loading–unloading, but also accounts for fatigue and training cycle identifications. For a successful design of SMA integrated
actuator systems, it is essential to include the microstructural inhomogeneity effects and the loading rate dependence of
the martensitic evolution, since these factors play predominant role in fatigue. In the proposed formulation, the evolution
of new phase is assumed according to Weibull distribution. Fourier transformation and finite difference methods are applied
to arrive at the analytical form of two important scaling parameters. The ratio of these scaling parameters is of the order
of 106 for stress-free temperature-induced transformation and 104 for stress-induced transformation. These scaling parameters are used in order to study the effect of microstructural variation
on the thermo-mechanical force and interface driving force. It is observed that the interface driving force is significant
during the evolution. Increase in the slopes of the transformation start and end regions in the stress–strain hysteresis loop
is observed for mechanical loading with higher rates.
相似文献
12.
On inner constraints in plane circular arches 总被引:1,自引:0,他引:1
G. C. Ruta 《Archive of Applied Mechanics (Ingenieur Archiv)》2004,74(3-4):212-222
Summary A one-dimensional model of plane circular arches with rigid sections is introduced. Suitable strain measures are defined as
deviations from rigid displacements. If the arch is thin, constitutive arguments make the shearing strain negligible. Hence,
the shearing indeformability will be assumed as inner constraint. By means of a formal power series expansion of the exact
measures of deformation it is shown that the shearing indeformability implies some constraints on the axial strain. In particular,
the first-order axial strain must vanish in the case of infinitesimal displacements. The same procedure is applied to pure
flexible arches, in order to compare the two sets of results. It is shown that the hypothesis of finite pure flexibility is
not compatible with small deformations of the arch. An example is provided to evaluate the effects of the two constraints
at the first non-linear step of the perturbation expansions.
This work has been supported by the “Progetto giovani ricercatori” grant of the University of Rome “La Sapienza” for the year
2002. 相似文献
13.
Zhilun Lu Qinglin Pan Xiaoyan Liu Yinjiang Qin Yunbin He Sufang Cao 《Mechanics Research Communications》2011,38(3):192-197
The behavior of the flow stress of Al-Cu-Mg-Ag heat-resistant aluminum alloys during hot compression deformation was studied by thermal simulation test. The temperature and the strain rate during hot compression were 340-500 °C, 0.001 s−1 to 10 s−1, respectively. Constitutive equations and an artificial neural network (ANN) model were developed for the analysis and simulation of the flow behavior of the Al-Cu-Mg-Ag alloys. The inputs of the model are temperature, strain rate and strain. The output of the model is the flow stress. Comparison between constitutive equations and ANN results shows that ANN model has a better prediction power than the constitutive equations. 相似文献
14.
A new experimental technique has been developed for the performance of high temperature, high-strain-rate experiments in the compression Kolsky bar (split-Hopkinson pressure bar or SHPB). The new technique (referred to as the High-Temperature Compression Kolsky Bar or HTCKB) uses an infra-red spot-heater to rapidly heat the specimen to the desired temperature, a!nd an electropneumatic actuation system to minimize the development of temperature gradients in the sample. The technique is cheap and relatively easy to implement and yet provides accurate, repeatable results. As an illustration of the application of the technique, we have examined the high-temperature response of the BCC metal vanadium at high-strain rates. Stress–strain curves are obtained for the material at strain rates of 4 × 103 s−1 and at temperatures ranging from 300 to 1100 K (27–800°C). Quasistatic (10−3 s−1) experiments have also been performed on vanadium over a slightly smaller range of temperatures, and the results are compared with the new high-temperature, high-strain-rate data. It is observed that the rate of thermal softening is a function of the strain rate. These results illustrate the importance of including the coupling between temperature and strain r!ate in thermoviscoplastic constitutive models. 相似文献
15.
Thermally actuated shape-memory polymers: Experiments, theory, and numerical simulations 总被引:2,自引:0,他引:2
Vikas Srivastava 《Journal of the mechanics and physics of solids》2010,58(8):1100-1124
With the aim of developing a thermo-mechanically coupled large-deformation constitutive theory and a numerical-simulation capability for modeling the response of thermally actuated shape-memory polymers, we have (i) conducted large strain compression experiments on a representative shape-memory polymer to strains of approximately unity at strain rates of 10−3 and 10−1 s−1, and at temperatures ranging from room temperature to approximately 30 °C above the glass transition temperature of the polymer; (ii) formulated a thermo-mechanically coupled large-deformation constitutive theory; (iii) calibrated the material parameters appearing in the theory using the stress-strain data from the compression experiments; (iv) numerically implemented the theory by writing a user-material subroutine for a widely used finite element program; and (v) conducted representative experiments to validate the predictive capability of our theory and its numerical implementation in complex three-dimensional geometries. By comparing the numerically predicted response in these validation simulations against measurements from corresponding experiments, we show that our theory is capable of reasonably accurately reproducing the experimental results. As a demonstration of the robustness of the three-dimensional numerical capability, we also show results from a simulation of the shape-recovery response of a stent made from the polymer when it is inserted in an artery modeled as a compliant elastomeric tube. 相似文献
16.
The effects of strain rate and temperature on the tension stress–strain responses of polycarbonate are experimentally investigated over a wide range of strain rates (0.001–1700 s−1) and temperatures (0–120 °C). A modified split Hopkinson tension bar is used for high-rate uniaxial tension tests. Experimental results indicate that the stress–strain responses of polycarbonate at high strain rates exhibit the nonlinear characteristics including the obvious yielding and strain softening. The tension behavior is strongly dependent on the strain rate and temperature. The values of yield stress and strain at yield present a dramatic increase at higher strain rates and decrease with the increase in temperature. Moreover, there exists a significant rate-sensitivity transition in the polycarbonate tension yield behavior. Based on the experimental investigation, a physically based three-dimensional elastoplastic constitutive model for the finite deformation of glassy polymers is used to characterize the rate-temperature dependent yield and post-yield behavior of polycarbonate when subjected to tension loading. The model results are shown close to the experimental data within the investigated strain-rate and temperature ranges. 相似文献
17.
Dynamic strain aging (DSA) is an important phenomenon in solute hardened metals and seriously affects the mechanical properties
of metals. DSA is generally induced by the interaction between the moving dislocations and the mobile solute atoms. In this
paper, only the interaction between moving dislocations and mobile solute atoms in a dislocation core area (core atmosphere)
will be taken into account. To establish the constitutive model which can describe the DSA phenomenon, we improved the Zerilli-Armstrong
dislocation-mechanics-based thermal viscoplastic constitutive relation, and added the effect of the interaction between the
moving dislocations and core atmosphere. Because the constitutive relation established is based on the Zerilli-Armstrong relation,
it can describe not only the DSA phenomenon, but also the mechanical behavior of metals over a broad range of temperatures
(77K∼1000K) and strain rate (10−4∼104 s−1). The model prediction for tantalum fits well with the experimental data.
Projected supported by the Chinese Academy of Sciences and the High Technical Project. 相似文献
18.
The thermo-viscoplastic behavior of three metals is characterized in a large range of loading conditions by using a new phenomenological
constitutive model. The flow stress is decomposed into the sum of an effective stress with an internal stress depending upon
an internal parameter which describes the strain hardening effect. The evolution of the internal stress is sensitive to the
history of strain-rate and temperature. A systematic method is used for determining the model’s parameters. The model predictions
show a good correlation with experimental data. Temperature history effects are especially analyzed. 相似文献
19.
Poly-Carbonate (PC) and Poly-Methyl-Methacrylate (PMMA) are lightweight and mechanically tough transparent glassy polymers. Their mechanical behavior at low to moderate strain rates has been well characterized; however, that at high strain rates needs additional work. We propose two modifications to existing pressure-dependent viscoplastic constitutive equations that enable one to simulate better mechanical deformations of PC and PMMA at high strain rates. First, the elastic moduli are taken to depend upon the current temperature and the current effective strain rate. Second, two internal variables are introduced to better characterize the strain softening of the material at high strain rates. A technique to find values of newly introduced material parameters is described. We compute the local temperature rise due to energy dissipated during plastic deformations. The true axial stress vs. the true axial strain curves in uniaxial compression from numerical simulations of the test configurations at high strain rates using the proposed constitutive equations are found to agree well with the experimental results available in the literature. 相似文献
20.
Two constitutive relations have been determined from test results that characterize, respectively, the uniaxial and photomechanical behavior of a polyester-styrene copolymer for strain rates from 10?5 to 3×103 in./in./s and strains up to 40 percent. The high-strain-rate data were obtained by means of a split-Hopkinson-bar apparatus. Intermediate-strain-rate tests, performed with the aid of a drop tower, were reported in an earlier paper. Quasi-static experiments were conducted on a standard testing machine. A nonlinear, four-parameter, elastic-viscoplastic model was constructed which describes the mechanical behavior. The parameters were determined by a least-mean-squares curve-fitting procedure. The viscoplastic parameters were found to obey a power law in strain rate. The photomechanical model was found to be linear with strain well into the plastic-deformation region, while the slope of the strain-birefringence curve for each strain rate also varied by strain rate to a power. 相似文献