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2015 Vol. 36, No. 2
Published: 2015-04-28
105
A unified analytical beam & a finite nodal-line method in solid mechanics
In view of the mechanics problems of beam-like structural members or systems that cannot be dealt with by existing beam theories, a unified analytical model for all beam-like members or structural systems, known as a Unified Analytical beam or a UA beam, and a novel computational methodology named Finite Nodal-Line (FNL) method are presented. By means of the UA beam theory and the FNL method, the analyses of arbitrary stocky shaped members and structural systems will be readily carried out. Furthermore, when the properties of a mechanics problem are consistent with the application conditions of a traditional classical beam, both the UA beam and traditional classical beam will possess an identical precision solution for the problem. The comparison study among different examples of beams is performed to verify the rationality of the UA beam theory and the validity of the FNL method.
2015 Vol. 36 (2): 105-113 [
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114
Mechanical behavior and energy absorption of graded honeycomb materials under out-of-plane dynamic compression
Honeycomb materials are of good energy absorption performance under impact loading. To further improve the specific energy absorption and crash load efficiency of the honeycomb materials, a new honeycomb model is proposed here, of which one geometry parameter or material parameter varies gradually along the honeycomb thickness direction. Based on the hexagonal configuration, the mechanical behavior and energy absorption of honeycombs with cell wall thickness or yield strength of based material varying gradually along the thickness direction are investigated under dynamic compression. It is demonstrated that by adopting proper grading exponents, honeycomb materials with graded distribution of cell wall thickness or yield strength of based material can bring down the initial peak stress as well as increase the specific energy absorption (SEA) and crash load efficiency (CLE). These results may pass new ideas to optimal design of honeycomb materials for energy absorption.
2015 Vol. 36 (2): 114-122 [
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123
The analytic solution of the laminated one-dimensional hexagonal quasicrystals
On the basis of constitutive equations and the simplified physical equations of one-dimensional hexagonal quasicrystalline materials, the stresses of quasicrystalline layer and elastic layer were assumed, respectively. Then the displacements of these two layers were derived. Utilizing the interface continuum conditions and the loosened boundaries, an analytic solution was derived for the laminated quasicrystalline cantilever beam with concentrated force at free end, which is helpful for the further research in the mechanical property of quasicrystalline coating.
2015 Vol. 36 (2): 123-128 [
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129
Effect of temperature on the electromechanical deformation of dielectric elastomer
Dielectric elastomer (DE) is a typical viscoelastic soft material, is capable of giant deformation under an electric field and has broad temperature applications. Temperature can significantly affect the performance of DE. However, few reports focused on the effect of temperature on the electromechanical deformation. In the current study, first, the in-plane deformation of most widely used DE (VHB 4910, 3M) under different temperatures was performed experimentally. The results show that the deformation of the viscoelastic DE increases with the increasing temperature and DE easily occurs electromechanical instability at a high temperature. Subsequently, based on the thermodynamics, we present a viscoelastic model to describe the electromechanical deformation of DE under different temperatures. The numerical results show that DE creeps with time due to the viscoelasticity and has bigger deformation at higher temperature until suffering electromechanical instability, which show well consistent with the experimental results.
2015 Vol. 36 (2): 129-136 [
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137
Study in the failure behavior of notched composite laminate under tensile load
The experiments have been completed under static tensile loading for different notched composite laminates. The strain gauges have been utilized to measure the change of strains in the different position of the specimen. The residual intensity of the laminate with the notch damage was measured. The effect of damage length and angle on the residual intensity of the laminate was discussed. The finite element models were set up to analyze the failure behavior of notched laminates under tensile load and determine the relation between the residual intensity and notch damage state. All prediction results have reasonably good correlation with the test results.
2015 Vol. 36 (2): 137-144 [
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145
Research on the Numerical Simulation of Dynamic Mechanical Behaviors of Concrete Subjected to Impact Loading
SHPB with the diameter of 74mm was used to study the dynamic mechanical properties of cement mortar and concrete under different impact velocities. The influence of impact velocity on the mechanical properties of concrete was analyzed. The dynamic response of concrete was simulated, which was loaded by rigid slab. The simulation results agreed well with experimental results. Numerical simulation shows that the peak stress of concrete increases with impact velocity, so concrete is rate-dependent. With the increase of the volume fraction of coarse aggregate, the peak stress of concrete increases firstly, then declines. When the volume fraction of coarse aggregate is equal to 40%, the peak stress of concrete is maximum value. Under the condition that the maximum diameter of coarse aggregate is kept unchanged, the peak stress of concrete declines with the minimum diameter of coarse aggregate. However, under the condition that the minimum diameter of coarse aggregate is kept unchanged, with the increase of the maximum diameter of coarse aggregate, the peak stress of concrete increases firstly, then declines, which provides theoretical guidance for the engineering application of concrete
2015 Vol. 36 (2): 145-153 [
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154
Investigations on loading rate effects and energy mechanism of granite
Loading rate has an important influence on rock mechanical properties and failure modes. Experiments on uniaxial compression and acoustic emission of different loading rates on granite were conducted by MTS810 servo-controlled testing machine and PCI-2 acoustic emission instrument. The results show that: (1) Stress-strain curves of granite under uniaxial compression have experienced compaction, elasticity, yield and failure four stages. Post-peak curves of the rock sample present stepped and segmented drop shape at loading rates from 0.001 mm/s to 0.01mm/s, and present a smooth, steeper continuous curve at loading rates from 0. 01 mm/s to 0. 1mm/s. (2)Peak strength and elastic modulus of rock increases with increasing loading rate, both present cubic polynomial relations with the logarithm of the loading rate. Peak strain decreases with increasing loading rate,which shows linear regression relationship with the logarithm of the loading rate. (3)As the loading rate increased from 0.001mm / s to 0. 1mm / s, the total strain energy was volatile, releasable elastic strain energy increased 60.42%, dissipated strain energy decreased 66.38%, the ratio of releasable elastic strain energy of the total strain energy increased 43.33%, the ratio of dissipated strain energy of the total strain energy decreased 66.67%, rock fracture mode changes from tensile shear failure to tensile splitting failure gradually, the number of broken pieces also increased. (4)When the loading rate from 0.001 mm / s to 0.1 mm / s, the failure process of rock sample is the same kind of damage although the failure mode is different. The energy dissipation makes rock damage and the strength loss, but the energy release makes the macrofracture surface be run-through, which towards the direction of the energy released by rifting or catapult destruction.
2015 Vol. 36 (2): 154-163 [
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250
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164
Bounded multi-axial elastic potentials with strain-stiffening effects for rubbery materials based on uniaxial data
It is indicated that the existing elasticity models with strain-stiffening effects for rubbery materials are involved in an issue concerning unbounded strain energy. Toward a solution to this issue, an explicit, straightforward approach is proposed to obtain multi-axial elastic potentials for incompressible rubberlike materials. Such potentials are derived directly from one-dimensional elastic potentials for uniaxial case by means of explicit procedures and, as such, bypass usual tedious numerical calculations in estimating a set of unknown parameters. It is shown that these potentials based solely on uniaxial data may accurately match data of four benchmark tests over the whole stretch range from small to large deformations. Also, they not only can well describe strain-stiffening effects, but can always give rise to bounded strain energy. Numerical examples are presented in fitting Treloar’s classical data.
2015 Vol. 36 (2): 164-170 [
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171
The application of wave front method in the Galerkin element-free method
Different from grid-based algorithm, meshless (or meshfree) method is a node-based algorithm that merely needs nodes information. Without the need of connecting nodes into mesh cell, this method is convenient with a good accuracy. The Galerkin element-free method (EFG) is a method based on global weak form and moving least square (MLS) approximation, which is widely used in computational mechanics. One disadvantage of this method is that, the number of nonzero elements in coefficient matrix produced in EFG is much more than in finite method, requiring bigger memory space. The wave front method is applied in finite method for a long time. But it has not used in meshless method yet. In this article, applying wave front method to EFG method is discussed. And some numerical experiments are presented.
2015 Vol. 36 (2): 171-178 [
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179
Anti-plane Analysis of a lip-shape crack of piezoelectricity of one-dimensional hexagonal quasicrystals
Based on the fundamental equations of peizoelasticity of quasicrystal materials, by using the symmetry operations of point groups, the linear piezoelasticity behavior of one-dimensional hexagonal quasicrystals is investigated, the control equations of anti-plane problems are derived, variable function method and the technique of conformal mapping in the anti-plane problem of a lip shape cracks of piezoelectricity of one-dimensional hexagonal quasicrystals is adopted. By using Cauchy integral formula, the analytical expressions of the field intensity factors and the mechanical strain energy release rate were presented with the assumption that the crack were electrically impermeable.
2015 Vol. 36 (2): 179-184 [
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205
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