Strain-softening Properties Research Articles

Unified Solution of Expansion of Cylindrical Cavity of Elastic-Brittle-Plastic Strain-Softening Materials with Different Elastic Modulus in Tensile and Compression

For strain-softening materials with different elastic modulus of tensile compression, two controlling parameters were introduced to take into account the different modulus and strainsoftening properties. By means of twin shear unified strength theory, unified solutions calculating stress and displacement fields of expansion of cylindrical cavity were derived. The effects caused by different elastic modulus in tensile and compression, different models and strain-softening rates on stress and displacement fields, development of plastic zone were analyzed. The results show the ultimate expansion pressure, stress and displacement fields and development of plastic zone vary with the changes of different elastic modular, different models and strain-softening properties.

Inelastic Dynamic Response of Structures Using Force Analogy Method

A new algorithm based on the force analogy method for studying the inelastic structural behaviors subjected to dynamic loadings is proposed. Inelastic analysis is performed based on varying the structural displacement field, which differs from the conventional method of changing stiffness. Each inelastic deformation of the structure is denoted as a degree of freedom, and therefore all inelastic behaviors are represented by a single equation. The algorithm is very time efficient because only initial stiffness is used, and it achieves high numerical accuracy when incorporating the use of a state space numerical integration method in dynamic analysis. Moreover, this algorithm is dynamically stable in analyzing structures with not only strain-hardening properties, but also elastic-plastic properties and strain-softening properties. Comparison between the proposed algorithm and an existing inelastic dynamic analysis software program is performed to demonstrate the accuracy and efficiency of this algorithm. Finally, application of the proposed algorithm to the dynamic response of a six-story hospital building is presented to show the complete inelastic analysis procedure in analyzing realistic structures.

An Insight into the Failure of Reinforced Sand in Plane Strain Compression by FEM Simulation

An FEM simulation of plane strain compression tests of dense Toyoura sand reinforced with reinforcement having a wide range of stiffness is described. Strain localisation is taken into account by modelling a shear band having a specific thickness and specific strain-softening properties determined based on experimental results. Global and local behaviour of the unreinforced and reinforced sand observed in plane strain compression tests are properly simulated.

Elongational viscosities of random and block copolymer melts

The influence of random and block copolymerized structures on the uniaxial elongational viscosity was investigated. The investigated random copolymers were poly(ethylene-random-ethyl methacrylate) with comb-branched structure and poly(styrene-random-acrylonitrile) with linear structure. The studied block copolymers were poly(styrene-block-ethylenebutylene-block-styrene) with linear structure. The elongational viscosities of random copolymers showed strain-hardening properties. The strain-hardening property was influenced little by comonomer contents and depended on whether copolymers had linear or branched structures. In contrast, the elongational viscosities of block copolymers gave strain-softening properties. The strain-softening property was not affected by strain rates and block comonomer ratios. The causes of strain-hardening and -softening properties are discussed from relaxation spectrum and damping function based on the Bernstein–Kearsley–Zapas model. The damping functions of linear and branched random copolymers agreed with those of linear and branched homopolymers, respectively. On the other hand, linear block copolymers exhibited stronger damping than linear homopolymers. It was concluded that strain-hardening and -softening properties in the elongational viscosity of random and block copolymerized structures are correlated with their damping functions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 1765–1774, 1998

Elongational viscosities of random and block copolymer melts

The influence of random and block copolymerized structures on the uniaxial elongational viscosity was investigated. The investigated random copolymers were poly(ethylene-random-ethyl methacrylate) with comb-branched structure and poly(styrene-random-acrylonitrile) with linear structure. The studied block copolymers were poly(styrene-block-ethylenebutylene-block-styrene) with linear structure. The elongational viscosities of random copolymers showed strain-hardening properties. The strain-hardening property was influenced little by comonomer contents and depended on whether copolymers had linear or branched structures. In contrast, the elongational viscosities of block copolymers gave strain-softening properties. The strain-softening property was not affected by strain rates and block comonomer ratios. The causes of strain-hardening and -softening properties are discussed from relaxation spectrum and damping function based on the Bernstein–Kearsley–Zapas model. The damping functions of linear and branched random copolymers agreed with those of linear and branched homopolymers, respectively. On the other hand, linear block copolymers exhibited stronger damping than linear homopolymers. It was concluded that strain-hardening and -softening properties in the elongational viscosity of random and block copolymerized structures are correlated with their damping functions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 1765–1774, 1998

Static versus propagative plastic strain localisations

In the present work, the following questions are addressed. What are the conditions for the occurrence of strain localizations, what are the factors governing the transitions between static strain localization and strain propagation, what is the nature of the dislocation mechanism governing slip propagation Within a microscopic approach it is necessary to deal with the collective behavior of a population of interacting dislocations. As the approach it is necessary to deal with the collective behavior of a population of interacting dislocations. As the elastic interactions of dislocations are long-range the recently developed three-dimensional computer simulation of dislocation dynamics and interactions is particularly suited to this purpose. In the first section, the simulation in only briefly described. The experimental conditions and input parameters selected correspond to copper single crystals deformed with a constant applied strain rate at room temperature and in double slip. A simplified local softening rule is then introduced, which makes use of two additional input parameters. The examples considered refer to the different types of plastic behavior met when the strain softening properties are varied. Finally, a simple analytical model leading to an instability map is presented and its predictions are compared with the results of the numericalmore » simulations.« less

Undrained Stress-Strain-Time Behavior of Clays

A single phenomenological equation is shown to provide an adequate and complete description of the undrained stress-strain-time behavior of clays under axisymmetric loading conditions for cases not involving any rotation of the principal stress axis directions. The basic form of the relationship is thereafter idealized so that mathematical solutions may be achieved in closed form. The rheological properties of clays are shown to greatly influence the results of undrained pressuremeter tests. It is demonstrated that a simple analysis of pressuremeter test results which disregards rheological effects leads to a large discrepancy between the predicted and the actual stres-strain behavior of the material. Detailed comparisons are made. Even if the material is actually strain-hardening for constant shear strain-rate loading conditions, the derived stress-strain curve from constant strain-rate pressuremeter tests will exhibit strain-softening properties at conventional testing rates.