Analytical Description of Neck Profile during Tensile Testing of Cylindrical Specimens

One of the problems of studying the rheological properties and plasticity of metals and alloys from the results of tensile tests of cylindrical specimens is the need to determine the stress triaxiality value, which depends on the shape and size of the neck formed. An analytical description of the neck profile makes it possible to increase the accuracy of experimental measurements of its dimensions, in particular, the radius of curvature in the smallest cross-section of specimen. This paper is devoted to searching a universal neck profile equation that allows calculating the radius of neck curvature regardless of the nature of the material hardening curve and the stage of strain localization. The exact surface equation is established and its accuracy is estimated for hardening and softening material.

Non-Classical Model of Dynamic Behavior of Concrete

Modeling of dynamic properties of concrete is presented in the paper. The non-classical model of dynamic deformation was proposed. The essence of this model is the method of determination of the initial dynamic yield surface. For this purpose, the dynamic strength criterion was used. The model describes the elastic properties until attaining the dynamic strength of concrete, perfectly plastic properties in the limited range of deformation, material softening, material dilatation, and cracking or crushing of material as the residual stress processes during tension or compression. Degradation of elastic material constants was taken into consideration. Comparative analysis with previously published experimental results and theoretical models demonstrated that the proposed model is well approximates the basic dynamic properties of concrete and can be used in numerical analysis to evaluate the dynamic load capacity of reinforced concrete structures.

Rheological Characterization of Agarose and Poloxamer 407 (P407) Based Hydrogels

ABSTRACTPoloxamer 407 (P407) is a biocompatible thermo-setting polymer, while agarose is a biocompatible thermo-softening material. It is interesting to mix them to examine any possible synergy in thermomechanical properties. In this study, rotational rheometer was adopted to study rheological properties of the mixtures of agarose/P407 gels with different concentrations at various frequencies, strain rates and temperatures. It has revealed that the addition of P407 decreased the gel stiffness by an order of magnitude. For the given combinations in this study, the increase in agarose concentration would increase both the storage modulus and loss modulus of the gel mixtures. The variation in P407 concentration (2.5%-10%) minimally changes the composite moduli. These agarose/P407 gel mixtures also exhibited shear thinning behavior. However, the addition of P407 (2.5%-10%) to agarose gel only has very small effect on thermomechanical properties of agarose gels. The overall transition temperature for these gel mixtures is governed by P407 melting point where the phase change starts around 55°C and the gels completely collapse at the melting temperature of agarose.

Homotopy Shear Band Solutions in Gradient Plasticity

Analytical shear band type solutions for finite domains are derived within the framework of gradient plasticity theory by employing the homotopy analysis method (HAM). Such types of solutions were available in the literature only for infinite domains in the nonlinear material softening regime and steady-state conditions, as well as for finite domains in the material hardening regime. HAM allows for solutions to be obtained for both hardening and softening material models, as well as for unsteady conditions periodic solutions are also derived. The HAM results are verified with numerical simulations, which show excellent agreement. Moreover, an error analysis is provided which guarantees the convergence of our series solution.

The Triple-Shear Unified Analytical Solution of Stress and Displacement of Softening Material Thick Walled Cylinder

Based on the further analysis to triple-shear unified yield criterion, the Lode parameter expression of the triple-shear unified yield criterion were given. This paper performs the analysis computation to softening material thick-walled cylinder under internal pressure based on triple-shear unified yield criterion. The analytical solution of stress and displacement is obtained. By using triple-shear unified yield criterion, more reasonable solution for different softening material can be derived.

Prediction of Machining Induced Surface Integrity Using Elastic-Viscoplastic Simulations and Temperature-Dependent Flow Softening Material Models in Titanium and Nickel-Based Alloys

In this study, the feasibility of predicting surface integrity and residual stresses by using elasto-viscoplastic finite element simulations and temperature-dependent flow softening constitutive material modeling is investigated. A friction determination method is proposed to identify friction coefficients in presence of tool flank wear. Serrated and cyclical chip formation has been simulated for using tools with and without flank wear. The predicted residual stresses and surface integrity is compared against experimental results from literature. Effect of friction on the residual stress profiles is also investigated. These results are highly essential in predicting machining induced microstructure alterations that are detrimental to fatigue life of nickel and titanium alloy components.

Dynamic Mechanical Tests on Magnesium Catalyzed Cast Polyamide 6 Composites Having Different Additives

Due to the effect of graphite and montmorrilonit additives, the impact strenght slightly decreases, but by the influence of softening material, the value of impact strength can be three times more than the pure PA6. It is determined that graphite can be added until 3%, montmorrilonit can be added until 6% and softening material can be added until 15% to the base matrix. These samples give basis for special characteristics examinations.