Compressive Deformation Mode Research Articles

An Evaluation of the Effects of Type and Temperature of Aqueous Media on the Compressive Strength of Glass-Epoxy Composites

Epoxy systems reinforced with E-glass fibers, exposed to 100 h in three separate media were subjected to compressive mode of deformation. The difference in weight, i.e., before and after exposure to 100 h, following immersion in media was noted. Compared to the data obtained at room temperature in plain water (i.e., PR), the absorption levels in plain water containing a small proportion of dilute HCl at room temperature (i.e., PAR) were lower while samples in plain water at elevated (50 C) temperature (i.e., PH) show higher absorption. The compression strength and fractographic features, noted on the compression failed samples, are reported in this work. The experiment reveals that the media exposed samples generally exhibit lower strengths compared to the dry (i.e., unexposed) samples. Among the media exposed samples, the PAR set shows a small rise in strength while the PR and PH sets display a lowering of values. These changes have been attributed to various factors like medium ingress into samples inducing an alteration in the response of the interface regions, presence of either lengthy or fragmented fibers and resin smear on the fibers. In PAR case, the lower diffusion helps first in lowering the extent of its recording a decrement in strength vis-à-vis the dry case and this trend may be countered by the size of the Cl being different and in the end a small rise in strength is recorded. The fractographic features reveal interface separation, either scattered debris or a cleaner surface of fibers or adherence of resin on fibers region as well as appearance or otherwise of long or short fibers depending on whether the tests were done on unexposed samples or on the ones subjected to immersion in a specific aqueous medium.

Compressive Behavior and Fracture Features of Rubber Bearing Glass-Epoxy Composites Exposed to Aqueous Media

Epoxy systems containing HTBN rubber material and reinforced with E-glass fibres, exposed to a fixed time duration in three separate media were subjected to compressive mode of deformation. The yield stress and fractographic features noted on the compression failed samples are reported in this work. The experiment reveals that the seawater exposed sample exhibits a drop in strength compared to dry (unexposed) sample. This kind of drop is maintained if the media is changed from seawater to distilled water. When HCl is included in seawater, the experiment shows a small rise in strength value. These changes have been attributed to various factors like medium ingress into samples assisting interface failure, the larger-sized Cl- influencing the extent of diffusion of medium into system and finally their participation in the deformation phenomena. The fractographic features reveal interface separations that show either scattered debris or a cleaner surface or display a whitish-coated matrix region depending on whether the tests are done on unexposed samples or on ones following the immersion in the media.

Effect of triggering on the energy absorption capacity of axially compressed aluminum tubes

The energy absorption performance of extruded aluminum tubing for space frames was evaluated using computer-simulated compressive tests and quasi-static compressive deformation tests. An experimental deformation test and its simulation were conducted for seven extruded tube specimens on which various types of triggering dents were introduced, and the test data were investigated via observation of deformation mode, maximum repulsive force, and absorbed energy. The results indicated that the computer simulation results correlated well with the compressive deformation mode, indicating that the simulation was useful for the evaluation of absorbed energy. When triggering dents were introduced at the folding sites pre-estimated by the computer simulation, energy absorption could be improved, and the half-dented specimens absorbed more effectively than the full-dented specimens. On the other hand, when triggering dents of the same interval were introduced without consideration of the peak location of the folding wave, inhomogeneous deformation, together with overall bending, occurred, and deteriorated energy absorption because energies in bending were not as effectively absorbed as on folding.

Microstructural and mechanical behavior of a duplex stainless steel under hot working conditions

In the hot deformation of the duplex stainless steels, the complexity of the microstructure evolution and mechanical response is increased as compared with those of single-phase ferritic or austenitic stainless steels. In the present work, plane strain compression and torsion deformation modes have been used to analyze the microstructural evolution and the mechanical behavior of a duplex stainless steel in as-cast and wrought conditions, as a function of spatial phase distribution, the nature of interface, and the relative mechanical properties of both phases. The law of mixtures has been used to explain the different flow curves obtained when changing the phase distribution and/or the deformation mode. On deforming as-cast microstructures, the deformation partitions vary heterogeneously between both phases and some austenite areas act as hard nondeforming particles. Cracks have been observed to occur at the interface of such regions, from relatively low strains, for which the initial Kurdjumov-Sachs orientation relationship between ferrite and austenite is still present.

A Viscoplastic Simulation of Texture Evolution during Extrusion of an Aluminium Alloy

Numerical simulations of texture development have been carried out for hot plane strain extrusion of an aluminium alloy using both finite element calculations and a polycrystal plasticity model. The latter is based on the Taylor localisation hypothesis (relaxed constraints) and a viscoplastic constitutive law. We have considered the {111} slip systems and the {100}, {110} and {112} non-octahedral systems. The finite element code first simulates the local extrusion strain paths of the material flow through the die. Secondly, for the different deformation paths between the centre section and the surface the polycrystalline model is used to calculate the local deformation texture evolution. The results are compared with experimentally measured deformation textures at different depths of an extruded bar of a 6082 aluminium alloy. Near the centre section both the numerical simulations and the experimental textures are in good agreement, with typical β-fibre hot rolling texture components as a consequence of the essentially plane strain compression deformation mode. Texture simulations using the non-compact slip systems give significantly better agreement than for slip restricted to the {111} planes. However, very near the surface where there is a very high shear component, none of the models gives good quantitative predictions although there is a reasonable qualitative agreement assuming non-octahedral slip.

Dynamic responses of the head and cervical spine to axial impact loading

This study explores the inertial effects of the head and torso on cervical spine dynamics with the specific goal of determining whether the head mass can provide a constraining cervical spine end condition. The hypothesis was tested using a low friction impact surface and a pocketing foam impact surface. Impact orientation was also varied. Tests were conducted on whole unembalmed heads and cervical spines using a drop track system to produce impact velocities on the order of 3.2 ms −1. Data for the head impact forces and the reactions at T1 were recorded and the tests were also imaged at 1000 frames s −1. Injuries occurred 2–19 ms following head impact and prior to significant head motion. Average compressive load a failure was 1727 ± 387 N. Decoupling was observed between the head and T1. Cervical spine loading due to head rebound constituted up to 54 ± 16% of the total axial neck load for padded impacts and up to 38 ± 30% of the total axial neck load for rigid impacts. Dynamic buckling was also observed; including first-order modes and transient higher-order modes which shifted the structure from a primarily compressive mode of deformation to various bending modes. These experiments demonstrate that in the absence of head pocketing, the head mass can provide sufficient constraint to cause cervical spine injury. The results also show that cervical spinal injury dynamics are complex, and that a large sample size of experimentally produced injuries will be necessary to develop comprehensive neck injury models and criteria.

Microstructure and mechanical properties of duplex tiAl alloys containing Mn

A study has been made of the effect of Mn on the structure and compressive mechanical properties of duplex TiAl alloys. In order to clarify the separate effect of Mn and Al contents, the effect of Ti/Al ratio was also studied by analyzing the behavior of alloys with different Ti/Al ratios at the fixed Mn content. Addition of 3 at.% Mn to the binary Ti53Al47 alloy decreases the tetragonality and the unit cell volume of γ structure. It also promotes the formation of twin-related structure, the refinement of interlamellar spacing and grain size, and the increase in the volume fraction of lamellar grains. Increase in Ti/Al ratio at the fixed Mn content results in the further decrease in the tetragonality and unit cell volume and the refinement of grain size, while it decreases the volume fraction of lamellar grains. The modification of microstructure directly influences the compressive properties and deformation mode of duplex TiAl alloys. It has been found that Mn addition and increase in Ti/Al ratio enhance the plasticity of duplex alloys. Generation of mobile dislocations at the twin intersections has been found to occur in Mn containing alloys. Such dislocation generation at the twin intersections as well as the promotion of deformation twins in Mn containing alloys are all beneficial for improving the ductility of duplex TiAl alloys.

On The Concept of Characteristic States of Cohesionless Soil and Constitutive Modeling

The concepts of two characteristic states and their representation as characteristic state lines in the stress space are introduced to describe volumetric behavior of cohesionless soil during shearing. The first characteristic state line represents the state of cohesionless soil at failure, while the second characteristic line represents the state at which the rate of volumetric strain momentarily vanishes as the soil passes from the compressive mode of deformation to the dilative mode of deformation during shearing. Explicit forms of the two characteristic state lines in the stress space are proposed and used to develop a constitutive model based on the framework of plasticity theory. The general forms of the characteristic state lines are verified using drained shear test data for a fine sand. Stress-strain and volumetric-axial strain responses are predicted using the proposed model and good correlations are observed with experimental data.

Development of orientation coherence in plane-strain deformation

Spatial orientation coherence in 20 pct channel-die compressed aluminum ingot is investigated using the two-point orientation coherence function (OCF) constructed from individual crystallite orientation measurements. It is found that orientation coherence clusters formed in the initially coherence-free ingot during deformation. The orientation coherence cluster consists of a central grain with lattice orientation (φ1, ϕ, φ2) surrounded by grains with lattice orientation (π + φ1, ϕ, φ2); this coincides with one of the processing-symmetry orientations of the central grain. The observed clustering is compared with simulations of structure evolution based upon the classical full-constraint Taylor model. As is expected, no coherence structure develops in these simulations. A mechanism of formation for the orientation coherence cluster is proposed based upon a requirement of stress equilibrium between neighboring grains, while maintaining, on average, strain compatibility with the overall plane-strain compression deformation mode. A simplified Fourier representation of the conditional two-point OCF is described, and a numerical scheme to obtain the expansion coefficients is proposed and tested.

Viscoelasticity and plasticity aspects of antiplasticization phenomena: Strain rate and temperature effects

Abstract The phenomenon of antiplasticization was examined for poly-vinyl chloride containing 10 phr tricresyl phosphate, by means of dynamic mechanical tests and with constant strain rate equipment, using both tension and plane-strain compression deformation modes. While the activation energy for both α and β relaxations was decreased by the addition of the plasticizer, the magnitude of β dispersions decreased and the modulus increased over a temperature range lying between the α and β transitions of the plasticized polymer. Similar changes were found with respect to the yield stress measurements, from which a contour diagram was drawn showing the strain rate/ temperature relationship of antiplasticization. The values of activation energy for yield phenomena were found to lie between those obtained for the α and β relaxations. The activation volume, on the other hand, was found to increase over the same temperature range in which antiplasticization is observed.