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One dimensional stress waves travelling in granular chains exhibit interesting characteristics such as filtering, tunability and wave mitigation because on the formation of solitary waves, and solitary wave trains, within them. An idealized one dimensional granular medium, consisting of a linear array of contacting spherical brass beads, was loaded dynamically in a modified split Hopkinson pressure bar, with loading pulses that span a variety of rates and profiles using pulse shaping techniques. Different chain lengths were studied to determine how solitary waves form in a varying length granular medium, as well as the speed of wave propagation. It is found that the wave speed propagates faster for longer chains of brass beads. The high loading rates of the Hopkinson bar also allowed us to investigate plastic dissipation effects in the granular chain when composed of different types of metals. To further our understanding of wave propagation in ductile ordered granular media, the experimental results are compared with companion numerical simulations based on a particle contact law that accounts for plastic dissipation. Knowing the behavior of a stress wave propagating through such materials can lead to arrangements that can produce desired stress wave mitigation characteristics as the waves travel through the granular chain.

An experimental study of in-plane tensorial stress determination from full-field phase-shifting photoelasticity and transmission Coherent Gradient Sensing (CGS) for stress intensity factor estimation is presented. Phase-shifting photoelasticity determines principal stress directions and the difference of principal stresses, while transmission CGS measures the x and y first derivatives of the sum of principal stresses. Combining these two methods for the same field of view allows for principal stress separation and, using the principal stress directions, the full in-plane stress tensor. The present study, which is the first experimental study for full-field tensorial stress determination around sharp cracks in a photoelastic material, applies this hybrid method for millimeter-scale fields of view including Mode I-dominant cracks in Homalite-100, a linear elastic brittle bulk polymer. The cases presented here range in Mode I stress intensity factor from about one-quarter of the fracture toughness to just below the fracture toughness. This experimental method can detect and determine mode-mixity ratios as small as 0:0043 with a range of –0:010 to 0:020. The experimental stress fields have excellent global agreement with the full-field 2D asymptotic crack solution using the experimentally calculated Mode I and Mode II stress intensity factors.

Experimental study was performed to investigate the fracture behavior of relatively brittle polymer foam. A single notch bending specimen made of a PVC core cell foam A-series, A 800 and A 1200, are used for the investigation. To measure the strain around the defect section, a 2D digital image correction (DIC) technique was used. The fracture initiation toughness was calculated from the load displacement curve and a strain fields obtained from DIC technique. Furthermore a study was performed to investigate the failure behavior of foam core with sharp cracks, notch and circular hole. To reduce the size effect, the net cross-sectional areas of the specimen for all the geometries considered are kept constant. An Instron tensile loading machine was used and the tensile load was measured directly through the load cell. The full strain field around the section was measured using DIC and the data points at the interest location were extracted. The result was compared with the dog-bone tensile experiment of intact specimen. It was observed that, the net section strength for specimen with cracks, notch and circular hole is higher than that of the intact foam core.

Plate impact experiments are a powerful tool in equation of state development, but are inherently limited by the range of impact velocities accessible to the gun. In an effort to dramatically increase the range of pressures which can be studied with available impact velocities, a new experimental technique is being developed. The possibility of using converging shock waves to produce a high pressure Mach reflection is examined. The technique proposed uses a composite target simply consisting of two concentric cylinders, with the only requirement being the initial shock speed in the outer cylinder is greater than that in the inner cylinder. Conically converging shocks will be generated at the interface due to the impedance mismatch and axisymmetric geometry of the composite target. Upon convergence, an irregular reflection must occur, at which point the conical analog of a Mach reflection develops. Once the Mach reflection reaches a steady state, the high pressure state in the Mach disk can be measured using velocity interferometry and impedance matching techniques. Experimental results on a copper inner cylinder are in good agreement with numerical simulations and data in the literature.

A new shear-compression experiment is developed to characterize the influence of hydrostatic pressure on the shear constitutive response of nearly incompressible viscoelastic materials undergoing large deformations. In this design, a uniform torsional shear stress is superposed on a uniform hydrostatic compressive state of stress generated by axially deforming samples confined by a stack of thin steel disks. The new design is effective in applying uniform multiaxial compressive strain while preventing buckling and barreling during inelastic deformation. In addition, it allows for the direct measurement of the stress and strain fields during the deformation history. The new shear-compression setup is developed to aid in characterizing the influence of pressure or negative dilatation on the shear constitutive response of viscoelastic materials in general and Polyurea in particular. Experimental results obtained with this technique illustrate the significant increase in the shear stiffness of polyurea under moderate to high hydrostatic pressures.

Two independent optical methods are used to analyze the dynamic material behavior of Mylar and Homalite-100 subjected to hypervelocity impact. Birefringent targets are loaded in tension inside a two-stage light-gas gun vacuum chamber, and are impacted with a 5 mg nylon slug at velocities between 3 and 6 km/s. Caustics and photoelasticity combined with high-speed photography are used to determine dynamic stress intensity behavior around the crack tip during and after impact. Homalite-100 lower crack tip speeds are subjected to reflecting boundary shear waves from the nylon impact, and thereby the crack path exhibits distinct kinks; whereas Mylar higher crack tip speeds provides distinguishable isochromatic patterns and an unadulterated fracture surface. Shear wave patterns in the target from photoelastic effects are compared to results from numerical simulations using the Overture Suite, which solves linear elasticity equations on overlapping curvilinear grids by means of adaptive mesh refinement.

This study aims to investigate the high-strain-rate shear response of viscoelastic elastomeric coatings at large strains and under elevated levels of hydrostatic pressure. Results of this study shed light on the combined effects of deformation rate and pressure which might promote a transition from viscoelastic to glassy behavior. This work utilizes a Split Hopkinson Pressure Bar (SHPB) apparatus in conjunction with a customized version of the recently proposed Shear Compression Specimen (SCS) which consists of a polymer gage section with two metal ends that remain essentially rigid during deformation. Detailed finite element simulations were used to customize the adopted specimen, to determine its proper dimensions and promote its functionality. The customized specimen permits subjecting the tested specimen to a state of uniform pressure and shear stress, while allowing for measuring pressure, shear stress and shear strain directly. Results obtained using the customized specimen, which are included in this paper, illustrate its usefulness in measuring the effect of high-strain-rate, large strain and hydrostatic pressure on the shear stress-strain response of viscoelastic elastomers.

The stress-fields near the crack tip for mixed-mode thermo-mechanical loading in functionally graded material (FGM) are developed using displacement potentials in conjugation with an asymptotic approach. The shear modulus, mass density and coefficient of thermal expansion of the FGM are assumed to vary exponentially along the gradation direction. Using insulated crack face boundary condition and steady state heat conduction assumption, the temperature field near to the crack tip is developed. By incorporating the developed temperature field equations with the displacement potentials, asymptotic thermo-mechanical stress field equations are derived. Finally, utilizing the minimum strain energy density criterion and the maximum circumferential stress criterion, the crack growth direction for various crack-tip speeds, non-homogeneity coefficients and temperature fields are determined.