Fracture Behavior of Prestressed Composites Subjected to Shock Loading: A DIC-Based Study

International Journal of Impact Engineering

2016

Dynamic stress-strain response of rigid closed-cell polymeric foams exposed to direct impact loading is investigated in this work by subjecting high toughness polyurethane foam specimens to direct impact with different projectile velocities and quantifying their deformation response with high speed stereo-photography together with 3D digital image correlation. The measured transient displacement field developed in the specimens during high stain rate loading is used to calculate the transient axial acceleration field throughout the specimen. A simple mathematical formulation based on conservation of mass is also proposed to determine the local change of density in the specimen during deformation. By obtaining the full-field acceleration and density distributions, the inertia stresses at each point in the specimen are determined through a non-parametric analysis and superimposed on the stress magnitudes measured at specimen ends, to obtain the full-field stress distribution. The process outlined above overcomes a major challenge in high strain rate experiments with low impedance polymeric foam specimens, i.e. the delayed equilibrium conditions can be quantified.

Section: Impact Loadingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of the dynamic stress–strain response of compressible polymeric foam using a non-parametric analysis

Koohbor

International Journal of Impact Engineering

2016

“…Using the camera delay time feature, the duration of the trigger is adjusted to capture images prior (reference image) and after deformation. The reference and the consequence images are then imported for further post processing following a well-documented procedure available in the literature [24][25][26].…”

Section: Specimen Geometry and Surface Preparation For Macro And Mesomentioning

confidence: 99%

Local Deformation and Failure Mechanisms of Polymer Bonded Energetic Materials Subjected to High Strain Rate Loading

Ravindran

Tessema

J. dynamic behavior mater.

2016

The dynamic multi-scale deformation mechanism of polymer bonded energetic material is investigated. Samples made of polymer bonded sugar (a known simulate for polymer bonded explosives) with 85 % sugar crystals and 15 % polymer binder are used. The samples are dynamically compressed using a split Hopkinson pressure bar. Using a high magnification, meso-scale 2D digital image correlation experimental setup, the local deformation is measured in situ at sub-grain scale. The macroscale deformation mechanism is also investigated with the help of 3D digital image correlation. From the mesoscale experiment, it is observed that the local strain distribution in the specimen is highly heterogeneous with large strain localization occurring at the polymer rich areas between the crystal boundaries. Deformations of the majority of the crystals are minimal, and usually realign themselves to accommodate large deformation of the binder by rigid rotation and sliding. Due to this, delamination of the polymer binder from crystals and binder cracking are the main local failure modes. It is also observed that the presence of small crushed crystals from material processing are the favorable sites for this opening mode failure.

“…Controlled direct impact was applied to the specimen using a shock tube apparatus. Details on the design aspects of the shock tube are beyond the scope of this work, but can be found elsewhere [19,23]. A schematic representation of the utilized shock tube is depicted in Fig.…”

Section: Direct Impact Experimentsmentioning

confidence: 99%

Characterizing the constitutive response and energy absorption of rigid polymeric foams subjected to intermediate-velocity impact

Koohbor

2016

Polymer Testing

As an optimum energy-absorbing material system, polymeric foams are needed to dissipate the kinetic energy of an impact, while maintaining the impact force transferred to the protected object at a low level. Therefore, it is crucial to accurately characterize the load bearing and energy dissipation performance of foams at high strain rate loading conditions. There are certain challenges faced in the accurate measurement of the deformation response of foams due to their low mechanical impedance. In the present work, a non-parametric method is successfully implemented to enable the accurate assessment of the compressive constitutive response of rigid polymeric foams subjected to impact loading conditions. The method is based on stereovision high speed photography in conjunction with 3D digital image correlation, and allows for accurate evaluation of inertia stresses developed within the specimen during deformation time. Full-field distributions of stress, strain and strain rate are used to extract the local constitutive response of the material at any given location along the specimen axis. In addition, the effective energy absorbed by the material is calculated. Finally, results obtained from the proposed non-parametric analysis are compared with data obtained from conventional test procedures.