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Advanced transparent materials are used in protective systems for enhancing the survivability of ground vehicles, air vehicles, and personnel in applications such as face shields, riot gear, and vehicle windows. Low velocity impact damage can limit visibility and compromise the structural integrity of a transparent system, increasing the likelihood of further damage or penetration from a high velocity impact strike. For this reason, it is critical to determine damage tolerance levels of transparent systems to indicate whether or not a component should be replaced. In this study, transparent laminate systems will be tested by comparing baseline conditions to experimentally controlled damage states. Destructive testing including air gun and sphere impact testing will be used to replicate low velocity impacts in the field. Characterization of the damaged state will include basic visual inspection as well as nondestructive techniques including cross-polarization, x-ray, and ultrasound. The combination of destructive testing and characterization of the resulting damage can help to establish a damage acceptance criterion for materials used in protective systems. [ABSTRACT FROM AUTHOR]

Decreasing the weight of protective systems, while minimizing the decrease in ballistic performance, is an ongoing goal of the Army. Ceramic materials are currently combined with other materials in these types of structures in order to decrease weight without losing ballistic performance. This includes structures in which the ceramic material is confined in some way and in which the ceramic material is completely encapsulated. Confinement or encapsulation of ceramic material within a structure generally adds complexity and cost. Relatively simple panel specimens fabricated with ceramic tiles on aluminum backings and side confinement using steel were evaluated using nondestructive methods, including x-ray computed tomography and ultrasonic testing. The nondestructive evaluation results will be discussed and compared, including the detectability and mapping of fabrication features. [ABSTRACT FROM AUTHOR]

The projected microwave energy pattern, wave guide geometry, positioning methods and process variables have been optimized for use of a portable, non-contact, lap-top computer-controlled microwave interference scanning system on multi-layered dielectric materials. The system can be used in situ with one-sided access and has demonstrated capability of damage detection on composite ceramic armor. Specimens used for validation included specially fabricated surrogates, and ballistic impact-damaged specimens. Microwave data results were corroborated with high resolution direct-digital x-ray imaging. Microwave interference scanning detects cracks, laminar features and material properties variations. This paper presents the details of the system, the optimization steps and discusses results obtained. [ABSTRACT FROM AUTHOR]

The paper is concerned with the channeling of elastic waves propagating in an eight-ply quasi-isotropic laminate arising from impulsive line sources of dislocation located at each of the seven interfaces in turn. The laminate is composed of identical layers of fiber composite material which is modeled as a transversely isotropic continuum with the axis of transverse isotropy along the fiber direction. The line sources set up a straight crested wave travelling along the laminate in the direction normal to the load line and the elastodynamic equations within each layer are solved by taking Laplace transforms with respect to time and Fourier transforms with response to the co-ordinate in the propagation direction. The resulting system of six first order differential equations in each layer are solved to obtain the transforms of the displacement and stress components throughout the laminate. The time history of any displacement or stress component at any location may then be recovered by numerical inversion of the double transform. This numerical inversion involves a summation over the normal modes of Rayleigh-Lamb waves and in an earlier paper, it has been shown that for some locations of the line source, the contribution to the upper surface normal displacement from the fundamental mode is swamped by contributions from some of the higher modes. Here, details are presented of the displacement variation through the laminate associated with the different Rayleigh-Lamb modes showing how the disturbance is channelled in some layers for specific locations of the source line. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It may be shown formally that one possible approach to evaluating the dynamic response of a multi-ply fiber composite plate to an impulsive point load is by integrating the response to a line load over all orientations of the load line. This is a computationally intensive exercise and as a preliminary step, it is instructive to consider the simpler generic problem of the dynamic response of a two-dimensional elastic medium to a point load. For a two-dimensional isotropic material, integration of the line load solutions may be performed analytically and leads, as is well known, to the Bessel function solution. For an isotropic material, analytic integration is not possible and it is necessary to carry out the integration numerically. The paper will report the results of the numerical integration for both the isotropic and anisotropic media, showing some of the contributions at a fixed location arising from the individual line loads. For any orientation of the line load, the contribution to the overall response is non-causal but complete integration leads to a properly casual solution. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]