Showing papers on "Ballistic impact published in 1989"

Alternative Test Methodology for Ballistic Performance Ranking of Armor Ceramics

Abstract: : A laboratory test method of ranking the ballistic performance of ceramic materials is under development at the U.S. Army Materials Technology Lab. by the Ballistic Impact Behavior Group and Armor Systems Team. Ranking are based on residual penetration of a tungsten long rod fired at constant velocity through a laterally confined ceramic into a semi-infinite steel backup. By varying the thickness or areal density of ceramic from zero to a value producing no residual penetration, a ballistic performance map for the ceramic is generated. Different materials can be compared on the basis of residual penetration observed for a given areal density. Ceramics tested to date include aluminum oxide in 90% and high purity forms, titanium diboride, silicon carbide, and boron carbide. Performance rankings observed for these materials are in agreement with the rankings yielded by conventional V50 protection ballistic limit test methods. This test method requires fewer shots than V50 tests, has sensitivity comparable to present test methods, and avoids the fundamental problem of V50 dependence on armor design. As a consequence, it should prove to be valuable for acceptance testing of production materials, comparison testing to rank the performance of new materials, and for parametric analysis of ballistic performance variations resulting from material properties, cell size, confinement, and similar factors.

Ballistic impact of ceramics

Abstract: The impact behaviour of a range of glass and ceramic materials has been studied using high-speed photography. A gas gun was used to project hardened spheres at plate specimens in the velocity range 30 to 1000m s-1. The target materials included soda-lime glass, boron carbide and various glass ceramics and aluminas. The performance of a particular ceramic was found to depend on a combination of parameters but of key importance was the relative hardness of the projectile and target materials. The fracture toughness, K(IC), had only a secondary effect.

Ballistic Properties of Composite Materials for Personnel Protection

Abstract: : The Australian Army currently has requirements for new combat and vehicle crewman helmets. Various polymer materials in the form of fibre- reinforced organic matrix composites have been shown to have sufficient resistance to ballistic impact to be regarded as attractive construction materials for personnel protective helmets. This report discusses the relative ballistic properties of those organic matrix composite materials which are considered as prime candidates to meet the requirements of the Army's new combat and vehicle crewman helmets.

High Speed Photographic Studies Of The Ballistic Impact Of Ceramics

Abstract: The impact behaviour of a range of glass and ceramic materials has been studied using high-speed photography. A gas gun was used to project hardened steel spheres at plate specimens in the velocity range 30m s-1 to 1000m s-1. The target materials included soda-lime glass, boron carbide and various glass ceramics and aluminas. The controlled impacts were viewed at microsecond framing intervals using a Hadland Imacon camera. The camera was triggered by the projectile interrupting a laser beam. Results from these experiments have identified the various failure modes of the materials and given quantitative data on the energetics of impact. The performance of a particular ceramic was found to depend on a combination of parameters but of key importance was the relative hardnesses of the projectile and target materials. Targets which were harder than the projectile (for example, alumina or boron carbide targets) deformed and fractured the projectiles and prevented penetration. However, targets which were softer than the projectile (for example, glasses and glass ceramics) were penetrated relatively easily. In both cases, the fracture toughness, KIc, had only a minor effect. The results emphasize the value of high-speed photography for studies of the complex phenomena involved.

On the behavior of ballistic impact into flexible protection systems

Abstract: Past photographic analyses have shown that a fabric impacted at ballistic speeds deforms into approximately a conical shape. By ignoring the complex fiber interactions and treating the deformed fabric as simply a homogenous, isotropic conical shell, the problem is simplified to one easily handled by conical shell analysis. Experimental data on projectile velocities and simple target properties, in combination with the proposed algorithm should allow one to predict geometry, strain in the fabric, and load applied by the fabric onto the projectile in successive time intervals during a simulated impact. Data on projectile exit velocity after penetration identifies the failure strain of the fabric. Through use of the model one can then predict the outcome of impacts involving different target thickness and different bullet sizes and shapes. An experimental program was performed, involving .22 and .357 bullets fired at Kevlar 29 fabric targets. Results compare favorably with the theory.

Evaluation of ARALL-4: An Aramid Fiber Reinforced Aluminum

Abstract: : ARALL- 4 was evaluated for the following: tensile properties at elevated temperatures; tensile properties in hot/wet conditions; moisture absorption; anisotropy and ballistic impact performance. The tensile properties of ARALL-4 exceed those of 2024-T8 in the longitudinal direction, but they are lower in the transverse direction. ARALL-4 retains excellent tensile properties after full saturation at 95% humidity and at 105 C. The moisture absorption of ARALL-4 is slow. The ballistic impact performance of ARALL-4 is inferior to several commonly used lightweight armor materials including: glass reinforced plastic, KEVLAR laminate, and titanium 6-4. Keywords: ARALL, Tensile properties, Ballistic properties, Moisture absorption, Anisotropy, Laminate.

A Computational Model of the Perforation of Multi-Layer Metallic Laminates

Abstract: : A model for the deformation of multi-layer metallic laminate targets during ballistic impact is described. The model divides the process into a stage of plug acceleration followed by dishing of the rear of the target, and allows for the effects of variable interlamellar bend strength. A computational procedure is described, as well as the mechanical test procedures to generate the input data for the program. Examples of the application of the model are described to illustrate the interpretation of results, the limitations of the model, and the use of the model is parametric studies for laminate design. The computer program is listed with typical input and output data. Keywords: Australia.

Optimization of Fracture Resistance in Composites

Abstract: : An interdisciplinary approach was taken to investigate structure property relationships in fibrous composites subjected to various stress states and environmental conditions. The ultimate goal was to reinforce our ability to optimize the fracture resistance in composites. The concept of controlled interlaminar bonding (CIB) was proposed and evaluated as a possible approach of improving the impact energy-absorbing capability or the damage tolerance in composites. Thickness-direction fibers, as introduced by stitching or braiding, can improve the interlaminar shear strength and interlaminar fracture toughness, thereby reducing or suppressing delamination in advanced composites. Failure mechanisms in the composites subjected to impact loading were investigated. The most critical material parameters that dictate the impact penetration resistance of composites were identified. Failure mechanisms of hybrid composites were studied as a ballistic impact studies was developed. The effect of residual thermal stresses on the impact response of composites was measured. New techniques for determining residuals stresses and internal damages in composites were discussed. A new energy-based fracture criterion for composites was proposed. Equations for determining the strain energy densities in composites under various loading modes were derived. A new way of determining the stress intensity factor in composite was developed, and applications of the J-integral approach to composites fracture problems were discussed.

Capabilities and some applications of the LLNL 100-kV electric gun

Abstract: The LLNL 100-kV electric gun is an experimental device for launching thin flyer plates at velocities as high as 20 km/s to study impact damage and shock-wave physics. The hypervelocity impact studies reported here include a damage study of spalling damage in aluminum, a study of one-dimensional shock-wave attenuation in materials, use of the well-characterized one-dimensional shock waves for equation-of-state measurements in various materials, and use of thin flyer plates at velocities up to 18 km/s to produce reverse ballistic impact on target objects such as rods to measure damage and fragmentation. Our studies include both experimental results and correlation with numerical calculations using a code such as DYNA2D. 2 refs., 9 figs.