Depth Of Penetration Data Research Articles

Depth of penetration experiments of S-2 glass/epoxy composites: A new Experimental Methodology in determining the rate dependent dynamic crush strength of composites

Depth of Penetration (DoP) experiments have been conducted on thick section S-2 glass/epoxy laminates impacted by 64 grain steel projectiles over an impact velocity range of 400 m/s to 1400 m/s. Under high velocity impact, the composite under the projectile is highly compressed and crushes into powder. A theoretical model is developed to reduce DoP data that relates the plastic/granular wave velocity, plastic/granular strain and strain rate during penetration to the strain rate dependent dynamic punch crush strength and plastic/granular erosion strain of composite for the first time in the literature. Punch crush strength is an important material property used in rate dependent progressive composite damage models. DoP experiments on thick section composites are presented to study the effects of fiber volume fraction, fabric architecture, and inelastic matrix behavior on depth of penetration and damage modes. The new data reduction methodology is used to calculate the rate dependent punch crush strength of glass/epoxy laminates.

Approximate solutions of finite dynamic spherical cavity-expansion models for penetration into elastically confined concrete targets

Confined concrete has superior anti-penetration performance over unconfined concrete. A finite dynamic spherical cavity-expansion approximation model with radially elastic confinement is proposed to analyze the confinement on concrete targets and predict the depth of penetration (DOP), taking steel-tube-confined concrete (STCC) targets normally penetrated by rigid projectiles as an example. Firstly, the validity of a nonlinear failure criterion to describe strength feature of concrete in the comminuted region is demonstrated by triaxial compressible tested data and the reference range of dimensionless parameter m in the modified Griffith criterion is recommended. Secondly, the relationship between the stresses in concrete and cavity-expansion velocity is developed. Furthermore, the confinement effects on response modes of confined concrete, radial stress at cavity wall and stresses distribution in concrete are analyzed. Lastly, an engineering model is also established to predict the DOP of STCC targets normally penetrated by rigid projectiles. The results show that the radial stress at cavity wall is not a constant during the cavity-expansion process in finite concrete with radially elastic confinement, which is different from the steady spherical cavity-expansion of infinite material in which the radial stress at cavity wall is a constant with constant cavity-expansion velocity. The possible response phases of confined concrete targets normally penetrated by rigid projectiles include “elastic-cracked-comminuted”, “cracked-comminuted” and “full-comminuted”, depending on the relationship among cavity-expansion velocity, radial confining stiffness and radius ratio of cavity to target. The DOP data from the engineering model established in this paper agree well with those of experiments in the published references.

The relationship between mechanical properties and ballistic penetration depth in a viscoelastic gel

The fundamental material response of a viscoelastic material when impacted by a ballistic projectile has important implication for the defense, law enforcement, and medical communities particularly for the evaluation of protective systems. In this paper, we systematically vary the modulus and toughness of a synthetic polymer gel to determine their respective influence on the velocity-dependent penetration of a spherical projectile. The polymer gels were characterized using tensile, compression, and rheological testing taking special care to address the unique challenges associated with obtaining high fidelity mechanical data on highly conformal materials. The depth of penetration data was accurately described using the elastic Froude number for viscoelastic gels ranging in Young’s modulus from ~60 to 630kPa. The minimum velocity of penetration was determined to scale with the gel toughness divided by the gel modulus, a qualitative estimate for the zone of deformation size scale upon impact. We anticipate that this work will provide insight into the critical material factors that control ballistic penetration behavior in soft materials and aid in the design and development of new ballistic testing media.

Penetration Deep of Non-Deformable Projectile into Concrete Targets

A dynamic cavity-expansion penetration model for concrete targets impacted by non-deformable projectile is developed. Based on the dynamic cavity-expansion penetration model, the equations of the final penetration depth were determined including the effect of additional mass and sliding frictional coefficient. The predicted final Penetration depth was compared with the depth of penetration data and a good agreement was achieved. The analysis indicated the additional mass was negligible compared to the mass of the projectile and independent of the striking velocity. When the friction between the concrete and the nose surface is assumed to be negligible, the final penetration depth increases slightly. The relationship between the principle stress difference at failure and unconfined compressive strength was determined by curve fitting.

Evaluation of fatigue damage in materials using indentation testing and infrared thermography

Damage identification due to fatigue has been studied on 304-Stainless Steel and Al-Cu-Mg alloys 2014-T651 and 7175-T7351, using two different experimental methods: a) cyclic indentation, and b) infrared thermography. Indentation response during load controlled cyclic loading is used to characterize fatigue response of materials. The load vs. depth of penetration data obtained continuously during fatigue testing is used to obtain information on cyclic stress-strain behavior and onset of failure. Infrared thermography is used to study the heat generation during fatigue loading on specimens. The variables that affect the process are: frequency of loading, magnitude of strain (elastic-plastic), thermal properties. The temperature curve can be considered to be having three regions, initial region of rapid increase in temperature, followed by stable temperature rise and final rapid heat generation prior to failure. The slopes in the initial region and stable region are independent of prior damage history in materials in case of specimens subjected to pure elastic load reversals. In case of elastic-plastic loadings, the rate at which the temperature rises in initial region changes as a function of fatigue damage and can thus be used to estimate prior damage in materials.

Penetration of concrete targets with ogive-nose steel rods

We conducted depth of penetration experiments in concrete targets with 3.0 caliber-radius-head, steel rod projectiles. The concrete targets with 9.5 mm diameter limestone aggregate had a nominal unconfined compressive strength of 58.4 MPa (8.5 ksi) and density 2320 kg/m 3. To explore geometric projectile scales, we conducted two sets of experiments. Projectiles with length-to-diameter ratio of ten were machined from 4340R c 45 steel, round stock and had diameters and masses of 20.3 mm, 0.478 kg and 30.5 mm, 1.62 kg. Powder guns launched the projectiles to striking velocities between 400 and 1200 m/s. For these experiments, penetration depth increased as striking velocity increased. When depth of penetration data was divided by a length scale determined from our model, the data collapsed on a single curve. Thus, a single dimensionless penetration depth versus striking velocity prediction was in good agreement with the data at two geometric projectile scales for striking velocities between 400 and 1200 m/s. In addition, we conducted experiments with AerMet 100R c 53 steel projectiles and compared depth of penetration and post-test nose erosion data with results from the 4340R c 45 steel projectiles.

Depth of Penetration During Electron Beam Welding

An examination of available solutions for the penetration depth for electron beam welding revealed that they have been based on mathematical models which are not truly representative of the physical phenomena. The deposition of electron beam energy has been represented by a steady line source. Experimental evidence, however, shows that due to an oscillating flow of the molten material, the electron beam energy is deposited on a surface which varies from close to horizontal to the sides of a cone-shaped cavity. To account for this a cylindrical constant temperature boundary condition was proposed. Results based on this model were found to agree within 20 percent with available depth of penetration data.