Defining Ballistic Experimental Methodology and Nose Performance Coefficients for Cross-Laminated Timber (CLT)
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Tri, Alexis Marie
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Abstract
Protective structures have traditionally relied on concrete and steel for ballistic resistance, but these materials are carbon-intensive and less suitable for certain military applications, such as rapid or temporary deployments. Recently, cross-laminated timber (CLT), an engineered wood product composed of stacked adhered lumber with alternating 90-degree orientations from layer to layer, has gained traction as a sustainable and rapidly assembled alternative to conventional materials. CLT systems are prime for temporary military construction due to their modular nature, so recent research has investigated the viability of CLT against extreme loading conditions, such as blast and ballistic impacts.
The current CLT ballistic testing protocol is based on the US National Institute of Justice (NIJ) Standard Test and Classification for Ballistic Resistant Materials typically applied to metallic and fiber body armor ballistic testing. Unlike metal and fiber composites, CLT exhibits more localized damage under ballistic impact, allowing for greater density of projectile impacts per surface area without shot interaction. To optimize shots per area in CLT ballistic experimentation, we subjected four Loblolly CLT target panels with varied projectile target proximities to 60 shots using a 0.5 in (1.27 cm) steel sphere projectile. Results and statistical analysis suggest that no shot path interaction occurs when impacts are spaced at least 2 in (5 cm) apart. Consequently, this study recommends reducing the standard shot spacing for partial penetration experiments from 7 in (17.8 cm) to a minimum of 2 in (5 cm) with a 0.5 in (1.27cm) steel sphere projectile. This article provides a significant contribution to the field by establishing a more efficient ballistic testing methodology tailored to CLT. The optimized approach allows for the collection of substantially more data while improving resource efficiency and reducing testing time.
Additionally, CLT’s ballistic response to varying projectile nose geometries remains unexplored. This research experimentally evaluated the penetration resistance of CLT target panels subjected to blunt (.357 and .44 Magnum) and spherical (0.5 in [1.27 cm] steel sphere) projectiles to quantify nose performance coefficients for predictive modeling within Department of Defense (DoD) design frameworks. We conducted a total of 90 ballistic experiments at the U.S. Army Engineer Research and Development Center (ERDC), generating partial and complete penetration series across a range of striking velocities. Results indicate that CLT’s ballistic resistance is highly dependent on projectile type. Blunt and spherical projectiles produced shallower penetrations and greater energy dissipation through crushing and shear plugging. The soft point projectile exhibited significant nose deformation, leading to higher energy absorption and reduced penetration efficiency. By adapting the Unified Facilities Criteria (UFC) predictive wood penetration equation with a CLT-specific nose performance coefficient, N ̅, we found that existing UFC models underpredict CLT’s resistance to nosed projectiles. These results of this research provide foundational data for developing predictive design criteria and improving CLT integration in protective infrastructure.
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2025-12
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Thesis (Masters Degree)