Ceramic materials have been extensively used in armor applications for both personnel and vehicle protection. As the types of threats have diversified recently, e.g., improvised explosive devices and explosively formed projectiles, a proper set of ceramic material selection criteria is needed to design and optimize corresponding mitigating structures. However, the dynamic fracture and failure behavior of engineering ceramics is still not well understood. Using examples of thin ceramic plates and confined thick ceramics subjected to kinetic energy projectile impact, this article provides a brief summary on the current understanding of dynamic failure processes of ceramics under dynamic penetration loading conditions. Laboratory examination of dynamic fracture of ceramics is conducted using split Hopkinson bars with various loading rates, stress states, and loading histories.

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The stress-strain response of a porcine muscle along and perpendicular to the muscle fiber direction was characterized over a wide range of strain rates under uniaxial tension. A modified Kolsky tension bar was used to conduct the experiments at high strain rates. Tubular specimen geometry was used to achieve uniform loading within the specimen and to minimize lateral inertia effect. Loading pulse was controlled to facilitate constant strain rates and dynamic stress equilibrium. Quasi-static experiments were also performed to explore the rate effects over a wider range of strain rates. The results show that the nonlinear tensile stress-strain responses in both directions along and perpendicular to the fibers are highly sensitive to strain rates. Compared with high-rate compression response, the strain rate sensitivity in the tensile test is less dependent on the fiber orientation to the loading direction.

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Resin uptake plays a critical role in the stiffness-to-weight ratio of wind turbine blades in which sandwich composites are used extensively. This work examines the flexural properties of nominally half-inch thick sandwich composites made with polyvinyl chloride (PVC) foam cores (H60 and H80; PSC and GPC) at several resin uptakes. We found that the specific flexural strength and modulus for the H80 GPC sandwich composites increase from 82.04 to 90.70 kN Á m/kg and 6.03 to 7.13 MN Á m/kg, respectively, with 11.0% resin uptake reduction, which stands out among the four core sandwich composites. Considering reaching a high stiffness-to-weight ratio while preventing resin starvation, 32% to 38% and 40% to 45% resin uptakes are adequate ranges for the H80 PSC and GPC sandwich composites, respectively. The H60 GPC sandwich composites have lower debonding toughness than H60 PSC due to stress concentration in the smooth side skin-core interphase region. The ailure mode of the sandwich composites depends on the core stiffness and surface texture. The H60 GPC sandwich composites exhibit core shearing and bottom skincore debonding failure, while the H80 GPC and PSC sandwich composites show top skin cracking and core crushing failure. The findings indicate that an appropriate range of resin uptake exists for each type of core sandwich composite, and that within the range, a low-resin uptake leads to lighter blades and thus lower cyclic gravitational loads, beneficial for long blades.

This study evaluates the loading rate and surface condition dependence of the flexural strength of a borosilicate glass. The glass specimens are subjected to three different surface treatments before four-point bending tests to study the effect of surface flaws. Quasistatic (Material Test System 810) and dynamic (Kolsky bar) experiments are performed at loading rates ranging from 0.7 to 4 Â 10 6 MPa/s. The results show that the flexural strength of the borosilicate glass has a strong dependence on the loading rate. A chemically etched surface produces an enhanced flexural strength by about an order of magnitude. Scanning electron microscopy images on fracture surfaces indicate that the failure is governed by different types of flaws under different surface treatment conditions. Edge failure is also identified for samples possessing high flexural strength.