Search

In modern warfare, oblique penetration is frequently observed when a penetration warhead mounted on a guided missile hits the target. When oblique penetration occurs on hard targets, such as reinforced concrete, the projectile experiences complex stress states along with tensile and compression stresses that can result in the deformation and fracture of the projectile. Therefore, the survivability of the projectile should be determined at the design phase. Structural survivability was assessed here through a correlated simulation considering a case where the projectile was fractured while penetrating into a 30° inclined concrete target at 333 m/s. For correlated simulation, we obtained the dynamic constitutive equation and fracture properties of the projectile material (AISI4340 steel) up to a strain rate of 1500 s−1. Furthermore, concrete material coefficients related to the strain rate sensitivity were calibrated using the test database. Computational analysis result agreed well with the actual test result.

An algorithm for extracting the equivalent stress versus equivalent plastic strain curve of a necking material in tensile test is proposed (the curve is called here the equivalent-plastic (EP) stress–strain (SS) curve). The presented algorithm traces the force–elongation curve via iterative finite element (FE) simulations without assuming a constitutive model and is suitable for a general-purpose FE solver available to a general audience. In the FE simulation and experiment, a slightly tapered geometry was employed around the specimen center to stably initiate necking there. The proposed algorithm and mentioned necking initiation method have been applied to extracting the EP SS curve of a high-strength steel material using an axisymmetric specimen. Because necking was initiated stably in simulation at the specimen center for a range of mesh sizes, the convergence of the extracted EP SS curve with the mesh size could be successfully verified. The EP SS curve of the tested material was extracted up to an EP strain of 0.85 with average strain intervals of approximately 2.5 mili-strain. The error values were less than 0.2 and 0.1% after four and seven FE simulations, respectively. The presented algorithm and necking initiation method in simulation can also be used for simultaneously quantifying the fracture EP strain of a necking material in the tensile test.

The tension/compression hardening behavior is important in sheet metal forming processes because of complicated loading paths. Experimental methods to measure the tension/ compression behavior have not considered the effect of the strain rate although the strain rate is related to the hardening behavior of sheet metal. The tension/compression tests need to be conducted considering the strain rate to acquire accurate hardening behavior.This paper deals with an experimental technique to measure the tension/compression behavior of sheet metal at various strain rates. A new clamping device was developed to prevent a sheet specimen from buckling under compression loading condition. Compared to previous clamping devices, the clamping device was devised to uniformly impose a clamping force and easily measure the strain from side of a specimen. Tension/compression tests have been conducted at various strain rates for SPCC and DP590 with displacement of 10%. Hardening curves under the tension or compression loading condition were obtained and analyzed with respect to the strain rate.