PSI - Issue 66

Sobhan Pattajoshi et al. / Procedia Structural Integrity 66 (2024) 167–174 Pattajoshi et al./ Structural Integrity Procedia 00 (2025) 000–000 5 subroutine, the resulting tensile stress-strain curve for an element subjected to a strain rate of 1 �� was generated and compared to the default RHT model, as shown in Fig. 1. The updated post-peak response now follows the exponential softening behavior as described by the equation above. 171

Fig. 1. Tensile stress-strain comparison of default RHT with modified model (single element analysis).

4. Results and discussion In their early research, Hanchak et al. [21] conducted experiments to validate a numerical model designed for a single-layer concrete target. They used a 30 mm caliber steel projectile with an ogival nose, featuring an ogive radius of 76.2 mm , and launched it at speeds between 330 m/s and 1100 m/s . The projectile weighed 0.50 kg , while the target material consisted of reinforced concrete with compressive strengths of 48 MPa and 140 MPa . The concrete slabs measured 610 mm × 610 mm × 178 mm and were reinforced using 5.69 mm diameter steel bars, spaced 76.2 mm apart in both the in-plane and out-of-plane directions. Given that minimal erosion was observed during the perforation tests, the projectile was assumed to behave as a rigid body. A finite element (FE) mesh size of 2 mm × 2 mm was selected for modeling the concrete slab after a mesh convergence study showed that further refinement did not lead to substantial improvements in simulation accuracy. This allowed for a detailed representation of the interaction between the projectile and the reinforced concrete, offering insights into the material response under high-speed impacts. Pattajoshi (2024) undertook an in-depth comparative study, comparing experimentally obtained impact damage areas [21] with those predicted via numerical simulations [4]. The numerically predicted crater sizes aligned closely with experimental results, though there was a slight underestimation of the spalling damage in the numerical models. Upon further analysis, the disparity in spalling damage was linked to variations in concrete strength, with a notable decrease in spalling damage seen in higher strength concrete (140 MPa ) compared to lower strength concrete (48 MPa ). This outcome aligns with the principle that concrete tensile strength inversely correlates with its compressive strength [22]. Numerical simulations revealed a distinct pattern: spalling damage was more extensive in the weaker 48 MPa concrete compared to the stronger 140 MPa variant. This discrepancy could be tied to the default parameters used for spalling damage in the RHT material model. To improve the accuracy of the simulations, the damage model was modified as discussed earlier. Numerical impact tests on concrete targets with compressive strengths of 48 MPa and 140 MPa were conducted using both the default and modified versions of the RHT model. The revised model demonstrated a marked improvement in representing spalling damage, particularly in the high-strength concrete, as shown in Fig. 3. This addresses a key limitation of the original RHT model, which previously failed to capture the extent of damage in the 140 MPa