Search Results (6)

To accurately characterize the damage of rock-like materials under simultaneous or alternating tensile and compressive loading, a dynamic damage constitutive model for rock-like materials based on elastic tensile strain is developed by integrating the classical compressive plastic damage model and the tensile elastic damage model. The model is based on the Holmquist–Johnson–Cook (HJC) and Kuszmaul (KUS) models, categorizing the element stress state into tensile and compressive states through positive and negative elastic volumetric strain. It utilizes elastic tensile strain to enhance the calculation method for tensile cracks, determining the tensile strength of the principal direction based on the contribution rate of tensile principal stress for uniaxial/multiaxial loading. Additionally, it establishes a maximum elastic tensile strain rate function to rectify the model’s effect on the tensile strain rate. Through the LS-DYNA subroutine development, the model proficiently delineates the distribution of ring-shaped cracks on the frontal side and strip-shaped cracks on the rear side of the reinforced concrete slab subjected to impact loading. Numerical simulations demonstrate that the model provides more accurate damage prediction results for stress conditions involving simultaneous or alternating compression and tension, offering valuable insights for damage analysis in engineering blasting or impact penetration. Full article

The nature of the fracture and fragmentation processes in concrete medium under blast loading is the transformation of the medium from continuum to discontinuity. Coupled with the significant rate correlation of concrete medium, its mechanical behavior presents a high degree of complexity. When tackling this problem, the finite element method (FEM) frequently encounters problems such as grid distortion and even negative volume, whereas the material point method (MPM) can efficiently avoid these problems. Furthermore, the original Holmquist-Johnson-Cook (HJC) model does not take the segmented characteristics of the calculation function for the dynamic increasing factor into consideration. As a result, in this article, first, the calculation function for the dynamic increasing factor in the HJC model was modified by the Split-Hopkinson Pressure Bar (SHPB) experiment, and an improved HJC model was proposed; second, an MPM simulation program was developed, and the improved HJC concrete model was embedded into the simulation program; and finally, the simulation program was verified by numerical examples, and the results show that the developed simulation program can better simulate the fracture and fragmentation process of the concrete medium under blast loading, especially the pulverization characteristics of the medium in the near zone of the load. Full article

Reactive powder concrete-filled steel tube (RPC-FST) is a critical supporting component of large-span, high-rise, and heavy-load structures. The collapse of RPC-FST may occur under explosive load. Therefore, investigation of the dynamic response is essential for understanding the mechanisms of collapse. In this article, the numerical simulation of reactive powder concrete (RPC) adopted the modified Holmquist–Johnson–Cook (HJC) model and the modified Karagozian and Case (K&C) model. The dynamic response of RPC-FST columns under explosive load is analyzed based on arbitrary Lagrange–Euler (ALE) method. The proposed model is verified by experimental results. Results show that the modified HJC model and modified K&C model can be applied to simulate the dynamic response of RPC-FST columns under explosive load. As compared with the modified HJC model, the modified K&C model has more accurate results. This phenomenon mainly accounts for the lack of ultimate strain of RPC (EFMIN). To analyze the reliability sensitivity of RPC-FST, an efficient probability analysis method is proposed based on the Kriging model and Monte Carlo simulation (MCS). The proposed method considers five nonlinear factors, including weight and distance of TNT, height and section diameter of RPC-FST, and steel tube thickness. Finally, the sensitivity of each factor is evaluated. Results show that TNT weight greatly influences the reliability of the RPC-FST, followed by TNT distance, RPC-FST height, RPC-FST section diameter, and steel tube thickness. In addition, the RPC-FST dynamic response analysis method based on the Kriging model and MCS can improve the calculation efficiency by more than 200 times compared with the ALE method. Full article

Ultra-high-strength concrete is a newly developed construction material that has a minimum 120 MPa or higher compressive strength. Recently, the usage of high-strength and ultra-high-strength concretes has become widespread due to the enhancement of the concrete technology. Many civil engineering structures constructed by using concrete materials are usually subjected to, in addition to static loads, dynamic loads due to earthquakes, wind and storm, impact and blast, which take place under high energy and high strain rate values. The effects of such loadings on the structure must be understood thoroughly. In recent years, the withstanding of a structure on these loading conditions has become a crucial issue for its impact on the economy and human safety. One of the approaches to fulfill these requirements is to develop high-strength or ultra high-strength concretes (UHSCs). In this study, an ultra-high-strength concrete with a compressive strength of 135 MPa was designed and developed. In order to determine the dynamic behavior of this UHSC, the specimens at three height/diameter ratios (approximately, 0.6, 1.0 and 1.2) were extracted from the prepared concrete mixtures. These concrete specimens were tested to determine both the quasi-static and dynamic compressive behaviors of the developed concrete. In the quasi-static compression tests, cylindrical specimens and a conventional compressive testing machine were used. In order to study the dynamic compressive behavior, a Split Hopkinson Pressure Bar (SHPB) test setup was used. In this test system, the time variations of compressive strength, the strain and strain rates under uniaxial pressure loading were experimentally evaluated and the deformation and fracturing processes of the specimens were recorded using a high-speed camera. The test results, based on the testing of 21 different specimens, have shown that the dynamic compressive strength values of the developed concrete varied in the range of 143 to 253 MPa, while the strain rate values varied in the range of 353 s⁻¹ to 1288 s⁻¹. Using the data generated in the SHPB tests, the parameters present in a Johnson–Holmquist–Cook concrete material model, which is used in numerical studies on the high strain rate behavior of concretes, were evaluated. Full article

Structures made of Roller Compacted Concrete (RCC) may be subjected to dynamic loads during their service life. Understanding the dynamic material properties of RCC and the performance of RCC structures is essential for better analysis and design of RCC structures. As full-scale tests are often unaffordable, numerical simulation methods are continuously employed. However, in numerical simulations, determining a reasonable constitutive relationship for RCC materials is still limited due to the complexity of the composite and the special rolling and compacting construction technology. In this paper, the triaxial compressive test and split Hopkinson pressure bar (SHPB) experimental results for RCC are introduced as an experimental foundation. Parameter calibrations and modifications in terms of the strength yield surface, the strain rate effect and the failure criterion for the RCC materials are presented. Numerical verification is illustrated for simulating the SHPB experiment and predicting the dynamic compressive characteristics of RCC specimens with a modified HJC model. The results reveal that the simulation results for the modified model have better agreement with the test data than those with the model before modification and have better simulation results. Sensitivity studies of the key parameters on the yield surface of the modified HJC model are conducted to improve the simulation effect for numerically predicting the performance of RCC structures exposed to explosive and impact loads. Full article

The traditional Holmquist-Johnson-Cook (HJC) constitutive model does not consider the effect of crack resistance, reinforcement and toughening effect of high parameter steel fiber on original concrete. The causes of the analysis effect of the high parameter reinforced concrete is not obvious. To address this problem, a dynamic constitutive model of high parameter steel fiber reinforced concrete is built in this paper. Based on the static constitutive model built by static force, a dynamic constitutive model is built based on the similarity between static and dynamic stress-strain curve. On this basis, the yield surface equation, state equation, and damage evolution equation of HJC constitutive model are constructed. An improved HJC constitutive model for high parameter steel fiber reinforced concrete is obtained by introducing the modification of the steel fiber reinforced, toughened, and strain rate effects into the HJC constitutive model. Dynamic analysis of high parameter steel fiber reinforced concrete is achieved by using the improved model. Experimental results show that the proposed model is effective in analyzing high parameter concrete and has strong applicability. Full article