Introduction to CoMat
The Concrete Damaged Plasticity (CDP) model supported by Abaqus/Standard and Explicit is a material model developed to simulate the plastic deformation and damage of concrete [1]. The CDP model allows for distinct definitions of plastic deformation and damage in both compressive and tensile directions, and supports strain rate, temperature, and field variable dependencies. Owing to its versatility in accommodating various load types such as monotonic loading, cyclic loading, and impact, numerous studies employing the CDP model have been conducted [2, 3].
Despite these advantages, converting stress-strain curves for compression and tension into the Abaqus input file format can be challenging and time-consuming for those lacking foundational knowledge in plasticity and damage. Broadly, two significant challenges are faced by Abaqus users when employing the CDP model:
(1) Selection of the Hardening-Softening Law for Stress-Strain Curve Generation
While metals have well-known stress-strain curves that are effectively represented by hardening laws such as Hollomon, Ludwick, and Swift, concrete behaves differently. It is often modeled in a simplified manner by dividing it into a few linear sections, as seen in models like Kent and Park [4] or the Massicotte model [5]. This approach often doesn't capture the complete hardening-softening behavior of concrete. In using the CDP model, there are numerous instances where instead of having a complete experimental stress-strain curve for concrete in compression and tension, reverse engineering is done based on the structural load-displacement curve. Therefore, for a high correlation between experiments and simulations during reverse engineering, an equation that can flexibly change the stress-strain curve to simulate concrete's hardening-softening behavior is essential.
(2) Creation of Plastic and Damage Tables for Abaqus Input File
To utilize the CDP model, inputs of both compressive and tensile direction's plastic and damage tables - a total of four tables - are required. In cases where there is no acquired experimental stress-strain curve for concrete, or when property adjustments are needed for correlation between experiments and simulations, repeated analysis may be needed, which can be time-intensive.
CoMat (Concrete Material Generator) has been developed to address these challenges. Through its GUI, users can input material parameters, and CoMat will plot the stress-strain curves in both compression and tension and automatically convert them into Abaqus input. For representing the compressive stress-strain curve of concrete, the hardening phase is modeled with a Parabolic function and the softening phase with a Weibull function. The tensile stress-strain curve applies a Power law Softening, enabling it to flexibly and accurately replicate experimental stress-strain data. Additionally, while traditional CDP Generator software requires third-party products like Matlab, CoMat operates independently without needing any third-party applications. This presentation will showcase a demonstration of CoMat, its validation using experimental data from Gao et al., 2020 [6], and examples of Abaqus modeling incorporating the CDP model generated by CoMat.
Reference
[1] Abaqus Documentation, 2023, Dassault Systèmes Simulia Corp., Providence, RI, USA.
[2] Minh HL, Khatir S, Wahab MA, Le TC, 2021, A concrete damage plasticity model for predicting the effects of compressive high- strength concrete under static and dynamic loads, Journal of Building Engineering 44, 103239.
[3] Qingfu L, Wei G, Yihang K, 2020, Parameter calculation and verification of concrete plastic damage model of ABAQUS, Materials Science and Engineering 794, 012036.
[4] Kent DC, Park R, 1971, Flexural members with confined concrete, Journal of the Structural Division 97, 1969-1990.
[5] Massicotte B, Elwi AE, MacGregor JG, 1990, Flexural strength of concrete beams with corroding reinforcement, ACI StructuralJournal 96, 149-159.
[6] Gao X, Zhou L, Ren X, Li J, 2020, Rate effect on the stress-strain behavior of concrete under uniaxial tensile stress, Structural Concrete, 1-16.