Constitutive and damage modelling of H11 subjected to low‐cycle fatigue at high temperature

Abstract

Hot‐work tool steel H11 is extensively applied in extrusion industries as extrusion tools. The understanding of its mechanical properties and damage evolution as well as failure is crucial for its implementation. In this paper, a finite element (FE) model employing Chaboche unified constitutive model and ductile damage rule is proposed to simulate the mechanical responses of H11 subjected to low‐cycle fatigue (LCF). Accumulated inelastic hysteresis energy is adopted to demonstrate the impact on damage initiation and evolution rules. A series of tension and LCF experiments were conducted to investigate H11's mechanical properties and its deterioration processes. In addition, to deeply understand the deformation and damage mechanism, scanning electron microscope (SEM) investigations were performed on the fracture section of gauge‐length part of the specimen after failure. Furthermore, the parameters in both constitutive model and damage rule are identified based on experimental data. The comparison of the hysteresis loop of the first cycle and stable cycle with different strain amplitudes demonstrates that the Chaboche constitutive model provides high precision to predict the evolution of mechanical properties. Based on the reliable achieved constitutive model, LCF behaviour prediction with damage rule was executed successfully using FE model and gains a good agreement with the experiments. It is believed that the proposed FE method lays the foundation of structure analysis and rapid design optimization in further applications.

Fatigue and ratcheting assessment of AISI H11 at 500°C using constitutive theory coupled with damage rule

“…Tests of different amplitudes of 0.8%, 1.0%, 1.1%, and 1.2% were conducted at different loading frequencies by guaranteeing the same loading strain rate. Some microscale interpretation related with this phenomenon has been given in previous work 33 based on some SEM investigations. The whole lifetime of strain cycling tests can be broken down into 3 stages (as shown in Figure 4B): (1) the initial stage, (2) the steady stage, and (3) the failure stage.…”

“…And the damage is accumulated with the deterioration of mechanical properties. Some microscale interpretation related with this phenomenon has been given in previous work 33 based on some SEM investigations. The lifetime is strongly correlated with loading strain amplitude.…”

“…More details about numerical model, boundary conditions, and loading etc can be found in previous work. 33 The unified plastic constitutive model coupled with damage has been programmed into user subroutine UMAT to conduct stress/ strain analysis incorporating damage. The comparison results of experimental data and FE model are shown in Figures 8 and 9.…”

Experimental investigations and damage growth modeling of EN‐AW 2024 aluminum alloy under LCF loading accounting creep pre‐deformation

“…A critical plane approach is often used based on the normal and share strain energy density parameter 43–45 or a special stress function is introduced, being a combination of normal and shear stresses 46,47 . The damage accumulation model is often made dependent only on inelastic hysteresis strain energy per cycle 48–51 . The well‐known Smith‐Watson‐Topper (SWT) model 52–55 is widely used also, where the damage state variable is a combination of the total strain amplitude and maximum stresses in the loading cycle.…”

“…46,47 The damage accumulation model is often made dependent only on inelastic hysteresis strain energy per cycle. [48][49][50][51] The well-known Smith-Watson-Topper (SWT) model [52][53][54][55] is widely used also, where the damage state variable is a combination of the total strain amplitude and maximum stresses in the loading cycle. In continuous damage mechanics, the damage growth process is often dependent on plastic deformation.…”