De-Guang Shang

A New Multiaxial High-Cycle Fatigue Criterion Based on the Critical Plane for Ductile and Brittle Materials

An improved high-cycle multiaxial fatigue criterion based on the critical plane was proposed in this paper. The critical plane was defined as the plane of maximum shear stress (MSS) in the proposed multiaxial fatigue criterion, which is different from the traditional critical plane based on the MSS amplitude. The proposed criterion was extended as a fatigue life prediction model that can be applicable for ductile and brittle materials. The fatigue life prediction model based on the proposed high-cycle multiaxial fatigue criterion was validated with experimental results obtained from the test of 7075-T651 aluminum alloy and some references.

Multiaxial high-cycle fatigue life prediction model based on the critical plane approach considering mean stress effects

The aim of this paper is to propose a modified multiaxial high-cycle fatigue criterion based on the critical plane approach. The proposed criterion contains three parameters, that is, shear stress amplitude, normal stress amplitude and mean normal stress. In order to take into account the mean shear stress effects, the critical plane is determined by the maximum shear stress. In the proposed multiaxial fatigue criterion, the influence of mean normal stress on fatigue damage is also considered. Based on the proposed criterion, the multiaxial fatigue life is predicted, and the results showed a good agreement with experimental data obtained from some literatures.

Analysis of fatigue damage repair based on laser shock processing for copper film

The effect of laser shock processing on fatigue life was investigated for pre-damaged polycrystalline copper film in this study. First, a series of laser shock processing experiments is performed by changing laser power density and number of pulses for the specimens with the same damage degree. The optimal repairing parameters of laser shock processing is identified by comparing with the fatigue lives of specimens before and after laser shock processing. Next, the effect of laser shock processing on the fatigue lives of the damaged and undamaged specimens under identical laser shock processing parameters is investigated. Finally, the opportunity of repair damage for the specimens with different damage degrees is discussed using the optimal processing parameters for the laser shock processing. The results indicated that laser shock processing has a great potential as a means of repairing the fatigue damage for film components.

A weight function method for multiaxial low-cycle fatigue life prediction under variable amplitude loading

A weight function method based on strain parameters is proposed to determine the critical plane in low-cycle fatigue region under both constant and variable amplitude tension–torsion loadings. The critical plane is defined by the weighted mean maximum absolute shear strain plane. Combined with the critical plane determined by the proposed method, strain-based fatigue life prediction models and Wang-Brown’s multiaxial cycle counting method are employed to predict the fatigue life. The experimental critical plane orientation and fatigue life data under constant and variable amplitude tension–torsion loadings are used to verify the proposed method. The results show that the proposed method is appropriate to determine the critical plane under both constant and variable amplitude loadings.

Multiaxial Fatigue Life Prediction Based on Short Crack Propagation Model with Equivalent Strain Parameter

The maximum shear strain and the normal strain excursion on the critical plane are regarded as the primary parameters of the crack driving force to establish a new short crack model in this paper. An equivalent strain-based intensity factor is proposed to correlate the short crack growth rate under multiaxial loading. According to the short crack model, a new method is proposed for multiaxial fatigue life prediction based on crack growth analysis. It is demonstrated that the method can be used under proportional and non-proportional loadings. The predicted results showed a good agreement with experimental lives in both high-cycle and low-cycle regions.

Life prediction approach based on the isothermal fatigue and creep damage under multiaxial thermo-mechanical loading

Based on the isothermal fatigue and creep damage, a life prediction approach under multiaxial thermo-mechanical loading was proposed in this investigation. In the proposed method, the multiaxial thermo-mechanical fatigue damage during one cycle period was divided into the isothermal fatigue damage and the creep damage. In order to evaluate conservatively, the isothermal fatigue damage during one cycle period was calculated by using multiaxial fatigue damage model at the maximum temperature during the whole period, and the creep damage during one cycle period was calculated by accumulating the creep damage of all portions originated from the divided time history for the axial load component and temperature history. The life prediction results by the proposed model showed a good agreement with experimental data for nickel-base alloy GH4169 and cobalt-base Haynes188 under axial-torsional thermo-mechanical loading.

Life prediction method of copper thin film repaired by laser irradiation based on healing variable

The cyclic stress–strain constitutive relationships for copper film smooth specimens with different damage degrees before and after laser irradiation treatment were investigated. Compared with the changes of the constitutive relationships under different damage degrees, a healing variable for the repaired copper film by laser irradiation was defined. Based on the analysis of the healing variable, a fatigue life prediction method was proposed. The experimental lives of the damaged notched specimens after laser irradiation treatment were used to verify the proposed life prediction method. The results showed that the predicted lives are in good agreement with the experimental results.

Fatigue Life Prediction Based on Local Strain Energy for Healed Copper Film by Laser Irradiation

Abstract Changes of total cyclic strain energy at the notch for copper film specimen were analyzed before and after laser irradiation treatment. The results showed that laser irradiation can increase total cyclic strain energy and the effect of increase is more evident for the damaged copper specimen. Based on the damage-healing mechanism, an enhancement parameter and a healing parameter were defined by the local cyclic strain energy. A new model based on local strain energy was proposed to predict residual fatigue life for the damaged copper film specimen after laser irradiation. The predicted results by the proposed model agree well with the experimental lives.

Recovery of Fatigue Damage and Life Prediction by Laser Irradiation Healing Treatment for Copper Film

A fatigue life prediction method was investigated after healing fatigue damage by excimer laser irradiation treatment for the damaged copper film. First, the variations of residual fatigue life and strain range for the damaged specimens after laser irradiation healing treatment were analyzed. The results showed that the fatigue damage can be effectively healed by laser irradiation for copper film. The presented healing phenomenon during laser irradiation process showed that the recovery of fatigue damage can result in the improvement in fatigue life for the damaged copper film. Then, based on the fact that the strain concentration factor of copper film had not been changed before and after laser irradiation treatment, a residual fatigue life prediction method was proposed by the local stress transformation. The predicted residual fatigue lives by the proposed method agreed well with the experimental results for copper film after laser irradiation treatment.

Equivalent damage-healing approach to residual fatigue life prediction for copper film by laser repair

A healing method for fatigue damage was investigated by laser shock peening and laser irradiation with excimer laser for polycrystalline copper film. It is found that the sum of the consumed fatigue ductility and the total fatigue ductility for the damaged specimen after both laser treatments is equal to the total fatigue ductility for the undamaged specimen after both laser treatments. The evolution of the damage healing can be replaced by that for the undamaged specimen after laser treatment. Based on the equivalent fatigue damage evolution, a residual fatigue life prediction method is proposed during the damage-healing process for the copper specimen. The predicted lives by the proposed method agree well with the experimental results.