Effect of stress state on the fracture behavior of Al6061-T6 via combined experimental and numerical approaches

Design methodology for supersonic air intakes

A generalized plasticity model incorporating stress state, strain rate and temperature effects

High-speed deformation fracture prediction of aluminum sheet, especially for biaxial tension state deformation, was a major problem in the development of electromagnetic bulging process. In this study, the biaxial tension failure limit of the AA5052 sheet was tested by the electromagnetic high-speed biaxial tensile testing equipment and quasi-static Nakazima experiment. A Digital Image Correlation (DIC) system was used to measure failure strain. Based on the tested data, a failure model considered stress state and strain rate coupling effect was established, which available for electromagnetic bulging failure prediction. Electromagnetic free bulging experiments were conducted to verify the failure criteria effectiveness. Results showed that the strain rate effects of the failure strain were influenced by the loading path. The strain rate effect of the sheet failure strain under plain strain state was higher than the loading stress triaxiality of uniaxial and biaxial tension state. Compared with the fracture prediction criterion ignored stress state effect on strain rate influence factor, the modified fracture model considered stress state and strain rate coupling effect could well predict the failure of electromagnetic bulging, which would exhibit different failure models at the rounded corner or the top under different discharge energies.

Effects of tensile and compressive stresses on damage evolution law of nuclear graphite

The current available models describing superplastic deformation do not account for a number of important characteristics, leading to the current limited predictive capabilities of deformation and failure. In this work, the effects of cavitation and stress state on deformation stability during superplastic forming are investigated using Finite Element simulations. The simulations are performed using constant strain rate forming and using a proposed optimization approach based on a multiscale failure criterion that accounts for stress state, geometrical necking, and microstructural evolution including grain growth and cavitation. The simulations are conducted for the superplastic copper-based alloy Coronze-638 and the superplastic aluminum alloy Al-5083 which are known to develop significant cavitation during deformation. The results clearly show the importance of accounting for microstructural evolution during superplastic forming, especially when the state of stress is biaxial. Furthermore, the results highlight the effectiveness of the proposed optimization technique in reducing the forming time and maintaining the integrity of the formed parts.

The regularities of the effect of a complex stress state on the strength of an AlMg5/epoxy adhesive joint are experimentally studied at −50 and +23 °C in tension+shear and compression+shear tests with different normal-to-shear stress ratios. The tests use modified Arcan specimens and Brazil-nut-sandwich specimens, with the lateral faces of the adhesive layer having a shape of a mushroom-like “ridge” aimed at reducing stress concentration at the specimen edges. An original computational model of a selected microvolume including the interface together with the adjacent substrate and adhesive layers is used to process the experimental results. The attainment of the threshold value of strain energy density in the selected microvolume, W*, is used as the failure criterion. The effect of the hardener composition, the testing temperature, and the value of the phase angle β determining the proportion of normal and shear stresses at the adhesive interface on the threshold value W* is detected. W*(β) diagrams (fracture loci) are plotted and analytically described logarithmic functions. They can be used to make strength calculations for adhesive joints in structures and metal-polymer composites.

A nanometer scale mechanism for micro crack propagation under uniaxial tension in single crystals is investigated using phase field crystal (PFC) simulation. The uniaxial tensile loading is strain controlled. And three initial typical stresses of pre-existing center crack in (111) crystal plane of face centered cubic structure are chosen to study the effects of initial stress state on micro-crack propagation. Moreover, the influences of different crystal orientations, when the crystal suffers from uniaxial tension, are also investigated. Due to the influence of time scale and length scale in the PFC method, the motion of dislocations, vacancies, shear band and twinning structure should be observed and described during the propagation process of micro cracks. In addition, the free energy curves of different processes are drawn and discussed in order to explain the different behaviors of the crystal in the propagation of cracks. Simulation results show that the propagation behavior of micro cracks can be closely associated with the initial stress state. It is found that the propagation behavior mainly occurs in the 11>(111) slip system. Besides, the crystal orientation has a significant effect on the mechanism of activation and evolution. In the pre-stretching system, slip dislocation is induced near the micro-crack tip, and then its slide in [011] direction will cause the cleavage of a certain crystal plane, and promote the micro cracks to extend. However, to a certain level, the propagating direction of the micro-crack tip will turn to another slip direction [101]. As a result, zigzag edge appears. By contrast, in the pre-shear system, the tip of the micro crack propagates in a cleavage mode, and results in the appearance of slip dislocation [101] near the micro-crack tip. Afterwards, the motion of slip dislocation promotes the production of vacancies. And owing to the aggregation and combination of vacancies, secondary cracks form and propagate in the process that follows. At the same time, in a pre-deviatoric system, the micro crack propagates forward with direct cleavage of [101] slip direction near the micro-crack tip until the single crystal sample fractures. Furthermore, no slip dislocation appears during the whole process. The mechanism of micro-crack tip propagating behavior varies with crystal orientation. When the crystal orientation angle is lower, the micro-crack tip prefers to produce slip dislocation around it, and the following dislocation slide will induce vacancies, then a secondary crack also forms because of the aggregation and combination of vacancies. On the other hand, when the aggregation degree is higher, the micro-crack tip is inclined to directly propagate in a cleavage mode, and its propagating direction is nearly perpendicular to the stretching direction.

Effect of fiber orientation, stress state and notch radius on the impact properties of short glass fiber reinforced polypropylene

Due to its numerous practical applications and intriguing phase transformation behavior, shape memory alloys (SMAs) have garnered significant research and development interests. In the past, most studies on the mechanical behavior of SMAs have been conducted under uniaxial stress loadings. Limited research on SMAs under shock loading has not provided conclusive results regarding their transformation behavior and transformation stress under such loading. Additionally, there is a lack of comprehensive understanding regarding the effects of different stress states on transformation behavior. The main objectives of this study are to address these issues. To achieve these objectives, a series of shock wave experiments were designed and conducted. Additionally, quasi-static and dynamic uniaxial stress experiments were carried out to establish a baseline for comparison. The results revealed that the transformation stress under dynamic uniaxial strain shock loading was approximately 1.92 GPa in contrast to 0.5 GPa (quasi-static) to 0.8 GPa (dynamic) observed in uniaxial stress loading. The transformation behavior exhibited noticeable rate sensitivity for both types of loading. There appeared to be a critical strain rate above which the austenite phase was driven to a metastable state. This estimated critical axial strain rate along the loading direction was approximately 2 × 103/s–4 × 103/s for uniaxial stress loading and approximately 2 × 106/s for uniaxial strain loading. The apparent high transformation stress for uniaxial strain loading can likely be attributed to a combination of high-pressure confinement and high strain rate. However, determining their relative contributions remains an open issue.

Effect of the triaxial stress system on fracture and flow of rocks

Fluid flow and heat transfer in microchannel devices for cooling applications: Experimental and numerical approaches

This paper describes a combined numerical and experimental effort to characterize the structure of wake turbulence. The numerical approach is based on detailed LES. The experimental approach is based on an innovative analysis applied on full-scale wake recordings obtained using a newly developed 2D lidar technology. Consistency between the numerical and experimental approaches in terms of wake turbulence characteristics is observed. Compared to conventional atmospheric boundary layer (ABL) turbulence, the wake turbulence is inhomogeneous with reduced length scales, increased intensity, and increased coherence decay.KeywordsWind TurbineLarge Eddy SimulationTurbulence IntensityAtmospheric Boundary LayerIntegral Length ScaleThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Flexural strength and defect behaviour of polygranular graphite under different states of stress

The effect of stress state on high-temperature deformation of fine-grained aluminum–magnesium alloy AA5083 sheet

Determination of shear behavior and constitutive modeling of the 603 steel over wide temperature and strain rate ranges