In this research, the feasibility of friction-stir welding (FSW) for dissimilar lap-joining of an aluminium-magnesium alloy (AA5058) and poly-methyl-methacrylate sheets to attain sound and ...defect-free joints was examined. The inter-mixing flow patterns between the metal and polymer counterparts during FSW were predicted by employing three-dimensional finite element models. It is shown that the bonding mechanism between the dissimilar materials is mechanical interlocking at the interface which controls the joint strength depending on the processing parameters. The most suitable dissimilar lap-joining regarding microstructural soundness is attained at w= 1600 rev min
−1
and v = 25 mm min
−1
. Under this condition, the maximum joint strength, which is about ∼60% of the weakest base material, is attained. Fractography indicates that the rupture occurs from the aluminium side.
Using salt caverns for underground gas storage (UGS) is an important energy storage solution. A coupled aero-thermo-mechanical (ATM) model with an integrated wellbore–3D realistic cavern geometry was ...established to investigate the thermodynamic behaviour of natural gas and the thermo-mechanical response of rock salt for UGS caverns. Unlike classical thermo-gas-mechanical (TGM) models that assume the cavern gas is an ideal gas and in an isotropic thermodynamic state, the ATM model solved thermodynamic properties for the real gas, and revealed the tempo-spatial varying gas state and its mechanism. Predictions of gas temperature, pressure and flux by ATM modelling well captured the in-situ measurements obtained by the distributed optical cable monitoring system during a one-month field testing at Jintan UGS site. Effects of the tempo-spatial varying gas state on the mechanical response were unveiled by ATM modelling. Predictions of mechanical response by TGM modelling shared similar patterns as that by ATM modelling, however, the TGM model tended to underestimate the risk of creep failure, tensile failure, fatigue failure and plastic damage due to the isotropic gas state. The proposed model could be used to improve the thermodynamic and mechanical predictions that are pertinent to the optimal design and the stability of caverns.
•A coupled aero-thermo-mechanical model with an integrated wellbore–3D real cavern geometry was established for UGS operation.•In-situ access to cavern temperature and pressure was achieved using the distributed optical cable monitoring system.•Tempo-spatial variation of gas thermodynamic state was unveiled by modelling and validated by site testing.•Effects of the tempo-spatial variation of temperature and pressure on thermo-mechanical response of the cavern was revealed.
Quantitative phase petrology analysis of two samples showing variable strain record and different peak pressure (P) conditions show that H2O is a key parameter in the development of contrasting ...high-pressure (HP) peak conditions in adjacent polymetamorphic rocks. A shear zone in a paragneiss from the Gran Paradiso nappe, Western Alps, shows an Alpine foliation and records a peak P of 1.9 GPa, for a temperature of 500 to 520 °C. A few tens of meters away from the shear zone, a paragneiss showing no apparent Alpine age deformation records a peak P of maximum 1.4 GPa for the temperature range of 500 to 520 °C. The H2O content of the latter has potentially been reduced to low contents following the pre-Alpine, Variscan amphibolite facies, and the absence of re-hydration prior to Alpine orogeny could have inhibited the formation of HP mineral assemblages. The validity of this interpretation is questioned here by considering the mechanical effect of H2O undersaturated rocks on deformation and P during deformation. Based on a thermo-mechanical numerical modelling study, we show that heterogeneities in fluid saturation conditions between rocks lead to strength contrasts that are sufficient to trigger a dynamic P in the range of several hundreds of MPa. In particular, the models successfully reproduce the measured peak P between the two paragneiss studied. This model could be applied to other H2O deficient rocks from HP tectonic units to further explore the role of H2O on the rheology and hence assess its potential impact in the preservation of low P bodies in otherwise HP units from continental collision settings.
•H2O saturation conditions impact not only the metamorphic evolution, but also the stress state and deformation.•Heterogeneous stress conditions develop during deformation of similar rocks with contrasting H2O saturation conditions.•Metamorphic pressure variations can be recorded due to local variability in H2O (under)saturation conditions•The history of polymetamorphic units constitutes a geological heritage controlling future metamorphism and deformation style.
•New conceptualization of heat source from keyhole to conduction welding attempted.•Effect of heat source on weld distortion has been illustrated.•An inter relation of stress, thermal field and ...porosities have been established.•Correlation of weld residual stress and HCF response have been attempted.
A study on porosity evolution, distortion evolution and metallurgical properties of laser beam welded AA 5024 (Al–Mg–Sc) alloy have been presented here. A comparative assessment was done for two welding types, i.e. deep penetration (keyhole) and partial penetration (conduction) welding were used for joining AA 5024 sheets. Detailed Finite element-based thermo-mechanical simulations have been carried out to simulate the temperature profiles and their temporal evolution of distortion and welding-induced stress for different keyhole and conduction heat sources. Extensive X-ray micro tomography investigation has been done to understand the physics behind the porosity formation. Bands of porosities have been observed in conduction welding at the edge of the weld pool. The inherent residual stress evolution was also mapped, and the reason behind the propensity to failure was investigated. High-cycle fatigue tests were done to check the endurance of these welded joints. The low power and high speed for keyhole welding and low power and low speed for conduction welding have been seen to give rise to minimal distortion. The conduction welded specimens at low speed, i.e. 0.5–1 m/min, and high power 3.5–4 kW region performed better under HCF.
Residual stresses and distortions are major obstacles against the more widespread application of wire arc additive manufacturing. Since the steep temperature gradients due to a moving localised heat ...source are inevitable in this process, accurate prediction of the thermally induced residual stresses and distortions is of paramount importance. In the present study, a computationally efficient thermo-mechanical model based on a semi-analytical thermal approach incorporating Goldak heat sources is developed for the process modelling of wire arc additive manufacturing. The semi-analytical thermal model makes use of the superposition principle, and thereby decomposes the temperature field into an analytical temperature field to account for the heat sources in a semi-infinite space and a complementary temperature field to account for the boundary conditions. Since the steep temperature gradients are captured by the analytical solution, a coarse spatial discretisation can be used for the numerical solution of the complementary Tˆ field. Thermal evolution is coupled to an elasto-plastic mechanical boundary value problem that computes the thermal stresses and distortions. The accuracy of the proposed model is evaluated extensively by comparing the thermal and mechanical predictions with the corresponding experimental measurements as well as the simulation results obtained by a non-linear transient model from the literature. A thin wall structure with a length of 500 mm and consisting of 4 layers is modelled. The peak normal stress along the deposition direction can be predicted with less than 10% error. Furthermore, the simulations show that the part distortions are very sensitive to the boundary conditions.
Friction Stir Processing, commonly known as FSP, is an innovative technique to refine microstructures and produce surface composites without any inherent defects. The heat generated during the FSP is ...primarily contributed by plastic deformation and edge friction which subsequently impacts the microstructure and the processed sample’s properties. In this article, FSP was performed at a tool stirring speed of 1000 rpm and 40 mm/min traveling speed. The temperature profile was obtained at arbitrary locations for AA7075 with and without Silicon Carbide (SiC). Channel and hole techniques were deployed to compare the temperature using type K thermocouples at three locations. It was found that the channel method has higher temperature values (Tp) than the hole method for both AA7075 and AA7075/SiC, whereas the Tp values for AA7075/SiC composites were found to be lowered than processed AA7075. Microstructure, mechanical, and corrosion properties were assessed for the AA7075 and AA7075/SiC. The interlayer difference between the processed and the unprocessed region has adverse effects on tensile strength. In contrast, the hardness and corrosion resistance improvement was accounted due to the uniform dispersion and pinning action of SiC. Thermo-mechanical modelling was carried out to simulate the temperatures at the plunging phase and was found to be in accordance with experimental results.
The formation of Tribological Surface Transformation (TST), known as white etching layer (WEL) in the wheel–rail contact, corresponds to progressive and irreversible transformations on the surface of ...material due to the interaction of contact between two materials. The presence of WEL, damages the rails and cracks could initiate easily. Understanding the mechanisms of formation of WEL is important to prevent the problem of Rolling Contact Fatigue (RCF) in the rail network. The formation of the WEL is assumed to be due to a cyclic shear loading (at a high-frequency), under hydrostatic pressure associated with a moderate rise in temperature. Based on Transformed Induced Plasticity models and a previous model, a thermo-mechanical model taking into account the hydrostatic pressure, the shear stress and the temperature is presented to predict the formation of the WEL. An internal variable, representing all the steps of evolution of the microstructure leading to the WEL formation is introduced. 2-D finite element simulations of the rail running band (in the longitudinal direction) submitted to a cyclic thermomechanical loading are conducted to identify the model. The results are in good agreement with experimental observations for the size of the transformed zone after a given number of trains. The non-uniform repartition of WEL observed on the running band on trains could be explained by local variations of the thermomechanical loading.
•A new thermomechanical model can predict theoretically the Tribological Surface Transformation.•The progressive formation of the White Etching Layer is modelled with an internal variable.•Dynamic variations of the wheel–rail contact conditions would catalyze the White etching layer formation.
