During the additive manufacturing (AM) process, energy is transferred from the energy beam to the processed material. The high-energy input and uneven temperature distribution result in the ...high-temperature gradient, large thermal stress, and warping deformation. The scanning strategy, one of the representative AM processing parameters, plays an important role in the microstructures, mechanical properties, and residual stresses of 3D printed parts. It is necessary to review the current state of research about scanning strategy in additive manufacturing, and this paper seeks to address this need. This review mainly focuses on the scanning strategies in selective laser melting process. Various scanning strategies and their effects on mechanical properties, microstructures, and residual stresses of selective laser melted parts are summarized. Finally, some suggestions on the optimization of scanning strategy for better performance are provided based on the above analysis.
In this study, SCM440 steel specimens with different surface morphology and hardness were prepared by shot peening and fine particle peening, followed by induction hardening and tempering at ...different temperatures. Rotating bending fatigue tests were performed for these specimens, and the combined effects of the surface dent formed by peening and residual stress on the fatigue limit of the induction hardened steels were quantitatively investigated. It was found that the fatigue limit of the induction hardened steel tended to decrease with an increase in the size of the particles used in the peening. The parameter of surface morphology that showed a good correlation with the fatigue limit of the induction hardened steel was the waviness parameter, but not the roughness parameter. Furthermore, a fatigue limit estimation for induction hardened steels with different surface morphology was described. The improvement in the fatigue limit of steels with surface dents due to compressive residual stress was more significant as the hardness decreased, and the maximum fatigue limit improved by compressive residual stresses increased as the size of surface dents decreased.
Small cracks propagate at the glass surface due to the combined effects of water vapor and applied load. This phenomenon is known as glass fatigue. In this study, four-point bending fatigue tests ...under static and cyclic loading conditions were conducted for the soda-lime glass plate specimens with the initial crack and indentation pit induced by Vickers diamond indentation. Fatigue cracks were observed by the in-situ crack observation system using optical microscopy in order to obtain the relationship between crack growth rate, da/dt, and maximum stress intensity factor, Kmax, during fatigue tests. The da/dt decreased and then increased with the Kmax value. In addition, photoelasticity was applied to measure the residual stress distribution generated on the surface of the glass. The results showed that the da/dt at the early stage varied with indentation load due to the residual stress, whereas the effect of the indentation load on the da/dt was not observed in the region without residual stress.
This report deals with the influence of particle temperature and velocity on the microstructure, mechanical properties and residual stress depth profile of plasma sprayed alumina coating. The ...coatings were produced by varying the particle temperature while maintaining a relatively fixed particle velocity, and vice versa. Residual stress profiles were acquired by measuring the stress in successive layers using X-ray Sin2ψ technique. A substantial increase in hardness and indentation modulus by 76% and 64%, respectively were observed with an increase in particle temperature. With an increase in velocity, coating porosity was found to decrease initially. However, at a high velocity, porosity again increased to a limited extent. The mechanical properties were found to depend strongly on porosity. An increase in particle temperature resulted in an increase in the tensile residual stress in the coatings. Moreover, partial recovery of the grit blasted compressive substrate occurred during spraying owing to an annealing effect.
•The effects of particle temperature and velocity on coating properties were decoupled.•Particle temperature has greater influence as compared to velocity.•Mechanical properties of the coatings improved with a decrease in porosity.•A higher particle temperature produced a higher tensile residual stress on the coating.•Partial recovery by annealing occurs in the substrate during coating deposition.
The additive manufacturing (AM) of aluminum alloys promises to considerably enhance the performance of lightweight critical parts in various industrial applications. AlSi10Mg is one of the compatible ...Al alloys used in the selective laser melting of lightweight components. However, the surface defects obtained from the as-built parts affect their mechanical properties, and thus represent an obstacle to using them as final products. This study aims to improve the surface characteristics of the as-built AlSi10Mg parts using shot peening (SP). To achieve this goal, different SP intensities were applied to various surface textures of the as-built samples. The SP results showed a significant improvement in the as-built surface topography and a higher value of effective depth using 22.9 A intensity and Gp165 glass beads. The area near the shot-peened surface showed a significant microstructure refinement to a specific depth due to the dynamic precipitation of nanoscale Si particles. Surface hardening was also detected and high compressive residual stresses were generated due to severe plastic deformation. The surface characteristics obtained after SP could result in a significant improvement in the mechanical properties and fatigue strength, and thus promise performance enhancement for critical parts in various industrial applications.
•We present a computational model of cardiac electromechanics of the left ventricle.•3D electromechanics is coupled with a 0D circulation model by a novel numerical scheme.•We show that the coupled ...model is compliant with the principle of energy conservation.•We employ a Neural Network based surrogate of an high fidelity active force model.•We present a robust algorithm to reconstruct the stress-free configuration.
We propose a novel mathematical and numerical model for cardiac electromechanics, wherein biophysically detailed core models describe the different physical processes concurring to the cardiac function. The core models, once suitably approximated, are coupled by a computationally efficient strategy. Our model is based on: (1) the combination of implicit-explicit (IMEX) schemes to solve the different core cardiac models, (2) an Artificial Neural Network based model, that surrogates a biophysically detailed but computationally demanding microscale model of active force generation and (3) appropriate partitioned schemes to couple the different models in this multiphysics setting. We employ a flexible and scalable intergrid transfer operator, which allows to interpolate Finite Element functions between nested meshes and, possibly, among arbitrary Finite Element spaces for the different core models. Our core 3D electromechanical model of the left ventricle is coupled with a closed-loop 0D model of the vascular network (and the other cardiac chambers) by an approach that is energy preserving. More precisely, we derive a balance law for the mechanical energy of the whole circulatory network. This provides a quantitative insight into the energy utilization, dissipation and transfer among the different compartments of the cardiovascular network and during different stages of the heartbeat. On this ground, a new tool is proposed to validate some energy indicators adopted in the daily clinical practice. A further contribution of this paper is the proposition of a robust algorithm for the reconstruction of the stress-free reference configuration. This feature is fundamental to correctly initialize our electromechanical simulations. As a matter of fact, the geometry acquired from medical imaging typically refers to a configuration affected by residual internal stresses, whereas the elastodynamics equations that govern the mechanics core model are related to a stress-free configuration. To prove the biophysical accuracy of our computational model, we address different scenarios of clinical interest, namely by varying preload, afterload and contractility.
TiAlN is one of the most widely used physical vapour deposition (PVD) coatings in the manufacturing industry. Naturally, the performance of this coating is dependent on its properties, which can be ...tuned and optimized according to the application. Residual stress is one of the properties which affects hardness, fracture toughness, and adhesion of the coating. Although it is difficult to make a general recommendation for desirable residual stress values, individual recommendations can be made based on a specific workpiece material and tool wear mechanism. In this regard, adhesion wear and the formation of built-up edge were identified as the dominant wear mechanism during dry turning of compacted graphite iron and a coating's residual stress should be adjusted to minimize the damage from adhesion wear. Therefore, the present work investigates cutting performance and related coating properties of multilayer thick TiAlN coatings with different residual stress designs. For this purpose, residual stress was adjusted by varying the substrate bias voltage during the deposition process. The effect of residual stress on properties such as hardness, yield strength, and adhesion were studied by nanoindentation and scratch tests. Moreover, the dominant wear pattern, especially on the rake face and cutting edge, was thoroughly studied using a scanning electron microscope (SEM). The results showed increased mechanical properties such as hardness and yield strength with higher substrate bias voltages and therefore higher residual stresses. However, the coating with the lowest compressive residual stress outperformed the other coatings during machining due to a combination of high adhesion to the substrate and low as-deposited defects which effectively delayed cutting-edge exposure.
•Residual stress of thick multilayer TiAlN coating is varied by adjusting bias voltage combination in a range of 1–5 GPa.•By increasing compressive residual stress of the coating hardness and yield stress increase and adhesion reduces.•With higher residual stress in the coating, higher as-deposited defects are present on the cutting edge.•Coatings performance is significantly improved with low compressive residual stress.
In this research, a finite element model was developed in order to simulate the two-step residual stress distribution of a thermal barrier coating system, considered to be used in diesel engine ...cylinder head, with a real roughness and real porosity. Two steps including the bond coat and the top coat deposition processes were taken into account. The real geometry of coating layers, including the roughness and the porosity, was also considered based on a scanning electron microscopy image. Then, effects of the convective heat transfer coefficient and initial substrate and substrate/bond coat preheating temperatures on the residual stress were studied. Obtained results illustrate that the residual stress, regarding the two steps of coating processes, are different, particularly in the substrate. Numerical results indicate that while the convective heat transfer coefficient in BC deposition had no striking effect, it was an influential factor in the residual stress distribution when TC was deposited. Moreover, preheating temperature for depositions of the bond coat layer and the top coat layer has a pivotal role in stress distribution of all layers. In addition, consideration of the porosity in the top coat layer causes remarkable decrease in axial stress distribution in substrate and much more local stress concentrations in TC layer compared to those of BC layer due to larger and more irregular pores.
•Welding residual stress distributions in rail head and web are different;•Residual stress affects the rail subsurface crack propagation path, life and rate;•The shear stress in different directions ...made the crack propagation paths different.
To accurately evaluate the influence of welding residual stress on the fatigue crack propagation behavior of rail, the distribution of residual stress of welded rail was predicted, the subsurface fatigue crack propagation type, path, rate and lifetime of the rail and the welded rail with residual stress were calculated and compared. The results showed that the subsurface crack propagated with II + III mixed-mode and the slip propagation of mode II was dominant for both the cases of residual stress existing and not, while the crack propagation path, rate and lifetime were quite different for the two cases. For horizontal circular cracks, when there was no welding residual stress, the crack propagation path was mainly transverse under wheel-rail contact load, the propagation rate was relatively small, and the propagation lifetime was longer. When there was welding residual stress, the crack propagated longitudinally, the crack propagation rate increased significantly, and the fatigue lifetime was shorter.
Abrasive waterjet peening (AWJP) has been used to modify the mechanical properties of components by introducing plastic deformation and compressive residual stress (CRS) into the workpiece surface. ...The present study aims to investigate the influence of different AWJP parameters on the surface integrity of Inconel 718 alloy. The AWJP with different pump pressures, standoff distances, traverse speeds, and abrasive flowrates are conducted on the Inconel 718 workpiece. The surface integrity response including surface topography, CRS, hardness, and microstructure of AWJP are investigated, and different AWJP parameters effect on changing trend of surface integrity response is discussed. Results show that the AWJP-treated workpiece with different parameters formed a footprint width of 3.0–4.3 mm, the key factor effect on footprint width is standoff distance. The maximum surface roughness of Sa = 9.06 μm occurs at pump pressure 300 MPa, and pump pressure is more sensitive than other AWJP parameters' effect on surface fluctuation and surface roughness. The thickness of the stress layer is approximately 100–180 μm, and the maximum CRS is larger than 1100 MPa. Pump pressure and standoff distance are two main factors that effect on CRS, while the changing rate effect on CRS is gradually slow with the increase of pump pressure and the reduction of standoff distance. The maximum hardness increases more than 20 % from 490 to 590 HV at a pump pressure of 300 MPa. The pump pressure is the key factor influencing on micro-hardness. The microstructure evolution on the sub-surface of AWJP treated workpiece was characterized by SEM and EBSD, which showed that grains refine and strengthening layer formed on the top surface of the AWJP-treated workpiece surface, also the cracks at pump pressure 300 MPa. The results revealed that AWJP has great development potential in Inconel 718 surface treatment, and pump pressure is the key factor that effect on surface integrity.
•Abrasive waterjet peening (AWJP) was performed on Inconel 718 alloy.•Surface topography surface roughness Sa is mainly affected by pump pressure.•The compressive residual stress (CRS) induced by AWJP is larger than 1000 MPa.•Maximum hardness occurs at pump pressure 300 MPa and increases larger than 20 %.•The near-surface grains are significantly refined with the action of the AWJP.
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