Increase In Compressive Stress Research Articles

SH wave propagation in a periodic cement-based piezoelectric layered barrier

The purpose of this study is to investigate SH wave in the periodic cement-based piezoelectric layered barrier to meet the needs of vibration control in complex engineering environments and improve the application of periodic vibration isolation barrier in civil engineering. The governing equation of SH wave in periodic barrier is established based on the periodic theory of phononic crystals. The band structures are calculated by plane wave expansion method, the transmission characteristics are computed by transfer matrix method, and the attenuation effect of the periodic barrier is verified by finite element method. The effects of geometric parameters, material parameters and initial stress on band structures are analyzed in details. The numerical results show that the number of unit cells, initial stress and material parameters of the periodic barrier have significant effects on the band gap. As the lattice constant of the structure increases and the equivalent elastic modulus decreases, the lower boundary and the width of the band gap decrease. With the increase of tensile stresses, whether the lower and upper boundary or the width of the band gap will all increase, while they are decrease with the increase of compressive stresses. This work provides an alternative avenue for the design of periodic layers as wave barriers.

Development of a pressurized internal cooling milling cutter and its machining performance assessment

In view of the serious problem of milling heat in milling nickel-based superalloys Inconel 718, this paper investigates the heat transfer performance of internal cooling in end milling Inconel 718, and the superiority of internal cooling milling cutter's heat exchange ability during processing is explored. The flow field characteristics of cutting fluid and milling temperature are studied by Computational Fluid Dynamics (CFD) and Finite Element Method (FEM). Compared with external flood cooling, the principle of internal cooling with excellent heat transfer performance is explained and the influence of coolant pressure on lubrication performance is analyzed. Experiments for end milling of Inconel 718 under different cutting speeds and cooling conditions have been carried out. The results indicate that the simulated and measured temperatures showed an acceptable agreement. The internal cooling has better heat transfer performance compared with flood cooling. With the increase of coolant pressure, the heat exchange efficiency is gradually enhanced. When the coolant pressure rises from 2 bar to 10 bar, the milling temperature at the measured point inside the workpiece reduces by 27.55 °C, the surface roughness reduces by 12.0%, the surface residual compressive stress increases by 68.37 MPa and better surface morphology is obtained. Besides, in the experimental range, with the increase of cutting speed, milling temperature increased, the pile-up effect on the sides of scratching was weakened and better machined surface integrity was found.

An Experimental Study on the Compressive Dynamic Performance of Rubber Concrete under Freeze-Thaw Cycles

An experimental study was conducted using a hydraulic servo machine to examine the compressive dynamic performance of rubber concrete under freeze-thaw cycles by considering 4 different numbers of freeze-thaw cycles and 8 different strain rates. The compressive stress-strain curves of rubber concrete under different loading conditions were obtained. By comparatively analyzing the mechanical characteristic parameters of the compressive stress-strain curves (i.e., peak stress, elastic modulus, and peak strain), the following conclusions were drawn: at the same loading strain rate, the compressive peak stress of rubber concrete is gradually decreased while the mass loss rate is gradually increased, as the number of freeze-thaw cycles increases. Compared to ordinary concrete, rubber concrete has a better frost resistance property. At the same number of freeze-thaw cycles, the compressive peak stress and elastic modulus of rubber concrete are gradually increased as the loading strain rate increases. The increase in the number of freeze-thaw cycles enlarges the increasing amplitude of the peak stress and elastic modulus under the action of loading strain rate. The compressive peak stress and elastic modulus dynamic increase factors of rubber concrete exhibit a linear relationship with the dimensionless logarithm of the loading strain rate. Meanwhile, a calculation model was proposed for the compressive peak stress dynamic increase factor of rubber concrete under the coupling effect of freeze-thaw cycles and loading strain rate, and the corresponding stress mechanism was discussed in detail. The research findings are of great significance to the application and development of antifreeze concrete in engineering practice.

Numerical study on laser shock peening of TC4 titanium alloy based on the plate and blade model

The compressive residual stresses and grain refinement induced by laser shock peening (LSP) are two very important surface strengthening mechanisms that are responsible for the significant improvements of the mechanical property and fatigue performance of metallic materials. A computation framework linking the dislocation-mechanism-based constitutive model with the dislocation density evolution model was developed and implemented into ABAQUS/Explicit code for numerical simulations of the residual stresses and grain refinement induced by LSP of TC4 titanium alloy. Two kinds of three-dimensional finite element models involving the plate model and TC4 blade model were respectively created to simulate the multi-LSP processes, and the effect of laser spot overlap ratio was accordingly investigated in detail. The obtained results show that with the increase of laser spot overlap ratio, the depths of both the compressive residual stresses and grain refinement increase, and with respect to the same depth, the compressive residual stresses increase and the refined cell size decreases. An attempt was made to employ the artificial neural networks (ANNs) to estimate the residual stresses and grain refinement induced by LSP of the whole TC4 blade model, and the ANNs-estimation approach presents the excellent efficiency in predicting the multi-LSPed results with inexpensive cost of numerical computation.

Unravelling the ion-energy-dependent structure evolution and its implications for the elastic properties of (V,Al)N thin films

Ion irradiation-induced changes in the structure and mechanical properties of metastable cubic (V,Al)N deposited by reactive high power pulsed magnetron sputtering are systematically investigated by correlating experiments and theory in the ion kinetic energy (Ek) range from 4 to 154 eV. Increasing Ek results in film densification and the evolution from a columnar (111) oriented structure at Ek ≤ 24 eV to a fine-grained structure with (100) preferred orientation for Ek ≥ 104 eV. Furthermore, the compressive intrinsic stress increases by 336 % to -4.8 GPa as Ek is increased from 4 to 104 eV. Higher ion kinetic energy causes stress relaxation to -2.7 GPa at 154 eV. These ion irradiation-induced changes in the thin film stress state are in good agreement with density functional theory simulations. Furthermore, the measured elastic moduli of (V,Al)N thin films exhibit no significant dependence on Ek. The apparent independence of the elastic modulus on Ek can be rationalized by considering the concurrent and balancing effects of bombardment-induced formation of Frenkel pairs (causing a decrease in elastic modulus) and evolution of compressive intrinsic stress (causing an increase in elastic modulus). Hence, the evolution of the film stresses and mechanical properties can be understood based on the complex interplay of ion irradiation-induced defect generation and annihilation.

Improvement of the wear resistance of EN8 steel by application of alternating magnetic field treatment

In the present paper, the tribological properties of untreated and magnetically treated EN8 medium-carbon steel were studied. Tribological tests were performed using a pin-on-disc friction and wear tester. The alternating magnetic field treatment has led to a reduction in the coefficient of friction by 18% and of the wear rate by 41% and to decreases in the surface roughness and the wear scar width by 30% and 12% respectively. Examination by means of transmission electron microscopy attributed these results to increased dislocation mobility and migration to the surface as a result of alternating magnetic field treatment leading to an increase in the Vickers microhardness and to an increase in compressive residual stresses at the surface.

The effect of rolling contact fatigue properties on 316 stainless steel under laser shock peening

In this paper, 316 stainless steel was treated by laser shock peening (LSP) technology, and the micro-hardness, residual stress and rolling contact fatigue (RCF) performance were investigated. The result suggests that LSP can effectively improve the RCF performance of 316 stainless steel. The main factor is that LSP can induce high amplitude compressive residual stress on the surface layer. With the increase of residual compressive stress, the worn mechanism of RCF surface changes from delamination to micro-plastic deformation. It is also found that the RCF of 316 stainless steel treated by LSP was sensitive to the contact stress.

Intervertebral Disc Mechanics With Nucleotomy: Differences Between Simple and Dual Loading.

Painful herniated discs are treated surgically by removing extruded nucleus pulposus (NP) material (nucleotomy). NP removal through enzymatic digestion is also commonly performed to initiate degenerative changes to study potential biological repair strategies. Experimental and computational studies have shown a decrease in disc stiffness with nucleotomy under single loading modalities, such as compression-only or bending-only loading. However, studies that apply more physiologically relevant loading conditions, such as compression in combination with bending or torsion, have shown contradicting results. We used a previously validated bone-disc-bone finite element model (Control) to create a Nucleotomy model to evaluate the effect of dual loading conditions (compression with torsion or bending) on intradiscal deformations. While disc joint stiffness decreased with nucleotomy under single loading conditions, as commonly reported in the literature, dual loading resulted in an increase in bending stiffness. More specifically, dual loading resulted in a 40% increase in bending stiffness under flexion and extension and a 25% increase in stiffness under lateral bending. The increase in bending stiffness was due to an increase and shift in compressive stress, where peak stresses migrated from the NP-annulus interface to the outer annulus. In contrast, the decrease in torsional stiffness was due to greater fiber reorientation during compression. In general, large radial strains were observed with nucleotomy, suggesting an increased risk for delamination or degenerative remodeling. In conclusion, the effect of nucleotomy on disc mechanics depends on the type and complexity of applied loads.

Effect of shot peening intensity on surface integrity of 18CrNiMo7-6 steel

The surface integrity of components treated by shot peening is determined by many influencing factors, which are generally divided into shot peening process parameter, procedure parameter and machine parameter. To understand the influencing relationship of these parameters, and thereby obtain the appropriate peening intensity for the engineering practice, this study experimentally examined the effect of different shot peening parameters on the peening intensity, and further explored the influence of which on surface integrity parameters of carburized steel rollers. It is found that the intensity is mainly affected by the shot diameter (36.73%), air pressure (32.07%) and shot flow rate (23.11%). The maximum compressive residual stress and surface hardness increase linearly as the intensity increases, reaching −1250 MPa and 785 HV at the intensity of 0.55 mmA, respectively. Surface roughness parameter Sq can be used to predict the surface hardness due to the approximately linear relationship between them.

Out-of-plane static compression and energy absorption of paper hierarchical corrugation sandwich panels

This study introduces the opinion of the corrugation hierarchy to develop the second-order corrugation paperboard, and explore the deformation characteristics, yield strength, and energy absorbing capacity under out-of-plane static evenly compression loading by experimental and analytical approaches. On the basis of the inclined-straight strut elements of corrugation unit and plastic hinge lines, the yield and crushing strengths of corrugation unit were analyzed. This study shows that as the compressive stress increases, the second-order corrugation core layer is firstly crushed, and the first-order corrugation structures gradually compacted until the failure of entire structure. The corrugation type has an obvious influence on the yield strength of the corrugation sandwich panel, and the yield strength of B-flute corrugation sandwich panel is wholly higher than that of the C-flute structure. At the same compression rate, the flute type has a significant impact on energy absorption, and the C-flute second-order corrugation sandwich panel has better bearing capacity than the B-flute structure. The second-order corrugation sandwich panel has a better bearing capacity than the first-order structure. The static compression rate has little effect on the yield strength and deformation mode. However, with the increase of the static compression rate, the corrugation sandwich panel has a better cushioning energy absorption and material utilization rate.

Electronic and optical properties of Janus monolayers MoXB2(X=S, Se): first-principles prediction

By means of comprehensive first-principles calculations, we studied the geometric structure, the stability and electronic properties of the new two-dimensional (2D) Janus MoXB2(X=S, Se) monolayers. Our calculations demonstrated that the predicted Janus MoXB2monolayers are all stable semiconductors with direct band gap. In this paper, we focus on impacts upon the electronic and optical properties of the MoXB2monolayers under the different biaxial strains. With the compressive stress increases, the MoXB2monolayers would become indirect band gap semiconductors, and then behave as semimetal. While under tensile strain, MoXB2still maintain direct band gap. In addition, the optical calculation shows that biaxial strain leads to blue shifts in the optical absorption and reflectivity. The result indicates that MoXB2may be promised nano candidate materials in optoelectronic devices.

Mechanical Properties Of Sandwich Composites Used For Aerofoil Shell Structures Of Wind Turbine Blade

The grid-scored foams contribute significantly to the overall mechanical properties of the sandwich structures, such as aerofoil shell structure of wind turbine blades which are subjected to different loads under operating conditions. The goal of the present paper is to examine the four-point bending, flatwise and edgewise compression and in-plane shear behaviour of sandwich panels composed of composite face sheets of E-glass/ bisphenol-A epoxy resin and plain and grid-scored PVC foams. The four-point bending failure load of the grid-scored foamed sandwich beams increased by 28.1% compared to the plain foamed ones. The flatwise compression strength of samples with grid-scored foam increased by 546% compared to plain foamed samples. The resin grids contributed to an increase in the flat-wise compression stress inducing the core crushing. Under the edgewise compression load, using the grid-scored foam increased the maximum load values by only about 2.9% relative to the plain foam. The reason for this small difference can be addressed as the facings are more effective in carrying the edgewise loadings. With the use of the grid-scored foam, an increase of 38.2% was obtained in-plane shear strength compared to plain foamed sandwich beams. The resin grids improved bonding between the facings and PVC foam.

Properties inhomogeneity of AM60 magnesium alloy processed by cyclic extrusion compression angular pressing followed by extrusion

A new severe plastic deformation (SPD) technique for improvement of the metallurgical properties of the magnesium alloys is presented. In this process, a cyclic extrusion compression angular pressing (CECAP) process is followed by an extrusion step in the outlet playing the role of additional back pressure. Therefore, more uniform and enhanced mechanical properties are expected in comparison with equal channel angular pressing (ECAP). In order to evaluate the effectiveness and capabilities of this new method, an AM60 magnesium alloy was processed. Finite element results exhibited a significant increase in strain values as well as uniform strain distribution for the new method. In addition, ~110% increase in compressive stress was observed in new method compared to the conventional ECAP. Experimental results revealed a noticeable increase in the hardness and strength of the specimens processed by the new technique as a result of the formation of finer grains and more homogeneous microstructure with good distribution of refined β-phase along the boundaries. It may be concluded that the new process is very promising for future magnesium alloy products.

Study on a stress-magnetic relationship of DO3 based on first principles

Based on the first principles, in this paper the stress-magnetic relationship model of the Fe3Si (DO3) phase in silicon steel was analyzed, and the band structure and electronic density states were calculated. The experimental results show that the atomic magnetic moment would increases with the increase of tensile stress, and decreases with the increase of compressive stress. The linear compressive strength of the DO3 crystal is stronger than the linear tensile strength, and this phenomenon could be explained by the band structure and electronic density states. In addition, the macro verification experiment is designed. The silicon steel plate is used as the verification experiment sample, the change of silicon steel magnetic properties during the tension and compression process is measured. The experimental results show that the magnetic properties of silicon steel show an increasing trend in the tension process and a decreasing trend in the compression process, which qualitatively proves the correctness of the first principle calculation results. The MFM measurement results confirm that the stress would affect the magnetic domain. The stress-magnetic relationship of DO3 would provide theoretical support for electromagnetic detection and reduction of residual stress in silicon steel.

Effect of deep rolling on subsurface conditions of CoCr28Mo6 wrought alloy to improve the wear resistance of endoprostheses

Wear of orthopaedic endoprostheses is associated with adverse local and systemic reactions and can lead to early implant failure. Manufacturing determines the initial subsurface microstructure of an alloy that influences the implant's wear behaviour. Therefore, this study aims at generating enhanced wear resistances by a modification of the surface and subsurface microstructure of a CoCr28Mo6 wrought alloy by applying deep rolling.The state of the art was investigated by means of eleven retrieved CoCr28Mo6 hip implant components from different manufacturers with respect to their subsurface microstructure and micro hardness profiles. CoCr28Mo6 wrought alloy samples (DIN EN ISO 5832–12) were aged at 750 °C for 24 h and/or plastically deformed by deep rolling with varying axial forces (170 N, 230 N and 250 N). The samples were metallographically prepared and investigated using optical and scanning electron microscopy with EDS and EBSD, micro hardness testing, XRD and tribological testing.The retrieved implant components revealed that, independent of the manufacturer, neither the head nor the stem trunnion exhibited a defined subsurface condition. The dominant phase within the implants was face-centered cubic (fcc). Some implants exhibited single hexagonal close-packed (hcp) grains due to a stress-induced phase transformation. The initial CoCr28Mo6 wrought alloy had a fcc crystal structure. After isothermal aging, the matrix entirely transformed to a hcp structure. In the initial fcc-condition, deep rolling generated a plastically deformed surface layer within the first 100 μm and stress-induced phase transformation to hcp was observed. Micro hardness gradients were present in the subsurface of up to 600 μm depth and exhibited a maximum increase of 34% by deep rolling in comparison to the initial fcc-matrix. This trend was confirmed by a correlated increase in residual compressive stresses. In tribological tests under serum lubrication, the modified samples generated lower wear in comparison to the contemporarily used fcc-matrix samples. This study demonstrates that deep rolling is an effective processing to modify the subsurface of a biomedical CoCr28Mo6 wrought alloy in order to increase the wear resistance. The intentional transformation from the fcc to the hcp phase induced by deformation offers great potential for implant application.

Effect of particle proximity and surface properties on the response of PBX under vibration

Accidental initiation of polymer bonded explosives (PBX) may take place during manufacturing, handling or transport. The sensitivity to initiation depends on the microstructural properties of PBXs, including particle size distribution, density, initial defects, porosity, etc. Finite element simulations of a representative PBX microstructure under ultrasonic vibration are used to understand the effect of relative particle locations and distance between particles on the local temperature rise in PBXs. The simulations show that larger particles damage earlier and the behavior of the smaller particles in the microstructure largely depends on their position with respect to the larger particles and the loading boundary. The adhesion between the particles and the polymer has a direct effect on the formation of hot-spots due to friction and through local increase of compressive stresses that may cause a surge in heat generation.

Formation of residual stresses during the restoration of parts by chrome electroplating

As the title implies the influence of the electrolysis on the nature and magnitude of residual stresses in the steel base and the chrome coating during restoration of parts has been considered. It has been shown that with an increase in compressive stresses on the surface, a decrease in tensile stresses in the chromium deposit and transition of tensile stresses to compressive ones near the boundary of the base are observed. A correlation between the parameters of the crystal lattice of electroplated chromium and the steel base has been established. The values of the tensile residual stresses in the chromium deposit decrease with increasing the compressive residual stresses in the base.

Influence of the Cross-Sectional Shape of a Reinforced Bimodular Beam on the Stress-Strain State in a Transverse Impact

The paper considers the stress-strain state of a reinforced concrete beam, as a bimodular material, under the action of an impact. The behavior of bimodular concretes with different moduli of elasticity in tension and compression has not been studied enough. At the same time, taking into account the bimodularity of concrete makes it possible to design a more economical structure, especially for dynamic load. In this article, the impact is considered as an absolutely plastic impact of an absolutely rigid body on an elastic system. The stress state is investigated for beams of rectangular, T-section and I-sections, and is compared with and without the bimodularity of reinforced concrete. The analysis of the dependence of the stress state on the shape, cross-sectional dimensions, and the location of reinforcing bars in the compressed and tensioned zones was carried out for lightweight concrete (Et < Ec) and for heavy concrete (Et > Ec) under the action of shock load with and without regard to the mass of the beam. The numerical study shows that taking into account the mass of the beam upon impact significantly decreases the magnitude of the normal stresses in both the tensioned and compressed zones. Beams of rectangular cross-section have the highest load-bearing capacity when the cross-section height is equal for both light and heavy concrete. An increase in the size of the flange of the I-beam in the stretched zone leads to a sharp decrease in normal tensile stresses and a slight increase in normal compressive stresses. The proposed engineering method makes it possible to numerically study the effect on the stress-strain state of a beam under the action of a concentrated impact of various geometric characteristics of the cross-section, bimodularity of the material, size, number and location of reinforcement.

Influence of Shot-Peening on Wear Resistance of Austempered and Quench-Tempered Ductile Irons

In this research, ball-on-plate reciprocating sliding wear tests were conducted on shot-peened specimens of ductile iron heat treated by either austempering or quench-tempering. Hardness and microstructure were evaluated to understand the phase transformation, and X-ray diffraction was used to measure the residual stress. It was found that feather-like ausferrite was formed when using high austempering temperatures. In sliding wear tests, austempered ductile iron specimens had better wear resistance than quench-tempered ductile iron specimens before and after receiving shot-peening. Crack and adhesive wear were the two main wear mechanisms on ductile iron specimens. The shot-peening resulted in the increase of residual compressive stress and surface hardness, which could retard the nucleation and propagation of cracks and reduce the amount and size of smeared areas.

Thermal transport measurement of three-dimensional graphene powders for application in energy devices

Three-dimensional graphene (3DG) has drawn much attention as a great potential electrode material for its extraordinary properties. However, the heat dissipation involved in the electrochemical reactions or Joule heating during the continuous charge-discharge cycles has become a critical challenge, which significantly affects the performance. In this work, we report the first experimental measurement on the thermal transport properties of 3DG powders under different temperatures and compressive stresses by using the laser flash method. High temperature and stress dependence of thermal transport in 3DG powders were observed from the measurements. The thermal diffusivity and thermal conductivity increase significantly from ~1.52 mm2/s to ~4.90 mm2/s and ~0.40 W/(m·K) to ~1.29 W/(m·K), respectively, with the temperature increment from 25°C to 120°C, corresponding to about 320% enhancement. Besides, we found the thermal conductivity quickly increases at the beginning and then gradually reaches to a saturation value of ~0.65 W/(m·K) with the increase of compressive stress. We proposed the temperature/stress-dependent thermal transport properties resulting from the reduction of thermal contact resistance, which dominates the thermal transport of porous material. These results provide useful guidelines for thermal design and benefit for effective thermal management of 3DG-based energy devices.