Increase In Compressive Stress Research Articles

A theoretical analysis of longitudinal temporomandibular joint compressive stresses and mandibular growth.

To determine if temporomandibular joint (TMJ) compressive stresses during incisor biting (1) differed between growing children over time, and (2) were correlated with Frankfort Horizontal-mandibular plane angle (FHMPA, °) and ramus length (Condylion-Gonion (Co-Go), mm). Three-dimensional anatomical geometries, FHMPA and Co-Go, were measured longitudinally from lateral and posteroanterior cephalographs1 of children aged 6 (T1), 12 (T2), and 18 (T3) years. Geometries were used in numerical models to estimate subject-specific TMJ eminence shape and forces for incisor bite-forces of 3, 5, and 8 Newtons at T1, T2, and T3, respectively. TMJ compressive stresses were estimated via two steps: First, TMJ force divided by age-dependent mandibular condylar dimensions, and second, modified by loading surfaces' congruency. Analysis of variance and Tukey honest significant difference post-hoc tests, plus repeated measures and mixed effects model analyses were used to evaluate differences in variables between facial groups. Regression analyses tested for correlation between age-dependent compressive stresses, FHMPA, and Co-Go. Sixty-five of 842 potential subjects had T1-T3 cephalographs and were grouped by FHMPA at T3. Dolichofacial (FHMPA ≥ 27°, n = 36) compared to meso-brachyfacial (FHMPA< 27°, n = 29) subjects had significantly larger FHMPA at T1-T3, shorter Co-Go at T2 and T3 (all P < .01), and larger increases in TMJ compressive stresses with age (P < .0001). Higher compressive stresses were correlated with larger FHMPA (all R2 ≥ 0.41) and shorter Co-Go (all R2 ≥ 0.49). Estimated TMJ compressive stress increases from ages 6 to 18 years were significantly larger in dolichofacial compared to meso-brachyfacial subjects and correlated to FHMPA and Co-Go.

Bending analysis of FG-GPLRC axisymmetric circular/annular sector plates by considering elastic foundation and horizontal friction force using 3D-poroelasticity theory

Composite structures encounter different types of imperfections and defects during the installation, working environment, and fabrication process. In the present research, a 3D-poroflexibility theory has been presented to study the bending responses of the functionally graded graphene nanoplatelets reinforced composite (FG-GPLRC) axisymmetric circular/annular sector plates on the elastic substrate. For modeling elastic substrate, horizontal friction force and the elastic foundation with five elastic parameters have been formulated. For obtaining the exact displacement and stress/strain responses of the current structure, a discrete singular convolution integration method (DSC-IM) has been utilized. Also, the outputs of the current research have been verified with the results of COMSOL Multi-physics software. Consequently, the outcomes demonstrate that GPL’s weight fraction, in-plane boundary condition, radial and circumferential initially stresses, and Biot's coefficient have a remarkable impact on the bending responses of the circular/annular sector plates. Also, when the normal compressive stress increases, the negative effect from normal tensile stress on the bending characteristics of the structures is more remarkable than the positive effect from normal compressive stress. Also, the effect of GPL’s weight fraction on the stress and displacement fields is more considerable at the higher value of the opening angle of the current composite structure.

Characteristics of Impulse Carburization LPC Process.

In the present work, Pyrowear53 steel was subjected to the impulse carburizing LPC process. After carburation, the material was quenched and tempered. Postprocessing analyses included the measurement of hardness, carbon content, residual austenite, and residual stresses. The results revealed that the thermochemical treatment resulted in the formation of an approximately 1200 µm wide carburized layer. The results of hardness, carbon content, and residual austenite measurement showed a continuous gradient (drop) in the measured values within the carburized layer. However, the results of residual stresses revealed the existence of a local extremum, namely, a zone with higher compressive stresses at the depth between 600 and 1000 µm. This was explained by a different temperature for initiation of martensite transformation as a function of carbon content. This difference resulted in the occurrence of two martensite expansion fronts at two different depths, resulting in an increase in compressive stresses at the noted depth range. Moreover, it was concluded that this region was present for material containing between 0.8 and 0.4 wt% carbon for Pyrowear53.

A parametric neutron Bragg edge imaging study of additively manufactured samples treated by laser shock peening

Laser powder bed fusion is an additive manufacturing technique extensively used for the production of metallic components. Despite this process has reached a status at which parts are produced with mechanical properties comparable to those from conventional production, it is still prone to introduce detrimental tensile residual stresses towards the surfaces along the building direction, implying negative consequences on fatigue life and resistance to crack formations. Laser shock peening (LSP) is a promising method adopted to compensate tensile residual stresses and to introduce beneficial compressive residual stress on the treated surfaces. Using neutron Bragg edge imaging, we perform a parametric study of LSP applied to 316L steel samples produced by laser powder bed fusion additive manufacturing. We include in the study the novel 3D-LSP technique, where samples are LSP treated also during the building process, at intermediate build layers. The LSP energy and spot overlap were set to either 1.0 or 1.5 J and 40% or 80% respectively. The results support the use of 3D-LSP treatment with the higher LSP laser energy and overlap applied, which showed a relative increase of surface compressive residual stress (CRS) and CRS depth by 54% and 104% respectively, compared to the conventional LSP treatment.

Study on the bearing capacity and chloride ion resistance of RC structures under multi-factor corrosive environment and continuous load

In this paper, the bearing capacity and chloride resistance of reinforced concrete (RC) structures under multi-factor corrosive environment and continuous load are investigated, and the correlation between the bearing capacity and chloride resistance is also studied. First, different corrosion environments and compressive stress conditions were simulated by freeze-thaw (F-T) cycles test, carbonization test and continuous loading test. Among them, carbonization test and F-T cycles test constitute corrosion cycle test. Then, according to the test results of bearing capacity, under the action of corrosion cycle test, the bearing capacity of RC beam decreases with the increase of corrosion cycles. The bearing capacity of RC beams have a tendency to rise first and then drop with the increase of compressive stress under the multi-factor corrosive environment. In addition, according to the test results of chloride ion erosion, the equation for calculating the corrosion resistance of chloride ion is established, and the resistance to chloride ion erosion increased with the increase of corrosion cycle. With the increase of compressive stress, the ability to resist chloride ion erosion displays the tendency rising up at the beginning and declining in late. Finally, through grey correlation analysis, the correlation between corrosion cycles and yield load is greater than the correlation between chloride ion erosion and yield load, while the correlation with ultimate load is opposite. Based on the results of correlation analysis, the bearing capacity decay equation is established.

Influence of Shot Peening on the Isothermal Fatigue Behavior of the Gamma Titanium Aluminide Ti-48Al-2Cr-2Nb at 750 °C

One possibility to improve the fatigue life and strength of metallic materials is shot peening. However, at elevated temperatures, the induced residual stresses may relax. To investigate the influence of shot peening on high-temperature fatigue behavior, isothermal fatigue tests were conducted on shot-peened and untreated samples of gamma TiAl 48-2-2 at 750 °C in air. The shot-peened material was characterized using EBSD, microhardness, and residual stress analyses. Shot peening leads to a significant increase in surface hardness and high compressive residual stresses near the surface. Both effects may have a positive influence on lifetime. However, it also leads to surface notches and tensile residual stresses in the bulk material with a negative impact on cyclic lifetime. During fully reversed uniaxial tension-compression fatigue tests (R = −1) at a stress amplitude of 260 MPa, the positive effects dominate, and the fatigue lifetime increases. At a lower stress amplitude of 230 MPa, the negative effect of internal tensile residual stresses dominates, and the lifetime decreases. Shot peening leads to a transition from surface to volume crack initiation if the surface is not damaged by the shots.

Using melt-electrowritten microfibres for tailoring scaffold mechanics of 3D bioprinted chondrocyte-laden constructs

Moulded hydrogels reinforced with melt-electrowritten (MEW) microfibres to tailor mechanical properties show promise in the articular cartilage regeneration field. We aim to transfer this knowledge to bioprinted constructs of volumetric dimensions towards real anatomical shapes, using a previously established alginate methylcellulose (algMC) blend. We show the potential of algMC to be a bioink for MEW fibre-reinforced 3D printed constructs that have tailorable mechanical properties and support long-term culture of bioprinted human chondrocytes. It is hoped that these composite algMC-PCL scaffolds have potential for use in auricular (ear) cartilage regeneration as an alternative to current reconstructive treatments using autografted rib cartilage or high-density polyethylene implants. Scaffolds of different designs were assessed to determine the effect of the hybrid structure on compressive strength, as well as an initial in vitro experiment with human chondrocytes to assess cell viability, DNA, sGAG, and collagen II content. The inclusion of MEW PCL scaffolds showed up to a 7.5-fold increase in the maximum compressive stress after 7 days of incubation in DMEM compared to algMC only scaffolds. In vitro work showed there was no significant differences in the cell viability between groups after 21 days of culture. However, DNA and sGAG content (relative to cell number) showed an increase in algMC scaffolds reinforced with MEW PCL sheets with 750 μm pores suggesting a more favourable stiffness for chondrocyte extracellular matrix (ECM) deposition. Future work will investigate how the scaffold stiffness changes over time as materials degrade and ECM is deposited as well as further in depth analysis of the biological performance with relevance to auricular cartilage. This microfibre reinforced algMC scaffold provides a promising way to tailor the mechanical properties of bioprinted structures for chondrocyte delivery at clinically relevant dimensions.

Experimental investigation of axial compressive behavior of square and rectangular confined concrete-masonry structural wall boundary elements

Reinforced masonry boundary elements (RMBEs) are critical components in determining the lateral response of reinforced masonry structural walls with boundary elements. Fundamental interpretation of the effect of various influential parameters on the RMBEs′ behavior is essential to enhance their stress–strain response. This study investigates, experimentally, the influence of various design parameters and construction procedures on the axial compressive behavior of fully grouted RMBEs built with C-shaped concrete-masonry blocks. Thirty-eight unreinforced and RMBEs were constructed and tested under concentric axial loading till failure. The effect of five parameters, namely, the vertical reinforcement ratio, the volumetric ratio of confinement reinforcement, cross-section configuration, stack pattern and running-bond, and pre-wetting of dry masonry shell before grouting, was investigated. The test results showed that increasing the vertical reinforcement ratio of the RMBEs resulted in a significant increase in the peak compressive stress and a considerable reduction in the corresponding strain ductility. Moreover, as the RMBEs volumetric ratio of transverse reinforcement doubled, the strain ductility witnessed a remarkable enhancement, whereas the peak compressive stress experienced an inconsistent trend. RMBEs built with rectangular C-shaped cross-sections exhibited comparable peak stress, smaller drop following the face shell spalling, and better strain ductility than square RMBEs. The running-bond pattern had a negative effect on both the peak stress and the strain ductility of dry RMBEs, although it exhibited comparable or even enhanced response in wet RMBEs compared to those built in the stack pattern. Pre-wetting of dry masonry shell before grouting was found to boost the peak compressive stress of unreinforced and RMBEs significantly. However, it adversely affected their strain ductility. Wet RMBEs showed a steeper post-peak descending branch compared to their dry counterparts. Indeed, the vertical reinforcement ratio and pre-wetting of dry masonry shell were the most critical parameters affecting the RMBEs peak compressive stress, whereas the confinement ratio mostly influenced the strain ductility. This study sheds light on the most critical parameters influencing the stress–strain components (i.e., strength and ductility) of RMBEs.

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.