MPa Compressive Stress Research Articles

Effect of uniaxial stress on magnetic property of laminated amorphous sheets up to kilohertz range

Amorphous alloys are widely used as the core material for motors and transformers, which are subjected to stresses during manufacturing and operation processes. For instance, the compressive stress can influence the magnetic properties of amorphous alloys which leads to local overheating in the device and reduce the reliability. A high-frequency magnetizer with a stress application unit is designed and constructed to investigate the magnetic properties of amorphous alloys up to kilohertz range under stress conditions. The amorphous alloy sheets will fracture under stress because of their poor ductility and brittleness, so this paper uses laminated amorphous alloy sheets as the sample. The hysteresis loops and loss characteristics of amorphous alloys under stress ranging from 20 MPa tensile stress to 20 MPa compressive stress at a frequency of 50 Hz to 4 kHz are investigated. This research can provide data support for the design of cores in electromagnetic devices.

The Onset of Recrystallization in Polar Firn

AbstractConstraining the onset of dynamic recrystallization (DRX) and its effects on the mechanical properties of firn is crucial for firn densification modeling. To that end, samples from a depth of 13 m in a Summit, Greenland (72°35′N, 38°25′W) firn core were subjected to creep tests at −14°C and 0.21 MPa compressive stress to strains of 7%, 12%, 18%, and 29%. Microstructural analyses using thin‐section imaging and microcomputed x‐ray tomography (micro‐CT) revealed smaller grain sizes, reduced specific surface area and connectivity, and increased density in relation to reduced porosity as the strain increases. These results show that DRX occurs in firn under creep, with strain‐induced boundary migration (SIBM) and nucleation and growth starting at ∼7%. DRX leads to elongated grains, reduced grain size, and the development of a preferred crystallographic orientation, indicating that DRX occurs by both SIBM and nucleation and growth.

Preparation of near fully dense (LaO1.5)x(ErO1.5)x(YO1.5)0.03-0.5x(ZrO2)0.97-x ceramics with restricted grain growth and high surface residual stress by hot pressing sintering at 950 °C

(LaO1.5)x(ErO1.5)x(YO1.5)0.03-0.5x(ZrO2)0.97-x ceramics with high density (98.1 %), high strength (1533 MPa), high surface residual stress (1305 MPa) and fine grain (96 nm) were prepared by ultra-low temperature hot pressing sintering. The results indicate that high pressure significantly promotes densification in the contact area of (LaO1.5)x(ErO1.5)x(YO1.5)0.03-0.5x(ZrO2)0.97-x ceramics particles and no effect on grain growth. Low temperature can effectively reduce the transition from tetragonal to cubic phase (T-C) and limit grain growth. In addition, 1305 MPa compressive stress on the surface of (LaO1.5)x(ErO1.5)x(YO1.5)0.03-0.5x(ZrO2)0.97-x ceramics were the main reason for the improvement of bending strength. This process provides a design idea for obtaining fine-grained fully dense structural ceramics.

Mechanically robust hydrogel from thermosetting polybenzoxazine with dual crosslinking network

The main chain of polymer composition in hydrogels is mostly aliphatic and the crosslinking density is usually low, which renders the hydrogels with low mechanical strength. In this work, a kind of thermosetting resin, benzoxazine is used as the starting material to prepare the corresponding hydrogels by one-pot synthesis. The organic gels are firstly formed in dimethylformamide with the aid of catalyst, followed by extraction of water to give the hydrogels. It is revealed that due to the presence of covalent crosslinking and abundant hydrogen bonding, the as-prepared rigid hydrogels show extremely high compressive strength. The hydrogel with 55.8 wt% of water shows yield strength about 20 MPa and sustains compressive strength of 75 MPa (compressive stress of 30 kN, compressive strain of 67 %) without cracking. The hydrogel also show extremely high dielectric constant of 392,000, dielectric loss of 971,000, and ionic conductivity of 1.7 × 10−3 S/m at 100 Hz. Moreover, the responsiveness to pH variation suggests its potential application as smart responsive materials. To show the superiority of preparing functional composite hydrogels using this strategy, electroconductive and magnetic fillers are introduced and the as-prepared composite hydrogels show good electromagnetic shielding performance.

Bearing Inner Ring Raceway Low-Temperature Aerosol Cooling Lubrication Grinding

A low-temperature aerosol cooling and lubrication grinding test bench was built to evaluate the cooling and lubrication performance of the low-temperature aerosol. The mechanism of grinding residual stresses in the inner ring raceway under the coupling effect of grinding force and grinding heat was studied, and the effects of the grinding process parameters and cooling and lubrication conditions on the distribution state of the grinding residual stresses in the surface layer of the inner ring raceway were revealed. The results showed that reducing the initial temperature of the grinding fluid could reduce the residual tensile stresses on the raceway surface. The results also showed that the low-temperature aerosol cooling lubrication method is conducive to the generation of the axial residual compressive stress of −500 MPa and tangential residual compressive stress of −300 MPa in the inner ring raceway surface layer of the bearing. Compared with the convective heat transfer coefficient, the effect of the initial temperature of the grinding fluid is smaller.

Remarkable age-hardening response and microstructural evolution of Mg–7Sn alloy

The poor age-hardening response of Mg alloys limited their development and applications. In this study, the age-hardening response of Mg–7Sn alloy has been improved significantly by a 40 MPa compressive stress aging at 220 °C. Phase transition from metastable βˈ (Mg3Sn) phase to β (Mg2Sn) phase occurs during the stress aging. The βˈ with L12 structure has an orientation relationship with the Mg matrix of (11¯0)β＇//(112¯0)α and [1¯1¯0]β＇//⌈0001¯⌉α. The precipitated sequence in the stress-aged alloy is S.S.S. (supersaturated solid solution)→GP→βˈ(Mg3Sn)→β(Mg2Sn). The stress-aged alloy exhibits a high peak-aged hardness (∼71 HV) and short time to reach the peak hardness (12 h) as compared with the aged alloy without the stress. Interestingly, a long-time aging platform with 71 HV for 96 h is observed during stress aging. The formation of the platform is related to a balance of hardening and softening arisen from microstructure evolution during stress aging. The stress aging provides a promising heat treatment way to improve aging hardening response of Mg alloys.

Microstructure and properties of laser-clad high entropy alloy coating on Inconel 718 alloy

In this study, CoCrFeNiMo0.2 high entropy alloy coating (average thickness of 990 μm) without defects was successfully prepared on the Inconel 718 substrate by laser cladding. Microstructure and properties were investigated systematically by multiple characterization methods. The EDS and ECC find that the coating has good metallurgical bonding with the substrate. The thermal erosion test indicates that the formation of a passive film with Cr and Mo elements improves the thermal erosion resistance of the coating. According to the results of microhardness tests, the average microhardness in the coating is about 328.9 HV (1.28 times of the substrate). The coating with low wear width (0.454 mm) and depth (7.085 μm) shows outstanding wear resistance due to the formation of the σ phase particles and the fine-grain strengthening. The coating surface's average residual stress is −723.3 MPa (compressive stress), which prevents crack generation. Furthermore, the corrosion resistance of the coating is obviously improved.

Fatigue Properties of Aluminum Alloy Sheet Treated with Shot-Peen Forming in Salt-Spray Environment

The effects of shot-peen forming on the fatigue properties of aluminum alloy samples were measured with a mechanical testing & simulation (MTS) tester in atmospheric and salt-spray environments. After shot-peen forming, the fatigue performance of the aluminum alloy sheet was significantly improved in both the atmospheric and the salt spray environment. Compared with the detail fatigue rating (DFR) value in the atmospheric environment, in the salt-spray environment, the DFR value of the original samples decreased to 110.82 MPa, decreasing by 4.47%. The DFR value of the shot-peen-forming samples decreased to 151.03 MPa, decreasing by 11.40%. Fatigue fracture characteristics demonstrate that the number of crack sources decreased after shot peening. However, the corrosion rate test in a neutral saline environment showed that the corrosion resistance of the aluminum alloy sheet decreased after shot peening. In the salt-spray environment, surface residual-stress analysis showed that there was about 30 MPa tensile stress on the original sample, and 100 MPa compressive stress on the shot-peened sample. Therefore, the improvement in the fatigue resistance of the aluminum alloy sheet after shot peening was largely due to the residual compressive stress introduced on the surface of the aluminum alloy.

Bovine pericardium leaflet damage during transcatheter aortic valve crimping: a study of the mechanisms

Leaflet damage has been documented to occur while deploying a transcatheter aortic valve (TAV) due to mechanical loads during the crimping procedures. In this study, the impact of compressive stress on folded leaflets was measured to investigate the mechanism of traumatic leaflet tissue damage. Numerical simulation of TAV crimping procedure was adapted to calculate stress magnitude and distribution of leaflets. A 20 mm balloon expanding short stent TAV with 0.25 mm thickness leaflets was used in the simulation. Then the calculated stresses were applied on leaflet material (bovine pericardium) samples by loading experiments. Mechanical properties evaluation combined with histological and microscopy observation were used to investigate the tissue damage. The elastic modulus and the tensile strength of the tissue began to decrease significantly at 2 MPa stress and 2.5 MPa stress, respectively. No significant differences were observed at 0–1.5 MPa stress. When the TAV was crimped to 14 Fr and 12 Fr, the 2 MPa greater areas on leaflets increased from 18.17% to 76.96%. 2 MPa compressive stress might be the threshold value for leaflet damage. The TAV crimping size should be paid attention to avoid the compressive stress higher than 2 MPa.

Influence of ultrasonic impact treatment on microstructure and mechanical properties of nickel-based alloy overlayer on austenitic stainless steel pipe butt girth joint

Ultrasonic impact treatment (UIT) is carried out on the Ni-based alloy stainless steel pipe gas tungsten arc welding (GTAW) girth weld, the differences of microstructure, microhardness and shear strength distribution of the joint before and after ultrasonic shock are studied by microhardness test and shear punch test. The results show that after UIT, the plastic deformation layer is formed on the outside surface of the Ni-based alloy overlayer, single-phase austenite and γ type precipitates are formed in the overlayer, and a large number of columnar crystals are formed on the bottom side of the overlayer. The average microhardness of the overlayer increased from 221 H V to 254 H V by 14.9%, the shear strength increased from 696 MPa to 882 MPa with an increase of 26.7% and the transverse average residual stress decreased from 102.71 MPa (tensile stress) to −18.33 MPa (compressive stress), the longitudinal average residual stress decreased from 114.87 MPa (tensile stress) to −84.64 MPa (compressive stress). The fracture surface has been appeared obvious shear lip marks and a few dimples. The element migrates at the fusion boundary between the Ni-based alloy overlayer and the austenitic stainless steel joint, which is leaded to form a local martensite zone and appear hot cracks. The welded joint is cooled by FA solidification mode, which is forming a large number of late and skeleton ferrite phase with an average microhardness of 190 H V and no obvious change in shear strength. The base metal is all austenitic phase with an average microhardness of 206 H V and shear strength of 696 MPa.

The effect of compressive stress on cavitation-erosion corrosion behavior of 304 stainless steel

PurposeThe purpose of this paper is to clarify the effect of compressive stress on cavitation-erosion corrosion behavior of 304 stainless steel.Design/methodology/approachCompressive stresses of 60 MPa and 120 MPa were applied to 304 stainless steel through a self-designed loading device, and cavitation erosion-corrosion tests were performed using an ultrasonically vibratory apparatus. Scanning electron microscope and X-ray diffraction were used to analyze the microstructure evolution, and corrosion behavior was studied by electrochemical analysis.FindingsThe cavitation weight loss of 304 stainless steel decreased with the compressive stress. After cavitation corroded for 8 h, the weight loss for the specimen with 120 MPa compressive stress was 5.11 mg/cm2, which was reduced by 56.7% from that of the specimen without loading stress (11.79 mg/cm2). The reason can be attributed to that compressive stress promoted the deformation-induced martensitic transformation during the cavitation process, which could not only provide a cushioning effect by absorbing cavitation impact energy but also improve the hardness of 304 stainless steel.Originality/valueCompressive stress was found to restrain the cavitation damage on 304 stainless steel, and the corresponding mechanism was proposed.

Shortened processing duration of high-performance Sm-Co-Fe-Cu-Zr magnets by stress-aging

Simultaneously achieving high energy product and high coercivity in the 2:17-type Sm-Co-Fe-Cu-Zr high temperature magnets has been closely relied on long-term isothermal aging to develop complete cellular nanostructure. In this work, we report a novel stress-aging approach that can substantially shorten the aging time to fabricate high-performance Sm-Co-Fe-Cu-Zr magnets. As exhibited by a model magnet Sm25Co50.2Fe16.2Cu5.6Zr3.0 (wt.%), applying 90 MPa compressive stress can shorten the aging time from 20 h for conventional isothermal aging to 10 h at the same aging temperature for achieving nearly equivalent magnetic performance. Further comparative study between the 10 h-aged samples under stress-containing and stress-free conditions revealed that the stress not only promotes the precipitation of the cell boundary phase that are essential for enhancing the coercivity but also accelerates the dissociation of the cell edge defects that are detrimental to squareness factor, without destroying the [001] crystallographic texture. Such microstructural improvements enable the achievement of high-performance with maximum energy product of ∼30 MGOe and coercivity above 35 kOe at reduced aging time.

Thermal and Mechanical Properties of Building Stones Used in Some provinces in the Marmara Region

In this study, some physical properties of Lefke (Bilecik), Keşan (Edirne), Çan (Çanakkale) and Küfeki (Istanbul) stones, which are used as building materials in their regions, were investigated. Samples were taken from two separate quarries for each stone, and after chemical analysis, thermal conductivity, compressive strength, water absorption, respiration ability and abrasion tests were performed. As a result of the tests, it has been revealed that i) Çan, Tüfekî and Lefke stones, among the ones examined, with low thermal conductivity coefficient values (0.342 W/mK, 0.564, 0.860 W/mK), can be used as briquettes, bricks or wall covering materials for thermal insulation and decoration purposes, ii) Keşan stone can be used in load-bearing wall material and wear-resistant flooring with 81.3 MPa compressive stress and 4.83% wear rate values and iii) four stones have rich reserves and low costs. The results were compared with other building materials especially in terms of energy saving, strength and comfort conditions.

Efficacy of Yishen Huoxue Tongluo() medicated serum on apoptosis of nucleus pulposus cells of human intervertebral disc under overload static pressure

To explore the efficacy of Yishen Huoxue Tongluo() decoction containing serum on the apoptosis of human disc nucleus pulposus cells under the overload static pressure stress and its related mechanism. Human nucleus pulposus cells were divided into three groups. The blank group had no intervention. The model group and traditional Chinese medicine serum intervention group were treated with 3 MPa compressive stress in vitro for 2, 4 and 6 hours. The changes and differences of morphology, growth status and ultrastructure of intervertebral disc nucleus pulposus cells were observed. The apoptosis rate of nucleus pulposus cells and nuclear factor kappa-B p65 (NF-κB p65), SRY-related high mobility group box 9 (SOX9), C/EBP-homologous protein (CHOP), matrix metalloprotein-13 (MMP-13) and corresponding gene expression were detected. At the same time, compared with the blank group, the nucleus pulposus cells in the model group were smaller in volume, less in cytoplasm and worse in growth; the nucleus pulposus cells in the traditional Chinese medicine serum intervention group were slightly larger in volume, more complete in morphology, richer in cytoplasm and better in growth. Under the same action time, the ultrastructure of nucleus pulposus cells in blank group was complete, and the structures of primary and secondary processes were not broken;and the ultrastructure of model group and traditional Chinese medicine serum intervention group were damaged, the main and secondary processes were broken to varying degrees, and there was no significant difference between the two groups. At the same time, the apoptosis rate of nucleus pulposus cells in model group was higher than that in blank group, while the apoptosis rate of nucleus pulposus cells in the traditional Chinese medicine serum intervention group was lower than that inmodel group, the difference was statistically significant (P<0.05); with the increase of action time, there was no significant difference in the apoptosis rate of nucleus pulposus cells between blank group and traditional Chinese medicine serum intervention group, and the apoptosis rate of nucleus pulposus cells in model group was increased. Compared with model group, the expression of NF-κB p65, CHOP, MMP-13 were decreased and SOX9 was increased in traditional Chinese medicine serum intervention group at the same time (P<0.05);with the increase of action time, the expression of NF-κB p65, CHOP and MMP-13 were increased, and the expression of SOX9 was decreased in blank group and model group(P<0.05), and the expression level of model group was higher than that of blank group(P<0.05). Overall observation by gene expression, under the same action time, the relative quantifications of NF-κB p65, CHOP and MMP-13 in traditional Chinese medicine serum intervention group were lower than that in model group, while SOX9 was increased (P<0.05);compared with model group, the relative quantifications of NF-κB p65, CHOP and MMP-13 in blank group were decreased(P<0.05), and the relative quantification of SOX9 was increased(P<0.05);with the increase of action time, the relative quantifications of NF-κB p65, CHOP and MMP-13 of nucleus pulposus cells in blank group and model group were increased and SOX9 was decreased(P<0.05). Yishen Huoxue Tongluo() decoction can reduce the apoptosis of nucleus pulposus cells under overload and static pressure, and has the effect of delaying the degeneration of nucleus pulposus cells. Its mechanism may be related to the decrease of CHOP, MMP-13 expression and the increase of SOX9 expression by inhibiting NF-κB p65 signal pathway of nucleus pulposus cells.

Analysis of the Static Behavior of a Single Tree on a Finite Element Model.

This work deals with the innovated complex process of tree risk assessment, from precise geometrical tree shape acquisition to building and analyzing a finite element model under specified load. The acquisition of the 3D geometry of the tree was performed by means of terrestrial laser scanning. Obtained point cloud was optimized and additionally converted to a 3D CAD model, representing the bearing skeleton compound of trunk and main branches. For structural analysis purposes, a finite element model (FEM) was built in the form of beam structure fixed to the ground. Particular beams were defined by geometry, material properties of wood, and cross sections. An acoustic tomography was applied for determination of the precise cross section on investigated locations of an analysis model. Finite element analysis performed on the computational model shows the bearing capacity and deformations of the whole tree structure caused by combinations of load cases like self-weight and static equivalent of wind load. The results of the structural analysis called attention to potentially dangerous places within the tree structure with extreme node displacements or tensile stresses on beams. Thus, we observed a maximal horizontal displacement of 280.4 mm in node N34 and dangerous tensile stress in node N26, where it reaches +23.6 MPa. After filtering some beams with an abnormal cross section geometry, the finite element analysis of the whole tree structure showed the highest tensile stress of +8.8 MPa and highest compressive stress of −8.9 MPa. The suggested method can be applied generally for the prediction of potentially risky tree suspected of breakage and especially for monumental trees, where the presented method can be mostly applicable.

Sacrificial Materials and Release Etchants for Metal MEMS That Reduce or Eliminate Hydrogen-Induced Residual Stress Change

Metal microelectromechanical systems (MEMS) provide attractive properties such as high reflectivity and high conductivity. They are typically processed using an organic sacrificial layer that is removed by an oxygen ash. This enables low-temperature processing but presents other problems. For example, ashing is not applicable to metals that are susceptible to oxidation. However, if an inorganic sacrificial silicon dioxide is used, its removal commonly involves acids, exposure to which can be detrimental to metals. For example, metallic films are susceptible to hydrogen incorporation, resulting in large compressive stress. In recent work with structural tantalum and sacrificial silicon dioxide as a model system, we demonstrated that hydrogen injected during the release process can induce 1200 MPa compressive stress. This work explores AlN and Cu as alternative sacrificial materials in which release etching of structural Ta by AZ 400K developer and FeCl3 solution, respectively, is hydrogen free. Isotropic release etching is observed for Cu at room temperature and for AlN above 60 °C. In comparison with 1200 MPa, the uniaxial stress change after structure release is 80 MPa compressive with Cu and is unchanged after AlN sacrificial etch. [2021-0005]

Revealing grain structure development and texture evolution during elastic stress-assist aging of Mg–Zn alloys

The evolution of grain structure and corresponding texture development of Mg alloys under the assist of multiple physical fields are interesting and meaningful topics, and are investigated in this paper in detail. The results show that the texture development of stress free (SF) aged alloy exhibits a remarkable difference in type and intensity to those of 100 MPa tensile stress (100-TS) and 100 MPa compressive stress (100-CS) aged alloys at 160 °C. In the early stage of SF aging, preferential growth of<11-20>//ED grains give rise to the enhancement of<11-20>//ED fiber component. The increased pinning force caused by considerable precipitates at high energy boundaries reduce the boundary mobility, and therefore lead to a weak basal texture at the end of aging. Heavily activated prismatic<a> dislocations under the action of 100-TS aging facilitate the precipitation of secondary phases at grain boundaries and lattice rotation induced continuous static recrystallization (CSRX) in the early stage of aging, which contributes to a weak basal texture and the formation of non-fiber texture. Upon further aging, the preferential growth of pre-existing<10-10>//ED grains and recrystallized grains formed by CSRX contribute the enhancement of<10-10>//ED basal fiber component. In the case of 100-CS aging, the slight growth of<11-20> grains and lattice rotation caused by prismatic<a> dislocations lead to the enhancement of<11-20>//ED texture component in the early stage of aging. After long-time compressive stress aging, preferential growth of<10-10>//ED grains gives rise to the formation of<10-10>-<11-20> double fiber components.

Effects of Thermal Residual Stresses on Tensile and Interlaminar Shear Behaviors of GLARE Laminates

The residual stresses caused by curing, forming and machining process significantly affect the mechanical behaviors of composite materials, especially for super hybrid structure like GLARE (glass fiber reinforced aluminum laminates). In this work, the curing thermal residual stresses characteristics of GLARE and corresponding effects on tensile and interlaminar shear behaviors were investigated. Firstly, the characteristics of residual stresses were described by a finite element (FE) model and verified by layer removal method. Then, thermal residual stresses were incorporated into FE mechanical behavior prediction models in the form of predefined field to analyze the effects on tensile and interlaminar shear behaviors. The corresponding simulation conclusions were consistent with the experimental observations. The results indicated that there were about 40 MPa tensile residual stress in aluminum layers and 70 MPa compressive residual stress in GFRP (glass fiber reinforced polymer) layers of GLARE. Residual stresses had obvious reduction effect on the yield strength of GLARE, and the prediction accuracy was hence improved by 9%. Moreover, the failure mode of tensile tests was hardly affected by the residual stresses, but the tensile strength and the initial damage loads were reduced slightly. In interlaminar shear tests, the peak load and initial damage load were reduced by the residual stresses in the adhesive layers of GLARE, and the interlaminar shear strength was slightly influenced. An edge failure mode caused by edge effect was observed during the propagation of the delamination cracks, which was verified by interlaminar shear finite element models and SEM (scanning electron microscope) images.

Characterizing surface viscoelastic integrity of ultra-fast photo-polymerized composites: Methods development

ObjectiveResin-Composites are now available designed for polymerization using 3 s of intense light irradiation. The aim was to develop an experimental method to probe their surface viscoelastic integrity immediately following such rapid photo-cure via macroscopic surface indentation under constant stress as a function of time. MethodsTwo bulk-fill composites (Ivoclar AG) were studied: Tetric PowerFill (PFill) and PowerFlow (PFlow). Split molds were used to fabricate cylindrical {4 mm (dia) × 4 mm} paste specimens, irradiated at 23 °C at 0 mm from the top surface with a BluephasePowerCure LED-LCU, with 3 s or 5 s modes, emitting 3 and 2 W/cm2, respectively. Post-irradiation specimens were immediately transferred to an apparatus equipped with a flat-ended indentor of 1.5 mm diameter. 14 MPa compressive stress at the indentor tip was applied centrally in < 2 min and maintained constant for 2 h. Indentation (I) magnitudes were recorded in real-time (t), with I(t) data re-expressed as % indentation relative to the 4 mm specimen height. After 2 h, the indentor was unloaded and indentation recovery was monitored for a further 2 h. Parallel sets of measurements were made where indentation was delayed for 24 h. Further measurements were made with more conventional composites: EvoCeram Bulk Fill (ECeram) and Tetric EvoFlow Bulk Fill (EFlow). These were irradiated for 20 s at 1.2 W/cm2. Kinetic data were curve-fitted to exponential growth functions and key parameters analyzed by ANOVA and post-hoc tests (α = 0.05). ResultsI(t) plots looked initially similar to bulk creep/recovery: rapid deformation plus viscoelastic response; then, upon unloading: rapid (elastic) recovery followed by partial viscoelastic recovery. However, unlike multiply irradiated and stored bulk-creep specimens, the present specimens were exposed to only 3 or 5 s “occlusal” irradiation; generating “hard” surfaces. Subsequently, during the 2 h indentation, the polymer matrix network continued to harden and consolidate. Upon initial loading, I(t) reached 2–3% indentation, depending upon the formulation. Upon unloading at 2 h, elastic recovery was only ca. 1 %. Delayed loading for 24 h, generated I(t) plots of significantly reduced magnitude. Most importantly, however, the I(t) plots for ECeram and EFlow, after 20 s irradiation, showed I(t) magnitudes quite comparable to the PFill and PFlow rapid-cure composites. SignificanceMacroscopic indentation creep has been shown to be a workable procedure that can be applied to rapid-cure materials to assess their immediate surface integrity and developing viscoelastic characteristics. The applied stress of 14 MPa was relatively severe and the indentation/recovery profiles of PowerFill materials with only 3 or 5 s irradiation demonstrated comparability with their established 20 s cure siblings, evidencing the suitability of the PowerCure system for clinical application.

Residual stresses induced by laser shock peening in orthopaedic Ti-6Al-7Nb alloy

Prolonged usage can lead to fatigue failures in prosthetic implants. This is an emerging concern for the prosthesis designer and as well as for end-users. Laser shock peening (LSP) can be used to improve the life of prostheses by introducing a compressive surface stress that delays or arrests the initiation of cracks. We report measurements of residual stresses induced by LSP in a medical-grade Ti-6Al-7Nb alloy. In this paper, the LSP introduced residual stress field was characterized by using Incremental Hole Drilling (IHD) with predictive modelling using an Artificial Neural Network (ANN). The Ti-6Al-7Nb samples were processed by a pulsed Nd: YAG laser with laser energy of 3 J, 5 J and 7 J with overlaps of 33%, 50% and 67%. The IHD results show that a range of −42 MPa to −516 MPa compressive residual stresses are formed at the near surface. The residual stress value and affecting layer depth are proportional to laser energy and overlap. What is more, a gradient descent learning algorithm was employed in ANN prediction. The microhardness, laser energy, overlap and depth are set as input parameters while the residual stresses are output. The predicted results have a good agreement with the experimental data with accuracy of 96.16% and 95.16%. It proves that ANN is applicable in LSP residual stress simulation when the experimental data is limited. The work in this paper enables to have subsequent predictions of fatigue life of implants via residual stress fields for future applications.