Maximum Compressive Stress Research Articles

Bone-like apatite formation in biocompatible phosphate-crosslinked bacterial cellulose-based hydrogels for bone tissue engineering applications

Addressing major bone injuries is a challenge in bone regeneration, necessitating innovative 3D hydrogel-based therapeutic approaches to enhance scaffold properties for better bioactivity. Bacterial cellulose (BC) is an excellent scaffold for bone tissue engineering due to its biocompatibility, high porosity, substantial surface area, and remarkable mechanical strength. However, its practical application is limited due to a lack of inherent osteogenic activity and biomineralization ability. In this study, we synthesized bone-like apatite in biocompatible BC hydrogel by introducing phosphate groups. Hydrogels were prepared using fibrous BC, acrylamide (AM), and bis [2-methacryloyloxy] ethyl phosphate (BMEP) as a crosslinker through free radical polymerization (P-BC-PAM). P-BC-PAM hydrogels exhibited outstanding compressive mechanical properties, highly interconnected porous structures, good swelling, and biodegradable properties. BMEP content significantly influenced the physicochemical and biological properties of the hydrogels. Increasing BMEP content enhanced the fibrous structure, porosity from 85.1 % to 89.5 %, and compressive mechanical strength. The optimized hydrogel (2.0P-BC-PAM) displayed maximum compressive stress, toughness, and elastic modulus at 75 % strain: 221 ± 0.08 kPa, 24,674.2 ± 978 kPa, and 11 ± 0.47 kPa, respectively. P-BC-PAM hydrogels underwent biomineralization in simulated body fluid (SBF) for 14 days, forming bone-like apatite with a Ca/P ratio of 1.75, similar to hydroxyapatite. Confirmed by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field-emission scanning electron microscopy (FE-SEM), this suggests their potential as scaffolds for bone tissue engineering. MC3T3-E1 osteoblast cells effectively attached and proliferated on P-BC-PAM. In summary, this study contributes insights into developing phosphate-functionalized BC-based hydrogels with potential applications in bone tissue engineering.

A simulation modeling methodology considering random multiple shots for shot peening process

Abstract Shot peening (SP) process is a typical surface strengthening process for metal and metal matrix composites, which can significantly improve the fatigue life and strength. The traditional SP simulation model falls short as it only takes into account one or a few shots, proving insufficient for accurately simulating the entire impact process involving hundreds of shots. In this study, a random multiple shots simulation modeling methodology with hundreds of random shots is proposed to simulate the impact process of SP. In order to reduce the simulation error, the random function Rand of MATLAB is used to generate the shot distributions many times, and the shot distribution closest to the average number is selected and the three-dimension parametric explicit dynamics numerical simulation model is built using ABAQUS software. Orthogonal experiments are carried out to investigate the influences of shot diameter, incident impact velocity, and angle on the residual stress distribution, roughness, and specimen deformation. Results showed that the average relative errors of maximum residual compressive stress, roughness, and deformation of specimen between simulation model and experimental value are 30.99, 16.14, and 16.73%, respectively. The primary factors affecting residual stress and deformation is shot diameter, and the main factor affecting roughness is impact velocity.

Influence of gradation in the reinforcement particles on the interfacial microstructure and mechanical properties of functionally graded composites

In this research, Al6061 alloy-based Functionally Graded Composites (FGCs) were fabricated by hot pressing which is composed of 7 layers with different proportions of Al2O3 reinforcement particles. The addition of Al2O3 particles is gradually increasing in the other layers from top to bottom (Layer 1 - Pure Al6061 alloy, Layer 2–5 wt% Al2O3, Layer 3–10 wt% Al2O3, Layer 4–20 wt% Al2O3, Layer 5–30 wt% Al2O3, Layer 6–40 wt% Al2O3, Layer 7–50 wt% Al2O3). Moreover, three different Al2O3 particle sizes (8, 16 and 32 µm) were used to fabricate three sets of FGCs. Reciprocating wear studies were performed and the result shows that the FGC with 8 µm Al2O3 particle size shows 85.5% improved wear resistance. Further, various wear mechanisms were investigated and finally compressive strength analysis proved that the homogenous distribution of Al2O3 particles in the FGC with 16 µm Al2O3 particle size helps achieve the maximum compression stress of 476.04 MPa compared with other FGCs.

Effect of different modified lignins on the properties of xylan composite hydrogels

AbstractTo improve the mechanical properties of hemicellulose hydrogel, a green, adjustable mechanical property, high swelling ratio (SR) composite hydrogel was successfully prepared by using modified lignin as a reinforcing agent. The structure and characteristics of the composite hydrogels were investigated by TGA, FTIR, SEM, rheological analysis, and SR. It can be found that the modified lignin could significantly improve the mechanical properties of the composite hydrogels. The maximum compressive stress of unmodified lignin hydrogel was 61.72 kPa and the compressive deformation was 75%. Compared with the unmodified lignin hydrogel, the mechanical properties were significantly improved, with the maximum compressive stress of the modified lignin hydrogel was 145.2 kPa and the compressive deformation was up to 90%. After adding modified lignin, the SR of the as‐prepared hydrogel was up to 155.17 g/g, which was much higher than that of unmodified lignin hydrogel (105.79 g/g). The composite hydrogel had good antioxidant properties, and the free radical removal rate can reach 85.3%, which is twice as much as that without the modified lignin. With cost‐effective lignin as a reinforcing agent, the as‐prepared hemicellulose hydrogel with adjustable mechanical properties is favorable for great application potential.

Research on the strengthening and retrofitting methods of existing wind turbine foundations with embedded‐ring

AbstractHigher demand for the load‐bearing ability of supporting foundations is required if its upper wind turbine is substituted by a larger one. Presently, there is a lack of strengthening and retrofitting methods for existing wind turbine foundations. A combined‐connection retrofitting method by adding anchor bolts to the existing wind turbine foundation with embedded‐ring is prompted in this study. Furthermore, a strengthening measure by adding a stiffening beam, expanding the foundation plate, and adding rock bolts to increase the ability to resist basal bending moment is proposed. Finite element analysis is conducted to analyze the effectiveness of the proposed strengthening and retrofitting methods for a 2 MW wind turbine foundation. The result shows that the peak stress of embedded‐ring is decreased by 36% by using the internal combined‐connection, and the peak tensile stress of concrete is reduced by 4.0%. When the external combined‐connection is adopted, the peak stress of the embedded‐ring is reduced by 69.3%, and the peak tensile stress of the concrete is reduced by 26.0%. It illustrates that the external combined‐connection method is more effective to increase the load‐bearing capability of the connection than the internal combined‐connection method. Additionally, the proposed strengthening measure by adding a stiffening beam, expanding the foundation plate, and adding rock bolts is effective to decrease the responses of foundation. The maximum tensile stress of concrete, the maximum compressive stress of concrete, and the maximum stress of the embedded‐ring are reduced by 19.8%, 31.3%, and 22.2%, respectively. To summarize, the proposed strengthening and retrofitting methods are capable of ensuring the safety and stability of higher‐power wind turbine operation.

Study on the microstructure and properties of rail cladding layer after laser quenching

The U71Mn rail surface processed by laser cladding suffers from large rough area and grain size at the top of cladding layer as well as residual tensile stress in the cladding layer. This paper proposes to remanufacture rail surface by combining laser cladding with laser quenching. The experiment results show that the quenched cladding layer was transformed from dendritic to equiaxed crystals at a specific quenching depth, with refine grains. Laser quenching results in dense martensite structure on the surface of the cladding layer. The hardness of the cladding layer after quenching is about 895 HV0.2, 18 % higher than that before quenching. The wear rate after quenching is 0.713 μm3/(N∙μm), with a decline of 22.3 % compared with that before quenching 0.918 μm3/(N∙μm), indicating that wear resistance is improved after laser quenching. In addition, the cladding layer after quenching exhibits stronger corrosion resistance than that before quenching, and internally it is transformed from tensile stress to compressive stress, with a maximum residual compressive stress of about −486 MPa, which endows the rail with stronger fatigue performance and longer service life.

Numerical and experimental study of a segmentally prefabricated orthotropic steel–ultra-high-performance concrete composite deck for long-span cable-stayed bridges

Utilizing the high strengths, toughness, and durability of ultra-high-performance concrete (UHPC), a segmentally prefabricated orthotropic steel–UHPC composite deck (POSUCD) system has been developed for long-span cable-stayed bridges. The deck system combines an orthotropic steel deck (OSD) with a reinforced UHPC layer using notched perfobond strips (NPBLs). The UHPC layer is prefabricated onto the OSD of the girder segment in the factory to form the POSUCD. After the precast UHPC layer is cured, the girder segments are transported to the bridge site and assembled. The precast UHPC layers are then connected via transverse wet joints before tensioning stay cables. Against the background of the Danjiangkou Reservoir Bridge with a main span of 760 m, finite element (FE) analysis was conducted to examine the stress state and flexural tests were carried out on local full-scale models to verify the feasibility of POSUCD. The results show that the prefabricated UHPC layer reduces the maximum static compressive stress of the steel deck in the girder system by 21%, and the stress ranges at fatigue-prone details of the steel deck are decreased by 28%–90% compared to traditional OSDs with asphalt overlay. Since the prefabricated UHPC layer helps withstand dead axial load in the main girder, the high compressive strengths of UHPC can be utilized more effectively than in deck systems with UHPC only used as a cast-in-situ overlay to resist vehicular wheel loads. The transverse wet joint interfaces were identified as the weakest aspect of the POSUCD, whether under tension or compression; however, their nominal flexural strengths along the longitudinal direction meet the required design standards. The shear resistance of NPBLs was also well confirmed by the minimal interfacial slip on the specimen when it reached the ultimate capacity under positive bending moment.

The effect of temperature on the mechanical behavior of Berea sandstone under confining pressure: experiments

For the first time, axial and circumferential (diametral) strains are measured directly on Berea sandstone cylindrical samples at different high temperatures as a function of confining pressure. The maximum compressive principal stress was in the direction perpendicular to the bedding plane. Tri-axial compression tests have been conducted under confining pressures ranging from atmospheric pressure to 12,000 psi “82.73 MPa” (gage), and the temperature was varied from room temperature (RT) to 250°F (121.11 °C). In all the experiments, specimens are dry, and no pore pressure is applied. Uniaxial axial force (100 lbs/min or 444.82 N/min) and strains in the three directions (varepsilon1, varepsilon2, varepsilon3) is directly measured from the strain gages mounted on the specimen; hence the study reflects the behavior of the Berea sandstone up to the initiation of the failure only. The experimental observations involving yield, failure, transition from brittle to ductile behavior, and their dependence on temperature and confining pressure are presented. Parameters like ductility and dilatancy (reflecting volumetric behavior before failure) and their variation with temperature and confining pressure are given. The initial yield and failure of Berea sandstone are presented in terms of the generalized von-Mises criteria, i.e., variation of octahedral shear stress () with the mean stress. The loads at yield and failure are found to decrease with increasing temperature and augment with increasing confining pressure. The ductility and dilatancy reduction are computed using measured strains with increasing temperature. With an increase in temperature, the volume decreases first, partly due to the initial closure of micro cracks and voids, then increases due to generation of additional microcracks and voids (damage). There is less volume decrease in the uniaxial test response at higher temperature as compared to the corresponding ambient temperature response. A monotonic increase in the octahedral shear stress at yield and failure is observed with increasing confining pressure.

Tectonic stress regime and faulting style analysis due to sequence of earthquakes in Western Nepal

The current study examines the source mechanism and the regional stress regime of a sequence of moderate-sized earthquakes between October 2022 and October 2023. ISOLA-GUI-a Matlab coded program has been used to estimate Moment Tensor Solution to understand the source mechanisms of the earthquakes in the region. The earthquakes are recorded at the broadband station arrays of the regional seismological network around the Tehri region, installed by the Indian Institute of Technology Roorkee in India. The study focuses on earthquakes with epicentral distances of less than 10°. The investigation aims to comprehend the source process by estimating the focal mechanisms utilizing regional waveform data and then inverting the acquired focal mechanism of these earthquakes to comprehend the active stress regime in the region. The obtained source mechanism reveals a predominance of a double-couple mechanism in faulting and hence, suggests that the majority of the seismic energy is released through shear motion along a defined fault plane. By revealing the complex interaction of geological forces in the Himalayan belt, this investigation will help us to better understand the distribution of stress and deformation patterns beneath the Earth's crust. The main emphasis lies on assessing stress distribution through the utilization of earthquake focal mechanism data and employing the Stress Inversion technique using the WinTensor program. The result of stress inversion suggests that the maximum compressive stress is plunging horizontally, while the minimum compressive stress is oriented vertically. Hence revealing a thrust stress regime in Western Nepal, trending in the NNE- SSW direction corroborating the ongoing tectonic processes associated with the collision of the Indian plate with the Eurasian plate.

Construction stability analysis of intersection tunnel in city under CRD method

The construction of city intersection tunnels cause multiple redistribution of surrounding rock stress, resulting in the engineering disasters such as instability in existing tunnels and collapses of ground buildings. To mitigate formation disturbances effectively, the Center Cross Diagram (CRD) method is employed in city tunnel construction. In this study, a numerical model for a city intersection tunnel is developed based on an underground circular roads project in Chongqing, China, to analyze the safety of the tunnel structure and the stability of ground buildings under the CRD method. The numerical simulation results obtain that the excavation of pilot-tunnel ➃ will reduce the surrounding rock stress and control the rock strata subsidence, and reveal that the excavation of pilot-tunnel ➃ is the key step of CRD method. The maximum compressive stress and tensile stress of surrounding rock first increase and then decrease during the excavation of pilot-tunnels ➀, ➁, ➂, and ➃. Simultaneously, the deformation of the ground building experiences a slow initial increase followed by a rapid rise before stabilizing. Furthermore, the excavation of the main tunnel leads to an increase of 0.73, 0.35, and 0.52 times in the vault subsidence value, left haunch convergence value, and right haunch convergence value of branch tunnel #1, respectively. Finally, the convergence process of branch tunnel #1 is discussed through the in-situ monitoring, which is divided into three stages: rapid deformation, deceleration deformation, and stable deformation. The final horizontal convergence value and subsidence value of cross-section K0+360 are respectively 84% and 78% of those at cross-section K0+395.

Biomechanical explanation of W-plasty effectiveness using a finite element method approach

The finite element method has often been used to assist analyzing local flaps in terms of deformation and stress measurements as it takes into account complex skin properties. We, herein, present an isotropic two-dimensional finite element skin model applied to the W-plasty method to demonstrate that the good outcomes of W-plasty should be attributed to the geometry itself, as it generates lower stresses. The skin was modeled as a two-dimensional (2D) planar geometry. The model was created and solved as a plane stress problem. The model was based on simulation of the loading and stitching of W-plasties of various angles. Each central triangular flap was segmented in nine triangular elements. The stitching was modeled with one suture at the top of each triangular flap with the center of the opposite corner. X- and Y-axis stresses and shearing stresses Txy in the elements involved in the broken stitching line, show lower stresses than the elements behind the stitching line. Interestingly, in the triangular flaps, the stresses were clearly lower than those of their neighboring areas. The maximum compressive stresses in the 2D model we used, correspond to the dog ears. We conclude that the effectiveness of W-plasty should be attributed not only to the scar orientation in relation to the relaxed tension skin lines but also to the special design of the triangular flaps used. This finding assists the general understanding of the method and should be taken into account by the clinician during flap designing.

Processing of Bimetallic Inconel 625-16Mo3 Steel Tube via Supercritical Bend: Study of the Mechanical Properties and Structure.

Incineration is currently the standard way of disposing of municipal waste. It uses components protected by high-temperature-resistant layers of materials, such as Inconel alloys. Therefore, the objective of the current paper is to study the mechanical properties and structure of a bimetallic Inconel 625-16Mo3 steel tube. The Inconel 625 layer was 3.5 mm thick and was applied to the surface of the tube with a wall thickness of 7 mm via the cold metal transfer method. The bimetallic tube was bent using a supercritical bend (d ≤ 0.7D). This paper is focused on the investigation of the material changes in the Inconel 625 layer areas influenced by the maximum tensile and compressive stresses after the bend. The change in layer thickness after the bend was evaluated and compared to the non-deformed tube. In addition, the local mechanical properties (nanohardness, Young modulus) across the indicated interfacial areas using quasistatic nanoindentation were investigated. Subsequently, a thorough microstructure observation was carried out in areas with maximum tensile and compressive stresses to determine changes in the morphology and size of dendrites related to the effect of tensile or compressive stresses induced by bending. It was found that the grain featured a stretched secondary dendrite axis in the area of tensile stress, but compressive stress imparted a prolongation of the primary dendrite axis.

The mechanism of the effect of dual-sided waterjet peening on the surface integrity and fatigue performance of 12 mm thick Inconel 718

This study aims to explore the mechanisms of residual stress formation and the effects on fatigue performance of 12 mm thick Inconel 718 under single-sided one-pass, two-pass, and dual-sided two-pass waterjet peening. Finite element models for waterjet peening and fatigue analysis were established using ABAQUS and Fe-safe, respectively. The study focused on analyzing the residual stresses, surface roughness, and fatigue cycle numbers of Inconel 718 after waterjet peening. The results were validated by conducting waterjet peening experiments and post-peening fatigue tests to ensure their reliability. The research findings indicated that the induced residual compressive stress was most effective with dual-sided two-pass waterjet peening, followed by single-sided two-pass and single-sided one-pass waterjet peening. Among them, after WJP-290 mm/s peening, the maximum residual compressive stresses for dual-sided two-pass, single-sided two-pass, and single-sided one-pass were 718.6, 906.4, and 1042.7 MPa, respectively. The maximum residual compressive stress depth after WJP-230 ∼ 290 mm/s peening was positively correlated with the jet velocity. Surface deterioration occurred after WJP-350 mm/s peening, leading to a significant reduction in the induced residual stress effect. After WJP-230 mm/s peening, the specimen exhibited an overall residual compressive stress of about 507.7 MPa at a depth of approximately 13.1 μm, with a total residual compressive stress depth of about 34.8 μm. Increasing the jet velocity to 290 mm/s shifted the maximum residual compressive stress depth to about 27.2 μm, with a maximum residual compressive stress increase of about 535 MPa, reaching 1042.7 MPa. At the same time, the overall residual compressive stress depth also increased to 39.9 μm. After increasing the jet velocity to 350 mm/s, a maximum residual compressive stress of about 708.7 MPa was induced at a depth of approximately 11.9 μm. The surface roughness, average roughness, and maximum roughness of the specimens were positively correlated with the jet velocity, with the most significant morphological changes occurring at the edges of the waterjet peened area, which coincided with the region prone to fatigue fracture in the cyclic fatigue tests. Increasing the number of jet impacts had a “peak-to-valley” effect on the surface of the peened specimens, making the surface flatter. The specimens peened with dual-sided waterjet showed significantly higher fatigue cycle numbers than those peened with single-sided waterjet. After WJP-230 mm/s peening, the fatigue life at stress levels of 93, 132, and 150 MPa was approximately 2,182,922, 258,000, and 56,575 cycles, respectively, which increased by about 399 %, 274 %, and 218 % compared to single-sided one-pass peening and by about 165 %, 139 %, and 125 % compared to single-sided two-pass peening.

Effects of peening velocity and coverage on peen forming

As an effective forming technique, peen forming is widely used in sheet metal components with large dimensions. However, the production efficiency is seriously limited as several peening tests are required before actual production. To address this issue, a numerical simulation method of peen forming was proposed. In this work, an elastoplastic peening finite element model was developed to study the relations between process parameters and forming effects. A set of peening forming tests with different coverages and velocities were conducted to validate the model. Results indicate that the maximum errors of converted arc height and forming curvature are less than 5% and 14%, respectively. Additionally, the saturation phenomenon can be observed as the peening coverage reaches 60%. The corresponding depth of the maximum compressive residual stress varies almost linearly with shot velocity. In addition, the best peening forming effect can been achieved a radius of curvature as low as 500 mm, which peening velocity selected 60 m/s.

Mapping of stress and structure controlled upper crustal anisotropy in Kumaon-Gharwal Himalaya

Shear wave splitting analysis of local earthquakes provides valuable insights into the structure and stress controlled upper crustal anisotropy signatures. We examine these signatures at the Kumaon-Garhwal Himalaya and provides an excellent example of anisotropic crustal structure in the ongoing continent-continent collision settings between Indian and the Eurasian plates. A total of 256 local earthquakes were selected for the analysis (1.0 ≤ M ≤ 5.4) between January 2017 and February 2021, recorded at a dense network of 51 broadband stations. The result indicates the observed crustal anisotropy is parallel to stress-aligned micro-cracks far from the major Himalayan fault zones and structure parallel near the fault zones. The dominant fast polarization directions (FPD) in the Inner Lesser Himalaya (ILH) and Higher Himalaya, are consistent with the maximum compressive horizontal stress directions (SHmax), essentially influenced by the local stress field. Whereas in the Outer Lesser Himalaya (OLH) and Sub Himalaya, fast directions are sub-parallel to the structural trends, suggesting that the anisotropy is associated with the shear fabric from recent deformation episodes related to structural induced anisotropy. The computed normalized delay times show a mean value of 1 ms/km, within the OLH and Sub-Himalaya, while in ILH and Higher Himalaya, this value increases up to 5.3 ms/km. The associated crack densities are 0.0038 and 0.0207, with shear wave velocity anisotropy of 0.38% and 2.07% respectively. Significant scatter within the depth range of 10–15 km is observed in normalized delay times, suggesting the source of anisotropy within the upper crust.

A numerical study on thermal bonding with preheating technique for polypropylene microfluidic device

Abstract This study presents a method for producing microfluidic chips from polypropylene using a pre-heated bonding area and thermal bonding technology. ANSYS was utilized to investigate the effects of bonding parameters and microchannel deformation and predict the bonding strength. Results show that careful control of these parameters is critical to achieve a strong and durable bond between the microfluidic chip layers. Higher bonding temperatures were found to lead to greater microchannel deformation, with deformation increasing significantly, as the temperature approached the material’s melting point. Increased bonding pressure after 1 MPa and a time of 300 s also led to greater microchannel deformation. The study’s analysis of stresses revealed that the maximum principle compressive stress on the edges of the bonding area increased significantly with pressure. Tensile testing showed that bonding strength was near failure at a tensile force of 5,500 N, indicating a bonding strength close to 1.5 MPa.

The Influence of Construction Methods on the Stability of Tunnels and Ground Structures in the Construction of Urban Intersection Tunnels

The construction of intersection tunnels in urban induces multiple stress redistribution in the surrounding rock, leading to engineering disasters such as instability in rock strata during excavation, disturbance of supporting structures in existing tunnels, and subsidence of ground adjacent buildings. Employing an appropriate construction method is crucial in circumventing excessive stress concentrations and large-scale rock strata subsidence, making it a key aspect of urban intersection tunnel engineering. In this paper, a numerical model for an urban intersection tunnel is developed based on an underground circular road project in a central business district. We conduct numerical simulations of the excavation processes using the full-section method, step method, and center cross diagram (CRD) method, respectively. The findings indicate that while different construction methods do not change the variation trends of surrounding rock stress and displacement, adjacent ground building deformation, and existing tunnel convergence, they affect the variation degrees. The maximum compressive and tensile stresses in the surrounding rock caused by the CRD method are the smallest, which are 3.56 MPa and 0.76 MPa, respectively. The maximum arch subsidence affected the amount, and horizontal convergence affected the amount of branch tunnel #1 caused by the CRD method are the smallest too, which respectively are 1.428 mm and 0.931 mm. The foundation subsidence and overall inclination of the ground building resulting from the three methods are identical. Then, we discuss the construction safety of the three methods and obtain the influence order on construction stability, which is as follows: full-section method > step method > CRD method. It is concluded that the CRD method is the most suitable for urban intersection tunnel engineering in terms of safety. This study could offer valuable insights for selecting construction methods in urban intersection tunnel engineering and provide a foundation for evaluating the safety and stability of tunnel construction.

Improvement of the high-temperature oxidation resistance of 254SMo using ultrasonic strengthening grinding

This paper used ultrasonic strengthening grinding (USGP) to process 254SMo welded joints. The mechanical properties of processed and unmachined samples of welded joints, including grain size, dislocation, microhardness, residual stress, and high-temperature oxidation resistance at 900 °C, were investigated. The results indicate that the grains of the processed samples exhibit significant refinement and a high dislocation density and that the maximum microhardness and residual compressive stress are 392.5 HV0.3 and −633.44 MPa, respectively. In addition, the processed sample exhibits excellent oxidation at high temperatures. At 900 °C, the mass gain of the USGP-processed sample is reduced by 47.5 % compared to its mass gain prior to processing. These results highlight the potential of this method in improving the high-temperature resistance of various mechanical components, particularly those made from special materials.

Non-contact measurements of residual stress distribution and grain size in titanium alloys with laser ultrasonic system

In this study, a laser ultrasonic method is proposed for nondestructive non-contact measurement of both the residual stress depth profile and grain size in Ti-6Al-4 V alloy processed by warm shot peening (WSP). The method utilizes a pulsed laser to generate a surface acoustic wave (SAW) along the cross-section of the sample, and a laser interferometer to detect SAW signals. Laser ultrasonic measurements were performed on the samples treated by WSP at different temperatures (32, 100, 200 and 300 °C). A theoretical model for calculating the residual stress profile and a model to correlate the center frequency shift and the mean grain size of the sample were presented. The results obtained by the laser ultrasonic method were compared with those obtained by X-ray stress measurement, center-hole drilling (CHD), and electron backscattering diffraction (EBSD). The proposed method can measure and locate the maximum compressive residual stress (CRS) in a peened surface layer with a high spatial resolution of approximately 30 µm, allowing for precise extraction of the residual stress profile. This method can also provide an estimation of the grain size through the same experiment. The developed method is promising for the quick and nondestructive measurement of the residual stress profiles and grain size of surface treated metallic materials.

Fatigue behaviors of ultrasonic surface rolling processed AISI 1045: The role of residual stress and gradient microstructure

In the study, AISI 1045 steel were treated by ultrasonic surface rolling processing (USRP) with different parameters in terms of coverage rate. The gradient structures characterized with refined polished surface, the sub-surface nano-lamellar microstructure with a maximum compressive residual stress of 453.4 MPa was obtained, which shall be responsible to the superior fatigue properties to the pristine. Furthermore, the comparative investigation of fatigue behavior demonstrates that the surface roughness has the pronounce effects on the resistance to crack initiation, though the excessive USRP with the surface roughing may result in the premature crack growth; in contrast to the gradient microstructure, the compressive residual stress may delay effectively the incubation and increase the growth resistance of the physically short crack. Besides, the benefit of gradient microstructure is relatively limited in the resistance of fatigue short crack propagation.