Residual Stress Concentration Research Articles

Numerical and experimental studies of the influence of curing and residual stresses on buckling in thin-walled, CFRP square-section profiles

The study provides the first comprehensive experimental and numerical study of thin-walled, carbon fibre square-section columns subjected to static compression. The profiles were manufactured from unidirectional prepreg tape of Hexcel AS4 high-strength carbon fibres in HexPly® 8552 thermoset resin with ply angles [45/−45/45/−45]s. The dimensions of the columns were: (height × width × length) 80 mm × 80 mm × 240 mm and the wall thickness was 0.92 mm.Advanced Finite Element Models (FEM) of the residual stresses generated during production were used as a basis for simulations of static compression. The deformation predicted by these models showed excellent agreement with 3D scans of the columns. These results also highlighted the residual stress concentrations generated at sample corners during production.It was found that the residual stresses from the autoclaving process significantly enhance the buckling load performance (by ~35%) and that the models provide an effective comparison with the experimental results (<10% error). This demonstrates the importance including residual stresses in FEM of buckling, but also highlights residual stress tailoring as a route to significantly enhance the buckling load capacity of carbon fibre systems used in industrial applications.

COMPUTATIONAL MICROSTRUCTURE-BASED ANALYSIS OF RESIDUAL STRESS EVOLUTION IN METAL-MATRIX COMPOSITE MATERIALS DURING THERMOMECHANICAL LOADING

A technique for computer simulation of three-dimensional structures of materials with reinforcing particles of complex irregular shapes observed in the experiments is proposed, which assumes scale invariance of the natural mechanical fragmentation. Two-phase structures of metal-matrix composites and coatings of different spatial scales are created, with the particles randomly distributed over the matrix and coating computational domains. Using the titanium carbide reinforcing particle embedded into the aluminum as an example, plastic strain localization and residual stress formation along the matrix-particle interface are numerically investigated during cooling followed by compression or tension of the composite. A detailed analysis is performed to evaluate the residual stress concentration in local regions of bulk tension formed under all-round and uniaxial compression of the composite due to the concave and convex interfacial asperities.

Numerical simulation of the effect of ultrasonic impact treatment on welding residual stress

Ultrasonic impact treatment (UIT) is an effective method that has been widely applied in welding structure to improve the fatigue properties of materials. It combines mechanical impact and ultrasonic vibration to produce plastic deformation on the weld joints surface, which introduces beneficial compressive residual stress distribution. To evaluate the effect of UIT technology on alleviating the residual stress of welded joints, a novel numerical analysis method based on the inherent strain theory is proposed to simulate the stress superposition of welding and subsequent UIT process of 304 stainless steel. Meanwhile, the experiment according to the process was carried out to verify the simulation of residual stress values before and after UIT. By the results, optimization of UIT application could effectively reduce the residual stress concentration after welding process. Residual tensile stress of welded joints after UIT is transformed into residual compressive stress. UIT formed a residual compressive stress layer with a thickness of about 0.13 mm on the plate. The numerical simulation results are consistent with the experimental results. The work in this paper could provide theoretical basis and technical support for the reasonable evaluation of the ultrasonic impact on residual stress elimination and mechanical properties improvement of welded joints.

Study of the influence of shape, orientation, and size of AlN in the γ′-free zone of nickel-based superalloys by microstructure-based numerical models

The influence of internal nitride particles in the γ′-free zone of nickel-based superalloys did not receive further attention, despite their significant impact on the overall mechanical properties. Based on theearlierexperimental results, aluminum nitride (AlN) formed in several areas under the oxide layerthat worsened the mechanical properties of a single-crystal nickel-based superalloy. The effect of size, morphology, and orientation of aluminum nitride particles on the residual stress was studied by numerical models based on the microstructure. The numerical results showed that the morphology of the internal nitride particles has a considerable effect on the residual stress field. A sharp transition of residual stress from tensile to compressive was observed across the AlN particle boundary. Although the shape parameters of block AlN particles such as roundness (R) and sphericity (Sph) had a significant effect on the residual stress concentration, the maximum residual stress had settled in acicular AlN particles at a pointed particle corner. The residual stress concentration increases with a decrease in pointed corner degree for those particles. Therefore, the acicular AlN particles increase the residual stress concentration up to 1.5 times more than that around AlN blocks. Furthermore, residual stress increased and became more interfering due to the affinity of the AlN particles in the γ′-free zone. Numerical simulations provided more insight into the degrading effect of aluminum nitride particles on the mechanical properties of the nickel-based superalloys.

Bonding and Thermal-Mechanical Property of Gradient NiCoCrAlY/YSZ Thermal Barrier Coatings with Millimeter Level Thickness

The thermal insulation properties of thermal barrier coatings (TBCs) can be significantly improved with increasing the coating thickness. However, due to the weak bonding of high-thickness TBCs, the low reliability and short lifetime greatly limits their application under some severe operating conditions. In this study, a novel and high-efficiency synchronous dual powder feeding method is used to deposit a series of gradient NiCoCrAlY/YSZ coatings with millimeter level thickness. The tensile bonding strengths and residual stress state of coatings are evaluated in order to explore the effect of thickness on the bonding strength of coatings. The results suggested that, due to some micro-convex structure at the “GC/TC” interface and inside “GC” layer, the bonding strength of 1000-μm-thickness gradient NiCoCrAlY/YSZ TBCs with the 4:6 and 2:8 hybrid ratios is over 44 MPa compared to the common TBCs. The fracture position gradually shifts from NiCoCrAlY bond coat to NiCoCrAlY/YSZ transition zone and finally to the YSZ top coat owing to the different position of residual stress concentrations. After thermal cycling tests, the 1000-μm-thickness gradient coating exhibits a higher thermal cycling life. Some coarse cracks initiate and propagate at the bottom region of TBCs, which is mainly due to thermal expansion mismatch stress that finally results in the failure of the gradient coating between the “BC” layer and the substrate.

A Segmented‐Target Sputtering Process for Growth of Sub‐50 nm Ferroelectric Scandium–Aluminum–Nitride Films with Composition and Stress Tuning

Harnessing the recently discovered ferroelectricity in scandium aluminum nitride (ScxAl1−xN) for the realization of integrated electronic and electromechanical devices requires a low‐temperature growth process that enables versatile control over film thickness, stoichiometric composition, and stress. Herein, a reactive magnetron sputtering process that enables extreme scaling of film thickness and tuning of composition and residual stress is reported on. Highly crystalline ScxAl1−xN films with thicknesses of over 25–250 nm with scandium concentrations of over 22–30 at% are sputtered using a segmented target created from scandium and aluminum tiles. The residual stress in the films is widely tuned from highly compressive to tensile using a pressure‐ and gas‐flow‐independent approach based on adjusting the electrical termination of the targets. The crystallinity, texture, and ferroelectric characteristics are measured for ScxAl1−xN films with different thicknesses, compositions, and residual stresses. The results highlight the consistent crystallinity and ferroelectric properties despite extreme thickness miniaturization to sub‐50 nm, and the large dependence of the coercive field on the residual stress and Sc concentration.

Influence of welding sequence on residual stress evolution in Incoloy825/X52 bimetallic clad plate butt-welded joints

Residual stress controlling is crucial for the service security of weldments. In this work, experimental measurements and finite element method were integrated to study the influence of welding sequence imposed on residual stress distribution of Incoloy825/X52 bimetallic clad plate joints. And the residual stress evolution law inside bimetallic clad plate joints during multi-layer and multi-pass welding was clarified. Results showed that the highest residual stress concentration was always generated in the translation layer and its surrounding region once the base, transition and flyer seam layer were all finished welding no matter what sequence was adopted. Welding sequence did have a significant influence on peak value and areas of both internal and surficial high-stress region of bimetallic clad plate joint.

Effect of local equivalent stress on fatigue life prediction of carburized Cr-Ni alloy steel based on evaluation of maximum crack sizes

The fatigue assessment methods considering surface strengthening process were proposed through experimental investigation of fatigue properties of carburized Cr-Ni alloy under stress ratios of 0 and 0.3. Interior-failure is caused by continuous debondings of refined grains due to stress concentration around interior-inclusion, while surface-failure is caused by grain dislocation slip around surface-inclusion. In view of the effect of local equivalent stress (residual stress, mean stress and stress concentration around the inclusion), the PRx-S-N curves of carburized Cr-Ni alloy steel were constructed based on the prediction of crack characteristic sizes by Generalized Extreme Values (GEV) and Generalized Pareto (GP) distributions under different cumulative probabilities, and the comparison shows that GP distribution can predict the fatigue strength better than GEV distribution. The fatigue life prediction models can be established by GP distribution for surface and interior failures, and the predicted results are in good agreement with the experimental results.

Fatigue life prediction of 2524‐T3 and 7075‐T62 thin‐sheet aluminium alloy with an initial impact dent under block spectrum loading

AbstractThis paper presents a fatigue life prediction model of post‐impacted sheets considering the effects of dent size and stress ratio. Low‐velocity impact tests at four different impact energies were performed on specimens cut from sheets of 2524‐T3 and 7075‐T62 aluminium alloy. Following the impact tests, static tensile and uni‐axial constant amplitude and block spectrum fatigue experiments were conducted. Numerical models were generated to determine the initial residual stress patterns, residual stress relaxation, and stress concentration factors around the impact dent. The S‐N curves and corresponding stress concentration factors and relaxed residual stresses of three of the post‐impacted specimens were used to determine the model parameters. Good agreement was achieved between the predictions and experimental results, and it has been demonstrated that the fatigue life prediction model can effectively simulate the effects of residual stress, stress concentration, and stress ratio on fatigue damage for post‐impacted thin sheet aluminium alloy materials.

In vitro and in vivo studies of biodegradable Zn-Li-Mn alloy staples designed for gastrointestinal anastomosis

Zn-0.8 wt.% Li-0.1 wt.% Mn wire with the diameter of 0.3 mm was fabricated and further processed into gastrointestinal staple, and its in vitro and in vivo biodegradation behavior and biocompatibility were studied systematically. The experimental Zn-Li-Mn alloy staple could deform from the original U-shape to B-shape without fracture, indicating its good mechanical property. Due to the residual stress concentration caused by anastomosis deformation, the feet and leg arc part of the staple were more prone to degradation. The Zn-Li-Mn alloy staple sustained integrity after immersion in Hanks’ solution and simulated gastric fluid (SGF) for 28 days, and the degradation rate in SGF was about 4 times of that in Hanks’ solution. Furthermore, Zn-Li-Mn alloy staples were utilized for gastrointestinal anastomosis in pig models, with clinically-used titanium alloy staples as a comparison. No anastomotic leakage and severe inflammation were observed after operation. The Zn-Li-Mn alloy staple maintained mechanical integrity within 8 weeks’ implantation. The gastrointestinal tissue healed after 12 weeks, and no obvious side effects were detected during the whole implantation period, demonstrating the good biocompatibility of Zn-Li-Mn alloy staple. Thus, Zn-Li-Mn alloy staple fabricated in this work displayed the promising potential in the gastrointestinal anastomosis.

Lean duplex TRIP steel: Role of ferrite in the texture development, plastic anisotropy, martensitic transformation kinetics, and stress partitioning

Constitutive micromechanical behavior of transformation induced plasticity (TRIP) stainless steel (SS) alloys was investigated using high-energy synchrotron x-ray diffraction (S-XRD) and in-situ neutron diffraction techniques. First, four different steel alloys were designed and produced: (1) a metastable austenitic TRIP SS, (2) a stable austenitic SS, which is a stable counterpart of the TRIP SS, (3) a lean duplex TRIP SS with ferrite and metastable austenite phases, and (4) a lean duplex stable SS, which is a stable counterpart of duplex TRIP SS. Then, effects of chemical composition, microstructure, and texture on the plastic anisotropy, martensitic transformation kinetics, and residual stress concentration during a tensile deformation were investigated. The results show that the plastic anisotropy, governed by the initial microstructure and texture, has insignificant effect on macroscopic tensile properties and martensitic phase transformation kinetics despite different R-values observed along different loading directions. On the other hand, the interplay between stress partitioning among constituent phases and martensitic phase transformation plays a critical role in the micromechanics of plastic deformation, and, consequently, determines the distributions of in-situ martensite fraction and residual stresses. The phase stress partitioning in the TRIP alloy clearly shows that a large tensile residual stress of 1.8 GPa can concentrate on the martensite phase with 30% plastic strain. In contrast, the introduction of the tensile load-sharing ferrite phase in the cost-effective lean duplex TRIP alloy significantly reduces the tensile residual stress concentration in the martensite phase, which could improve the formability of high-strength TRIP steels.

Method of Evaluating Residual Stresses in the Product Material

The method of evaluating the level of residual surface stresses in the products without the loss of their integrity at elastoplastic strains and under static and cyclic loading by scattering of hardness characteristics is proposed. Residual surface stress levels are assessed not by absolute hardness values but by the state of material structure. Its homogeneity coefficient in the Weibull distribution, characterizing the scattering of large-scale hardness data, was taken as a calculated structure damage parameter and evaluated by the LM-hardness method based on direct multiple independent hardness measurements. The estimation of residual stresses is built upon the correlation relation between the material structure damage and residual stresses. By comparing the measured parameters of structure homogeneity, charactering their damage level in the region of residual stresses, with the structure parameter in the region free from them, their level is determined. In the absence of such a region, residual stresses are evaluated by comparing the homogeneity parameter of the product element in their region with that of a reference sample made of the same material and subject to the same operating loads as the examined product. The product quality can be estimated by the regions of high residual stress concentrations, comparing the parameters obtained in its different characteristic sections. Correlation relations, determining the values of residual stresses, are found from preliminary experimental tests of the material specimens by constructing the structural parameter – stress diagram at a preset loading step. The structure parameter is measured by scattering its large-scale hardness measurements.

Alternative Fastening Mechanism for Shear Connectors with Cold-Formed Steel Shapes Involved in Composite Sections

Over the past few decades, the use of steel-concrete composite sections has increased globally, in order to take advantage of compression strength in concrete and tensile strength in steel, ensuring its fastening through stress transfer elements denominated shear connectors. The main connection systems endorsed by the current design codes are used by applying welding as fastening mechanism to fix connectors. However, this thermal procedure produces concentration of residual stresses during cooling process, and risk of perforation in Cold-Formed Steel sections (CFS), affecting the behavior efficiency of the composite sections. In this research, self-drilling screws are proposed as an alternative mechanical system for connectors fastening. An experimental program was carried out to validate capacity and performance of the system, through Full-Scale Beam Tests. According to results, self-drilling screws are a viable alternative to be used as fastening mechanism in shear connectors for CFS and concrete composite sections. Composite system achieved to develop full capacity, even in inelastic range, without disconnection between materials. Self-drilling screws remained fixed on steel shapes without mechanical damage, allowing greater deformations, than structural service conditions.

Effects of pre-contoured and in situ contoured rods on the mechanical strength and durability of posterior cervical instrumentation: a finite-element analysis and scanning electron microscopy investigation.

Finite-element analysis. Intraoperative contouring of rods is a common procedure for spine surgeons to match the native curvature of the spine, but it may lead to premature weakening of the rod. This study investigated the effect of different bending methods on rod fatigue performance. Rod failure in the cervical spine is of clinical concern, particularly when spanning the cervicothoracic region and when considering corrective osteotomies for deformity correction and global spinal alignment. Finite-element models were developed to simulate rod bending (3.5mm D, 40mm L) to achieve a 23° angle with 3 different bending methods: French single, multiple bending, and in situ bending. Simulations were conducted in 4 steps: rod bending, rod spring back, residual stress relaxation, and F1717 mechanical test simulation. French single bending resulted in the highest residual stress concentrations for both titanium (TiAlV) and cobalt chrome (CoCr) at 783MPa and 507MPa, respectively. During F1717 test simulation, the French single bent rod had its highest tensile stress in the middle, with 917MPa and 623MPa, respectively, for TiAlV and CoCr, compared to in situ (580MPa and 586MPa for TiAlV and CoCr) and the French multiple bent rod (765MPa and 619MPa for TiAlV and CoCr). The computational model found that CoCr rods made the construct least prone to deformation. French single bend with TiAlV rods put the construct at highest risk of failure. CoCr rods led to minimal physical changes in microstructure while showing evidence of flattening.

Ensuring industrial safety of pipelines with developed hard sections

Oil refining and petrochemicals have a wide demand for pipelines from heat resistant chromium steels. One of the main reasons for frequent failures of more stressed joints may be the presence of wide solid and brittle layers having significant areas in metal volume with maximum clusters of imperfections of metal structure and creating excessive concentration of additional residual deformations and stresses in welded joints, which are most saturated with defects inherent in welded joints. Presence of such extended sections leads to reduction of process strength of welded joints, increases tendency to formation of cold cracks and sharply limits time of laying of thick-walled welded joints of pipelines before subsequent high-temperature thermal treatment. The work carried out studies on welding pipe blanks in order to compare different methods of 5CroMo16 steel treatment during welding and determine the most efficient mode. Regularities of stressed state of different-module structural elements with wide solid layers are established.

Modeling Concentration of Residual Stresses and Damages in Salt Rock Cores

The authors perform numerical modeling of processes which create individual history of mechanics and mechanical condition of salt rocks nearby a roadway. The influence of a sampling point (roof or sidewall) and life time of the roadway on the residual stress level and quality of a sample is estimated with regard to microinhomogeneity. The effect of the specified factors on the mechanical characteristics of a sample in standard compression testing is demonstrated.

Interfacial microstructures, residual stress and mechanical analysis of hot isostatic pressing diffusion bonded joint of 93W–4.9Ni–2.1Fe alloy and 30CrMnSiNi2A steel

• A HIP diffusion bonding technique was investigated as a method of joining W–steel joint circular sleeve. • The diffusion zone of the joint interface consists of W/steel diffusion layer and Ni–Fe/steel diffusion layer. • The fracture occurs predominantly in W–Ni–Fe alloy near the joint interface due to the residual stress concentration. • Steel can reduce residual stress and avoid large stress concentration by generating plastic deformation. Circular sleeves of 93W–4.9Ni–2.1Fe alloy (W–Ni–Fe) and 30CrMnSiNi2A steel were connected by a hot isostatic pressing (HIP) diffusion bonding method. W–Ni–Fe/steel joint mock–up with a dimension of 30 ID mm × 50 OD mm × 50 H mm was successfully fabricated. Metallographic analysis with field–emission scanning electron microscope (FE–SEM) revealed the diffusion zone of the joint interface consists of W/steel diffusion layer and Ni–Fe/steel diffusion layer. Electron probe microanalysis (EPMA) and X–ray diffraction (XRD) analysis exhibits the brittle intermetallic phase Fe 7 W 6 is formed at the W/steel diffusion zone. The average tensile strength of ∼310.5 MPa along with 8.6 % elongation has been obtained for the HIP diffusion couple and the fracture occurs predominantly in W–Ni–Fe near the joint interface because of the thermal stress concentration. Thermally induced stresses and strains in the W–Ni–Fe/steel HIP joint were analyzed using finite element method (FEM). The results reveal that the peak equivalent residual stress on entire joint is located at the W–Ni–Fe side near the interface close to the free surface. Meanwhile, the steel substrate releases the residual stress by generating plastic deformation.

Simulation Design of 30KHz Ultrasonic Rolling Tool Head

In order to explore the types of ultrasonic rolling tool head used in ultrasonic rolling and finishing processing device, ANSYS Workbench is taken as a tool to simulate the machining process of ultrasonic rolling processing through transient dynamic analysis, and the maximum residual stress distribution and stress concentration of 45 steel workpiece are analyzed. Based on the simulation result, the ball-type ultrasonic rolling tool head is selected in this work. In addition, the transient dynamics module of ANSYS Workbench is also used to simulate the ultrasonic rolling tool head of different structure parameter, in that way, the accurate and reasonable structure parameters of rolling components of ultrasonic rolling tool head can be achieved. The results of this work show that a ball-type ultrasonic rolling tool head of a diameter of 8mm can make the maximum residual stress minimum and stress concentration slightest under the condition of normal processing of the 45 steel workpiece. In other words, it suggests that this ultrasonic rolling tool head can produce the best surface quality of 45 steel workpiece.

Research on Residual Stress Simulation on High Performance Aluminum Alloy Manufacturing

High-performance manufacturing is an integrated manufacturing of surface integrity and anti-fatigue surface strengthening to improve the service performance of key components. The stress concentration, fatigue failure and poor reliability cause by traditional processing have become technical bottlenecks restricting the development of industry. In order to research the influence of high performance manufacturing on the fatigue performance of workpieces, the residual stress distribution of 7050 aluminum alloy high performance manufacturing was studied by simulation. The stress layer on the surface of the workpiece was mainly tensile stress which was formed during cutting process, and it implied that the fatigue resistance of the workpiece was not effectively improved. The ultrasonic rolling strengthening treatment can effectively eliminate the residual tool marks and stress concentration. It was noted that stress layer of ultrasonic rolling was deeper than the cutting process, and the stress layer was mainly composed of residual compressive stress. The residual stress increased first and then decreased with the increased of depth, which can significantly improve the fatigue performance and service life of the workpiece.

Modeling Concentration of Residual Stresses and Damages in Salt Rock Cores

Modeling Concentration of Residual Stresses and Damages in Salt Rock Cores