High Bending Stresses Research Articles

Small DNA circles as bacterial topoisomerase I inhibitors.

Bacterial topoisomerase I is a potential target during the course of antibacterial drug therapy. In our studies, specifically designed small DNA circles with high bending stress were synthesized. It is demonstrated that small DNA circles showed high inhibitory effect on the activity of bacterial topoisomerase I and the single-stranded regions associated with bending deformation in DNA circles are believed to be the crucial factor for trapping the enzymes and decreasing the effective concentration of the topoisomerases in the reaction solution. In addition, the DNA circles showed high thermal stability and excellent nuclease resistance. In consideration of the low cytotoxicity of DNA-based biopharmaceuticals, our results may provide a new idea for the future design and optimization of DNA-based therapeutic agents for antibacterial therapy.

Flexural performance of TRC-strengthened RC beam under chloride environment

PurposeTextile reinforced concrete (TRC) has excellent bearing capacity and anti-crack and corrosion resistance capacity, which are suitable for strengthening concrete structure under harsh environments.Design/methodology/approachIn this thesis, flexural properties of RC beams strengthened with TRC under chloride wet–dry cycles were studied and the effects of the concentration of the salt solution, number of wet–dry cycles, bending stress level and TRC form were considered. Four-point bend loading mode was adopted for the step-loading procedure.FindingsAs the number of wet–dry cycles was relatively few, the trend of the yield and ultimate load with the increasing concentration of salt solution and wet–dry cycles were not obvious. However, the beams under high sustained bending stress level (0.5) had a decrease in the bearing capacity and an increase in mid-span deflection because of the larger degree of the corrosion of steel bars and the weaker bond capacity between the steel bar and concrete. Besides, there was little difference between the precast TRC plate and the casting TRC on beams in terms of the capacity of anti-crack, bearing and deflection.Research limitations/implicationsIn this paper, preliminary work has been carried out, but some of the factors were not comprehensive considered, which are inevitable. As the time of dry–wet cycles was short and TRC layer had good anti-crack and anti-permeability performance, smaller chloride ions’ penetration resulted in the corrosion ratio of steel bars to be lower.Practical implicationsIt should be noted that under high corrosion rates of the reinforcement, the whole TRC strengthening layer might be spalled off if only the strengthening form at the beam bottom is used, and thus the U-type strengthening form could be considered, which means that the beam is strengthened at both the bottom and side surfaces.Originality/valueThis research only considers the flexural performance of the beams strengthened with TRC in conventional environment, and there is little research on the TRC-strengthened beam under corrosion environment. On the basis of previous research, this paper carried out the experimental study on beams strengthened with TRC under chloride wet–dry cycle environment, and the effects of the concentration of the salt solution, number of wet–dry cycles, bending stress level and TRC form were considered.

Pushing to the Limit: Samsung Galaxy Note 7 and Fitbit Flex 2

The ongoing demand for smaller and lighter devices, with batteries having longer usage times, has put increasing operational pressure on the batteries. The use of higher capacity cathodes, increasing areal capacity and thinner separators are some of the approaches used to achieve higher energy densities. Here we report two case studies on batteries from the Samsung Galaxy Note 7 phone and fitness tracker wristband, Fitbit Flex 2, highlighting where the device manufacturers were pushing the boundaries to achieve this higher energy density. In September 2016, several reports were published of the Samsung Galaxy Note 7 phone batteries overheating, exploding or catching fire, which led to a total product recall of the Samsung Galaxy Note 7 phone. “The launch of what was supposed to be its flagship model has turned into a fiasco for the world's largest smartphone maker”, the BBC reported1. We carried out a more in-depth investigation, “Looking Deeper into the Galaxy (Note 7)2”, inspecting each of the battery components. The study incorporated X-ray computed tomography, thermal imaging and scanning electron microscopy (with energy dispersive spectroscopy), to identify the most likely root causes of the battery failure. The findings reveal that thermal properties of the battery is not thought to be a contributing factor to battery failure but are from battery design/cell manufacturing defects: (1) Unintended folding of the anode coating at the corner near to the anode tab resulted from insufficient space to safely accommodate the electrodes; (2) No Insulating tape on the cathode tab, and (3) un-bonded welding sections with protrusion features observed at the cathode tab which may penetrate the separator. Such flaws can lead to internal short circuit between the cathode and anode; (4) A much thinner separator (≤ 5 µm, with <1 µm Al2O3 coating on both sides) used in Galaxy Note 7 also increased the likelihood of separator damage which can lead to short circuit. The ceramic coating layer detached itself quite easily when the cell was unravelled, indicating a lack of interfacial integrity. We also report another forensic investigation on a miniature lithium ion rechargeable cylindrical cell with a diameter of 3.65 mm and length in 20 mm, and nominal capacity of 15 mAh, which is fitted in Fitbit Flex 2 fitness tracker. This miniature cylindrical cell shows an impressive volumetric energy density of 503 Wh/L despite having a limited space. The unravelling of the jelly roll shows severe anode coating delamination from the copper current collector, transferring unto the separator. The high bending stress exert on the cell components when rolled up to a 3 mm diameter jelly roll has resulted severe delamination of the anode coating. 1. http://www.bbc.co.uk/news/technology-376154962. Melanie J. Loveridge, Guillaume Remy, Nadia Kourra, Ronny Genieser, Anup Barai, Mike J. Lain, Yue Guo, Mark Amor-Segan, Mark A. Williams, Tazdin Amietszajew, Mark Ellis, Rohit Bhagat and David Greenwood, Looking Deeper into the Galaxy (Note 7). Batteries 2018, 4 (1), 3. Figure 1

Effectiveness of various isometric exercises at improving bone strength in cortical regions prone to distal tibial stress fractures.

A computational model was used to compare the local bone strengthening effectiveness of various isometric exercises that may reduce the likelihood of distal tibial stress fractures. The developed model predicts local endosteal and periosteal cortical accretion and resorption based on relative local and global measures of the tibial stress state and its surface variation. Using a multisegment 3-dimensional leg model, tibia shape adaptations due to 33 combinations of hip, knee, and ankle joint angles and the direction of a single or sequential series of generated isometric resultant forces were predicted. The maximum stress at a common fracture-prone region in each optimized geometry was compared under likely stress fracture-inducing midstance jogging conditions. No direct correlations were found between stress reductions over an initially uniform circular hollow cylindrical geometry under these critical design conditions and the exercise-based sets of active muscles, joint angles, or individual muscle force and local stress magnitudes. Additionally, typically favorable increases in cross-sectional geometric measures did not guarantee stress decreases at these locations. Instead, tibial stress distributions under the exercise conditions best predicted strengthening ability. Exercises producing larger anterior distal stresses created optimized tibia shapes that better resisted the high midstance jogging bending stresses. Bent leg configurations generating anteriorly directed or inferiorly directed resultant forces created favorable adaptations. None of the studied loads produced by a straight leg was significantly advantageous. These predictions and the insight gained can provide preliminary guidance in the screening and development of targeted bone strengthening techniques for those susceptible to distal tibial stress fractures.

Effect OF NaOH Treatment on Bending Strength Of The Polyester Composite Reinforce By Sugar Palm Fibers

The objective of this research is to investigate the effect of NaOH treatment on bending strength of lamina composite reinforced by sugar palm fiber. To know of mechanism fracture can be done with visual inspection of the fracture surface. The Materials used are random sugar palm fibers that have been in the treatment of NaOH, polyester resin and hardener. Sugar palm fibers after washed and dried then soaked NaOH with a long time soaking 0, 2, 4, 6 and 8 hours. The bending test specimens were produced according to ASTM D 790. All specimens were post cured at 62°C for 4 hours. The Bending test was carried out on a universal testing machine. The SEM analysis has conducted to provide the analysis on interface adhesion between the surfaces of fiber with the matrix. The result shows that polyester composite reinforced by sugar palm fiber has highest bending stress 176.77 N/mm2 for 2 hours of a long time soaking NaOH, the highest flexural strain 0.27 mm for 2 hours of a long time soaking NaOH, elongation 24.05% for 2 hours of a long time soaking NaOH and the highest bending modulus 1.267 GPa for 2 hours of a long time soaking NaOH. Based on the results, it can be concluded that the polyester composite reinforced by sugar palm fiber has the optimum bending properties for a long time soaking 2 hours. The fracture surface shows that the polyester composite reinforced by sugar palm fiber pull out that indicate weakens the bond between fiber and matrix.

Numerical Investigation of Design Parameters Influence on Stress Distributions in Horizontal Multi-saddle Cylindrical Pressure Vessel

The Industrial autoclaves which are used for curing the Fly Ash brick are to be designed as pressure vessels. They are typically distinguished from other pressure vessels by their length. They are oriented horizontally and saddles are used to support along the length. These large horizontal autoclaves can be twin supported or Multi-saddle supported depending on the length of the autoclave. They are prone to high circumferential and bending stress in vessel and saddle regions. Various factors plays crucial role in stress distribution in the saddle vessel interface area. To find out the influence of design parameters parametric study has been carried out. The industrial case study of autoclave has been taken and CAD model has been developed with actual dimension of the pressure vessel. Further finite element analysis has been carried out to check the effect of various parameters on the stresses state of the pressure vessel. The combined effect of various design parameters needs to be checked out and for that the design of experiment has been carried out by response surface methodology. The centre composite design has been selected for the purpose. Linear model is fitted for stress in horn area while quadratic model is fitter for stress in rib and flange area. The suggested model can be used for mapping in design space and also can be useful for optimization

Bend Straightening of a Carbonitrided Gear Shaft – Consequences on Residual Stresses and Retained Austenite near the Surface*

Abstract Carbonitriding of shafts in drive technology is strongly connected with distortion. Bend straightening is an important process step in order to eliminate distortion without removing the hardened surface layer. As shown in several investigations, even for simple part geometries, bending induced stresses and plastic deformations have a strong impact not only on the residual stress state but also on the microstructure after straightening. As gear shafts become increasingly filigree and complex in their geometry, the components state after straightening is only understood in rare cases. Due to indispensable, function based notches as well as changes in the cross section, these effects will occur especially in areas of small cross sections or notches in conjunction with high bending stresses. It is the objective of this work, to characterize these critical areas with respect to the distribution of residual stresses and retained austenite along the circumference as well as in the in-depth direction. Therefore, the measured distributions of residual stresses, integral width values and retained austenite near the surface will be presented and discussed. For this purpose a carbonitrided gear shaft taken out of a large production volume was investigated before and after a commonly used straightening operation.

Analysis of Fatigue Failure of Francis Turbine Runner at Derbendikhan Hydropower Station

Fatigue failures in Francis turbine runner are frequently occurred in hydropower plants, causing unexpected plant downtime and considerable financial loss. Decades of operational experience have shown that turbine runners develop fatigue cracks in areas, where stress concentrations and material defects coincide. In Francis turbine runners, cracks tend to propagate from the transition of the welded T-joint between the blade and the band or crown. This type of turbine runner, which operate under a wide range of heads and outputs, are subjected to considerable dynamic forces which can lead to fatigue cracking. The magnitude of these forces is a function of the hydraulic pressure, the water velocity and the geometry of the stationary parts guiding the water into the runner.&#x0D; This paper presents the water pressure and bending stresses for different operational conditions in a Francis runner of a Derbendikhan hydropower station. At the first step, the dynamic fluid calculation is used to determine the fluctuating water pressure on the blade of the runner. At the second step, for a period of operational nominal bending stress due to the fluctuating water pressure are determined. The result indicates that the hydropower plant was operated with the high fluctuating water pressure which is responsible for inducing bending stress response. The high bending stress on the blade is a probable reason for fatigue failure. Furthermore, the paper discusses the fatigue analysis of the runner. Typical results are presented and discussed.

Retrieval and clinical analysis of distraction-based dual growing rod constructs for early-onset scoliosis

Background ContextGrowing rod constructs are an important contribution for treating patients with early-onset scoliosis. These devices experience high failure rates, including rod fractures. PurposeThe objective of this study was to identify the failure mechanism of retrieved growing rods, and to identify differences between patients with failed and intact constructs. Study Design/SettingGrowing rod patients who had implant removal and were previously enrolled in a multicenter registry were eligible for this study. Patient SampleForty dual-rod constructs were retrieved from 36 patients across four centers, and 34 of those constructs met the inclusion criteria. Eighteen constructs failed due to rod fracture. Sixteen intact constructs were removed due to final fusion (n=7), implant exchange (n=5), infection (n=2), or implant prominence (n=2). Outcome MeasuresAnalyses of clinical registry data, radiographs, and retrievals were the outcome measures. MethodsRetrievals were analyzed with microscopic imaging (optical and scanning electron microscopy) for areas of mechanical failure, damage, and corrosion. Failure analyses were conducted on the fracture surfaces to identify failure mechanism(s). Statistical analyses were performed to determine significant differences between the failed and intact groups. ResultsThe failed rods fractured due to bending fatigue under flexion motion. Construct configuration and loading dictate high bending stresses at three distinct locations along the construct: (1) mid-construct, (2) adjacent to the tandem connector, or (3) adjacent to the distal anchor foundation. In addition, high torques used to insert set screws may create an initiation point for fatigue. Syndromic scoliosis, prior rod fractures, increase in patient weight, and rigid constructs consisting of tandem connectors and multiple crosslinks were associated with failure. ConclusionThis is the first study to examine retrieved, failed growing rod implants across multiple centers. Our analysis found that rod fractures are due to bending fatigue, and that stress concentrations play an important role in rod fractures. Recommendations are made on surgical techniques, such as the use of torque-limiting wrenches or not exceeding the prescribed torques. Additional recommendations include frequent rod replacement in select patients during scheduled surgeries.

Fatigue crack propagation in additively manufactured porous biomaterials

Additively manufactured porous titanium implants, in addition to preserving the excellent biocompatible properties of titanium, have very small stiffness values comparable to those of natural bones. Although usually loaded in compression, biomedical implants can also be under tensional, shear, and bending loads which leads to crack initiation and propagation in their critical points. In this study, the static and fatigue crack propagation in additively manufactured porous biomaterials with porosities between 66% and 84% is investigated using compact-tension (CT) samples. The samples were made using selective laser melting from Ti-6Al-4V and were loaded in tension (in static study) and tension-tension (in fatigue study) loadings. The results showed that displacement accumulation diagram obtained for different CT samples under cyclic loading had several similarities with the corresponding diagrams obtained for cylindrical samples under compression-compression cyclic loadings (in particular, it showed a two-stage behavior). For a load level equaling 50% of the yield load, both the CT specimens studied here and the cylindrical samples we had tested under compression-compression cyclic loading elsewhere exhibited similar fatigue lives of around 104 cycles. The test results also showed that for the same load level of 0.5Fy, the lower density porous structures demonstrate relatively longer lives than the higher-density ones. This is because the high bending stresses in high-density porous structures gives rise to local Mode-I crack opening in the rough external surface of the struts which leads to quicker formation and propagation of the cracks. Under both the static and cyclic loading, all the samples showed crack pathways which were not parallel to but made 45° angles with respect to the notch direction. This is due to the fact that in the rhombic dodecahedron unit cell, the weakest struts are located in 45° direction with respect to the notch direction.

Self-Healing of Wind Turbine Blades Using Microscale Vascular Vessels

Development of high bending stresses due to a sudden gust of wind is a significant cause for the failure of wind turbine blades. Self-healing provides a fool proof safety measure against catastrophic failure by healing the damages autonomously, as they originate. In this study, biomimetic, vascular channel type of self-healing was implemented in glass fiber reinforced polymer matrix composite that is used in wind turbine blades. Microscale borosilicate tubes are used to supply the healing agent to the epoxy type of thermoset polymer matrix, and the healing was very effective. However, 25% decrease in tensile strength and 9% decrease in three-point bending flexural strength were imminent with the inclusion of a single layer of vascular vessels in the composite material. Three-point bending tests were performed before and after self-healing of flat specimens to find the extent of recovery of flexural strength on using vascular channel type of self-healing. An average recovery of flexural strength of 84.52% was obtained using a single layer of vascular vessels on the tensile stress side of three-point bending. Breakage and bleeding of the healing agent within the composite specimens during three-point bending tests were observed in real-time. Based on the encouraging findings, the above self-healing feature was successfully implemented in a prototype wind turbine.

Effect of Na substitution and Ag addition on the superconducting properties of Bi-2212 textured materials

The effect of Ag addition on the structural and superconducting properties of Bi2Sr2Ca0.925Na0.075Cu2Oy + x wt% Ag materials with x = 0, 1, 3, and 5 prepared by sol–gel method, followed by directional growth using the laser floating zone (LFZ) technique has been investigated. Powder XRD measurements demonstrate that all samples are composed by nearly single Bi-2212 phase. SEM micrographs and EDX results confirms that Bi-2212 is the major phase with minor amounts of a Bi-free one (Sr,Ca)CuO2 and metallic Ag. According to the magnetic results, Ag does not modify the superconducting critical temperature, T c , but significantly increases the magnetic hysteresis loop area. The magnetic critical current density is maximum in the 3 wt% Ag containing samples, due to the larger grain clusters found in these samples, reaching 2.1 × 105 A/cm2 at 10 K. Moreover, Ag addition also improves the rods mechanical properties, determined by three point bending tests. The highest bending stress is also reached in the 3 wt% Ag samples.

Flexural Capability of Patterned Transparent Conductive Substrate by Performing Electrical Measurements and Stress Simulations.

The suitability of stacked thin films for next-generation display technology was analyzed based on their properties and geometrical designs to evaluate the mechanical reliability of transparent conducting thin films utilized in flexural displays. In general, the high bending stress induced by various operation conditions is a major concern regarding the mechanical reliability of indium–tin–oxide (ITO) films deposited on polyethylene terephthalate (PET) substrates; mechanical reliability is commonly used to estimate the flexibility of displays. However, the pattern effect is rarely investigated to estimate the mechanical reliability of ITO/PET films. Thus, this study examined the flexible content of patterned ITO/PET films with two different line widths by conducting bending tests and sheet resistance measurements. Moreover, a stress–strain simulation enabled by finite element analysis was performed on the patterned ITO/PET to explore the stress impact of stacked film structures under various levels of flexural load. Results show that the design of the ITO/PET film can be applied in developing mechanically reliable flexible electronics.

Fretting fatigue life investigation of AL7075-T6 alloy coated by multilayer thin solid films of TiCr/TiN/CrN and Ti/Cr/TiN/Cr/CrN/TiCrN

Due to the increasing requirements in the aerospace and automotive industries, engine and structural parts must also have an increasing life. This leads to an improvement in the fretting fatigue strength of aluminum alloys over 107 cycles, and sometimes even more. Fretting is a surface degradation process as a result of chemical and mechanical attack between two contacting surfaces by small amplitude oscillatory movement, which is closely related to fatigue, wear, and corrosion. The surface treatments and coatings are expected as a suitable strategy for fretting damage. In this research work, two types of thin solid films TiCr/TiN/CrN (three layers) and Ti/Cr/TiN/Cr/CrN/TiCrN (six layers) were coated onto Al7075-T6 alloy using the physical vapor deposition magnetron sputter technique to enhance the fretting fatigue lives. The result shows that the fretting fatigue lives of three layers deposited substrates were improved at high and low cyclic fatigue of 101% and 34%, respectively. Fretting fatigue lives of the six layers deposited specimens were developed at high and low bending stresses (high and low cyclic fatigue) of 121% and 55%, respectively.

Upheaval buckling of in-service cased insulated flowline

ABSTRACTAn upheaval buckling prediction approach is proposed for a high-temperature cased insulated flowline (CIF). Based on the tensile cracking and compression crushing analyses of the CIF concrete-weighted coats, the curvature-related nonlinear bending stiffnesses of CIF systems are discussed. A changeable stiffness is included in this buckling prediction approach developed using a transfer matrix method. Due to a relatively low bending stiffness, greater curvature and higher bending stress would be induced in the carrier pipe at field-joint positions in the buckling response of CIF systems, while the shear force change would be induced in the five pipe coats of CIF systems. Using the approach developed in this paper, the field-joint stress of a CIF carrier pipe and the interlayer shear forces of the CIF pipe coats can be obtained along the buckling path of the CIF systems by plotting the relationship curves between the carrier pipe axial forces and the CIF buckle lengths.

Failure and thermo-mechanical stress analysis of the exhaust valve of diesel engine

Abstract In this work the failure analysis of the exhaust valve of diesel engine was performed. Visual examination of damaged engine parts showed that on the fracture of exhaust valve the beach marks, typical for fatigue failure were observed. Additional observations of the crack initiation zones indicated that the crack origins were not covered by material defects or corrosion products. In order to explain the reason of premature valve damage, the non-linear finite element analysis was utilized. The discrete model of simplified valve system composed of the valve guide, the poppet valve and the seat face was defined. In numerical analysis both the mechanical force arising from the valve spring and also the thermal load resulting from the non-uniform temperature field were defined. The results of nonlinear static analysis showed that in the engine without any disturbances, the maximum principal stresses in the critical zone of the valve have low values. The examination of another (non-defected) valve from damaged engine head indicated that irregular carbon deposit was located on the valve face. The results of stress analysis performed for the valve with the carbon deposit showed, that in the valve stem a high bending stresses were occurred.

Fracture Problem of the Valve of Piston Engine

In this paper the fracture problem of exhaust valve of the piston engine was investigated. Visual inspection showed that on the fractured surface of the valve the beach marks, typical for fatigue failure were observed. The crack origin was not covered by corrosion products or material defects. In order to explain the reasons of damage of the valve, the non-linear finite element method was utilized. The numerical model composed of the poppet valve, the guide and the seat face was defined. In the analysis both the mechanical load resulting from the valve spring and also the thermal load arising from a non-uniform temperature field were defined. The loads were at first defined separately in order to check which load component has a dominant influence on the stress level. In third load case (which represents the operational thermo-mechanical engine conditions) the mentioned loads were defined simultaneously. The results of performed computations showed that the operational dynamic stress (in the critical zone of the valve where the crack appeared) is more than 12 times lower than the yield stress of the material. It means that the premature fatigue fracture of the valve was probably caused by any phenomenon concerned with the increase of the operational stress in the valve. The additional observation of the second (non-damaged) valve from the same engine head showed that the carbon deposit was located on the valve face. The results of the stress analysis of the valve with additional carbon particle showed, that in the valve stem a high bending stress was observed.

High-Performance Flexible Transparent Electrode with an Embedded Metal Mesh Fabricated by Cost-Effective Solution Process.

A new structure of flexible transparent electrodes is reported, featuring a metal mesh fully embedded and mechanically anchored in a flexible substrate, and a cost-effective solution-based fabrication strategy for this new transparent electrode. The embedded nature of the metal-mesh electrodes provides a series of advantages, including surface smoothness that is crucial for device fabrication, mechanical stability under high bending stress, strong adhesion to the substrate with excellent flexibility, and favorable resistance against moisture, oxygen, and chemicals. The novel fabrication process replaces vacuum-based metal deposition with an electrodeposition process and is potentially suitable for high-throughput, large-volume, and low-cost production. In particular, this strategy enables fabrication of a high-aspect-ratio (thickness to linewidth) metal mesh, substantially improving conductivity without considerably sacrificing transparency. Various prototype flexible transparent electrodes are demonstrated with transmittance higher than 90% and sheet resistance below 1 ohm sq(-1) , as well as extremely high figures of merit up to 1.5 × 10(4) , which are among the highest reported values in recent studies. Finally using our embedded metal-mesh electrode, a flexible transparent thin-film heater is demonstrated with a low power density requirement, rapid response time, and a low operating voltage.

Failure Analysis of a Striking Bar

This paper describes the failure investigation of a tubular shaft that is part of a hammer drill assembly. The failure investigation was particularly challenging as the fracture surfaces were completely damaged during service subsequent to the failure process. However, careful examination of the component and its assembly revealed many clues that pointed to the root causes of failure. The basic failure mode was identified as torsional fatigue failure in combination with high bending stresses. The failure was determined to be originated on the inside diameter of the tubular shaft. The root causes were determined to be operational overload in the presence of rough machining marks on the bore surface and higher than necessary operating torque required to overcome the dry adhesive friction in the system. The preventative measures recommended were manyfold including improving surface finish on the bore diameter, reducing dry sliding friction, decreasing the overall level of dynamic loads by appropriate design changes, and adding a surface strengthening heat treatment.

Effects of residual stresses and compressive mean stresses on the fatigue strength of longitudinal fillet-welded gussets

AbstractResults from fatigue testing of small-scale specimens are widely used to study residual stress effects on fatigue of welded structures. It was observed from a literature that welding distortion may cover residual stress effects due to high-bending stresses from clamping. Here, presented are fatigue test results and results from residual stress measurements from welded longitudinal stiffeners in different residual stress conditions. The axial welding distortion was corrected for all samples by straightening reducing effects from clamping and making residual stress effects visible. It was found that the fatigue strength depends strongly on the stabilized residual stresses, especially at high numbers of load cycles. It could be shown that residual stresses at the weld toe either were far below the yield strength or were degraded mainly at the first load cycle but still have major effects. This was investigated at two stress ratios of R = −1 and R = −3.