Peak Tensile Stress Research Articles

Numerical Simulation of Double-Sided Double Arc Welding without Back Chipping Based on MSC.MARC

Numerical simulation based on MSC.MARC was applied to predict the residual stress in double-sided double arc welding (DSDAW). The distribution of residual stress field in the welding seam was simulated and the actual situation in experiment of the residual stress was also measured. It shows that the calculated results are in good agreement with the experimental ones. The residual stress of conventional welding (CW) or a single arc welding (SAW) is calculated too. Moreover, the welding residual stress field of thick metal plates welded by DSDAW was carried out and compared with that of the CW method with back chipping. The result shows that the DSDAW technology had some excellent characteristics of smaller angular deformation, lower residual peak tensile stress, and well-proportioned stress distribution, which testifies that the welding procedures in DSDAW are reduced and the welding efficiency and quality of the welding joint are improved in great margin.

A pseudo-tetragonal phase of superhard B8C16(N6CO)

A superhard phase of I-B8C16(N6CO) with pseudo-tetragonal structure is predicted using first-principles calculations. The structural stability, ideal tensile strength, theoretical hardness and chemical bonding of I-B8C16(N6CO) are investigated. The phonon dispersions indicate this phase is dynamically stable at ambient conditions. Enthalpy calculations indicate it is thermodynamically favorable than the previously synthesized tetragonal B8C16(N6CO). The band structure indicates that the predicted I-B8C16(N6CO) is a semiconductor with a direct band gap of about 1eV. Theoretical hardness demonstrated that I-B8C16(N6CO) is a potential ultra-hard material with a Vickers hardness of about 75GPa, significantly harder than c-BN. Also, the lowest peak tensile stress is calculated to be 48.7GPa in the y-axis direction, which is higher than that of recently synthesized superhard material like γ-B28 and BC5. The results provide insight into exploration of the B–C–N–O quaternary superhard materials for potentially technological applications.

On the evolution of local material properties and residual stress in a three-pass SA508 steel weld

In multi-pass welds, the development of residual stress generally depends on the response of the weld metal, heat-affected zone (HAZ) and nearby parent material to complex thermo-mechanical cycles. Here, the evolution of local material properties and residual stress was investigated for each of these zones during the manufacture of a three-pass groove weld in SA508 steel. Residual stress distributions were measured by neutron diffraction for a sample in which only one weld bead had been deposited, and again for a completed three-pass weld. The evolution of material properties was also characterised by measuring local hardness and conducting tensile tests on small coupons that were extracted from the same welded specimens. Overall, the addition of subsequent weld passes resulted in lower peak tensile residual stresses in the weld as a whole, softening of the HAZ, modest cyclic hardening in nearby parent metal, and some softening in the low-carbon weld metal.

Large residual strains are present in the intervertebral disc annulus fibrosus in the unloaded state

The intervertebral disc annulus fibrosus (AF) is subjected to high circumferential tensile stresses resulting from nucleus pulposus pressurisation under axial compression. In other pressure containing tissues, such as blood vessel walls, residual compressive stresses along the inside surface of the tissues without pressurisation reduce peak tensile stresses under pressurisation. This study hypothesised that similar patterns of residual stress exist in the annulus fibrosus. Accurate characterisation of residual stresses is essential for both the incorporation of nonlinear material descriptions into models of the disc as well as the design of effective annulus repair strategies. By imaging nine bovine caudal discs before and after the release of residual stresses via incision, we measured a mean residual stretch of 0.86±0.13 at the inner AF and 1.02±0.08 at the outer AF. These stretch values were used to calculate a gradient of residual stress ranging from −230±22kPa of compression at the inner AF to 54±0.2kPa of tension at the outer AF. Material models of AF have assumed that the AF was in a stress free reference state when there are no external loads. However, this study documents that there are large residual stresses in the AF even without external loads. The release of residual tension in the outer AF by herniation, needle injection or incisions makes closure difficult and may accelerate degeneration of the surrounding tissue. Retention of these residual stresses may be essential to maintaining disc mechanical function and to producing viable AF repair techniques.

Effect of Y and Zn Substitution on Tensile Properties of 6H-Type LPSO Phase in Mg<sub>97</sub>Zn<sub>1</sub>Y<sub>2</sub> Alloy

The effect of Y and Zn substitution on tensile properties of 6H-type ABCBCB LPSO phase in Mg97Zn1Y2alloy has been studied from first principles calculations. From obtained tensile stress-strain relations, at small strains anisotropy of Young’s modulus for Mg95Zn is larger than that for Mg95Y, whereas at lager strains anisotropy of peak tensile stress for Mg95Zn is smaller than that for Mg95Y. The ideal tensile strengths for both Mg95Y and Mg95Zn phases occur in direction, and the ideal tensile strength is increased with single Zn atom substitution. The detailed electronic structure investigations show that the hybridization between Mg and Y (or Zn) atoms is obvious, and the directional bonding between Mg and Y (or Zn) atoms would lead to large anisotropy of tensile stress-strain relations. As the strain increase, the directional bonding between Mg and Y (or Zn) atoms is weakened, the stability would be lowered, and the phases are finally fractured.

Dynamic tensile strength of polyurea

Abstract

FEM of Residual Stress of EDMed Surfaces

Objective of the present work is to model EDM process using ANSYS software, and to investigate the effects of most significant machining parameters (pulse current and pulse duration) on the residual stresses developed in the beneath the spark produced by a single spark. The workpiece material is AISI D2 tool steel. The FEA model is then used to study the relation between these parameters and maximum temperature attended at the end of heating cycle along with residual stress produced at the end of cooling cycle. To establish the residual stresses in the work piece during EDM, the temperature distribution at the end of pulse duration in the work piece has to be estimated first, latter on after cooling the residual stress is determined. In addition, residual stress which is the main aspect responsible for component failure, and the location of tensile peak stress, at the end of cooling cycle are investigated.

Response of Open Cell Aluminum Foams to Fully Reversed Cyclic Loading

The response of metal foams to fully reversed cyclic loading has been investigated much less than the response to tension-tension and compression-compression cyclic loads. This paper describes tests of open cell aluminum foams that are subjected to fully reversed cyclic loading. Three different damage measures are evaluated as candidates for tracking the damage state in the material. These measures and associated failure criteria track the peak tensile stress, the peak compressive stress, and the ratio of the prepeak tensile and compressive material stiffnesses in each cycle. The peak tensile stress measure and criterion gave the most stable results. Finally, the fatigue lifetime is modeled by using a statistical Weibull model.

The Forming Principle of Reflection Cracks of Composite Lay in Old Bridge Reinforcement

In order to study the transverse reflection crack of concrete composite lay in old bridge reinforcement, aiming at the forming process of the reflection crack, the theoretical model of its peak tensile stress and its separation distance is presented, and its forming mechanism is analysed. Based on the theoretical model, the influence of the thickness overlay, and constraint under the concrete composite lay are studied to the transverse reflection crack. Based on these researched results, the peak tensile stress and its separation distances is calculated by given theoretical model , and the results reveal shrinkage cracks rely on the restraint condition , elastic modulus, shrinkage ratio and the thickness of the composite-slab.

Effect of trailing heat sink on residual stresses and welding distortion in friction stir welding Al sheets

This paper investigates a trailing heat sink, which was designed and applied to friction stir welding (FSW) in order to control the residual stresses and welding distortion. Residual stresses, residual plastic strains and welding distortion of 2024-T3 and 5083-H321 Al sheets welded by FSW with and without the trailing heat sink were compared. The optimal placement of the heat sink was discussed. The results revealed that the reductions in peak tensile stresses were 66% for 2024-T3 and 58% for 5083-H321 by application of the trailing heat sink in FSW. In addition, the welding distortion could be reduced drastically by this method. The 5083-H321 sheet with a size of 1000×100×3·5 mm welded by this method was very flat and had almost no distortion. This method achieved in-process control of stresses and welding distortion, without additional complicated work before or after welding operation.

Fatigue damage development in pure polycrystalline magnesium under cyclic tension–compression loading

Abstract Cyclic deformation and fatigue damage development of pure polycrystalline Mg were investigated by conducting fully reversed strain-controlled tension–compression experiments along the extrusion direction at two strain amplitudes of 1% and 0.12%, respectively, in ambient air. At a strain amplitude of 1%, the tensile peak stress exhibited significant cyclic softening while the compressive peak stress showed moderate cyclic hardening. At a strain amplitude of 0.12%, marginal cyclic hardening was observed symmetrically at the tensile and compressive peak stresses. To study the fatigue damage development, a series of experiments using companion specimens were interrupted at the specified loading cycles. The morphology of fatigue damage on the specimen surface was examined by high resolution scanning electron microscope (SEM). With a strain amplitude of 1%, grain boundary cracking and twin tip damage were detected right after the second loading cycle. During the initial ∼80% fatigue life, microcracks were incessantly initiated with limited propagation that was observed to inhabit on both the grain boundary and the twin boundary. Final fracture surface was characterized by densely distributed cleavage facets along twin lamella boundaries together with tearing/shearing ridges. At a strain amplitude of 0.12%, initiation of microcrack by grain boundary cracking occurred at the loading cycle between ∼50% and ∼70% fatigue life. Both intergranular and transgranular propagation modes were observed. The early-stage transgranular propagation was dominated by slip-induced cleavage cracking on both basal and non-basal slip planes. Crystal sugar-like structure and cleavage facets were found on the initiation site on the final fracture surface. Early-stage initiation and transgranular propagation modes were discussed on their dependences of cyclic loading magnitudes.

Creep and Environmental Effects on the High Temperature Creep-Fatigue Behavior of Alloy 617

Abstract Alloy 617 is the leading candidate material for an intermediate heat exchanger (IHX) of the very high temperature reactor (VHTR), expected to have an outlet temperature as high as 950°C. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior. Strain-controlled low cycle fatigue (LCF) tests including hold times up to 1800 s at maximum tensile strain were conducted at 950°C and a total strain range of 0.3 % in air and in a simulated VHTR impure helium. For similar test conditions, the creep-fatigue behavior was globally similar in both environments. The fatigue resistance decreased when a hold time was added at peak tensile strain, consistent with the observed change in fracture mode from transgranular to intergranular. Further increases in the tensile hold time, beyond 180 s, were not detrimental to the creep-fatigue resistance. The influence of oxidation on the fatigue crack initiation and propagation is discussed. Bulk damage in the form of grain boundary cracking was present in the interior of the creep-fatigue specimens. This bulk cracking was quantified and found to be similar for hold times of up to 1800 s consistent with the saturation in failure lives.

Experimental Study of Uniaxial Tensile of High Performance Ductile Engineered Cementitious Composites

The tensile properties of high performance ductile engineered cementitious composites are tested through 60 specimens divided into 5 groups according to adding 5 various PVA fibres, the tensile strength, tensile elasticity modulus and the tensile pseudostrain-hardening stress-strain curves are obtained, the corresponding matrices are also tested for tension, the tensile strength relationships between different PVA fibres, and between tensile elasticity modulus and tensile strength are proposed according to the test results. In addition, multicracking can be see, and the ultimate tensile strain of partial high performance ductile engineered cementitious composites with filling different PVA fibres can reach to 3% which is 1000 times of the plain concrete. The influences of matrix and the different PVA fibres on ultimate tensile strain, peak stress and peak strain are analyzed by experimental data. At last, the tensile pseudostrain-hardening stress-strain curves are discussed, the experimental conclusions can provide a lot of experimental and theoretical bases for making the composites hold the high ductility consumption ability.

Numerical investigation on residual stress distribution and evolution during multipass narrow gap welding of thick-walled stainless steel pipes

Abstracts The detailed pass-by-pass finite element (FE) simulation is presented to investigate the residual stresses in narrow gap multipass welding of pipes with a wall thickness of 70 mm and 73 weld passes. The simulated residual stress on the outer surface is validated with the experimental one. The distribution and evolution of the through-wall residual stresses are demonstrated. The investigated results show that the residual stresses on the outer and inner surfaces are tensile in the weld zone and its vicinity. The through-wall axial residual stresses at the weld center line and the HAZ line demonstrate a distribution of bending type. The through-wall hoop residual stress within the weld is mostly tensile. After the groove is filled to a certain height, the peak tensile stresses and the stress distribution patterns for both axial and hoop stresses remain almost unchanged.

Dynamic strain aging in low cycle fatigue of duplex titanium alloys

The influence of dynamic strain aging (DSA) on low cycle fatigue (LCF) in duplex Ti-6-4 and SP700 titanium alloys was studied. LCF was performed within the temperature range from 350 °C to 450 °C, at strain rates of 10 −3 s −1 and 10 −4 s −1, and strain amplitudes of 1.25% and 2%. DSA appeared as serrations at the plastic portion of the cyclic stress–strain hysteresis loop, as well as stress humps appearing in the cyclic stress response (CSR) curve of peak tensile stress response versus cycle number. Strain-induced micro twin formation was only observed in the sample after fatigue with 2% strain amplitude under a 10 −4 s −1 strain rate, indicating that it is a DSA induced phenomenon.

Numerical modelling of failure of cement concrete using a unit cell approach

In this paper, a unit cell based approach is followed, where a unit cell consisting of one aggregate surrounded by mortar matrix is used for numerical simulation of mechanical response of cement concrete. Unit cell approach is a simple mathematical approximation that helps us to simplify the simulation of mechanical response of multi-phase composites. To model the failure of matrix, brittle cracking model is used, where the entire fracture zone is represented by a band of micro cracked material. Current study involves; (a) failure analysis of the concrete unit cell when it is subjected to tensile loads, and (b) parametric study of variation of peak strength with shape and volume fraction of aggregate. In this study, circular and square aggregates at various orientations are modelled. The simulation results predict that the peak tensile stresses are not very sensitive to the volume fraction of aggregates, when the unit cell is subjected to tensile loads. This paper effectively demonstrates the power of unit cell model in simulating the nonlinear mechanical response of cement concrete when it is subjected to tensile loading.

Dislocation structure evolution and its effects on cyclic deformation response of AISI 316L stainless steel

The cyclic deformation response of an austenitic stainless steel is characterised in terms of its cyclic peak tensile stress properties by three stages of behaviour: a hardening stage followed by a softening stage, and finally a stable stress response stage. A series of tests have been performed and interrupted at selected numbers of cycles in the different stages of mechanical response. At each interruption point, specimens have been examined by transmission electron microscopy (TEM) with different beam directions by means of the tilting function in order to investigate the formation and the development of dislocation structures from the as-received condition until the end of fatigue life. A new 3D representation of dislocation structure evolution during cyclic loading is proposed on the basis of the microstructural observations. The 3D representation provides a deeper insight into the development of dislocation structures in AISI 316L during low cycle fatigue loading at room temperature. By investigating the dislocation evolution, the study shows that the hardening response is mainly associated with an increase of total dislocation density, whereas the softening stage is a result of the formation of dislocation-free regions. Further development of the dislocation structure into a cellular structure is responsible for the stable stress response stage.

The elevated-temperature mechanical behavior of peak-aged Mg–10Gd–3Y–0.4Zr Alloy

Mg–10Gd–3Y–0.4Zr (wt.%) was peak-aged (solution heat-treatment at 490 °C/8 h with subsequent aging at 250 °C/16 h) and tested in tension and compression at temperatures between 25 °C and 350 °C, in fatigue at 25 °C and 300 °C, and in tensile creep at 250 °C and 300 °C. The tensile and compression testing showed high values of ultimate tensile stresses (UTS) and compressive peak stresses, both of which were above 300 MPa at temperatures up to 250 °C. At temperatures higher than 250 °C, the peak stresses rapidly decreased. The fatigue experiments indicated that the fatigue lives were not sensitive to temperatures between 25 and 300 °C. The fatigue limit was between 50 and 75 MPa. The creep experiments suggested that in the applied stress range of 30–120 MPa the dominant secondary creep deformation mechanism was dislocation climb. The dense distribution of precipitating prismatic particles in the matrix of the magnesium solid solution aided the creep resistance. In the lower-temperature and lower-applied stress creep regime (e.g. longer creep life), intensive creep cavitation was observed at the grain boundaries in the form of cavitated grain facets and a high fraction of cavitated boundaries (∼45%). In the higher-temperature and higher-stress creep regime, failure occurred in the form of mixed grain boundary cavitation and cracking. In both cases the preferred cavity and crack nucleation sites were particles of secondary phases situated on the grain boundaries or triple junctions.

Influence of prosthesis design and implantation technique on implant stresses after cementless revision THR

BackgroundFemoral offset influences the forces at the hip and the implant stresses after revision THR. For extended bone defects, these forces may cause considerable bending moments within the implant, possibly leading to implant failure. This study investigates the influences of femoral anteversion and offset on stresses in the Wagner SL revision stem implant under varying extents of bone defect conditions.MethodsWagner SL revision stems with standard (34 mm) and increased offset (44 mm) were virtually implanted in a model femur with bone defects of variable extent (Paprosky I to IIIb). Variations in surgical technique were simulated by implanting the stems each at 4° or 14° of anteversion. Muscle and joint contact forces were applied to the reconstruction and implant stresses were determined using finite element analyses.ResultsWhilst increasing the implant's offset by 10 mm led to increased implant stresses (16.7% in peak tensile stresses), altering anteversion played a lesser role (5%). Generally, larger stresses were observed with reduced bone support: implant stresses increased by as much as 59% for a type IIIb defect. With increased offset, the maximum tensile stress was 225 MPa.ConclusionAlthough increased stresses were observed within the stem with larger offset and increased anteversion, these findings indicate that restoration of offset, key to restoring joint function, is unlikely to result in excessive implant stresses under routine activities if appropriate fixation can be achieved.

Change of stress-strain hysteresis loop and its links with microstructural evolution in AISI 316L during cyclic loading

The cyclic deformation behaviour of an austenitic stainless steel and its links with microstructure are examined by analysing changes in the stress-strain hysteresis loop characteristics and dislocation condition with increasing cycle number. In terms of peak tensile stress, AISI 316L exhibits a hardening stage followed by a softening stage, and finally a stable response stage, during strain-controlled cyclic loading. During the hardening stage, dislocation density increases, mainly in the form of planar structures, i.e. stacking faults, pile-ups. Dislocations then rearrange to form walls and channels during the softening stage, which further develop to become a cellular structure later in this stage and during the final stable response stage. An analysis of the change in hysteresis loop shape during cyclic loading shows that the increase in dislocation density is responsible for an increase in effective stress. In addition, the long range internal stress (back stress), which is strongly sensitive to dislocation distribution and dislocation structure, is mainly responsible for the cyclic deformation response. The loop shape parameter and other quantities derived from the stress-strain hysteresis loop also evolve along with the development of the dislocation condition.