Longitudinal Tensile Stress Research Articles

Stresses and fatigue of laser welds

The paper deals with the specific properties of laser welds in fine-grained high-strength steels. The main topic, however, are residual stresses in laser welds, their impact on the mechanical properties and fatigue behaviour of such welds. As documented, fatigue cracks initiate mainly on micropores or other subsurface defects. From X-ray diffraction studies it follows that thermal expansion is primarily responsible for the longitudinal tensile stresses, whereas transverse compressive stresses are caused by phase transformations. The behaviour of transverse stresses also explains why fractures in laser welds occur completely outside the weld metal and the heat-affected zone.

Application of the Finite Element Method to Reveal the Causes of Loss of Planeness of Hot-Rolled Steel Sheets during Laser Cutting

A finite element technique is developed to simulate the stresses and the strains during strip flattening to reveal the causes of the cutting-assisted loss of planeness of hot-rolled steel sheets processed in roller levelers. The loss of planeness is found to be caused by a nonuniform distribution of the flattening-induced longitudinal tensile stresses over the strip thickness and width. The application of tensile forces to a strip in a roller leveler decreases this nonuniformity and prevents loss of planeness in cutting.

Strength evaluation of unidirectional carbon fiber-reinforced plastic laminates based on tension–compression biaxial stress tests

Biaxial stress tests of carbon fiber-reinforced plastic (CFRP) laminates were performed to investigate failure criteria under biaxial loads. Specimens of unidirectional CFRP laminates were subjected to a tensile load in the longitudinal fiber direction and a compressive load in the transverse fiber direction. An exclusive jig was used to perform biaxial stress tests with a commonly used single-axis testing machine. Measurements were obtained by controlling the displacement ratio between compressive and tensile displacements. The critical tensile and compressive stresses were then calculated using a constitutive equation. The critical longitudinal tensile stress markedly dropped with increasing the compressive load. The failure criteria of the biaxial stress tests were expressed as the ellipse, of which the major and minor axes were the longitudinal tensile/transverse compressive strengths or fracture strains, respectively. Scanning electron microscope observations suggest that fiber/matrix interfacial debonding due to the compressive load could decrease the critical longitudinal tensile stress.

Influence of martensitic transformation on welding residual stress in plates and pipes

ABSTRACTMartensitic filler metals with low transformation temperatures can efficiently mitigate harmful tensile welding residual stress. It is vital to clarify the difference in the influence of martensitic transformation for different shapes of welded joints. This article outlines the influence of martensitic transformation in a butt-welded plate and a butt-welded pipe which were designed to have the same dimensions of the cross-section perpendicular to weld line. A clear difference in the influence of martensitic transformation was found in these two joints. Longitudinal tensile stress in weld zone is efficiently reduced in both joints, whereas longitudinal tensile stress is formed in base metal near the weld zone in the pipe. A notably greater influence on transverse stress is found in the pipe than in the plate.

A Comparison of the Constitutive Response of Austenitic and Ferritic Steels under Welding Processes

The need to accurately measure and predict weld residual stresses (WRS) has led to several examinations intent on developing best-practice guidelines in the assessment of welded structures. The present investigation examines two benchmark weld specimens; both specimens are autogenous edge-welded beams, with welds deposited using a mechanised tungsten inert gas process. However, one of the beams was made from AISI 316LN austenitic steel, while the other was made from SA508 Gr.3 Cl.1 ferritic steel. Considerable differences in the cross-weld residual stress profile were observed between the two beams, prompting a detailed examination of why such differences exist. Computational weld mechanics was used to assess both processes; model validation was achieved using previously reported WRS and micro-hardness measurements. A comparison of the numerical solutions indicates that the shape misfit resulting from a sharp weld-induced thermal gradient causes significant longitudinal tensile stresses in the heat-affected zone in both specimens. The presence of influential solid-state phase transformations in the ferritic specimen leads to the formation of compressive stresses in the weld metal, while the stresses remain tensile in the weld metal region of the austenitic specimen. The compressive stresses in the ferritic specimen serve to offset the tensile stresses in the HAZ, leading to a reduction of the self-equilibrating WRS present in the ferritic parent metal.

Residual stress distribution in friction stir welded ODS steel measured by neutron diffraction

The residual stress distributions in oxide dispersion-strengthened steel plates, joined by Friction Stir Welding, have been mapped using neutron diffraction. The measured stress maps were interpreted in terms of the temperature profiles measured for welds using three different tool traverse speeds. The largest peak longitudinal tensile stresses, ∼1200MPa, were found in the weld produced using the fastest tool traverse speed, and corresponds to relatively high cooling rates. A reduction in tool traverse speed yields a significant decrease in tensile residual stresses in the thermo-mechanically affected zone of the welds, but also causes higher peak temperatures during welding. The transverse residual stresses were not found to be affected by the tool traverse speed and were significantly lower in magnitude than the longitudinal stresses. Additionally, the torque profiles measured during welding increased with the amount of material stirred and therefore correlated with the width of the thermo-mechanically affected zone of the welds.

Modeling and estimation of process-induced stress in the nanowire field-effect-transistors (NW-FETs) on Insulator-on-Silicon substrates with high-k gate-dielectrics

An analytical model including the simultaneous impact of lattice and thermo-elastic constant mismatch-induced stress in nanowires on Insulator-on-Silicon substrate is developed. It is used to calibrate the finite-element based software, ANSYS, which is subsequently employed to estimate process-induced stress in the sequential steps of NW-FET fabrication. The model considers crystal structures and orientations for both the nanowires and substrates. In-plane stress components along nanowire-axis are estimated for different radii and fractions of insertion. Nature of longitudinal stress is observed to change when inserted fraction of nanowires is changed. Effect of various high-k gate-dielectrics is also investigated. A longitudinal tensile stress of 2.4 GPa and compressive stress of 1.89 GPa have been obtained for NW-FETs with 1/4th and 3/4th insertions with La2O3 and TiO2 as the gate-dielectrics, respectively. Therefore, it is possible to achieve comparable values of electron and hole mobility in NW-FETs by judiciously choosing gate-dielectrics and fractional insertion of the nanowires.

MANUFACTURE OF ACOUSTICAL ONE SIDE-WAFFLE PANEL MADE OF NATURAL RESOURCES WITH HYDRAULIC HOT PRESS MACHINE

Waste generated from natural resources should be recycled as more useful materials. This research has produced acoustical waffle panel material which is useful as an absorber on the noisy housing. Acoustical waffle panels was made by Hydraulic Hot Press machine. The purpose of this discussion is to describe the machine design process and compare waffle panels made of coconut fiber and wood sawdust in the best acoustic performances. The result is that the hydraulic hot press machine has the structural strength and stability on the load of 2,500 N and 5,000 N. The hot press machine is safe for both the transverse tensile stress and longitudinal tensile stress which are smaller than the allowable stress of steel material of 40 at 1,100 kg/cm2. It also has the highest Sound Transmission Loss (STL) with the value of 40. 059 dB.

PROCESS RESIDUAL STRESSES IN THE PRODUCTION OF ZIRCONIUM SHEETS

The study reviews an experimental and theoretical method of residual stress detection in metal strips made of zirconium alloys showing transversely isotropic properties after cold rolling. Research results demonstrate significant transverse and longitudinal residual tensile stresses appearing on a strip surface. The nature of their distribution is qualitatively consistent with known patterns of distribution of these values during rolling process.

Effects of Solar Temperature Gradient on Long-Span Concrete Box Girder during Cantilever Construction

AbstractThree-dimensional (3D) finite-element analysis of a 106 × 200 × 106-m concrete box girder was conducted to study the effect of solar temperature gradients on long-span bridges during construction. Segments over the internal piers and at midspan were investigated to obtain temperature distributions and thermal stresses during critical times of the day. On the basis of results of the thermal analysis, temperature gradients were developed for 0600 and 1500 hrs. to be used on the entire bridge. The maximum longitudinal tensile stress in the girder was 2.67 MPa, whereas lateral tensile stress could reach 4.41 MPa. Therefore, appropriate measures must be taken during construction to avoid cracking of the box girder. A 3D model of half the entire bridge was analyzed to obtain the effects of thermal loads on the bridge in its longest cantilever construction stage. The maximum vertical deflection at the cantilever end reached 46.0 mm at 1500 hrs., when the effect of temperature was highest. It was conclude...

New method of assessing susceptibility of welds to transverse cracking

A method for assessing the susceptibility of a weld to transverse cracking is proposed based on a newly designed test specimen featuring a transverse gap in the centre to control restraint and produce a large residual stress in the weld metal. Through FEM simulation of the effects of the weld bead length on the longitudinal residual tensile stress (σx) after welding, it is confirmed that the transverse gap can significantly increase σx after welding. Furthermore, with a fixed transverse gap length, σx increases monotonically with the length of the weld bead. Two different commercial weld wires were used to check the effectiveness of this method; the experimental results obtained indicate that the critical cracking length of the weld bead differs depending on the weld wire used. The critical length of the weld bead can therefore be used as an effective index of its susceptibility to transverse cracking.

Анализ напряженно-деформированного состояния в черновых проходах непрерывной прокатки электротехнической меди

The aim of the work is to analyze the stress-strain state in rough rolling in Mannesmann Demag Sack continuous mill. Computer experiments involved the use of DEFORM software package, and the finite element method was used to solve the problem. The change of the billet shape, distribution of the strain degree, strain rate and longitudinal stresses are analyzed. In the fourth rolling pass, the zones of increased strain (up to 1.00 and above) are arranged along the circle arcs adjacent to the roll gap. The highest strain rate (up to 145 s –1 ) is also achieved at the inlet of the deformation zone directly beneath the rolls. It is established that in all rough passes the greatest strain is localized at the outlet of the roll gap near the peripheral zones. The highest strain rate in each investigated pass is observed in contact areas at the inlet of the deformation zone. The largest longitudinal tensile stresses arise at the inlet and outlet of the deformation zone in non-contact areas. At the same time emergence of a large tensile stress on free surfaces during rolling of a rectangular billet in an oval caliber is revealed which can lead to the disclosure of cracks inherited from the foundry process.

Effect of maleated compatibilizer on anisotropic mechanical properties, thermo-oxidative stability and morphology of styrenic based thermoplastic elastomer reinforced with alkali-treated pineapple leaf fiber

Composites of styrenic based thermoplastic elastomer reinforced with pineapple leaf fiber (PALF) were prepared by melt mixing on a two-roll mill, sheeted out with some stretching to preferentially orient the fiber along the machine direction and then compression molded to form a composite sheet. The effects of alkali treatment of PALF surface and compatibilizer loading on thermo-oxidative stability, tensile and dynamic mechanical properties of the composites were investigated. The alkali-treated PALF showed a smooth surface and has higher thermo-oxidative stability when compared with the untreated fiber. The respective increase in thermo-oxidative stability was found for the composites of alkali-treated fiber and alkali-treated fiber with the presence of compatibilizer. The tensile stress in the longitudinal direction clearly increased with fiber loading. The reinforcing performance was clearly improved for the alkali-treated fiber composite system when compared with that of the untreated fiber composite. For the alkali-treated PALF containing compatibilizer system, the longitudinal tensile stress of the composite could be improved further as higher than four times that of the neat matrix. The results of stress ratio anisotropy revealed that the improvement in tensile stress for the treated fiber composite systems was observed in longitudinal direction under stretching up to 250 % strain. The effects of fiber surface treatment and compatibilizer were less significant in the transverse direction. The glass transition temperatures for soft and hard phases of the elastomer matrix were not significantly affected by fiber treatment and compatibilizer loading.

Numerical Investigation on Interruption in the Welding Process Used in Shipbuilding

Interruptions in the welding process in shipbuilding are unavoidable because of complex geometry and human fatigue. This article presents an uncoupled three dimensional finite element (FE) modeling technique for bead-on-plate welding and an interruption in the welding process for low carbon and high notch toughness steel plate typically used in shipbuilding. The goal of the FE model was to successfully predict the effect of various time delays in the welding interruption on the residual stress distributions. The FE results are compared with the experimental results for the validation of the model. The experimental work was completed using the neutron diffraction method. The element birth-and-death algorithm was used in ANSYSW to simulate the filler metal deposition. A double ellipsoid heat source was used to simulate the heat source of the weld pool. The FE model considers the temperature dependent nonlinear material properties and uses the temperature-dependent combined coefficient of heat loss. The study found that weld interruptions in the welding process change the residual stress patterns and cause an increase in the maximum longitudinal tensile residual stresses. However, the maximum longitudinal compressive stress reduces as a result of interruptions in the weld process. This study found that a weld interruption duration of approximately 2 minutes is optimum for both fatigue and buckling strength. This study also analyzed the effect of preheat on longitudinal residual stress distribution and concluded that a suitable short time lag without any preheat is equivalent to preheat after a long welding interval.

Effect of tool rotational speed on residual stress, microstructure, and tensile properties of friction stir welded 6061-T6 aluminum alloy thick plate

In the present study, the effect of tool rotational speed on residual stress, microstructure, and tensile properties of friction stir welded AA 6061-T6 was investigated. AA 6061-T6 plates with a thickness of 16 mm were friction stir welded using three different tool rotational speeds of 500, 700, and 900 rpm and a constant welding speed of 120 mm/min. The results indicate that the longitudinal residual stress distribution is an M-shaped distribution in the transverse direction; in weld region, the tensile longitudinal stress in the advancing side is larger than that in the retreating side. With increasing rotation speed, the values of the tensile longitudinal residual stresses increased slightly, the peak tensile longitudinal stresses appear at the edge of the shoulder in the AS of the joints, and the maximum value of tensile longitudinal residual stress was 153 MPa with the rotation speed of 900 rpm which reaches up to 55 % of the yield strength of AA 6061-T6. Meanwhile, only the appearance of welded joint with 700 rpm is smooth. The grain size in WNZ grows up with increasing the rotation speed. The microhardness variation is determined by microstructure evolution, and the average microhardness decreases with increasing the rotation speed. The welded joint with the rotation speed of 700 rpm performs the maximum tensile strength of 236 MPa which is 76 % of the base material strength.

Analysis of stress-induced mobility enhancement on (100)-oriented single- and double-gate n-MOSFETs using silicon-thickness-dependent deformation potential

The stress effect in uniaxially strained single- and double-gate silicon-on-insulator n-type metal oxide-semiconductor field effect transistors (MOSFETs) with a (100) wafer orientation is analyzed. A model of silicon-thickness-dependent deformation potential is introduced to accurately calculate the mobility using a Schrödinger–Poisson solver. Simulation results using the model exhibit excellent agreement with the measured mobility for both the unstrained and strained conditions. Electron mobility enhancements with longitudinal and transverse tensile stress conditions are simulated as a function of silicon thickness. The mobility enhancement in the single-gate case has one peak point, whereas it produces two peak points in the double-gate case. An in-depth analysis reveals that this phenomenon results from the hump in the energy difference between the Δ2 and Δ4 valleys, which in turn results from the volume inversion in the double gate.

ANALYSIS OF DEFLECTED MODE IN THE DEFORMATION ZONE DURING THE ROD ROLLING IN VARIOUS CALIBER SYSTEMS BASED ON THE MODELING BY FINITE ELEMENT METHOD

In the article the stressed state of metal in the deformation zone during hot rolling of rod using the finite element method for computer simula- tion in program system DEFORM-3D are analyzed. The methodology for evaluation of the stressed state during the high-speed hot rolling of rod is presented. The known systems of calibers are analyzed. The factors of roll pass design, which influence the magnitude and distribu-tion of the longitudinal tensile stresses in the deformation zone, are determined.

Magnetoimpedance and Field Sensitivity of CoFeSiB Amorphous Ribbons under Applied Tensile Stress

Magnetoimpedance (MI) and field sensitivity of CoFeSiB amorphous ribbons were investigated at frequencies ranging from 0.2 to 12 MHz after tensile stress applied. Experimental results indicate that the MI of amorphous ribbons can be significantly improved by applying a suitable longitudinal tensile stress. Applying tensile stress induces a rearrangement of domain walls which influences the circumferential anisotropy and magnetic permeability result in improving the MI response. The maximum MI response of 145 % and maximum field sensitivity of 6.32 %/Oe at frequency of 4 MHz were obtained, when tension was equivalent to 120 MPa. So the tensile stress as new method can be effective, cheap, and fast in sensor applications, and result of this investigation can be applied for the design of the stress sensors based on the giant magnetoimpedance effect.

Evaluation of Transverse Tensile Stress Characteristics of GdBCO Coated Conductors

Recently, GdBCO coated conductor (CC) coils for high field magnets are investigated for practical use. GdBCO CC coils are subjected to longitudinal and transverse tensile stresses in their operation, so there is some research for mechanical properties of the GdBCO CCs in the recent years. Fujikura has also researched mechanical properties, for example, tensile or delamination strength, of the GdBCO CCs. In this report, we investigated pin-pull delamination test in Liquid nitrogen (LN2) to research mechanical delamination and critical current (Ic) degradation strength. We found out mechanical delamination strength is corresponding to Ic degradation strength. In addition, we experiment repeated transverse tensile stress on GdBCO CCs in LN2, most of the samples have more than 50 times at 50MPa, which corresponds to single delamination strength, and there is no Ic degradation before mechanical delamination.

表面機械加工層を有する低炭素オーステナイト系ステンレス鋼の溶接熱影響部に生じる極大残留応力とその影響因子

In this study, the effects of work-hardening and pre-existing stress in the machined surface layer of low-carbon austenitic stainless steel on the welding-induced residual stress were experimentally investigated through the use of weld specimens with three different surface layers; as-cutout, mechanically-polished and electrolytically-polished. The high tensile and compressive stresses exist in the work-hardened surface layer of the as-cutout and mechanically-polished specimens, respectively. Meanwhile, no stress and work-hardened surface layer exist in the electrolytically-polished specimen. TIG bead-on-plate welding under the same welding heat input conditions was performed to introduce the residual stress into these specimens. Using these welded specimens, the distributions of welding-induced residual stress were measured by the X-ray diffraction method. Similarly, the distributions of hardness in welds were estimated by the Vickers hardness test. And then, these distributions were compared with one another. Based on the results, the residual stress in the weld metal (WM) is completely unaffected by the machined surface layer because the work-hardened surface layer disappears through the processes of melting and solidification during welding. The local maximum longitudinal tensile residual stress in the heat affected zone (HAZ) depends on the work-hardening but not on the existing stress, regardless of whether tensile or compressive, in the machined surface layer before welding. At the base metal far from WM and HAZ, the residual stress is formed by the addition of the welding-induced residual stress to the pre-existing stress in the machined surface layer before welding. The features of the welding-induced residual stress in low-carbon austenitic stainless steel with the machined surface layer and their influential factors were thus clarified.