Maximum Total Strain Research Articles

Assessing river bank erosion on Majuli Island for strength and stability in resilient protection

ABSTRACT The present study addresses the issues and challenges of Brahmaputra river bank erosion near Majuli Island, Assam. For field study, the most vulnerable locations, namely (i) Ahatguri area, (ii) Okhala Chuk, (iii) Kamalabari ferry ghat, (iv) Cinnatoli Chapori and (v) Kandhulimari area are taken into consideration. Geometrical as well as geotechnical investigations were carried out to obtain detailed information for the stability analysis of river bank slopes of selected sites. Through 2-D finite element-based numerical tool PLAXIS2D, results indicated low stability of river bank due to low shear strength and ingress of moisture. To improve the strength and stiffness of the river bank soil, authors suggest a soil stabilisation technique using a Cement-Soil mixture with a 1:25 ratio (4%). The influence of improvement in the geotechnical properties was noted with the improvement in the stability of the river bank soil when assessed numerically. Results depicted that under ‘saturated and stabilized condition’, approximately 99% reduction in maximum total displacement and 55–85% reduction in maximum total strain was observed at all the five critical locations studied. Factor of safety values of stabilised bank was increased by 4.5 to 12 times, compared to the corresponding results obtained for ‘saturated and unstabilized’ condition.

Improving concrete fatigue resistance with COVID-19 rubber gloves: An innovative sustainable approach

Since the COVID-19 outbreak in late 2019, a surprisingly large amount of personal protective equipment, such as medical rubber gloves, have been frequently used, and this medical waste can cause very major environmental problems. A multidisciplinary collaborative approach is needed to combat the pandemic and lessen the environmental risks associated with the disposal of medical waste. This study developed an innovative approach by incorporating shredded rubber glove fibers (RGF) into aggregates to enhance the fatigue resistance of concrete. In this study, different volume contents (0.5%, 1.0%, 1.5%, 2.0%) of RGF were added to the aggregate for the first time. The effects of different RGF contents on the fatigue characteristics of concrete were examined through repeated loading tests and SEM analysis. The results show that the width and number of cracks produced by rubber glove fiber concrete (RGFC) after repeated loading are significantly reduced compared with normal concrete (NC). Following repeated loading, RGFC exhibited higher total, plastic, and elastic strain values than NC, demonstrating greater deformability and elasticity. However, the maximum total strain growth rate and the total strain growth range of the RGFC group were only 2.26 × 10−3/time and 14.0%, which were significantly smaller than the 3.8 × 10−3/time and 31.7% of the NC group, showing better stability, corresponding to enhance the fatigue resistance of concrete. The interfacial transition zone (ITZ) was abnormally smooth with a thin thickness and no visible gaps were discovered, based on the results of SEM test performed on the RGFC. The findings obtained in this study may provide new ideas for the resource utilization of medical waste.

Obtaining an Equiaxed Ultrafine-Grained State of the Longlength Bulk Zirconium Alloy Bars by Extralarge Shear Deformations with a Vortex Metal Flow.

The method of radial shear rolling makes it possible to achieve comparable to high pressure torsion (HPT) method ultrahigh degrees of total strain level in combination with the vortex metal flow character for long-length large bulk bars unable by HPT and many other processes of sever plastic deformation (SPD). Sequential rolling of the Zr-1%Nb alloy was carried out under extreme conditions on two radial shear rolling mills with a total diameter reduction ε = 185% and a maximum total strain level = 46 mm/mm. The strain level and its cross-section distribution assessment by finite element method (FEM) simulation was studied. The final bar cross-section structure type distribution detailed study 1 mm resolution by electron back scatter diffraction (EBSD) mapping was performed. A gradient structure with a predominance of the equiaxed ultrafine-grained (UFG) state was found. The deformation level rising did not allow to refine it in the periphery zone more than that obtained nearly middle of the processing, but it allows for significant change in the axial zone structure. The additional large warm deformations by radial shear rolling have no additional grain refinement effect for already 300-600 nm refined zone. An equiaxed UFG structure was obtained in a relatively large volume of the sample with a reduced gradient towards the non-UFG center zone in regard to known works.

Parametric stress-strain analysis for upstream slope of the asphaltic concrete core rockfill dams in static state

In this study, the effects of various geometric parameters of a dam in 2D static analysis of stress-strain on the upstream slope of the asphaltic concrete core rockfill dams were investigated. For this purpose, first the geometric characteristics of a large number of world's dams were collected and assessed, then by geometric modeling of these dams, many numerical models were developed for static analysis using GeoStudio software in eight height classes, three cases of upstream and downstream slopes, three different shape and thickness of the asphaltic concrete core under different Impounding states including "Full Reservoir", "Half full Reservoir", "End of construction and "Rapid Drawdown on a rigid type of foundation. The results of this study demonstrated that in four different construction and impounding states and in three different cases of slopes, Increasing the height parameter, causes increasing the Maximum total stress, Maximum total strain, Shear strain and Maximum shear stress for all construction and impounding states. The Maximum total stress decreased for all operating situations as the upstream slope reduced. According to the obtained results from the static stress-strain analysis, increasing both vertical and inclined asphaltic concrete core thicknesses, leads to decreasing the Maximum shear stress in Full Reservoir state but it increases in other state of impoundment. Moreover, by comparing the displacements related to specified points on the upstream slopes, increasing the height parameter, leads to increasing both horizontal and vertical displacements, the volumetric strain, deviator strain and deviator stress for all impounding conditions. In the following, the additional results were provided along with diagrams for further analysis.

Plastic and Elastic Strains in Poplar Wood under High-Pressure Densification

HighlightsHigh-pressure densification (HPD) resulted in more than 100% increase in the density of poplar wood.Density of wood during HPD treatment was up to 300% and 100% higher than observed before and after HPD.A method was developed to measure elastic recovery in the radial and tangential directions under HPD.Abstract. Plastic and elastic strains of poplar wood in the radial and tangential directions were investigated after high-pressure densification (HPD) using a special method that detected the elastic strain. There was a large difference in plastic and elastic strains obtained in compressed wood between the radial and tangential directions. The maximum total strain in the radial and tangential directions reached 26.9% and 66.9%, respectively, when compressed at 150 MPa for 300 s. Longer holding time (300 s) increased the plastic strain, by reducing the elastic strain, when the applied pressure was lower than 60 MPa. In addition, a large difference in compressed wood density prevailed when still under pressure as compared with the density measured after the pressure treatment, and both were nearly 1 to 3 times higher than the density of fresh wood. Further, the maximum density observed under pressure was related to the maximum reported density of dry crystalline cellulose plus the entrapped moisture. The mechanical properties of densified wood were also investigated and found to depend on the pressure treatment conditions. Keywords: Elastic strain, High-pressure densification, Mechanical properties, Plastic strain, Wood density.

Fatigue properties of Fe-28Mn-6Si-5Cr-0.5NbC alloy

In this study, we conducted a low-cycle fatigue testing in a Fe-28Mn-6Si-5Cr-0.5NbC (FMS) alloy and a SUS304 steel. The fatigue tests were made using a servo hydraulic fatigue testing machine of capacity 50kN, at maximum total strain amplitudes (εta) of 2.0%, 1.4%, 0.9%, 0.6%. In the SUS304 steel, with decrease in applied strain amplitude, stress-strain hysteresis loop is reduced. On the other hand, the stress response of the FMS alloy is almost unchanged, irrespective of the applied strain amplitude. The life to failure of the FMS alloy is 4 times higher at εta=0.6%, and twice at εta=0.9% and at εta=1.4% than the SUS304 steel. In addition, the stress amplitude of the FMS alloy is 2 times higher at εta =0.6 %, and 1.5 times higher at εta =0.6% than the SUS304 steel. The prolonged fatigue life of the FMS alloy is attributable to the reversible deformation associated with the transformation pseudo-elasticity that can reduce the accumulated strain.

Strain controlled fatigue testing of the metastable β-titanium alloy Ti–6.8Mo–4.5Fe–1.5Al (Timetal LCB)

The present work covers the mechanical behaviour of Timetal LCB under fatigue loading and utilizes transmission electron microscopy (TEM) to study the associated microstructural evolution. Fatigue specimens were taken out of LCB wire made for automotive suspension spring manufacturing in a solution treated as well as an additionally aged state. Uniaxial fatigue tests were carried out in total strain control with R = 0.1. Solution treated specimens tested at 3% and 4% maximum total strain showed a saturating force response, which differed from all other total strain controlled tests, and a distinct fracture behaviour. In addition, an increase of the dynamic Young's modulus is observed under these test conditions and in this material state. These findings are interpreted as a deformation induced precipitation of nanosize α- or ω-phase. In the aged state, the α-phase carries the major part of deformation work, noticeable by distinct α-substructures in fatigued specimen states.

Brittle-to-ductile transition in ultrathin Ta/Cu film systems

Current semiconductor technology demands the use of compliant substrates for flexible integrated circuits. However, the maximum total strain of such devices is often limited by the extensibility of the metallic components. Although cracking in thin films is extensively studied theoretically, little experimental work has been carried out thus far. Here, we present a systematic study of the cracking behavior of 34- to 506-nm-thick Cu films on polyamide with 3.5-to 19-nm-thick Ta interlayers. The film systems have been investigated by a synchrotron-based tensile testing technique and in situ tensile tests in a scanning electron microscope. By relating the energy release during cracking obtained from the stress-strain curves to the crack area, the fracture toughness of the Cu films can be obtained. It increases with Cu film thickness and decreases with increasing Ta film thickness. Films thinner than 70 nm exhibit brittle fracture, indicating an increasing inherent brittleness of the Cu films.

In Situ X-Ray Diffraction Study of Load Partitioning and Microyielding for the Super Duplex Stainless Steel SAF2507 (UNS S32750)

The deformation behaviour of the super duplex stainless steel SAF2507 (UNS S32750) under successive uniaxial tensile loading-unloading was investigated with respect to load sharing and inter-phase interactions. The steel consists of 58% austenite and 42% ferrite in volume. By insitu X-ray diffraction experiment the evolution of phase-specific stresses with applied load was monitored for three successive loading-unloading cycles with the maximum total strains being 0.34%, 0.75% and 1.63%, respectively. It was found that yielding occurred earlier in the austenitic phase than in the ferritic phase during the first loading cycle. In the followed loading cycles, both phases yielded under larger but similar applied stresses. Due to a similar behavior of the phases in the elasto-plastic regime inter-phase interactions were relatively weak. Low microstresses induced by the plastic straining resulted in somewhat larger stresses in the ferritic phase.

Size distribution of surface cracks and crack pattern in austenitic SUS316 steel plates fatigued by cyclic bending

The size distribution of surface cracks and the crack pattern were examined on the specimens of the SUS316 steel plates fatigued by cyclic bending. The size distribution of the cracks could be approximated to a logarithmic normal distribution, irrespective of the maximum total strain range or the number of fatigue cycles. The number of the cracks (Nu) of the length (x′) equal to or larger than a given size (X) could be approximated to a power law, Nu∝ X−a, with a scaling exponent a at the larger crack sizes in the fatigued specimens of the SUS316 steel. The value of a decreased with increasing the number of fatigue cycles because of the increase in the number and size of fatigue cracks, and was larger in the specimens tested at the smaller total strain range. Effects of experimental variables on the scaling exponent (a) were also shown in this study. The fractal dimension of spatial crack distribution (the fractal dimension of crack pattern) (D) increased in the range from about 0.9 to about 1.2 with increasing the number of fatigue cycles, and was larger in the specimens fatigued at the larger total strain range. There was a negative correlation between the value of a and the value of D on fatigue cracks, although there was no unique relationship between these two values.

Mechanical behaviour and microstructural evolution of a microalloyed C-Mn steel during hot forming process

The mechanical behaviour of a C-Mn steel is investigated under different thermomechanical paths, in order to determine its constitutive equation in industrial hot rolling conditions. Compression tests were performed and the maximum admissible strain level so that friction remains negligible was determined by numerical simulation. The limited maximum total strain requires selecting the key features of the thermomechanical path. It is shown that the austenitising temperature has a great influence on the mechanical and microstructural evolution of the steel. The influence of recrystallization in the roughing mill on the mechanical behaviour has been investigated by double compression tests, and seems not to be very important. The influence of strain and austenitising temperature on the phase transformation has also been studied. The austenitising temperature strongly affects the grain size, and the kinetics of phase transformation can be well understood using this parameter. But the strain raises the transformation start temperature up to a point at which the grain size is not a relevant parameter.

Package-to-Board Attach Reliability — Methodology and Case Study on OMPAC Package

Over molded pad array carrier (OMPAC), also called plastic Ball Grid Array (pBGA) package family offers increased I/O density at the board level; further, package size and thickness are reduced in comparison to other competing package types leading to many product applications. The OMPAC package is investigated for solder pad interconnect reliability. Elastic and inelastic finite element method (FEM) simulations are employed with experimental temperature cycling data. Linear elastic analyses are performed for various package parameters that influence the stress distribution in the solder pad interconnect for temperature loading. The package parameters considered are (a) ratio of thickness of die to substrate (tdie/tsub.), (b) ratio of width of die to substrate (wdie/wsub.), and (c) ratio of height to diameter of the solder pad interconnect ((h/d)pad). The results are evaluated based on the maximum Tresca (maximum shear stress) failure criterion. The key parameter is (h/d)pad ratio. As this ratio increases, the maximum Tresca failure criterion decreases. The performance of the solder pads are evaluated based on the maximum total permanent strain (plastic + creep) range per temperature cycle. FEM simulation was performed up to eight consecutive temperature cycles. The permanent strain (plastic + creep) range were calculated for each temperature cycle and observed that after a few temperature cycles the strain ranges stabilize. The maximum stabilized total permanent strain range is in the inner solder pad and is equal to 0.005. This maximum total strain range in the solder pad per temperature cycle loading can be used to estimate the life time of the solder pads. The FEM simulation results are correlated with the experimental data. Both the simulation and the experimental results are indicate that the outer pads are not as critical as the inner or the middle pads. The experimental results indicate that there is slightly larger probability for the middle pads to fail before the inner pads. However, the simulation data indicate that the inner pads are more critical than the middle pads. We believe that this small discrepancy in simulation result is due to the actual temperature variation on the package not being included in the present analysis.

A TWO-PHASE OPTIMIZATION METHOD FOR MINIMUM-WEIGHT DESIGN OF TRUSSES

In this paper, a new twp-stage procedure for the minimum weight design of trusses is proposed. In the first stage (behavior phase) of optimization the behavior variables (joint displacements) are chosen as basic unknowns and the optimum displacement state of the truss or its searched region is found by using a maximum total strain energy criterion with linear programming. In the second stage (structural phase) the design variables (cross-section areas) are chosen as basic unknowns and the minimum weight design of the truss is obtained by using another linear program or a direct search technique. This method is effective for the minimum weight design of truss type structures with stress, displacement and geometric constraints. In most cases it can avoid the need for repeated iterations and structural reanalyses. Moreover, a minimum-maximum total strain energy criterion to select the optimal layout of structures is presented in this paper.

Fatique design of machine elements using the “Bagci line” defining the fatigue failure surface line (mean stress diagram)

Recently proposed fatigue failure surface line of Bagci that updates the Modified Goodman's, Gerber's, and Kececioglu's mean stress diagrams for the fatigue design of machine elements subjected to cyclic combined stresses having nonvanishing mean stress is presented [1]. It fits the most recent fatigue data well and defines the two design zones in the mean stress diagram in one zone limiting the zone by the yield strength of the material, thus, providing a unified fatigue design equation for machine members. Its incorporation with the basic stresses according to different strength theories, such as the maximum distortion energy theory, maximum shearing stress theory, maximum total strain energy theory, and Coulomb-Mohr theory is given. The method of determining theoretical geometric stress concentration factor for combined state of stress—which is used along with the notch sensitivity of the material to determine a fatigue strength reduction factor—is also given. Applications of the Bagci line to the fatigue design of machine members are shown with numerical examples.

The effects of out-of-phase biaxial-strain cycling on low-cycle fatigue

The effects of out-of-phase or nonsynchronous straining on low-cycle fatigue was investigated. Biaxial strains were imposed on thin-walled tubular 7075-T6 aluminum specimens by tension—compression and torsion. Phase angles of 0 deg, 30 deg, 45 deg, 60 deg and 90 deg were applied between two strains. It was found that out-of-phase cycling has an effect on the failure mode in the low-cycle-fatigue range. An analysis based on the maximum total strain in three-dimensional strain is proposed for treating “out-of-phase” straining conditions in low-cycle fatigue.