Longitudinal Compressive Strain Research Articles

Experimental study on the dynamic characteristics of bi-block ballastless track under the combined action of vehicle load and temperature gradient

The unit ballastless track structure, persistently exposed to environmental conditions, experiences significant vertical temperature gradients, leading to warping deformation of the track bed and impacting track smoothness. This study investigates the relationship between temperature gradients and warping deformation of the track bed through the analysis of on-site measurement data combined with a dynamic simulation model. It also examines how temperature gradients influence the dynamic response and the interlayer contact area of the ballastless track. Findings reveal that vertical displacement of the track bed follows a diurnal cycle and shows a positive correlation with temperature gradients, with pronounced differences between the slab's corners and center. Under a positive temperature gradient, the vertical displacement of the track bed is high in the middle and low at the ends, with the vehicle load causing longitudinal tensile strain in the slab’s side surface center. Conversely, under a negative temperature gradient, the vertical displacement is low in the middle and high at the ends, with the vehicle load inducing longitudinal compressive strain in the slab’s side surface center. Additionally, warping deformation of the track bed leads to incomplete contact with the base plate, creating a local support state and reducing interlayer contact area as the gradient increases. Positive temperature gradients result in an "oval" distribution of interlayer delamination areas, while negative gradients mainly affect the sides and ends. Dynamic loads from trains temporarily counteract warping deformation, briefly increasing the interlayer contact area, but their effectiveness diminishes as temperature gradients rise.

Raising the stimulated Brillouin scattering threshold power by a longitudinal compression gradient in a fiber amplifier

We propose and demonstrate an analysis of our approach to enhance the threshold power of stimulated Brillouin scattering (SBS) in optical fibers, using a longitudinal compressive strain gradient. We derive analytical expressions for the power spectral density of the backscattered Stokes wave in the general case of passive and amplifying optical fibers, by considering the strain and optical power distributions. Our method provides an accurate prediction of the SBS gain spectrum, which we illustrate with a quantitative comparison between measurements and calculations of the SBS Stokes spectra, before and after applying the compression gradient. Our experimental results demonstrate the successful enhancement of the SBS threshold power by a factor of about three for the passive fiber and two for the amplifying fiber. The enhancement that we manage to calculate in the case of the passive fiber is in perfect agreement with the experimental results.

Strain and Strain Rate Tensor Mapping of Medial Gastrocnemius at Submaximal Isometric Contraction and Three Ankle Angles.

The aim of this study is to analyze the muscle kinematics of the medial gastrocnemius (MG) during submaximal isometric contractions and to explore the relationship between deformation and force generated at plantarflexed (PF), neutral (N) and dorsiflexed (DF) ankle angles. Strain and Strain Rate (SR) tensors were calculated from velocity-encoded magnetic resonance phase-contrast images in six young men acquired during 25% and 50% Maximum Voluntary Contraction (MVC). Strain and SR indices as well as force normalized values were statistically analyzed using two-way repeated measures ANOVA for differences with force level and ankle angle. An exploratory analysis of differences between absolute values of longitudinal compressive strain (Eλ1) and radial expansion strains (Eλ2) and maximum shear strain (Emax) based on paired t-test was also performed for each ankle angle. Compressive strains/SRs were significantly lower at 25%MVC. Normalized strains/SR were significantly different between %MVC and ankle angles with lowest values for DF. Absolute values of Eλ2 and Emax were significantly higher than Eλ1 for DF suggesting higher deformation asymmetry and higher shear strain, respectively. In addition to the known optimum muscle fiber length, the study identified two potential new causes of increased force generation at dorsiflexion ankle angle, higher fiber cross-section deformation asymmetry and higher shear strains.

Mechanical response of cross-tensioned concrete pavement: experimental study and finite element

ABSTRACT The cross-tensioned concrete pavement (CTCP) has good bearing capacity, anti-crack ability and convenient construction characteristics due to the cross-tenioned prestressed strands placed inside the concrete. In order to study the mechanical response of pavement in construction process, an assembled monolithic structure for CTCP has been proposed and its mechanical response was analyzed through full-scale experiments and finite element model. The results of full-scale experiments show that the longitudinal and transverse compressive strain of concrete respectively exceeds 40μϵ and 20μϵ in the area of laying cross-tensioned prestressed strands with increase of the number of cross-tensioned strands. The end of CTCP is one of the weak areas, which may produce certainly transverse tensile stress. The results of finite element model show that the transverse tensile stress in ending region is mainly affected by the angle of cross-tensioned prestressed strands and its ratio. There is transverse tensile stress at the end of the pavement when the angle of cross-tensioned prestressed strands is small and its ratio is large, which can be offset by arranging transverse prestressed strands. Furthermore, an empirical formula to calculate transverse prestressed strands ratio at the end of pavement is given based on the results of finite element simulation.

Mechanical Test of Sleeve Grouted Lapping Connectors under Uniaxial Tension and High-Stress Repeated Tension and Compression Loading

In this study, uniaxial tension tests and high-stress repeated tension and compression tests were conducted on 32 APC (all vertical members precast in concrete structures) connectors. After high-stress repeated tension and compression, the bearing capacities of the connector specimens improved due to the strengthening of the steel bars, and the ductility of the specimens was reduced due to the further development of cracks between the steel bars and the grout. The residual deformation values of the specimens, namely u0 (uniaxial tension) and u20 (repeated tension and compression), were reduced with the increase in the lapping length of the specimens. The longitudinal compressive strain and hoop tensile strain of the middle section of the sleeve near the steel bar side were reduced under the ultimate load state when the specimens were stretched under uniaxial tension and in the last tension process after repeated loading with the increase in the lapping length. The distribution and development of the longitudinal compression stress of the sleeve were analysed based on the bonding stress of the steel bar and concrete. Finally, the ultimate bonding strength and critical lapping length formulas were proposed, which involved the introduction of a grouting defect coefficient ω.

Residual post fire strength of non-prismatic perforated beams

The main aim of this study is to assess the performance and residual strength of post-fire non-prismatic reinforced concrete beams (NPRC) with and without openings. To do this, nine beams were cast and divided into three major groupings. These groups were classified based on the degrees of heating exposure temperature chosen (ambient, 400, and 700°C), with each group containing three non-prismatic beams (solid, 8 trapezoidal openings, and 8 circular openings). Experimentally, given the same beam geometry, increasing burning temperature caused degradation in NPRC beams, which was reflected in increased mid-span deflection throughout the fire exposure period and also residual deflection after cooling. But on the other hand, the issue with existing openings was exacerbated. The burned NPRC beams were then gradually cooled down by leaving them at ambient temperature in the laboratory, and the beams were loaded until failure to examine the effect of burning temperature degree on the residual ultimate load-carrying capacity of each beam by comparing them to unburned reference beams. It was found, increasing the exposure temperature leads to a reduction in ultimate strength about (5.7 and 10.84%) for solid NPRC beams exposed to 400 and 700°C, respectively related to unburned one, (21.13 -32.8) % for NPRC beams with eight trapezoidal openings, and (10.5 - 12.8) % for those having 8 circular openings. At higher loading stage the longitudinal compressive strain of Group ambient in mid-span of solid beams reach 2700 με, while the others with openings exhibit divergent strain higher than that, it’s about 3300 με meanwhile, the lower chord main reinforcements have been pass beyond yielding stress. Exposure to high temperatures reduces rafters’ stiffness causing a reduction in load carrying capacity, companion with premature failure consequently reduce the strain at the ultimate stage.

Analysis and suppression of flange wrinkling in AHSS chain-die forming channels with a curved axis

Chain-die forming can be used to manufacture Advanced High Strength Steels (AHSS) channel components. Flange wrinkling is one of typical defects for chain-die formed products. The purpose of this paper is to investigate the cause of flange wrinkling in chain-die forming of AHSS and to propose a potential method to suppress it. A hat channel product with a curved axis is formed as a benchmark to illustrate the mechanism of flange wrinkling in chain-die forming. When forming such a profile, longitudinal compressive strain of the sheet metal is geometrically necessary, and the compression has to be achieved by plastic wrinkling due to the insufficient restricted boundary condition. Finite element models are established to better understand the complex interaction between the tools and plate. An initial imperfection calculated from the differential equilibrium equations for elastic plates with small deflections is implemented into the finite element model to predict occurrence of the flange wrinkling. In order to eliminate the wrinkling defect, an M-shaped die design is proposed, which intends to provide additional restriction to the sheet metal and increase longitudinal and transversal tension. A three-factor, three-level Design of Experiment (DOE) scheme for the M-shaped die design is conducted. The DOE results show that a benign wrinkling always corresponds to a larger compressive strain and the width of the ears for M-shaped dies is a decisive factor to suppress wrinkling. The verification experiments show that the plastic flange wrinkling is completely eliminated by employing the proposed method.

Plastic hinge and seismic structural measures of terminal stirrup-confined rectangular CFT columns under low-cyclic load

Based on the plastic-damage constitutive model of concrete and elastic-plastic mixed strengthen constitutive model of steel material, the finite element software ABAQUS was used to build an elaborate 3D finite element (FE) solid model and perform pseudo-static analysis of terminal stirrup-confined concrete-filled rectangular steel tubular columns (SCFT) in this study. The FE model considers the confinement effect of both the steel tube and the stirrups exerting on the core concrete and the cumulative damage effect due to the horizontal cyclic load. Good agreement was achieved between the FE results and the existing quasi-static experimental results regarding to the load-displacement hysteretic curves, load-displacement skeleton curves, load-strain ratio curves, and local buckling-displacement curves. Based on the validated model, a total of 315 full-scale column models were established and extensive parametric analysis was conducted. The results indicate that: (1) When the axial compression ratio n is up to 0.8, the seismic behavior of rectangular CFT columns with bidirectional stirrups is significantly better than those counterparts with ring stirrups having the same volume stirrup ratio. (2) When the longitudinal compressive strain of steel tube reaches 30 times of the yield strain, plastic hinge is formed at the end of SCFT column and the stirrups can effectively reduce the plastic hinge length. A formula of plastic hinge length suitable for different axial compression ratios and equivalent stirrup ratios is proposed. (3) According to the results of parametric analysis, the seismic structural measures including reasonable equivalent stirrup ratio and region height of terminal stirrups are proposed for different axial compression ratios and strength matching patterns between steel tube and core concrete.

Flexural and compressive creep behavior of UHPFRC specimens

The long term behavior of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) is analyzed in this study. The experimental campaign covered creep in compression and creep in flexure in cracked state. Three types of specimens were cast: cylindrical specimens (Ø100 × 200 mm) for compressive creep and shrinkage, and prismatic specimens type regular “R” (150 × 150 × 600 mm) and type slim “S” (150 × 40 × 600 mm) for flexural creep in cracked state. Specimens R were notched up to 50 mm in depth to weak the central section and then pre-cracked until 0.65 mm of Crack Mouth Opening Displacement (CMOD). Specimens S were pre-cracked unnotched until a loss of 50% of stiffness was observed. Flexural creep tests were performed during 270 days under load, and until 360 days the compressive tests. Measurements from three experimental sources were obtained: CMOD, compressive strains on top of prismatic specimens and longitudinal compressive strains in cylindrical specimens. Creep coefficients and parameters related with deferred deformations velocity were obtained from all three sources. Creep coefficients under flexure at 270 days ranged from 0.62 to 1.20 in the tensile zone, and from 0.72 to 0.90 in the compressive zone. Creep coefficient in compression at one year was 1.07, which is consistent with values found in the literature. Deferred deformations velocities at early ages were greater in specimens R than in specimens S, and a secondary creep stage was achieved in all specimens after 210 days of sustained loading.

Axial Compression Behavior of the High-Strength Concrete Squat Wall with Distributed Steel Tubes

Three high-strength concrete walls with distributed steel tubes (HC-DST squat walls) and three high-strength concrete-filled steel tubes (CFSTs) were tested to study the mechanical behavior of this type of squat wall. The strains of the steel tubes and the failure mode and axial force distribution of the squat wall were analyzed. Then, the mechanism behavior and the axial capacity formula for this type of shear wall were obtained. The rotation angle of the principal strain of the steel tube was between 3° and 7°. Therefore, the minimum principal strain and the maximum principal strain of the steel tube were replaced by the longitudinal compressive strain and the circumferential strain of the steel tube, respectively. The axial force of each part of the squat wall was distributed according to the vertical compressive stiffness before the peak load. Finally, the parametric analysis of the HC-DST squat wall was performed using the finite element method. The analysis results indicate that the axial capacity of the HC-DST squat wall increases with the increase of the confined area ratio or steel area ratio and decreases with an increase in the confinement coefficient.

Piezoresistivity of polymer-matrix carbon fiber filament in plane stress state

In this work, the relation between 2D- and 3D-strain based piezoresistive gauge factors for carbon fiber filament in plane stress states is developed theoretically. For measuring the gauge factors, carbon fiber filaments are attached to the base specimen surface at different angles. Their resistance response to multidimensional strain field is investigated by four-point bending tests. Piezoresistive models of carbon fiber filament in plane stress states are created using the test results. In the test setup, carbon fiber filaments are placed both on the tension side and the compression side. Both the models show that the piezoresistive response of carbon fiber filament is dominated by the longitudinal strain. Based on the inequality in the sensitivities to tensile strain and compressive strain, the piezoresistive models are modified further. The modified piezoresistive models reveal the following 3D-strain based gauge factors: 1.82 for longitudinal tensile strain, 1.64 for longitudinal compressive strain, 0.10 for transverse tensile strain, and −0.25 for transverse compressive strain. The 2D-strain based gauge factors depend not only on the polarity of the longitudinal strain and transverse strain, but also on the polarity of the strain in the thickness direction. The piezoresistive models are verified experimentally.

Determination of the longitudinal compressive strength of a CFRP ply through a tensile test on a laminate

In this study, an innovative test is proposed to identify the longitudinal compressive strength of a unidirectional ply. The key idea consists in designing a laminate that, when subjected to a tensile loading, fails by compressive failure in its central 90°-ply, due to the Poisson effect, without any prior damage. Six specimens have been tensile tested to failure. No intra-laminar matrix damage could be detected before the final failure. Fibre kinking in the 90°-ply is observed experimentally in the failed specimens. This damage mechanism, located in the gauge section of the specimens, leads to the final failure. A fast computational identification method is used to determine the longitudinal compressive stress and strain within the 90°-ply at failure, from this specific tensile test. The identified average failure properties are consistent with those obtained through conventional compression tests, but the associated scattering is much lower. Consequently, this innovative method leads to an increase in the design allowable, resulting in higher performance designs.

Dynamic Changes at Yahtse Glacier, the Most Rapidly Advancing Tidewater Glacier in Alaska

Since 1990, Yahtse Glacier in southern Alaska has advanced at an average rate of ∼100 m/yr despite of a negative mass balance, widespread thinning in its accumulation area, and a low accumulation-area ratio. To better understand the interannual and seasonal changes at Yahtse and the processes driving these changes, we construct velocity and ice surface elevation time series spanning the years 1985-2014 and 2000-2014, respectively, using satellite optical and synthetic aperture radar (SAR) observations. In terms of seasonal changes, we find contrasting dynamics above and below a steep (up to 18% slope) icefall located approximately 6 km from the terminus. Above the icefall, speeds peak in May and reach minima in October synchronous with the development of a calving embayment at the terminus. This may be caused by an efficient, channelized subglacial drainage system that focuses subglacial discharge into a plume, resulting in a local increase in calving and submarine melting. However, velocities near the terminus are fastest in the winter, following terminus retreat, possibly off of a terminal moraine resulting in decreased backstress. Between 1996-2014 the terminus decelerated by ∼40% at an average rate of ∼0.4 m/day/yr , transitioned from tensile to compressive longitudinal strain rates, and dynamically thickened at rates of 1-6 m/yr , which we hypothesize is in response to the development and advance of a terminal moraine. The described interannual changes decay significantly upstream of the icefall, indicating that the icefall may inhibit the upstream transmission of stress perturbations. We suggest that diminished stress transmission across the icefall could allow Yahtse’s upper basin to remain in a state of mass drawdown despite of moraine-enabled terminus advance. Our work highlights the importance of glacier geometry in controlling tidewater glacier re-advance, particularly in a climate favoring increasing equilibrium line altitudes.

Flexible roll forming of an automotive component with variable depth

The conventional roll-forming process is limited to components having a constant cross section, while the recently developed flexible roll forming (FRF) process allows the production of components in which the section varies over the length of the part; this permits optimisation in terms of strength and weight. There has been an uptake of FRF in the heavy vehicle industry for the production of long and high-strength structural parts, but passenger car bodies are more complex and generally parts require variations in width and also in depth. The widespread application of FRF in the automotive industry, therefore, requires the formation of components that have intricate variations in profile depth over the length of the part. In this work, the FRF of an automotive bumper section is analysed numerically using the commercial software package COPRA® FEA RF. A detailed analysis of the distribution and history of plastic strain in longitudinal, transverse and thickness directions is performed and related to the shape defects observed in the process. The analysis shows that when forming variable depth components, zones of compressive longitudinal strain exist, that lead to wrinkling defects. These can be reduced by applying additional flange contact during the operation.

Experimental Analysis of Local and Average Dynamic Longitudinal Engineering Compressive Strains in Ductile Porous Rod After the Taylor Direct Impact Experiment

Experimental Analysis of Local and Average Dynamic Longitudinal Engineering Compressive Strains in Ductile Porous Rod After the Taylor Direct Impact Experiment

Experimental analysis of density and compressive strain of porous metal with the use of Taylor test

The article presents a new experimental method of analysis of density and longitudinal engineering compressive strain (LECS) in porous ductile rod, plastically deformed with a Taylor direct impact experiment (Taylor DIE). Two essential singularities in the distribution of the LECS are revealed, namely: maximum of the LECS e r max occurs near the rod striking end (Fig. 2), and at high impact velocities ( U > 100 m/s) e r max decreases along with an increase of the rod initial porosity, this behaviour is inverse to that under static loading. The dynamical density – LECS curves for porous copper are also presented in the paper. According to the authors’ best knowledge, these singularities have not been published in available literature so far.

Trailing heat sink effects on residual stress and distortion of pulsed laser welded Hastelloy C-276 thin sheets

A three-dimensional finite element model (FEM) was established to reveal the thermal-mechanical behaviors of pulsed laser welding (PLW) with and without trailing heat sink. Experiments were carried out to measure the welding temperature histories, residual distortions and solidification profiles. The simulation results agree well with the corresponding experimental measurements. The peak values of the temperature and transient longitudinal tensile stresses valleys in the weld increase as the cooling intensity increases from 5000 to 15,000W/(m2K), while those of the temperature and transient longitudinal compressive stresses near the weld decrease. The peak values of the longitudinal residual compressive stresses and plastic strains, and the maximum deflections in longitudinal and transverse direction decrease as the cooling intensity increases from 5000 to 15,000W/(m2K). The magnitudes of the transverse shrinkage distortions increase as the cooling intensity increases from 5000 to 15,000W/(m2K). The proper cooling intensity to reduce the residual stresses and distortions of the PLW with the trailing heat sink is detected at 10,000W/(m2K). The trailing heat sink is technically feasible for actual pulsed laser restraint welding in Hastelloy C-276 thin sheet structures.

Flange Wrinkling in Flexible Roll Forming Process

Flexible roll forming is an advanced sheet metal forming process for producing variable cross section profiles. Flange wrinkling at the transition zone where the cross section changes is a major defect in the flexible roll forming process. In this paper, the flange wrinkling at the transition zone is studied using finite element analysis. The results showed that the strip deformation at the transition zone can be considered as a combination of two strip deformations observed in the conventional roll forming process and the flanging process. According to finite element analysis results, when the flange wrinkling occurs, compressive longitudinal strain is smaller than the necessary compressive longitudinal strain calculated by mathematical modeling to obtain the intended profile geometry in the compression zone. Therefore, comparison of compressive longitudinal strain obtained from the finite element analysis and the necessary compressive longitudinal strain is a good criterion to predict the flange wrinkling occurrence. A flexible roll forming setup was developed. Longitudinal strain history is obtained from the finite element simulation and is compared with the experimental data from the flexible roll forming setup. Results show a good agreement and confirm the finite element analysis.

Anisotropic interactions and strain-induced topological phase transition in Sb2Se3and Bi2Se3

Based on first-principles calculations, we study the dependence of topological phase on anisotropic interactions in Bi${}_{2}$Se${}_{3}$-type materials. By applying different strains in order to vary interactions, we reveal that the topological phase is insensitive to lateral interaction but can be effectively tuned by longitudinal interaction. Longitudinal strain is inhomogeneous in the studied systems. The interquintuple interaction plays a dominant role in determining the topological phase. We explain the puzzling band-topology difference between Sb${}_{2}$Se${}_{3}$ and Bi${}_{2}$Se${}_{3}$ and propose an approach to tuning the topological phase by strain. It is found that Sb${}_{2}$Se${}_{3}$ can be converted into a topological insulator by applying compressive longitudinal strain while the converse strain can turn Bi${}_{2}$Se${}_{3}$ into a normal insulator. We have studied thin films of Sb${}_{2}$Se${}_{3}$ and Bi${}_{2}$Se${}_{3}$ and also observed a strain-induced topological phase transition.

Enhanced Hole Mobility in High Ge Content Asymmetrically Strained-SiGe p-MOSFETs

The hole mobility characteristics of 〈110〉 /(100)-oriented asymmetrically strained-SiGe p-MOSFETs are studied. Uniaxial mechanical strain is applied to biaxial compressive strained devices and the relative change in effective hole mobility is measured. The channel Ge content varies from 0 to 100%. Up to -2.6% biaxial compressive strain is present in the channel and an additive uniaxial strain component of -0.06% is applied via mechanical bending. The hole mobility in biaxial compressive strained-SiGe is enhanced relative to relaxed Si. It is observed that this mobility enhancement increases further with the application of 〈110〉 longitudinal uniaxial compressive strain. The relative change in mobility with applied stress is larger for biaxial compressive strained-SiGe than for Si and increases with the amount of biaxial compressive strain present in the channel.