Low Compressive Loads Research Articles

Large mechanical damping behaviors in a Heusler-type Co53V30.5Ga12Mn4.5 polycrystalline alloy

Shape memory alloys exhibit strong damping capacity owing to the formation and motion of internal interfaces during the hysteretic superelastic response. Here, we report large mechanical damping behaviors in a Co53V30.5Ga12Mn4.5 polycrystalline alloy. By using Mn substitution for V to strengthen the ferromagnetic coupling in association with the martensitic transformation, the thermal hysteresis in the Co53V30.5Ga12Mn4.5 alloy is enhanced to 31.1 K. Under a low compressive loading of 248 MPa, a large dissipated energy of 2.45 MJ m–3 and a high specific damping capacity (SDC) of 0.39 can be achieved. Moreover, a long-term cyclability of over 10,000 superelastic cycles with the SDC higher than 0.32 is also obtained. Developing high-performance damping materials with the integration of low driving stress, high damping capacity and long fatigue life is of great importance for damping applications.

Predicting the Influence of Shear on the Seismic Response of Bridge Columns

In the seismic design and evaluation of bridges, a method is required for determining the shear strength of reinforced concrete columns to avoid brittle shear failures. In addition, detailed design and evaluation often require predictions of the complete hysteretic response of bridge columns to accurately model the nonlinear dynamic response of the bridge. Predictions of the shear strength of columns using the provisions of the AASHTO Specifications are compared with the reversed-cyclic loading test results of shear-critical columns. It is found that the Simplified Procedure results in very conservative predictions of the seismic shear strength. The General Procedure provides conservative and more accurate predictions of the seismic shear strength. It is suggested that the AASHTO reduction factor on the concrete contribution resisting shear for low compressive axial load levels be removed. Nonlinear finite element analysis predictions are made for a selection of rectangular and circular columns tested in reversed-cyclic loading and are compared with the experimental results. The ability of nonlinear finite element analysis to predict the reversed-cyclic loading responses of columns with a wide range of variables and having different failure modes is demonstrated.

Stress - strain state dams on a loess subsidence base

The article presents the calculation of the stress-strain state of an earthen dam on a loess base on a computer. The calculation of the joint operation of the dam with the foundation was carried out using finite difference methods using shifted approximating grids (displacements and velocities are determined at the nodes of one mesh; deformations and stresses at the nodes on the other). The use of the developed algorithm, on the one hand, and the improvement of the mathematical model of the soil, based on experimental studies of samples for expansion, on the other hand, make it possible to assess the formation of trenches by calculation methods. The obtained calculation results are compared with the data of experimental model studies of the stress-strain state of an earthen dam with a subsidence base on a centrifuge. The correctness of the previously stated position was confirmed that for calculations of crack formation, the values of the limiting extensibility of the soil should be taken. It is necessary to determine these values by simulating the complex stress state of soil samples in laboratories. The areas of the dam have been identified as potentially the most in terms of cracking (a ridge zone with low compressive loads, close to uniaxial expansion in terms of operating conditions, and near-edge buried in places of a sharp break in the slope of the banks with significant stresses and destruction of soil material in a complex stress state by tension with sliding).

A study of mechanoelectrical transduction behavior in polyvinyl chloride (PVC) gel as smart sensors

Polyvinyl chloride (PVC) gels are soft electroactive polymers (EAPs) being researched for soft robotic applications. Sensing properties of these EAPs have not been investigated in detail in regard to fundamental mechanoelectrical transduction behavior, but this smart material has been shown to exhibit a detectable response to external stimuli. This study shows PVC gels to be an extremely sensitive material when undergoing mechanoelectrical transduction and explores some response dependencies and proposes a theoretical framework for mechanoelectrical transduction within the gel. The work presented here also uncovers a very interesting phenomena under extremely low compressive loads during the initial contact with the gel. This phenomenon is attributed to a surface tension creeping motion onto the loading surface with an accompanying polarity inversion in the sensing signal relative to fully loaded gels in compression. Experimental work on hysteresis was also completed showing very little memory in steady state mechanoelectrical response to repeated stepped loading cycles. This study demonstrates the mechanoelectric ability of PVC gels to perform in sensing experiments and acts as a fundamental framework to further broaden the applications of PVC gel sensors.

Design and testing of a conventional clutch filled with magnetorheological fluid activated by a flexible permanent magnet at low compressive load: Numerical simulation and experimental study

Abstract In this research article, the working of conventional clutch (CC) filled with magnetorheological (MR) fluid was tested at low compressive load. The flexible permanent magnetic sheet (FMS) controlled the chain strength of MR fluid. A single clutch plate based on FMS was fabricated and tested on the developed test rig. The characteristics of the developed single plate MR clutch (SPMRC) were found by the testing and mathematical calculations. Magnetic circuit analysis presents the magnetic field distribution in the developed MR clutch. The mathematical expression for the torque transmission due to shear and compression is presented. COMSOL Multiphysics 5.3a software is used for the magnetic field simulation at different loading conditions. The temperature distribution in the developed clutch is simulated and experimented. It is observed from the results that the input shaft oscillation in the reduces more during disengagement in the SPMRC than the CC.

Impact of preheating on the mechanical performance of different MgO-C bricks—Intermediate temperature range

This work analyses the mechanical behavior of MgO-C refractories at an intermediate temperature of 1000 °C. Conditions similar to those occurring during the in-service pre-heating of steelmaking ladles are simulated by thermal treatment before the mechanical testing. Stress-strain curves were determined under compressive loading at RT and 1000 °C. The impact of the thermally activated physicochemical transformations on the mechanical response of the materials was evaluated in terms of parameters such as strength, fracture deformation, secant modulus and yield strength. The presence of Al seems to be deleterious when longer soaking times at 1000 °C were applied, which was attributed to the progressive damage related to in situ phase formation. On the other hand, when heating these types of refractories simultaneously with the application of a low compressive load, the closure of previously formed microcracks (self-healing) was considered to be mainly responsible for their mechanical behavior.

Mechanical Behavior of Pericopsis elata Relative to Age during Growth

The assamela (afrormosia) whose scientific name is “Pericopsis elata” (Harms), a large tree of great commercial value, is an exploited species. It is considered “endangered” by the IUCN.” Trees ready for harvesting are scarce because the logging diameter, which has been set at 100 cm, is very big. The studies recommended by the Cameroonian government as part of the ITTO/CITES project activities should be carried out to determine a new minimum logging diameter as the diameter increases with age. No credible solution is provided in the scientific literature to compensate for its scarcity of exploitation. Moreover, little or no information is available for describing the variation of its mechanical properties over time in order to determine the age at which its wood mechanical properties are good enough to be marketable. It is in this context that this work was undertaken. In this study, we adopted an experimental approach to evaluate the mechanical properties of this species exploited in southeast Cameroon. We then studied the variations in these properties as a function of tree age in order to propose leads for their exploitation. Thus, the compression and bending tests allowed us to estimate the relationship between the mechanical properties in three main directions of the log (MOE in compression and bending, failure stress in compression and bending, and creep in compression) and age (or diameter). We also used the 10‐hour creep under low axial compressive loading data to implement the theoretical fractional Maxwell (MF) model, which was compared to the experimental data. For this purpose, after three months of natural drying in the laboratory, we evaluated the above mechanical properties according to age. This study shows that the mechanical properties change as the diameter increases and change very quickly from 70 cm diameter upwards. From the analysis of the experimental data, we deduced that the minimum diameter of exploitable trees should be equal to 80 cm corresponding to the age of about 200 years.

Dynamic shear modulus and damping ratio of clay mixed with waste rubber using cyclic triaxial apparatus

In view of its appropriate engineering properties and environmental benefits, waste rubber is being increasingly used in engineering applications. Along with static loading, clay-rubber mixture (CRM) can be also utilized under dynamic loading. Due to a lack of detailed research on dynamic and static properties of CRMs, the effects of 0–30% rubber content on geotechnical properties of clay soil (CS) was investigated in this study through strain-controlled monotonic and cyclic triaxial tests. Moreover, the structure of the CRM and pure rubber was observed under a binocular microscope. The results indicated the effects of rubber size, rubber content, and shear strain amplitude on strength, volumetric strain, damping ratio, and shear modulus of the CRM. The results correspondingly demonstrated a good cohesion between clay and rubber grains as well as an appropriate strength and shear strain for the given mixture. According to the results of the dynamic tests, the highest damping ratio was obtained with 10% rubber content. In addition, the shear modulus showed a downward trend as the rubber content and the shear strain amplitude augmented. The use of rubber powder rather than granular rubber also enhanced the damping ratio by 10% on average. In contrast, the granular rubber boosted the shear modulus by 13% as compared with the rubber powder. Based on the results, it is recommended to use 10% rubber powder in executive operations to achieve the highest damping ratio. Considering the static strength of the CRM and its good damping ratio under cyclic loading compared with pure soil, it is suggested to be used in situations wherein soil could be subjected to low compressive loads combined with cyclic loading.

Characterization of Effective In-Plane Electrical Resistivity of a Gas Diffusion Layer in Polymer Electrolyte Membrane Fuel Cells through Freeze–Thaw Thermal Cycles

The electrical property of gas diffusion layers (GDLs) plays a significant role in influencing the overall performance of polymer electrolyte membrane fuel cells (PEMFCs). The electrical degradation performance of GDLs has not been reported sufficiently. Understanding the electrical degradation characteristics of GDLs is vital to better fuel cell performance, higher efficiency, and longer service time. This paper investigated the effective in-plane electrical resistivity of a commercial GDL by considering environmental and assembly conditions similar to those in use for the operation of PEMFCs. The effective in-plane electrical resistivity of the GDL, subjected to a series of freeze–thaw thermal cycles, was characterized to study its progressive electrical degradation with thermal cycles. Experimental results indicated that, under low compressive loads, the effective in-plane electrical resistivity of the commercial GDL showed weak anisotropy, and was greatly influenced by the transformation of carbon fiber connection in the porous layer. In particular, the thermal aging treatment on the GDL through the first 100 freeze–thaw cycles contributed a lot to its in-plane electrical degradation performance.

Influence of rafted microstructures on creep in Ni-base single crystal superalloys: a 3D discrete dislocation dynamics study

Ni-base single-crystal superalloys exhibit a dynamic evolution of their microstructure during operation at elevated temperatures. The rafting of γ′ precipitates changes the mechanical behavior in a way that was understood insufficiently. In this work, we combine a phase-field method with a discrete dislocation dynamics model to clarify the influence of different rafted microstructures with the same initial dislocation density and configuration on creep behavior. The unrafted and rafted microstructures of Ni-base single crystal superalloys are simulated by a phase-field crystal plasticity method. By introducing these microstructures into a 3D discrete dislocation dynamics (DDD) model, the creep behavior under uniaxial loads of 350 and 250 MPa along [100] direction at 950 °C is studied. Due to the negative lattice mismatch of Ni-base superalloys, the N-type rafting with the formation of plate-like γ′ precipitates occurs under uniaxial tensile loads along {100} direction at high temperatures, while the P-type rafting with the formation of rod-like γ′ precipitates occurs under compressive loads. Taking the cuboidal, N-type rafted and P-type rafted microstructures as the initial and fixed microstructures for the same loading conditions, it is found from DDD simulations that the rafted microstructures result in smaller creep deformation than the cuboidal microstructure. The reason for this is that the coalescence of γ′ precipitates during the rafting diminishes the width of some γ channels, so as to increase the local Orowan stresses which retard the dislocation glide. For tensile loads, the N-type rafted microstructure has the best creep resistance. For a low compressive load, the P-type rafting shows a better creep resistance than N-type rafting.

Thermomechanical wrinkling and strength of sandwich panels with nanoscale or microscale randomly reinforced core

Wrinkling represents one of the failure modes in sandwich structures, although in practical designs the loss of strength and global buckling often occur at lower compressive loads. However, the properties of both polymeric matrix in the facings as well as the polymeric core degrade under an elevated temperature. As a consequence, wrinkling that does not present a problem at the room temperature may become a dominant mode of failure at elevated temperatures. In this article, we suggest that a reinforcement of the core material with stiff random nanoscale or microscale reinforcements may alleviate wrinkling. The solution accounts for the thermal loading history and the effect of temperature on the stiffness of the materials of the core and facings. While nano or microscale reinforcements increase the capacity of the structure to resist wrinkling, the strength of the core may be compromised due to the presence of such inclusions in the core material. Accordingly, the residual stresses in the reinforced core are evaluated using a finite-element method and accounting for the effect of temperature on the properties and stresses. It is demonstrated that both wrinkling and the core strength analyses should account for the effect of temperature on the material properties.

Experimental investigation on seismic behavior of square CFT columns with different shear stud layout

This study evaluates the seismic behavior of the square concrete-filled steel tube (CFT) column under cyclic loading. A total of nine large-scale square CFT columns with different shear stud layout and axial compressive load ratio designed according to the recommendations of the engineering practice were investigated. Seismic performance of these specimens was discussed in terms of damage mode, force-displacement relationship, deformation capacity, stiffness degradation, and energy dissipation capacity. Test results show that the axial compressive load ratio has a significant effect on the hysteresis loops of the square CFT columns. Shear stud has an obvious improvement of the local buckling of the steel tube in specimens with low axial compressive load ratio. However, it is not as much expected improvement on the local buckling of the steel tube when subjected to high axial compressive force. In addition, energy dissipation capacity of the square CFT column is shown to be insensitive to the shear stud layout.

In-plane drift capacity at near collapse of rocking unreinforced calcium silicate and clay masonry piers

In recent years, seismic assessment of existing unreinforced masonry (URM) structures is being increasingly based on nonlinear methods. The in-plane displacement capacity represents one of the most crucial yet still debated features of the nonlinear behaviour of URM piers. International codes often employ empirical models to estimate the pier ultimate drift. These models usually depends on the failure mode (flexure or shear) and on the properties of the pier (such as geometry, material properties, boundary or loading conditions).The present work focuses on the displacement capacity of Dutch masonry piers, or walls comparable to those, failing after the activation of a rocking mechanism. As a consequence, a dataset of 38 quasi-static tests on URM piers representative of the Dutch masonry is constructed and statistically analysed. The dataset, that includes also new laboratory tests recently performed at Delft University of Technology, consists of both calcium silicate and clay brick masonry piers characterised by low axial compressive loads and limited thickness. The displacement capacity of calcium silicate masonry is of special interest because it was not investigated in the past as extensively as for clay brick masonry. The analysis of the dataset highlights the influence of axial load ratio, aspect ratio and pier height on the drift capacity of Dutch rocking URM piers, whereas the other parameters do not appear to have a remarkable impact. Subsequently, a new empirical equation is derived and calibrated against the dataset. The accuracy of the proposed equation is assessed by comparing it to empirical models recommended in international standards and in the literature. For the considered dataset, representative of Dutch rocking URM piers, the proposed equation improves the accuracy of the predictions and fairly reproduces the dependence of the experimental drift capacity on the principal wall parameters.

In-situ synchrotron X-ray diffraction study of dual-step strain variation in laser shock peened metallic glasses

Atomic-structure evolution is significant in understanding the deformation mechanism of metallic glasses. Here, we firstly find a dual-step atomic strain variation in laser-shock-peened (LSPed) metallic glasses during compression tests by using in-situ synchrotron X-ray diffraction. Under low compressive load, LSP-deformed zone's atomic-structure shows low Young's Modulus (E); with load increase, atomic-structure are re-hardened, showing high E. An atomic deformation mechanism is proposed by using flow unit model, that LSP could induce interconnected flow units and homogenize the atomic-structure. These interconnected flow units are metastable and start to annihilate during compressive loading, causing the dual-step atomic strain variation.

Dynamic tensile test of fly ash concrete under alternating tensile–compressive loading

In order to obtain the post-peak stress–strain curve of plain concrete, the strain-controlled uniaxial tensile tests are carried out on cylindrical specimens. The tensile cyclic tests are performed between a lower compressive load and an upper load to the envelope curve. Test results have shown that residual strain accumulates slowly when the concrete is subjected to alternating tensile–compressive loading, during which the microcracks increase and aggregate. Meanwhile, the rates of stiffness degradation with cycles are similar in all cases. In the study, an analytical model of the post-peak cyclic behavior of concrete is proposed. The strain is decomposed into classical linear elastic strain and non-classical strain described in the Presach–Mayergoyz model, which describes the hysteresis behavior of concrete well from a microscopic point of view. A good agreement is obtained between the test data and calculated results.

Research on the Fatigue Properties of High Strength Concrete after Exposure to High Temperature under Low Cyclic Compressive Loading

By using an electrohydraulic servo fatigue testing machine, fatigue tests were performed on C60 high strength concrete (HSC) under low cyclic compressive loading after undergoing normal temperature, 200°C, 400°C, 600°C, and 800°C. Failure patterns of high strength concrete under low cyclic compressive loading were observed. The influence of the high temperature process on the static elastic modulus of high strength concrete was analyzed. By studying the development law of fatigue strain, regression equations of fatigue strain after different high temperatures were established. Furthermore, the fatigue deformation modulus ratio was defined as the damage variable and the relationship models between the high temperature process and the fatigue damage were established. It provides the experimental foundation for fatigue damage analysis of high strength concrete in objective working conditions, which includes repeated loading and different high temperature processes.

Experimental investigation on seismic performance of corroded reinforced concrete moment-resisting frames

For reinforced concrete (RC) structures located in seismic zones, reinforcement corrosion over time may have adverse effects on their seismic performance. Therefore, it is necessary to evaluate the effect of reinforcement corrosion on the seismic behavior of RC structures. In this study, an experimental study on corroded RC moment-resisting frames was carried out to investigate the effect of longitudinal reinforcement corrosion on the seismic behavior of RC frames. Six frame specimens, including five corroded frames and one frame without corrosion, were tested under quasi-static cyclic loading. The corrosion ratio of longitudinal reinforcement and the axial compression ratio were the main variable parameters. It was found that with the increase of corrosion ratio, the lateral load carrying capacity as well as the deformation capacity of RC frames decreased roughly linearly, and the energy dissipation capacity reduced approximately exponentially. For corroded frames with low axial compressive load level, the lateral strength and energy dissipation capacity were enhanced with the increase of the axial compression ratio, and the effect of axial compression ratio on the deformation capacity was insignificant. For frames with larger corrosion ratio or higher axial compression ratio, damages at beam ends developed more significantly during the loading process. In comparison with the beam, the damage evolution of columns was less affected by the corrosion ratio and axial compression ratio.

Measurements and theoretical modeling of effective thermal conductivity of particle beds under compression in air and vacuum

Effective thermal conductivity experiments were carried out with spherical particle beds under low and high compressive pressure loading in vacuum and air. A theoretical model was proposed for the effective thermal conductivity of particle beds based on the experimental results. The model incorporates heat conduction by particles including contact thermal resistance between particles, conduction through the gas in between particles, and radiation between particles, and includes two fitting parameters, namely the coefficient of heat conducted through the fluid, and the macro-contact thermal resistance. The predictions from the theoretical model satisfactorily match the experimental data for the bed effective thermal conductivity over the range of applied loading pressures on particles with different Young's modulus and the gas environment. The model can be used generally to describe the effect of compression stress or pressure on effective thermal conductivity of particle beds.

Investigation on Microstructure and Martensitic Transformation Mechanism for the Warm-Stamped Third-Generation Automotive Medium-Mn Steel

With the development of the automotive industry, the application of the high-strength steel (HSS) becomes an effective way to improve the lightweight and safety. In this paper, the third-generation automotive medium-Mn steel (TAMM steel) is studied. The warm-stamped TAMM steel holds the complete and fine-grained martensitic microstructure without decarbonization layer, which contributes to high and well-balanced mechanical properties. Furthermore, the martensitic transformation mechanism of the TAMM steel is investigated by the dilatation tests. The results indicate that the effects of the loading method on the Ms temperature under different loads are different. The Ms temperature is hardly influenced under the tensile loads and low compressive load. However, it is slightly decreased under the high compressive load. Moreover, the effects of the strain and strain rate on the Ms temperature are insignificant and can be neglected. As a result, this research proves that the martensitic transformation of the TAMM steel is rarely influenced by the process parameters, such as stamping temperature, loading method, load, strain, and strain rate. The actual stamping process can be designed and controlled accurately referring to the continuous cooling transformation (CCT) curves to realize the required properties and improve the formability of the automotive part.

Design, Manufacture and Testing of Capacitive Pressure Sensors for Low-Pressure Measurement Ranges

This article presents the design, manufacture and testing of a capacitive pressure sensor with a high, tunable performance to low compressive loads (<10 kPa) and a resolution of less than 0.5 kPa. Such a performance is required for the monitoring of treatment efficacy delivered by compression garments to treat or prevent medical conditions such as deep vein thrombosis, leg ulcers, varicose veins or hypertrophic scars. Current commercial sensors used in such medical applications have been found to be either impractical, costly or of insufficient resolution. A microstructured elastomer film of a polydimethylsiloxane (PDMS) blend with a tunable Young’s modulus was used as the force-sensing dielectric medium. The resulting 18 mm × 18 mm parallel-plate capacitive pressure sensor was characterised in the range of 0.8 to 6.5 kPa. The microstructuring of the surface morphology of the elastomer film combined with the tuning of the Young’s modulus of the PDMS blend is demonstrated to enhance the sensor performance achieving a 0.25 kPa pressure resolution and a 10 pF capacitive change under 6.5 kPa compressive load. The resulting sensor holds good potential for the targeted medical application.