Compressive Mechanical Stress Research Articles

Effect of raw coal gangue coarse aggregates on mechanical properties and compressive stress–strain response of concrete

AbstractRaw coal gangue (RCG) as one of the solid wastes can result in serious ecological and environmental pollution. Utilization of RCG as coarse aggregates in concrete can mitigate the demand for natural aggregates in engineering construction to a certain extent. This study aims to assess the impact of utilizing raw coal gangue aggregates (RCGAs) on the mechanical behaviors and compressive stress–strain responses of concrete. For this purpose, a total of 90 concrete specimens were prepared, varying in RCGA replacement ratios of 0, 30%, 50%, 70%, and 100% and water‐to‐cement (w/c) ratios of 0.37 and 0.47. The slump, compressive and splitting tensile strengths in cubes, and complete compressive stress–strain curves of RCGA concrete were obtained and discussed. Results indicated that as RCGA was incorporated, the peak stress and elastic modulus of concretes with 0.37 and 0.47 w/c ratios decreased by 26%–51% and 23%–57%, respectively. In addition, the crack development and microstructural characteristics of RCGA concrete were analyzed by digital image correlation and scanning electron microscopy (SEM), respectively. The SEM analysis indicated that the interface transition zone between RCGAs and mortar was relatively thick and loose compared to that between coarse natural aggregates and mortar, indicating the poor mechanical properties of RCGA concrete. Finally, based on the test data, a normalized stress–strain model for RCGA concrete was proposed, taking into account the influence of RCGA replacement.

Real-Time Observation of Nanoscale Kink Band Mediated Plasticity in Ion-Irradiated Graphite: An In Situ TEM Study.

Graphite IG-110 is a synthetic polycrystalline material used as a neutron moderator in reactors. Graphite is inherently brittle and is known to exhibit a further increase in brittleness due to radiation damage at room temperature. To understand the irradiation effects on pre-existing defects and their overall influence on external load, micropillar compression tests were performed using in situ nanoindentation in the Transmission Electron Microscopy (TEM) for both pristine and ion-irradiated samples. While pristine specimens showed brittle and subsequent catastrophic failure, the 2.8 MeV Au2+ ion (fluence of 4.378 × 1014 cm-2) irradiated specimens sustained extensive plasticity at room temperature without failure. In situ TEM characterization showed nucleation of nanoscale kink band structures at numerous sites, where the localized plasticity appeared to close the defects and cracks while allowing large average strain. We propose that compressive mechanical stress due to dimensional change during ion irradiation transforms buckled basal layers in graphite into kink bands. The externally applied load during the micropillar tests proliferates the nucleation and motion of kink bands to accommodate the large plastic strain. The inherent non-uniformity of graphite microstructure promotes such strain localization, making kink bands the predominant mechanism behind unprecedented toughness in an otherwise brittle material.

Uniaxial compressive mechanical properties and stress–strain model for roller-compacted concrete with initial damage subjected to freeze–thaw cycles

Roller compacted concrete (RCC) often remains in a damage state as a result of improper vibrating compaction control, which makes it more susceptible to the action of freezethaw (FT) cycles in cold regions and thus results in the degradation of mechanical behaviors. In this paper, the influences of initial damage and FT cycles on the physical and mechanical behaviors of RCC were systematically examined through physical tests, including FT cycle tests, pore structure tests and uniaxial compressive tests. An in situ vibrating compaction procedure was employed in the experiment to accurately replicate the field compaction process for RCC under laboratory conditions, and the dynamic elasticity modulus (DEM) was adopted as the non-destructive testing (NDT) index to quantify the initial damage caused by improper RCC construction control. The results indicated that the higher values of initial damage and FT cycles exhibited a greater influence on the frost resistance and pore structure distribution. Remarkable attenuation of compressive strength and elastic modulus and an increase in peak strain were observed to occur in RCC when the initial damage degree exceeded 0.1 and the number of FT cycles exceeded 75. Finally, the uniaxial compressive stressstrain model was established through segmented linear regression analysis based on the Weibull-Lognormal model. The proposed model was validated to be effective and reasonable in predicting the mechanical properties of RCC under the combined effects of initial damage and FT cycles.

The Impact of Mechanical Compression on the Postharvest Quality of ‘Shine Muscat’ Grapes during Short-Term Storage

Mechanical stress induced by compression during preharvest and postharvest handling of fresh fruit is a major factor influencing the quality of fresh fruit. The degree of compression primarily governs the extent of quality deterioration. However, research on the damage mechanisms of mechanical compression in table grapes remains scarce. This investigation evaluated the impact of varying compression levels (0%, 20%, 40%, 60%, and 80%) on the postharvest quality attributes of table grapes. Changes in postharvest physical properties (overall appearance and color), structural properties (firmness, springiness, cohesiveness, and chewiness), physiological qualities (total soluble solids, titratable acidity, ascorbic acid, malonaldehyde content, and relative electrical conductivity), and cell microstructure of the berries was determined at 4 °C during 15 d of storage. Mechanical compression contributed to the deterioration of the quality of table grapes during storage, resulting in increased weight loss, decay rate, malonaldehyde content, and relative electrical conductivity; and decreased total soluble solids, titratable acidity, and ascorbic acid content. Furthermore, as compared to the control group, mechanical compression resulted in substantial yellowing and diminished textural qualities of grapes. In particular, compression treatment caused significant deformation of grape cell microstructure. In conclusion, mechanical compression stress significantly affects the physical and physiological properties of postharvest table grapes, as well as the internal cellular organization. As compression levels increase, the quality of table grapes progressively deteriorates, leading to a substantial reduction in storage life and commercial value. This study offers essential information for devising damage prevention strategies in preharvest and postharvest handling of table grapes.

A Novel Banana Fiber Reinforced Green Composite from Maleated Castor Oil and Linseed Oil

In recent decades, the consumerist society has recognized the consequences of petrochemicals, hence the interest of scientists has been drawn toward renewable products obtained from biological sources. In this study a novel biocomposite with the use of the least chemicals was fabricated by crosslinking maleated castor oil (MACO) and linseed oil (LO) by free radical polymerization, using benzoyl peroxide (BPO) as the free radical initiator. The significance of this study is that the polymer matrix is derived entirely from vegetable oils with slight modifications. Banana fibers are one of the strongest natural fibers that may be taken from the banana pseudo-stem that is discarded after the fruit is harvested. To convert this post-harvest waste into a value-added product, NaOH-treated banana fibers were used as the reinforcement for the developed composite. The characterization of the fibers and the composites was carried out by performing Fourier-transform infrared spectroscopy (FT-IR), X-Ray diffraction analysis (XRD), Dynamic mechanical analysis, tensile and compressive stress analysis, Scanning electron microscopy (SEM), Thermogravimetric (TG)/derivative thermogravimetric (DTG) and thermal conductivity analysis. Composites were also analyzed for their water absorptivity and chemical resistivity. The influence of varying banana fiber weights on the composite’s mechanical strength was investigated using a dual cantilever flexural test. It revealed that the composite’s strength increased with increasing fiber content until 50% (w/w) and then dropped as the fiber content increased further. The maximum tensile strength of the optimum composite was 16.92 ± 4.70 Megapascal (MPa) and the composite was resistant against a compressive force of 4,500 kN without any fractures. The composites’ water absorptivity and chemical resistivity tests revealed that increasing the fiber content enhanced the composites'swelling. The composite was acidic and saline water resistant, but not alkaline solution resistant. Additionally, the thermal conductivity measurements of the composite showed that the composite is a thermal insulator. The composite with 50% (w/w) fiber load, 20% (w/w) BPO, 10% (w/w), LO and 20% (w/w) MACO exhibited the best overall performances.

Compressive stress–strain curve of recycled concrete under repeated loading

In order to study the compressive mechanical properties and stress–strain relationships of recycled aggregate concrete(RAC) under repeated loading with equal stress, the stress–strain curve tests of 45 RAC specimens under constant repeated loading and varying repeated loading were completed using recycled coarse aggregate(RCA) substitution rate and repeated load amplitude (LA) as parameters. The effects of RCA substitution rate and LA on the peak stress, peak strain and elastic modulus of concrete were analyzed to establish the relationship between the above mechanical parameters and the repetitive LA. Meanwhile, the calculation equations of the loading and unloading strain and the equation of the stress–strain curve under the repetitive load were established. The results show that: the peak stress of RAC decreases and the peak strain increases gradually with the increase of LA, showing a quadratic function; The elastic modulus decreases linearly with the increase of LA; Also, the strain ratio at the beginning of loading point and at the end of unloading point increases as a power function with the increase of strain ratio at the beginning of unloading point. Based on WEIBULL distribution, it is found that an equation of loading and unloading curves in repeated phase is similar to the monotonic equation. And the equations and measured curves of the damage constitutive model in the loading phase can be well predicted.

On-Chip Electrostatic Actuation of a Photonic Wire Antenna Embedding Quantum Dots

A photonic wire antenna embedding individual quantum dots (QDs) constitutes a promising platform for both quantum photonics and hybrid nanomechanics. We demonstrate here an integrated device in which on-chip electrodes can apply a static or oscillating bending force to the upper part of the wire. In the static regime, we achieve control over the bending direction and apply at will tensile or compressive mechanical stress on any QD. This results in a blue shift or red shift of their emission, with direct application to the realization of broadly tunable sources of quantum light. As a first illustration of operation in the dynamic regime, we excite the wire fundamental flexural mode and use the QD emission to detect the mechanical vibration. With an estimated operation bandwidth in the GHz range, electrostatic actuation opens appealing perspectives for the exploration of QD-nanowire hybrid mechanics with high-frequency vibrational modes.

Formation of Head/Tail-to-Body Charged Domain Walls by Mechanical Stress.

Domain walls (DWs) in ferroelectric materials are interfaces that separate domains with different polarizations. Charged domain walls (CDWs) and neutral domain walls are commonly classified depending on the charge state at the DWs. CDWs are particularly attractive as they are configurable elements, which can enhance field susceptibility and enable functionalities such as conductance control. However, it is difficult to achieve CDWs in practice. Here, we demonstrate that applying mechanical stress is a robust and reproducible approach to generate CDWs. By mechanical compression, CDWs with a head/tail-to-body configuration were introduced in ultrathin BaTiO3, which was revealed by in-situ transmission electron microscopy. Finite element analysis shows strong strain fluctuation in ultrathin BaTiO3 under compressive mechanical stress. Molecular dynamics simulations suggest that the strain fluctuation is a critical factor in forming CDWs. This study provides insight into ferroelectric DWs and opens a pathway to creating CDWs in ferroelectric materials.

Compressive stress drives adhesion-dependent unjamming transitions in breast cancer cell migration.

Cellular unjamming is the collective fluidization of cell motion and has been linked to many biological processes, including development, wound repair, and tumor growth. In tumor growth, the uncontrolled proliferation of cancer cells in a confined space generates mechanical compressive stress. However, because multiple cellular and molecular mechanisms may be operating simultaneously, the role of compressive stress in unjamming transitions during cancer progression remains unknown. Here, we investigate which mechanism dominates in a dense, mechanically stressed monolayer. We find that long-term mechanical compression triggers cell arrest in benign epithelial cells and enhances cancer cell migration in transitions correlated with cell shape, leading us to examine the contributions of cell–cell adhesion and substrate traction in unjamming transitions. We show that cadherin-mediated cell–cell adhesion regulates differential cellular responses to compressive stress and is an important driver of unjamming in stressed monolayers. Importantly, compressive stress does not induce the epithelial–mesenchymal transition in unjammed cells. Furthermore, traction force microscopy reveals the attenuation of traction stresses in compressed cells within the bulk monolayer regardless of cell type and motility. As traction within the bulk monolayer decreases with compressive pressure, cancer cells at the leading edge of the cell layer exhibit sustained traction under compression. Together, strengthened intercellular adhesion and attenuation of traction forces within the bulk cell sheet under compression lead to fluidization of the cell layer and may impact collective cell motion in tumor development and breast cancer progression.

Features of the porous morphology of anodic alumina films at the initial stage of disordered growth

A characteristic feature of disordered porous anodic film growth at the initial stage of aluminum anodizing was revealed by varying the electrolyte type and anodizing voltage. The samples were obtained by the electrochemical oxidation of thin aluminum films (100 nm thick) on SiO2/Si substrates in a 0.3 M oxalic acid at 10–50 V and were studied by SEM. The ImageJ analysis of the images revealed the simultaneous development of two large groups of pores: major pores with a large diameter and minor pores with a smaller diameter. When anodizing in oxalic acid at 10–50 V, it has been shown that the ratio of the diameters of the major and minor pores remains constant and is about 1.17. Using a geometric model, we demonstrated that the centers of the minor pores are located inside the elementary hexagonal cell formed by the centers of the major pores. Moreover, our results are very close to the theoretical value of 2/√3. At the initial stage of disordered pore growth, the development of minor pores rather than major pores is not a random process and is determined by energy-efficient conditions for the development of pores inside the hexagonal cells formed by the major pores. The increase in compressive mechanical stress in the anodic film leads to an interruption in the development of such pores.

Mechanical Characterization of Nb3Sn Cable Insulation Systems Used for HL-LHC Accelerator Magnets at Ambient Temperature

The performance of accelerator magnets is strongly relying on the dielectric strength and mechanical robustness of the insulation system. This is in particular relevant for the current development of high field superconducting Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn magnets with the insulation system made from resin-impregnated glass fibres. During the assembly and operation at cold temperature, this insulation system is exposed to high mechanical compressive and shear stresses. The focus of the study was the investigation of the mechanical shear strength of the insulation composite. The experimental tests have been performed at room temperature, determining the mechanical strength and the failure mechanisms of the cable insulation system. Within this test the inter-laminar shear strength (ILSS) and non-standardized combined shear compressive strength were determined. The test sample preparation was based on the manufacturing procedures and materials used in the series fabrication for the CERN HL-LHC Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils. The individual insulation systems are varying in the S2-glass yarn density, the sizing, and the fibre volume fraction. Furthermore, the presence of mica insulation on the mechanical strength has also been studied. This paper describes the applied measurement procedures used during the test campaign, and presents the relevant measurement results, identifying the mechanical limitations of the insulation system.

POSSIBILITY OF IDENTIFYING DEFECTS IN MASSIVE CAST STRUCTURES BY NON-DESTRUCTIVE TESTING METHODS

In the context of improving methods and means of non-destructive testing (NDT), along with increasing in formativeness, complex technical problems arise. For example, when examining structural elements with a service life of more than 20 – 30 years, modern NC tools detect defects that have not been rejected by the manufacturer. Assessment of the impact of such defects on the operability of the structure requires a comprehensive study using NC and strain gauge. The purpose of the work is to evaluate the parameters of defects in a cast part of a hydraulic stamping press with a service life of more than 60 years in order to make a decision on the possibility of its further operation. The defect was investigated using magnetic powder, eddy current and ultrasonic control methods. By means of strain gauges, mechanical stresses are measured directly during operation. The indicator pattern of the magnetic particle inspection defect has signs uncharacteristic for fatigue defects: branching, intermittent and broken (not smooth) character. To quantify the degree of smoothness of the indicator pattern, it is proposed to use a fractal dimension, which for the defect under study was 1.07. The estimated depth of the defect detected by the eddy current method was from 4 to 6 mm, by ultrasound – from 8 to 18 mm. The presence of an echo signal by a direct converter indicates the volumetric nature of the defect. After mechanical removal of the surface layer with a thickness of 2 mm in some areas, the width of the defect increased to 2 mm, and the depth to – 20 mm. On the inner side surface of the defect, a dense, dark scale characteristic of high temperatures is visually determined.The defect is classified as a casting shell with a depth of 20 mm. No traces of fatigue failure were found. Compressive mechanical stresses with an amplitude of no more than 41 MPa amounted to less than 20 % of the fatigue endurance limit of 35L steel. During the year, the average number of working cycles is 20 thousand, repeated examination of the press defect is recommended in 5 – 10 years (100 – 200 thousand cycles).

The biomechanical efficacy of a dressing with a soft cellulose fluff core in protecting prone surgical patients from chest injuries on the operating table.

Pressure ulcers are soft-tissue damage associated with tissue exposure to sustained deformations and stress concentrations. In patients who are proned for ventilation or surgery, such damage may occur in the superficial chest tissues that are compressed between the rib cage and the support surface. Prophylactic dressings have been previously proven as generally effective for pressure ulcer prevention. In this study, our goal was to develop a novel computational modelling framework to investigate the biomechanical efficacy of a dressing with a soft cellulose fluff core in protecting proned surgical patients from chest pressure ulcers occurring on the operating table, due to body fixation by the Relton-Hall frame. We compared the levels of mechanical compressive stresses developing in the soft chest tissues, above the sternum and ribs, due to the trunk weight, whilst the body is supported by the Relton-Hall frame pads, with versus without the prophylactically applied bilateral dressings. The protective efficacy index for the extremely high stresses, above the 95th-percentile, were 40.5%, 25.6% and 24.2% for skin, adipose and muscle, respectively, indicating that the dressings dispersed elevated soft-tissue stresses. The current results provide additional support for using soft cellulose fluff core dressings for pressure ulcer prophylaxis, including during surgery.

Enabling high efficiency magnetic refrigeration using laser powder bed fusion of porous LaCe(Fe,Mn,Si)13 structures

The aim of this study is to assess the processability of the LaCe(Fe,Mn,Si) 13 magnetocaloric material using laser powder bed fusion (LPBF) to create room temperature high surface-area-to-volume magnetic refrigeration media. LPBF process optimisation was performed on block samples, focusing on the build densification and the microstructural development. The porosity fraction decreased with the increase in laser energy density (E), however, cracks and keyholes were induced at E ≥ 140 J/mm 3 . Following thermal heat treatment and quenching, the magnetic entropy change (ΔS) of the blocks increased with the increase in E, due to the increase in homogeneity, where the maximum value achieved at a Curie temperature (T c ) of ~290 K for the sample built using E = 123 J/mm 3 was 4.9 J/kg K. Meanwhile, the samples built using E > 140 J/mm 3 showed higher ΔS max values that reaches 7.2 J/kg K but at lower T c of 260 K and the samples are rich in cracks. The block sample built using E = 123 J/mm 3 is recommended as the optimum condition, where it shows the lowest defects and the highest room temperature ΔS with highest compressive mechanical stress value of 90 MPa. A microchannel block sample was built using the optimum condition, which shows ΔS max value of 4.2 J/kg K with adiabatic temperature change of 1.4 K at µ 0 H = 1 T, which is close to the value of the block sample revealing the consistency in the magnetocaloric properties between the block and the porous samples.

Macromolecular crowding limits growth under pressure.

Cells that grow in confined spaces eventually build up mechanical compressive stress. This growth-induced pressure (GIP) decreases cell growth. GIP is important in a multitude of contexts from cancer, to microbial infections, to biofouling, yet our understanding of its origin and molecular consequences remains limited. Here, we combine microfluidic confinement of the yeast Saccharomyces cerevisiae, with rheological measurements using genetically encoded multimeric nanoparticles (GEMs) to reveal that growth-induced pressure is accompanied with an increase in a key cellular physical property: macromolecular crowding. We develop a fully calibrated model that predicts how increased macromolecular crowding hinders protein expression and thus diminishes cell growth. This model is sufficient to explain the coupling of growth rate to pressure without the need for specific molecular sensors or signaling cascades. As molecular crowding is similar across all domains of life, this could be a deeply conserved mechanism of biomechanical feedback that allows environmental sensing originating from the fundamental physical properties of cells.

Influence of Controlled Shot Peening on Mechanical Properties and Compressive Residual Stress of Al6061-TiB2 Composite

Influence of Controlled Shot Peening on Mechanical Properties and Compressive Residual Stress of Al6061-TiB2 Composite

Condylar Resorption Following Compressive Mechanical Stress in Rabbit Model - Association of Matrix Metalloproteinases.

Idiopathic condylar resorption (ICR) is a morphological change of the condylar head that occurs following orthodontic treatment or orthognathic surgery. This complication is serious, as it can cause relapse after mandible treatment. The aim of this experimental study was to evaluate the mechanism of influence of condylar resorption on compressive mechanical stress in temporomandibular joint following a change in occlusal position by mandible advancement. An osteotomy procedure at the midline of mandible was performed in 15 rabbits, with the left side moved forward by 3.5 mm. Advancement of the left side of the mandible resulted in compressive mechanical stress on condylar head on the left side. Samples were subjected to micro-computed tomography, histological staining and immunohistochemistry. The area and depth of anterior condylar resorption at two weeks were significantly different as compared to those at one week (p<0.05). TRAP staining confirmed the significantly largest number of TRAP-positive cells after two weeks (p=0.02), compared to one week. MMP-3 and MMP-13 immunostaining of the anterior condylar head at two weeks revealed high levels of both proteins from the surface to the deep layer of cartilage. Compressive mechanical stress following mandible advancement results in load on the anterior surface of the condylar head, which leads to bone resorption there, and induces MMP-3 and MMP-13 related to degradation of condylar head cartilage.

Modeling of nonlinear and hysteretic behaviors in the ferroelectric materials under strong electrical and mechanical driving levels

The ferroelectric materials have been used in several piezoelectric sensors and actuators applications. Under strong mechanical and electrical driving levels, the nonlinear behavior of these ferroelectric materials can be described by the second order piezoelectric constitutive equations. However, their hysteretic behavior cannot be modeled by these equations. In this paper, a novel phenomenological model was developed to describe the nonlinear and hysteretic behaviors of the ferroelectrics subjected to strong electrical and mechanical strengths. The model, based on the theory of Landau-Devonshire, can simulate the polarization/electric field hysteretic cycles of the ferroelectrics under mechanical compressive stress. It can also describe the evolutions of relative permittivity/electric field and piezoelectric coefficient/electric field of the ferroelectric materials under compressive stress. Simulated behaviors are finally compared with experimental data obtained for a soft PZT and good agreements were found.

Determination of Bacterial Concrete Strength Using Bacillus Subtilis and Lightweight Expandable Clay Aggregate

This study examines the impact of bacterial concrete on strength and self-healing. Bacterial concrete has better compressive strength, permeability, corrosion resistance, chemical precursors, alkalinity resistance, and mechanical stress. Bacillus subtilis calcium lactate and spore powder effects are explored in this study, and the influence of this bacterial form on strength and self-healing capacity to crack repair. The Bacillus subtilis concentration 105 cells/mL is used in concrete with calcium lactate 0.3% of cement. In another trial, calcium lactates 0.3% and spore powder 0.5% of cement with Bacillus subtilis concentration of 105 cells/mL and lightweight expandable clay aggregate (LECA) is 30% replaced to the coarse aggregate used in concrete respectively. The conventional concrete and bacterial concrete cubes were molded with dimensions of 150 mm x 150 mm x 150 mm, cylinders with dimensions of 100 mm x 200 mm, and a beam with dimensions of 100 mm x 100 mm x 500 mm. These specimens were evaluated after 7 and 28 days of cure. The compressive, split tensile, and flexural strength of bacterial concrete was raised by 23%, 8%, and 7%, respectively when compared to conventional concrete. Thus, the experimental findings reveal that Bacillus subtilis at 105 cells/ml cells with 0.3% calcium lactate has a substantial impact on the strength and self-healing of bacterial concrete.

Compressive mechanical properties of cement mortar containing recycled high-density polyethylene aggregates: Stress–strain relationship

This study contributes to the understanding of the effect of recycled high-density polyethylene (HDPE) aggregates on the compressive mechanical properties and stress–strain relationship of cement mortar. HDPE aggregates recycled from plastic wastes were used to substitute natural sand in cement mortar, thereby offering a novel approach to plastic waste management and reducing the overconsumption of limited natural resources. The compressive behavior of cement mortar containing 0–100% HDPE contents was investigated after 7 and 28 days. The experimental results showed the negative effect of HDPE aggregates on the modulus of elasticity (Ec) and compressive strength (fcmax) of cement mortar. However, the substitution of natural sand with HDPE aggregates reduced the density and increased the axial deformation capability of cement mortar, particularly when the volumetric substitution percentage exceeded 50%. The Ec, peak strain, and ultimate strain exhibited strong relationships with the substitution percentage and fcmax. Furthermore, the proposed empirical relationships between the parameters were evaluated. Finally, stress–strain models of HDPE mortars were established based on the available models for concrete. The proposed models appropriately predicted the complete stress–strain curves of cement mortars containing various amounts of plastic content.