Strength Behavior Research Articles

Assessing cement paste strength evolution under curing: An experimental and numerical investigation through equivalent stiffness parameter identified by embedded piezo sensors

Equivalent stiffness is one of the most important mechanical parameters of any concrete structure which allows engineers to predict the behaviour of the structure. This paper identifies the equivalent stiffness parameter through an embedded piezo sensor (EPS) in the strength development of cement paste using the electro-mechanical impedance (EMI) technique through experimental and numerical investigation. The experiments were conducted on the cement paste specimens; and the compressive strength (destructively) and EMI response were obtained during curing process. Further, a numerical model of cement paste specimen with EPS is developed to validate the EMI response. In addition, an equivalent stiffness parameter is identified from the experimental and simulation EMI data. It is found that the variation in conductance signature during curing process and strength development is effectively captured by the EPS. The identified equivalent stiffness either calculated from experimental or simulation data followed a similar behaviour of the compressive strength.

Mechanical Properties of Latex-Modified Cement Stone under Uniaxial and Triaxial Cyclic Loading.

During the cyclic injection and extraction process in underground storage wellbores, the cement sheath undergoes loading and unloading stress cycles. In this study, we investigated the mechanical properties of latex-modified cement stone (LMCS), widely used in oil and gas wells, through uniaxial and triaxial cyclic loading and unloading tests. The aim of the study was to determine the effect of various loading conditions on the compressive strength and stress-strain behavior of LMCS. The results show that the stress-strain curve of LMCS exhibits a hysteresis loop phenomenon, with the loop intervals decreasing throughout the entire cyclic loading and unloading process. As the number of cycles increases, the cumulative plastic strain of the LMCS increases approximately linearly. Under uniaxial cyclic loading and unloading conditions, the elastic modulus tends to stabilize. However, under triaxial conditions, the elastic modulus increases continuously as the number of cycles increases. This result provides data for engineering predictions. Furthermore, a comparison of the uniaxial and triaxial cyclic loading and unloading of LMCS shows that its cumulative plastic strain develops rapidly under uniaxial conditions, while the elastic modulus is larger under triaxial conditions. These findings provide a valuable reference for constructing underground storage wellbores.

Residual strength and critical state of strain softening–hardening considering thermal effect for brittle rocks

Since the post failure of rock has a significant effect on the performance of excavation, the residual strength of rock considering the thermal effect, is important for deep rock engineering, such as sequencing in underground excavation and tunnel support design. From the micromechanical perspective, this paper presents novel models of residual strength and critical state of strain softening–hardening, considering the thermal effect for brittle rocks. The model of the residual strength for brittle rocks was established by considering the thermal effect. Then, the criterion was proposed under for critical state of stress softening and strain hardening by considering the thermal effect. The new models include independent parameters with physical meaning. Finally, the reliability of the proposed model and criterion was verified by comparing theoretical predictions and experimental data. It was found that the proposed models can provide an effective means to predict the residual strength behavior and critical state of strain softening–hardening, considering the thermal effect for brittle rocks.

Experimental study on the mechanical behavior of laminates made by fiber steering: influence of fiber angle and tow width

Abstract This work considers the effects of fiber trajectory and prepreg width on the material strength and failure behavior of variable stiffness composites. The test matrix was designed according to commonly used fiber placement trajectory and width of prepreg in engineering. Different trajectories were compared for tensile, compressive, bending, shear and CAI strengths. For tensile and compressive performance, curved ply specimens have varying degrees of decrease compared to straight ply specimens; For shear and bending performance, the optimal layup sequence is [±45/〈30|45〉]. For impact toughness, curved ply is significantly higher than straight ply, and the CAI strength of straight ply exceeds that of curved ply. For variable stiffness laminate with different fiber angles and tow widths, the maximum tensile, compressive and CAI strengths were reduced by up to 66%, 56%, and 27%, and the maximum bending strength, shear strength and impact toughness were increased by up to 53%, 23%, and 10.3%, respectively. The increase in width of prepreg leads to an increase in defects between fiber bundles which weakens the tensile/compressive performance but enhances the shear/bending performance.

Enhancing mechanical performance and water resistance of Careya-Banana fiber epoxy hybrid composites through PLA coating and alkali treatment

The ongoing research focuses on exploring the potential of Careya arborea (CA) fiber, banana fiber (BF), and epoxy composites as sustainable alternatives to petroleum-based products and synthetic fibers. The aim is to enhance the interfacial bonding and overall performance of these composites while reducing reliance on traditional materials. The study investigates the adhesion between CA fiber, BF (both chemically treated), and epoxy with polylactic acid (PLA) coating. Specifically, it examined how the PLA coating affects the mechanical properties, including tensile strength, flexural strength, impact resistance, and water absorption behavior, of the fabricated composites. Mechanical characterizations of the composite specimens are conducted following ASTM standards. The PLA-coated and NaOH-treated specimens significantly improved their tensile strength (20.56%) and flexural strength (16.7%), and significantly reduced their water absorption capacity (by 47.6%) compared to the untreated ones. These findings highlight the promise of using treated natural fibers and PLA coatings to create more sustainable and high-performance composite materials.

Experimental study on effect of grouting and high temperature on the anisotropic compressive strength behaviour of soft jointed rocks with an impersistent flaw

This study investigates the effect of different in situ conditions like flaw infill, heat-treatment temperatures, and sample porosities on the anisotropic compressive response of jointed samples with an impersistent flaw. Jointed samples of different porosities are prepared by mixing Plaster of Paris (POP) with different water contents, i.e. 60% (i.e. for lower porosity) and 80% (i.e. for higher porosity). These samples are grouted with different infill materials, i.e. un-grouted, cement and sand-cement (3:1)-bio-concrete (SCB) mix and subsequently subjected to different temperatures, i.e. 100 °C, 200 °C and 300 °C. The results reveal the distinct stages in the stress-strain responses of samples characterized by initial micro-cracks closure, elastic transition, and non-linear response till peak followed by a post-peak behaviour. The un-grouted samples exhibit their lowest strength at 30° joint orientation. The ratios of maximum to minimum strength are 3.11 and 3.22 with varying joint orientations for lower and higher porosity samples, respectively. Strengths of cement and SCB mix grouted samples are increased for all joint orientations ranging between 16.13%-69.83% and 18.04%–73% at low porosity and 22%–48.66% and 27.77%–51.57% at high porosity, respectively as compared to the un-grouted samples. However, the strength of the grouted samples is decreased by 66.94%–75.47% and 77.17%–81.05% at lower porosity, and 79.37%–82.86% and 81.29%–95.55% at higher porosity for cement and for SCB grouts with an increase in the heating temperature from 30 °C to 300 °C, respectively. These observations could be due to the suppression of favourable crack initiation locations, i.e. flaw tips along the samples due to the filling of the crack by grouting and generation of thermal cracks with temperature. The mechanism of strength behaviour is elucidated in detail based on fracture propagation analysis and the anisotropic response of with or, without grouted samples.

Production of rubberized concrete utilizing reclaimed asphalt pavement aggregates and recycled tire steel fibers

The integration of waste tire elements into concrete, specifically granular rubber and discrete steel fibers, signifies a substantial advance in the pursuit of sustainable alternatives for rigid concrete pavements. This incorporation not only improves the ductility of rigid concrete pavements, but also augments their energy absorption capabilities. Similarly, replacing natural aggregates in concrete with reclaimed asphalt pavement (RAP) aggregates makes a large contribution to the reduction of negative environmental impacts, while conserving natural resources from depletion. This investigation explores the potential application of recycled rubber particles from waste tires (WTRR) and RAP aggregates as partial substitutes for natural fine aggregates, and evaluates their impact on the performance of rigid concrete pavements. Eight mixes were cast, each with two variables: (i) fine aggregate type (fine rubber (FRu) aggregates, fine asphalt (FAs) aggregates, and combinations of both types of aggregate) replacing 50 % of the natural fine aggregate; and (ii) waste tire recycled steel fibers (WTRSF) content (0 and 40 kg/m3). The axial compressive stress–strain, flexural load–deflection, and direct shear strength behaviors, together with the dry unit weight and volume of permeable voids for all concrete mixes were investigated and compared. The results show that, although the flexural and shear strengths decrease with the inclusion of FRu and/or FAs, the use of WTRSF noticeably mitigates the losses in strength that arise from the use of WTRR and/or RAP aggregates alone. The inclusion of WTRSF enhances the strain capacity of the concrete and allows the development of adequate post-peak energy absorption capacity in flexural and shear loading. Additionally, the dry unit weight of the proposed composites decreased by as much as 8 %, and their volume of permeable voids lies within the limits of high-durability concrete mixes (9–12 %). Hence, the proposed sustainable concrete composites are promising composites for rigid concrete pavement construction.

Treatment of Marine Clay Strength Behavior by Demolished Tile Materials and Cement

Known as a problematic soil in the civil engineering field, a sustainable solution to marine clay soil strength behaviour is needed. Another major concern in the engineering field is the solid waste management. Demolished Tile Material (DTM) is one of the largest contributors to construction waste. By utilizing DTM as a stabilizer product to treat marine clay soil, both problems can be minimized. The primary objective of this study is to assess the improvement in marine clay soil's strength characteristics through the addition of DTM and cement. Various proportions of DTM (4%, 8%, 12%, 16%, and 20%) were incorporated into the soil, with a constant 10% cement content. Unconfined Compressive Strength (UCS) measurements were taken at different curing times (0, 7, 14, 28, and 60 days). Results indicate a significant increase in UCS after treating marine clay with DTM and cement, with the most substantial improvement observed at 16% DTM content. The study also emphasizes the role of curing time in enhancing soil strength. The research findings shows that the potential of repurposing DTM for soil stabilization, reducing construction waste, and promoting environmentally responsible construction practices. This study also contributes to the sustainable development of marine clay areas in Malaysia and offers valuable insights for soil engineering and waste management in construction projects.

A new strategy for manufacturing, modeling, and optimization of 3D printed polylactide based on multiple nonlinear neuro regression analysis and stochastic optimization methods

Although there are many studies related to design, modeling, and optimization of fused deposition modeling (FDM) process parameters in the literature, the absence of a systematic approach to increase the reliability of model selection and optimization results is an important shortcoming that must be addressed. To make up for this deficiency, a new strategy was proposed to obtain desired quality on mechanical properties by adjusting FDM process parameters. This attempt involves manufacturing, modeling, and optimization point of view. The D-optimal method was employed to form experiment set, including process parameters. A hybrid approach neuro regression combining artificial neural network (ANN) and regression analysis together was used for modeling of FDM process. The most significant advantage of the neuro-regression approach compared to ANN is that the mathematical models can be used directly without needing any transformation. This is not possible in neural networks and, therefore, significantly limits and complicates the use of models obtained using ANN. The present study aims at optimization of the FDM process parameters, including infill density, infill pattern, layer thickness, and print speed on ultimate strength, fracture strength, and fracture strain for polylactide (PLA). In this regard, modified versions of the optimization algorithms Differential Evolution, Nelder Mead, and Simulated Annealing were used to find the best or elite designs. Linear or nonlinear models consisting of polynomial, trigonometric, and logarithmic expressions and their hybrid forms were employed to define the strength and strain behavior of PLA. It is concluded that (a) implementations of the optimization algorithms provide a 19% improving the minimum strain value if it is compared with the experimental results, (b) infill pattern types ( x2) were found as honeycomb, triangle, and cubic for the designs in terms of maximum fracture strength, minimum strain, and maximum ultimate tensile strength respectively, (c) many alternatives near optimum local designs could be obtained based on Nelder Mead algorithm for fracture strength and ultimate strength parameters. Thus, this allows work in a wide range of applications without depending on a single result for production.

Development of the triaxial equipment: a state of art

Triaxial shear testing is one of the most crucial investigations in geotechnical laboratories. It is essential for designing specific projects and understanding soil behavior in geotechnical engineering. Since Casagrande developed the modern shear apparatus at Harvard University, it has been refined to provide a more accurate characterization of shear strength behavior. This research paper aims to offer a concise overview of triaxial equipment development, focusing on apparatus that is easy to set up, prepare, and operate reliably, while remaining cost-effective. The primary objective is to contribute to the accurate determination of suitable techniques and devices that meet specific testing objectives. We review the theoretical background of both the triaxial apparatus and the direct shear box and illustrate the basic working principles of various volume change measurement techniques using triaxial devices. We also present different operational principles employed in designing volume change devices for soil testing. Our analysis reveals that some of these devices require complex operational techniques and equipment, making them challenging to use for repetitive testing. Consequently, we conclude that the ideal volume change device for soil mechanics testing should prioritize robustness and ease of operation.

Experimental Study on Concrete Strength Behavior Using Plastic Waste as a Partial Replacement of Fine Aggregate

Waste from plastic materials is outstripped due to the growth of industrialization and urbanization. Plastic materials are non-biodegradable; decomposition is not possible all the time. The recycling of plastic materials by using them in concrete will be a great deal for plastic management. This research investigation aims to measure the optimum percentage of plastic in concrete without a reduction in concrete strength and shear behavior of reinforced concrete. Using the provision of Mix Design ACI 211.1-91, the M28 concrete grade was created. Plastic materials have been collected and passed through a No-4 sieve (4.76mm). The combination of fine aggregates and ground plastic materials (RPET, PP) in the weight fraction of fine aggregate mix (0%, 2%, 4%, 6%, 8%, 10%) was used in the concrete. Concrete beams (750´150´150 mm) are reinforced with two 12 mm longitudinal steel bars in the tension zone, with proper clear cover for testing the shear capacity. In order to conduct the compressive and tensile splitting test, concrete specimens with a diameter of 100 mm and a height of 200 mm were used. The experimental findings demonstrate guidelines for using plastic as a partial replacement within 2% to 4% of fine aggregate to produce the best outcomes.

Residual and damage properties of recycled brick powder-UHPFRC after high temperature

This research explores the impact of temperature, Recycled Brick Powder (RBP) replacement rates, and cooling methods on the mechanical characteristics of Ultra-high-performance fibre reinforced concrete (UHPFRC). Additionally, the material morphology and pore structure at elevated temperatures are thoroughly examined through Scanning Electron Microscope (SEM), X-ray diffraction (XRD), and mercury intrusion (MIP) tests. The findings reveal a pattern in the behavior of residual compressive strength, splitting tensile strength, and residual fracture energy as the target temperature increases. Initially, these properties increase and then decrease. Specifically, a threshold temperature of 400 °C is identified for compressive strength. For splitting tensile strength, threshold temperatures under natural cooling and water cooling are 400 °C and 200 °C, respectively. The threshold temperatures for residual fracture energy at substitution rates of 30%, 0%, and 50% with RBP are determined to be 400 °C, 200 °C, and 200 °C, respectively. when the RBP content is 30%, UHPFRC shows superior mechanical performance during the entire heating process. The performance under water cooling is weaker than that under natural cooling. Additionally, this study also proposed the evaluation and calculation models of residual compressive strength, residual splitting tensile strength and residual fracture energy considering the influence of simulated fire temperature.

Mechanical behavior of unsaturated soils from suction controlled ring shear tests

The shear strength behavior associated with a large shear deformation of both the fine- and coarse-grained unsaturated soils is important in interpreting and forecasting the initiation and movement of landslides. For this reason, a suction-controlled ring shear apparatus was designed by introducing modifications to the conventional Bromhead ring apparatus extending the axis translation technique. A series of suction-controlled ring shear tests were performed on fine- and coarse-grained unsaturated soil specimens subjecting to large shear deformation. The experimental results are presented and interpreted for highlighting: (i) the shear stress/void ratio-shear displacement relationships; (ii) the envelopes of the residual shear strength; (iii) the void ratio, water ratio and degree of saturation of the fine-grained soil specimens sheared to the residual state under different net normal stresses and matric suctions. These results provide valuable information toward understanding and interpreting the behaviors of landslides in unsaturated soils that experience the first failure and the reactivation along a pre-sheared slip surface.

Fatigue damage evolution behaviors and fractional fatigue mechanical model of monzogabbro under true triaxial disturbance test

The disturbance wave caused by excavation or blasting of underground surrounding rock causes fatigue degradation effect of rock and eventually leads to disasters. However, the fatigue damage characteristics and fatigue models of rock under true triaxial disturbance are scare. Therefore, a series of true triaxial disturbance tests were conducted to investigate the rock fatigue deformation, strength and damage behaviors under different conditions. The evolutions of static damage and fatigue damage are separated and investigated respectively. Fatigue deformation and damage of rock under true triaxial stress undergoes three stages: attenuation, constant velocity and acceleration stage. The crack initiation stress can be as the initial condition of the fatigue deformation; the fatigue critical stress σdc of rock entering the acceleration failure stage was proposed and explored, with increasing frequency, σdc increase slightly and with increasing σ2, σdc increase obviously. Then, a novel fractional fatigue mechanical model considering the fatigue damage and intermediate principal stress effects of rock under true triaxial disturbance was proposed. The theoretical results of the model agree well with the results of the tests. Finally, the sensitivity analysis of stresses and model parameters and the model predictions under other untesting conditions were carried out to improve the understanding and prediction level of fatigue failure in underground engineering.

Investigation of Conditions for Using Mass-Produced Waste Glass as Sustainable Fine Aggregate for Mortar

To address the environmental issues arising from the growing scarcity of natural fine aggregates (NFA) and landfilling of waste glass, research is being conducted globally to utilize waste glass as a sustainable fine aggregate. However, contradictory results have been obtained regarding the effect of the type of waste glass and the physical properties of waste glass fine aggregate (GFA) on concrete, making it challenging to promote the use of GFA in concrete. Therefore, to promote the use of GFA in concrete, it is necessary to examine it under field conditions, such as mass-production processes or real-scale concrete applications. This study introduced a mass-production process for GFA, and the effect of mass-produced GFA on mortar was evaluated. The fine aggregate properties (particle aspect ratio, crushing rate, and solubility) of the GFA and the effects of color, content, and particle size on the mortar properties (compressive strength, flexural strength, and ASR expansion behavior) were analyzed, along with the results reported in previous studies. Consequently, the high aspect ratio and microcracks in the particles of mass-produced GFA led to an increase in the strength reduction and ASR expansion of the mortar. These effects appear to be particularly severe for transparent GFA. Overall, this study proposed the content of GFA within 20% or the replacement of fine particles (< 500 μm) in NFA as a condition for sustainable fine aggregate.

Dissimilar impact spot welding of high-thickness aluminum-steel sheets using vaporizing foil actuators

The automotive industry’s shift towards multi-material structures necessitates efficient joining of aluminum and steel, yet techniques for high-thickness (>2 mm) dissimilar AA6XXX-HSLA steel pairs, remain underexplored. This study explores vaporizing foil actuator welding for spot welding 2.5 mm AA6111-HSLA 340 steel pairs, demonstrating successful joint formation via lap-shear testing and microscopy. Post-weld heat treatment influences joint strength and fracture behavior, with intermetallic compound (IMC) formation at the weld interface affecting mechanical properties. IMC cracking is observed in heat-treated samples. Fracture analysis reveals material transfer and secondary brazing action outside the weld zone. VFAW lap-shear failure loads outperform other joining techniques.

Comparative study of microstructure and mechanical properties of cold rolled and annealed CoCrFeNi-MEA and CoCrFeNiMn-HEA fabricated by laser energy deposition

Equi-atomic quaternary CoCrFeNi Medium-entropy alloy (MEA) and quinary CoCrFeNiMn high-entropy alloy (HEA) are fabricated by laser energy deposition, followed by 5-pass cold rolling to total reduction of 70 % and annealing at temperatures of 600–1000 °C for 1 h. CoCrFeNi-MEA is severely cracked while CoCrFeNiMn- HEA is slightly cracked after cold rolling. Hardness of as deposited and fully recrystallized (heat treating temperature at 800–1000 °C) CoCrFeNi-MEAs are slightly higher than those of CoCrFeNiMn- HEAs, due to the larger atomic size misfit and lattice strain in CoCrFeNi-MEA than in CoCrFeNiMn-HEA. However, the higher microhardness of CoCrFeNiMn-HEAas-rolled than CoCrFeNi-MEAas-rolled is associated with the higher strain state in CoCrFeNiMn-HEAas-rolled than in CoCrFeNi-MEAas-rolled. With the increase of heat-treating temperature, microhardness of CoCrFeNi-MEA increases first and then decreases due to the precipitation hardening effect of Cr-rich (B2) particles in CoCrFeNi-MEAR-600. Microhardness of CoCrFeNiMn-HEA decreases with the increase of annealing temperature because of the weaker precipitation hardening effect of MnNi phase (L10) and Cr-rich particles (BCC) after annealing at 600 ℃ and higher temperatures. CoCrFeNi-MEAR-700 is much harder than CoCrFeNiMn-HEAR-700 because CoCrFeNi-MEAR-700 is partially recrystallized and CoCrFeNiMn-HEAR-700 is fully recrystallized. Strength behavior of the two alloys is consistent with microhardness behavior. {100}<110> texture component is acquired in both CoCrFeNi-MEAas-rolled and CoCrFeNiMn-HEAas-rolled. <111>//ND texture is observed in both alloys after annealing at 600 ℃. Orientation of recrystallized grains is random in both alloys. Size of recrystallized grains in CoCrFeNiMn-HEA is slightly larger than those in CoCrFeNi-MEA since homologous temperature (T/Tm) of CoCrFeNiMn-HEA is slightly higher than that of CoCrFeNi-MEA.

Mechanical behavior of Al /AL2O3p-SiCp hybrid composite fabricated by hot pressing method

Hybrid particulate metal matrix composites with specific strength can be used in various applications. The mechanical properties of these composites can be improved by correctly choosing the type, volume fraction, size, and distribution of reinforcements and metal matrix. In this research, to make Al/Al2O3-SiC hybrid composites, aluminum chips were prepared by machining, and then the chips were coated with Al2O3 and SiC reinforcements by suspension method. For composite making, first, aluminum-coated chips were molded inside a steel mold and after heat treatment at 645 °C for 2 h the chips were hot pressed. The microstructure of the fabricated composites was examined by optical and SEM microscope, and then compression and tensile strength behavior were studied. The microstructural results showed a sound composite without any porosities and cracks. The hybrid composite with 12 wt% reinforcements showed high compressive strength (370 MPa).

Research on the Effect of Static Pressure on the Rheological Properties of Waxy Crude Oil

In this paper, with the application of a MARS 60 high-pressure rheometer, experimental tests are conducted on Shengli crude oil to test its gel point, viscosity and thixotropy under different static pressures. Consequently, the effect of static pressure on the rheological parameters of waxy crude oil is revealed. It is proven that with the increase in the static pressure, the gel point of Shengli crude oil increases linearly, and the viscosity also gradually increases. The power law equation is employed to describe the relationship between the apparent viscosity and shear rate of Shengli crude oil under different static pressures. With the increase in the static pressure, the consistency coefficient (K) increases linearly, and the rheological index (n) decreases linearly. The relationship between the viscosity of Shengli crude oil and the static pressure and shear rate can be obtained. The Cross thixotropic model is used to describe the thixotropic curve of Shengli crude oil under different static pressures. With the increase in the static pressure, the thixotropic coefficient of consistency (ΔK) and the structure fracture constant (b) increase linearly. This is because a high pressure results in high structure strength and strong non-Newton rheological behavior in gelled crude oil and also causes remarkable structure fracture in crude oil. The results in this paper can provide an important theoretical basis for crude oil production and transportation.

Assessment of bone strength and fracture behavior of degenerative vertebrae through quantifying morphology and density distribution

Assessment of bone strength and fracture behavior of degenerative vertebrae through quantifying morphology and density distribution