Higher Peak Strength Research Articles

On recyclability of thermosetting polymer and wood dust as reinforcement in secondary recycled ABS for nonstructural engineering applications

The management of thermosetting plastic solid waste has become serious issue worldwide due to its highly stable long-chain molecular structure and its recycling is the only way to reduce harmful effects. Also, depletion of natural resources like wood at alarming rate creates worldwide environment issues. In this article, feedstock filament for three-dimensional printing (in nonstructural engineering applications) of thermoplastic composite based on secondary (2°) recycled acrylonitrile butadiene styrene (ABS) as matrix reinforced with waste bakelite powder (BP) (thermosetting) and wood dust (WD) with twin-screw extrusion (TSE) process has been prepared (to impart desired mechanical/thermal/rheological and morphological properties).The results indicated that reinforcement of BP/WD initially increases the melt flow rate (MFR) of composite filament as compared to 2° recycled ABS. However, with increase in percentage of reinforcement beyond a certain limit, the MFR of the composite filaments starts decreasing. The mechanical, rheological, morphological, and thermal properties related to fused filaments prepared by TSE process have been explored in this research work and it has been observed that ABS composite filaments reinforced with 10% by weight of BP possess high peak strength (PS), high energy carrying capacity, more thermal stability, and contains low porosity. Based upon combined optimized extrusion parameter settings for maximizing the PS and percentage break elongation, 10 kg load, 225°C processing temperature, and 70 r min−1 are the best settings for both the composite filaments (ABS + BP, ABS + WD), and the corresponding values for ABS + BP and ABS + WD composite filament are 30.58 MPa (5.15%) and 25.65 MPa (6.05%), respectively.

Nonlinear Behavior of Marine Soil on the Dynamic Stability of Upper Wharf Structures: A Numerical Simulation Approach

Shen, C.; Qian, J.; Chen, X.; Xie, F., and Zhu, J., 2021. Nonlinear behavior of marine soil on the dynamic stability of the upper wharf structures: A numerical simulation approach. Journal of Coastal Research, 37(1), 149–155. Coconut Creek (Florida), ISSN 0749-0208.This paper investigates the influence of mechanical behavior of marine soil on the dynamic stability of the upper wharf. A series of triaxial consolidation undrained shear tests and one-dimensional consolidation compression tests was conducted to analyze the influence of fine particle content on the nonlinear behavior of marine soil. It was found that the relationship between stress and strain, the undrained shear strength, and residual strength of soil samples strongly correlated with the content of fine particles. In addition, the content of illite soil had a significant impact on the characteristic of the stress–strain curves, with a threshold of about 10%. A numerical model of the foundation-pile-superstructure under wave load was established. The results showed that the dynamic response of a wharf under wave load depended on the strength and nonlinear behaviors of the marine soil foundation. The strain-softening foundation with high peak strength led to more damage on the wharf. However, the strain-hardening characteristics resulted in more damage on the wharf when the peak strength was low. This suggests that the mechanical properties of soil foundation should be taken into account for the long-term durability and stability in the design of the wharf.

A novel coupled FDM‐DEM modelling method for flexible membrane boundary in laboratory tests

SUMMARYDifficulties are involved in discrete element method (DEM) modelling of the flexible boundary, that is, the membranes covering the soil sample, which can be commonly found in contemporary laboratory soil tests. In this paper, a novel method is proposed wherein the finite difference method (FDM) and DEM are coupled to simulate the rubber membrane and soil body, respectively. Numerical plane strain and triaxial tests, served by the flexible membrane, are implemented and analysed later. The effect of the membrane modulus on the measurement accuracy is considered, with analytical formulae derived to judge the significance of this effect. Based on an analysis of stress‐strain responses and the grain rotation field, the mechanical performances produced by the flexible and rigid lateral boundaries are compared for the plane strain test. The results show that (1) the effect of the membrane on the test result becomes more significant at larger strain level because the membrane applies additional lateral confining pressure to the soil body; (2) the tested models reproduce typical stress and volumetric paths for specimens with shear bands; (3) for the plane strain test, the rigid lateral boundary derives a much higher peak strength and larger bulk dilatation, but a similar residual strength, compared with the flexible boundary. The latter produces a more uniform (or ‘diffuse') rotation field and more mobilised local kinematics than does the former. All simulations show that the proposed FDM‐DEM coupling method is able to simulate laboratory tests with a flexible boundary membrane.

Effect of incorporating multifilament polypropylene fibers into alkaline activated fly ash soil mixtures

Soil stabilization is a well-known methods for the treatment problematic soils. Its advantages over soil replacement include low cost and fast implementation. The alkaline activation of soft soils is a new technique that has been proposed recently to stabilize soft soils. However, its strengthening mechanism and the final product in terms of stiffness and brittleness resemble those observed in cemented soils. In other words, the residual strength which emerges when approaching failure is very low, and this results in immediate damage to building structures. These shortcomings need to be overcome, particularly in places where seismic loading can be expected. In the case of cemented columns under heavy embankments, horizontal displacement is likely to occur under seismic loading. This will result in the failure of stabilized material due to frail bending moments, making greater residual strengths more important than higher peak strengths. To address this problem, a fix fly ash content of 40% and polypropylene fibers in the range of 0.5%, 0.75%, 1%, and 1.25% were considered. Compressive, flexural and indirect tensile strength test results revealed the feasibility of polypropylene fibers to improve post-peak behavior, thus allowing for higher residual strength after failure.

A study on Bonded Block Model (BBM) complexity for simulation of laboratory-scale stress-strain behavior in granitic rocks

The emergent macroscopic behaviors of Bonded Block Models (BBM) are governed largely by the properties assigned to their three components – blocks, contacts and zones (blocks are discretized using finite-difference zones). Over the years, different representations of these components, including elastic/inelastic zones and heterogeneous/homogenous blocks and contacts (corresponding to different mineral grains and associated mechanical properties), have been employed to simulate various aspects of rock behavior. However, there isa lack of understanding of the capabilities of these model representations with respect to their ability to replicate specific rock mechanical attributes. The goal of this study was to test a variety of model representations and evaluate their capabilities in terms of reproducing mechanical behaviors observed for a granitic rock type.It was found that inelastic zones were necessary to capture high confinement peak strengths while incorporation of heterogeneity was necessary to replicate the micro-cracking process. The heterogeneous, inelastic BBMs could match all the calibration targets and is identified as the best representation formodeling the full range of granitic rock behaviors. To help researchers select an appropriate BBM representation for modeling different aspectsof rock behavior, a summary table outlining the capabilities of the different model representations is also provided.

Influence of Coating on Mechanical Performance of Lap-Spliced Carbon Fiber-Textile Reinforced Mortar (TRM)

In this study, the effect of coating methods in the lap splice area on mechanical performance of lap-spliced carbon textile reinforced mortar (TRM) composites was investigated. The coating methods included textile reinforcement coated with epoxy, textile reinforcement coated with aluminum oxide powder and epoxy, and textile reinforcement coated with aluminum oxide powder, epoxy, and carbon fiber fabrics. It appears that the coated specimens showed higher peak strength and ultimate strain than those of the uncoated one.

Multimaterial printing and characterization for mechanical and surface properties of functionally graded prototype

In this work, an effort has been made for multimaterial three-dimensional printing of functionally graded prototypes of polylactic acid matrix (tensile specimens as per ASTM D638 type IV) followed by characterization of mechanical and surface properties. The work is an extension of previous reported studies on twin-screw extrusion process for the preparation of multimaterial wires as feedstock filaments in possible three-dimensional printing applications. The results of the study suggest that the highest peak strength (46.28 MPa) and break strength (41.65 MPa) was obtained for multimaterial three-dimensional printed samples at infill density 100%, infill angle 45°, and infill speed of 90 mm/s on commercial open source fused deposition modeling setup. Further surface hardness measurements performed on two extreme surfaces (top surface comprising magnetite (Fe3O4)-reinforced polylactic acid and bottom with polylactic acid without any reinforcement) revealed that the hardness for the bottom layer was more than the hardness for the top layer. From fractured surface analysis (using photomicrographs), it has been observed that the three-dimensional printed samples with low infill density resulted into more void formation due to which the performance while mechanical testing was poor in comparison to samples printed with higher infill density. The results are also supported by rendered images of photomicrographs, which revealed that high roughness value of samples printed with low infill density was also one of the reasons for poor mechanical performance of multimaterial three-dimensional printed functionally graded prototypes.

Influences of root concentration and suction on Chrysopogon zizanioides reinforcement of soil

The influences of root concentration and suction were investigated on Chrysopogon zizanioides (vetiver grass) root-reinforcement of clayey sand, using suction-monitored direct shear tests at four different suctions ranging from zero to 50 kPa. The vetiver grass specimens were grown in containers for about a year until they showed various root concentrations prior to testing. Of all suctions, soil samples with greater root concentrations had a higher peak strength and were more ductile than those without roots. Unsaturated root-reinforced soils contracted while the non-reinforced soils dilated during shearing. The rate of increase in root cohesion with root concentrations were highest at the suctions around 20 kPa. The rates of increase in shear strength with suction were similar for non-reinforced soils and reinforced soils up to a threshold in root concentration beyond which the rate became slightly smaller. The obtained relationships between root area ratio and strength were used in the infinite slope stability calculation of an instrumented slope based on field pore-water pressure and mini-rhizotron measurements. The analysis showed that in unsaturated condition, the stabilizing effect of suction was greater than that of roots, while in saturated condition, the stabilizing effect of root reinforcement was more important especially for shallower depth.

High strain rate response of bio-composites using split Hopkinson pressure bar and digital image correlation technique

ABSTRACTIn this research, high strain rate response and energy absorption characteristics under dynamic compression loading of five different bio-composites were studied using a compression split Hopkinson pressure bar (SHPB) and DIC (digital image correlation) technique. This study is to map suitability of plant-based materials instead of petroleum-based plastic as a constituent raw material in composites. Bio-composites panels were made from Southern yellow pine (SYP), Corn starch (CS), and Methylene diphenyl diisocyanate (MDI) using a Dieffenbacher hot press. The ability of non-contact DIC analysis served as a valuable tool to measure the strains over a large range of deformation in wood-based bio-composites subjected to high strain rate compressive loading. Among all, Material 2 bio-composite with high manufacturing pressure had highest peak strength, shows that material behaviour at high strain rates is strongly dependent on the manufacturing pressure during fabrication. Presence of corn starch marginally increased the energy absorption capacity.

Influence of bedding and cleats on the mechanical properties of a hard coal

The extensive bedding and cleats have a great influence on the mechanical properties of coal. The previous research mainly focused on the bedding effect, and few studies took the influence of both bedding and cleats into consideration. The scanning electron microscopy (SEM), uniaxial compression experiments, and acoustic emission (AE) monitoring were conducted on one hard coal specimen with different bedding and cleat angles. The experimental results show that for the bedding dip of 0° and face and butt cleat dip of 90°, the properties of coal specimens were characterized by the highest peak strength, the drastic failure process, the post-peak brittle behavior, the long initial quiet stage, and the short violent booming stage of AE hits number. For the bedding and face cleat dip of 45°, and the butt cleat dip of 90°, the properties of coal specimens were characterized by the lowest peak strength, the slip failure mode, the step-like drops of the post-peak stress-strain curve, and the several peaks of AE hits number. On the other hand, for the bedding and butt cleat dip of 90°, and the face cleat dip of 0°, the properties of coal specimens were presented as tensile failure mode with plate cracks, the short non-linear stage and the slight step-like drops of stress-strain curve, the short initial quiet stage of AE hits number, and the large value of elastic modulus. Then, a theoretical model of coal containing bedding and cleats was established in this paper. The simulation results of peak strength and failure mode verified the proposed model. The simulation of coal strength shows that bedding had the decisive influence on the uniaxial compressive strength of coal, while the weakening effect of cleats was non-negligible. When bedding and cleats were taken into consideration together, the minimum peak strength was reduced and the bedding dip related to the minimum peak strength changed.

Structural Behavior of Durable Composite Sandwich Panels with High Performance Expanded Polystyrene Concrete

Sandwich panels comprising prefabricated ultra-high performance concrete (UHPC) composites can be used as eco-friendly and multi-functional structural elements. To improve the structural and thermal performance of composite sandwich panels, combinations of UHPC and expanded polystyrene (EPS) beads were investigated. High-performance expanded polystyrene concrete (HPEPC) was tested with various EPS bulk ratios to determine the suitability of the mechanical properties for use as a high-strength lightweight aggregate concrete. As a core material in composite sandwich panels, the mechanical properties of HPEPC were compared with those of EPS mortar. The compressive strength of HPEPC is approximately eight times greater than that of EPS mortar, and the thermal conductivity of approximately a quarter that of EPS mortar. The structural behavior of composite sandwich panels was empirically analyzed using different combinations of cores, face sheets, and adhesive materials. In the flatwise and edgewise compression tests, sandwich panels with HPEPC cores had high peak strengths, irrespective of the type of face sheets, as opposed to the specimens with EPS mortar cores. In the four-point bending tests, the sandwich panels with HPEPC cores, or reinforced UHPC face sheets combined with adhesive mortar, exhibited higher peak strengths than the other specimens, and failed in a stable manner, without delamination.

Shear strength of interfaces between unsaturated soils and composite geotextile with polyester yarn reinforcement

Composite geotextiles with polyester yarn reinforcement have been commonly used in combination with unsaturated soils. Both unsaturated and saturated shear strength of the interfaces were investigated between a composite geotextile and three major types of materials: silty sand (SM), low-plasticity silt (ML) and high-plasticity clay (CH) in a direct shear box. The interfaces were formed using two methods (A and B) to reflect the wide range of possible contact conditions in practice. Method A involved statically compacting the soil directly on top of the composite geotextile, while for Method B, the soil was statically compacted in a separate mold and later brought into contact with the composite geotextile. Type B interfaces required a larger displacement to mobilize the shear strength than Type A interfaces. The ultimate failure envelopes of SM and ML soils were similar to those of their interface shearing. Notably, the failure envelopes for the clay-geotextile interface of both types were higher than that of clay alone. The unsaturated soil-only shearing had a higher peak strength and tended to dilate more than saturated soil-only shearing, while unsaturated soil-interface shearing appeared to be more contractant than saturated interface shearing. The strength variations with suction for all tested soils and interface shearing were clearly non-linear. A new model that takes account of the condition of soil-geotextile contact intimacy is proposed for predicting the variation of interface strength with suction, based on the variation of the soil's apparent cohesion with suction and the geotextile-water retention curve.

Geomechanical Studies on Granite Intrusions in Alxa Area for High-Level Radioactive Waste Disposal

Geological storage is an important concept for high-level radioactive waste (HLW) disposal, and detailed studies are required to protect the environment from contamination by radionuclides. This paper presents a series of geomechanical studies on the site selection for HLW disposal in the Alxa area of China. Surface investigation in the field and RQD analyses on the drill cores are carried out to evaluate the rock mass quality. Laboratory uniaxial and triaxial compressive tests on the samples prepared from the drill cores are conducted to estimate the strength properties of the host rock. It is found that the NRG sub-area has massive granite intrusions, and NRG01 cored granite samples show the best rock quality and higher peak strength under various confinements (0–30 MPa). NRG01 granite samples are applied for more detailed laboratory studies considering the effects of strain rate and temperature. It is observed that the increasing strain rate from 1.0 × 10−5–0.6 × 10−2·s−1 can lead to a limited increase on peak strength, but a much more violent failure under uniaxial compressive tests on the NRG01 granite samples, and the temperature increasing from 20 °C–200 °C may result in a slight increase of UCS, as well as more ductile post-peak behavior in the triaxial compressive tests.

Effects of Electric Current on the Microstructures and Mechanical Properties of Artificial Aged 6061 Alloy

The influences of electric current on the microstructures and mechanical properties of 6061 aluminum alloy were investigated by electric conductivity measurement, tensile test, scanning electron microscope and transmission electron microscope. When applying electric current both at solid solution and ageing treatment, the alloy has the highest peak strength, and the time to peak strength shortens by 12h. The electric current applying during either solid solution or ageing, increases the density and size of β'' phase.

Reaction-induced rheological weakening enables oceanic plate subduction.

Earth is the only terrestrial planet in our solar system where an oceanic plate subducts beneath an overriding plate. Although the initiation of plate subduction requires extremely weak boundaries between strong plates, the way in which oceanic mantle rheologically weakens remains unknown. Here we show that shear-enhanced hydration reactions contribute to the generation and maintenance of weak mantle shear zones at mid-lithospheric depths. High-pressure friction experiments on peridotite gouge reveal that in the presence of hydrothermal water, increasing strain and reactions lead to an order-of-magnitude reduction in strength. The rate of deformation is controlled by pressure-solution-accommodated frictional sliding on weak hydrous phyllosilicate (talc), providing a mechanism for the ‘cutoff' of the high peak strength at the brittle-plastic transition. Our findings suggest that infiltration of seawater into transform faults with long lengths and low slip rates is an important controlling factor on the initiation of plate tectonics on terrestrial planets.

Monotonic Direct Simple Shear Tests on Sand under Multidirectional Loading

AbstractStress–strain responses of Leighton Buzzard sand are investigated under bidirectional shear. The tests are conducted by using the variable direction dynamic cyclic simple shear (VDDCSS). Soil samples are anisotropically consolidated under a vertical normal stress and horizontal shear stress and then sheared in undrained conditions by applying a horizontal shear stress acting along a different direction from the consolidation shear stress. The influence of the orientation and magnitude of the consolidation shear stress is investigated in this study. There have been only a few previous studies on soil responses under bidirectional shear, of which most studies do not consider the impact of the magnitude of the consolidation shear stress. They are compared with current studies, indicating both similarities and differences. Generally, all test results indicate that a smaller angle between the first and second horizontal shear stress leads to more brittle responses with higher peak strengths, and a larg...

Hydro-mechanical behavior of sandstone with interconnected joints under undrained conditions

In rock masses containing multiple joint sets the joints will intersect. The geometric nature of such joint intersections can influence the hydro-mechanical response of jointed rock. An undrained experimental study was performed on fully-saturated, doubly-jointed sandstone specimens. Testing considered a variety of joint orientations and interconnected joint configurations, and various values of confining and initial pore-water pressure. Test results revealed three failure mechanisms: (1) shearing (through intact material); (2) crushing failure in the vicinity of the joint junction point (with associated sliding on joints), and (3) sliding along a preferred joint plane. Using these results, a ‘failure mode matrix’ was developed to assist in prediction of failure mechanisms for different joint angles and intersection configurations, at different confining pressures. Greater peak induced pore-water pressures were observed for symmetric interconnected joint configurations than skew-symmetric configurations, for all confining pressures, though the difference was significantly more pronounced at higher confining pressures. Greatest peak strength values were obtained for joint geometries in which both interconnected joints were at a low angle. When both joint angles were greater than the friction angle of the joints, peak strength did not show a noteworthy difference between symmetric and skew-symmetric joint configurations for relatively low confining pressures. However, at higher confining pressures, skew-symmetric joint configurations showed considerably higher peak strength than symmetric joint configurations. These behaviors were attributed to differences in failure mechanism (between symmetric and skew-symmetric specimens) and the influence of failure mechanism and confining pressure on end friction and specimen response.

Influence of Cement Treatment on Unconfined Compressive Strength and Compressibility of Lean Clay with Medium Plasticity

This study presents the experimental results on the use of cement in modification and stabilization of medium plastic clays. Samples of lean clay were mixed with Portland cement in percentages of 5 and 10 % by dry weight of the soils that had water contents of 40 and 60 %. The curing time of the samples varied between 7 and 28 days. The effects of cement addition on the workability, unconfined compressive strength (UCS) and compressibility of lean clay were examined. The plasticity index showed a steady decrease for all samples leading to higher workability especially in higher cement contents. The results of UCS tests demonstrated that UCS increased up to five times by the addition of 10 % cement to the soil at the end of 28 days. Specimens with lower water content had higher peak strengths. Samples exhibited ductile, semi-brittle, and brittle type of failures depending on their water and cement contents. Brittleness index was used to quantify the mechanical behavior of the soil and the brittleness index increased distinctively as a result of cement treatment. Deformability index was proposed as an alternative to evaluate the deformation behavior of specimens. Moreover, a relationship to determine the UCS development with curing time was proposed. The results of consolidation tests indicated that the compression index decreased and preconsolidation pressure increased by increasing the cement content. The preconsolidation pressure values were found to be related to the UCS values by a ratio of 1.4 for the cement-treated clay.

Binding energy of the ground and first few excited states of hydrogenic donor impurity in a rectangular GaAs quantum dot in the presence of electric field

Within the quasi-one-dimensional effective potential model and effective mass approximation, we calculate the ground and the first 9 excited-state binding energies of a hydrogenic donor impurity in a rectangular quantum dot (RQD) in the presence of electric field. The analytical form of the quasi-one-dimensional effective potential replacing the three-dimensional Coulomb potential in our model is derived by Fourier transforms. We discuss detailedly dependence of the binding energies on the impurity positions and electric fields. For the ground-state binding energy, our results qualitatively agree with that of Mendoza et al. (2005) in which they only calculated the ground-state binding energies in cubic quantum dots by variational method. However, for first 9 excited-state binding energies, such dependence has complex manner since there are two or three peaks in the electronic probability density distribution curves. The strengths and positions of these peaks in RQD affect the interaction potential between electron and impurity, which appears to be the critical control on the binding energies of impurity. The applied electric field pushes the positions of these peaks downwards, and the strengths of peaks located at the upper half of RQD increase while the strengths of lower peaks firstly decrease, then increase with increasing electric field. The high peak strength can lead to increase of the binding energy while the large distance between the position of peak and impurity center results in reduce of the energy, which is an interesting competition. This competition is more obvious for excited-state binding energies of off-central impurity.

Eccentric Axial Load Capacity of High-Strength Steel-Concrete Composite Columns of Various Sectional Shapes

AbstractTwo concrete-filled steel tube columns and four concrete-encased steel columns using high-strength steel (yield strength fys=913, 806, and 812 MPa) and high-strength concrete (compressive strength fc′=94, 113, 104, and 184 MPa) were tested to investigate the effect of various sectional shapes and configurations on the eccentric axial load carrying capacity. This study focused on maximizing the contribution of the high-strength steel, preventing early crushing of the concrete (1) by using steel tubes or closely spaced ties for lateral confinement, (2) by using ultra high-strength (200 MPa) concrete with a high-crushing strain, and (3) by placing L-shaped steel sections at the corners of the cross section. The test results showed that the steel tube successfully restrained early concrete crushing and developed its full plastic stress; unlike expectation, early crushing occurred in the ultra high-strength concrete column; and the concrete-encased L-section column had higher peak strength and flexural...