Monotonic Uniaxial Loading Research Articles

New interpretation model of the effect of short PE fibers in TRM on tensile behavior

An experimental investigation was conducted on the tensile behavior of textile reinforced mortar (TRM) composites containing different volumes of short polyethylene (PE) fibers in a cementitious matrix to improve the tensile strength and cracking mode of TRM. This investigation mainly aimed to study the action mechanism of short fibers and propose a reasonable textile-short fiber-matrix interface model. The short fiber content was varied, as was the matrix type and the number of grid layers. Ten groups of TRM tensile specimens subjected to the monotonic uniaxial tensile loading were fabricated and tested to examine their tensile characteristics. The results showed that the multiple-cracking behavior and failure mode of TRM were significantly improved by adding PE fibers into the matrix. The tensile strength was increased by 25.8–167.2 %. After the uniaxial tensile tests, the microscopic investigation of the interface between the textile and matrix was conducted on the tensile specimens using an environmental scanning electron microscope (ESEM). The significant influence of the short PE fibers on the improvement of the interface bonding between the textile and matrix was confirmed. More importantly, based on the ESEM results, a novel interface model was proposed to promote understanding of the action mechanism of short fibers.

Biomechanical and biochemical changes in murine skin during development and aging

Aging leads to biochemical and biomechanical changes in skin, with biological and functional consequences. Despite extensive literature on skin aging, there is a lack of studies which investigate the maturation of the tissue and connect the microscopic changes in the skin to its macroscopic biomechanical behavior as it evolves over time. The present work addresses this knowledge gap using multiscale characterization of skin in a murine model considering newborn, adult and aged mice. Monotonic uniaxial loading, tension relaxation with change of bath, and loading to failure tests were performed on murine skin samples from different age groups, complemented by inflation experiments and atomic force microscopy indentation measurements. In parallel, skin samples were characterized using histological and biochemical techniques to assess tissue morphology, collagen organization, as well as collagen content and cross-linking. We show that 1-week-old skin differs across nearly all measured parameters from adult skin, showing reduced strain stiffening and tensile strength, a thinner dermis, lower collagen content and altered crosslinking patterns. Surprisingly, adult and aged skin were similar across most biomechanical parameters in the physiologic loading range, while aged skin had lower tensile strength and lower stiffening behavior at large force values. This correlates with altered collagen content and cross-links. Based on a computational model, differences in mechanocoupled stimuli in the skin of the different age groups were calculated, pointing to a potential biological significance of the age-induced biomechanical changes in regulating the local biophysical environment of dermal cells. Statement of significanceSkin microstructure and the emerging mechanical properties change with age, leading to biological, functional and health-related consequences. Despite extensive literature on skin aging, only very limited quantitative data are available on microstructural changes and the corresponding macroscopic biomechanical behavior as they evolve over time. This work provides a wide-range multiscale mechanical characterization of skin of newborn, adult and aged mice, and quantifies microstructural correlations in tissue morphology, collagen content, organization and cross-linking. Remarkably, aged skin retained normal hydration and normal biomechanical function in the physiological loading range but showed significantly reduced properties at super-physiological loading. Our data show that age-related microstructural differences have a profound effect not only on tissue-level properties but also on the cell-level biophysical environment.

Damage analysis of functionally graded materials: A finite element investigation utilizing the Gurson–Tvergaard–Needleman (GTN) model for notched plates

This study examines the mechanical behavior of notched materials under severe uniaxial monotonic loading until failure. Instead of focusing on the structural damages caused by notches, this study explores the complex loading experienced by notches. Finite element analysis of notched specimens is performed using ABAQUS-explicit. It is based on Von Mises’ flow theory and the Gurson–Tvergaard–Needleman damage model for void growth and coalescence. Functionally graded materials are strategically applied around the notches to enhance structural integrity. Concept-1 is proposed near the notch for maximum reinforcement, while Concept-2 is proposed in the central graded area for the optimal transition between the two concepts. A volumetric fraction index is an essential tool for enhancing gradation design robustness. As a result, the model can accurately predict ductile ruptures and void evolutions, proving that gradation concepts play a pivotal role in the behavior of structures. As a result of analyzing structures subjected to severe loads in real-world environments within industries such as aerospace, automotive, and construction, this groundbreaking work contributes to the fundamental understanding of the mechanical behavior of materials under extreme loading conditions.

The axial tensile performance of DSCW-RC joints with lap-spliced bars

Joints formed between double-skin concrete shear walls (DSCWs) and reinforced concrete (RC) foundations commonly utilize lap-spliced bars to transfer forces. However, the behavior and design of these critical connections have not been thoroughly investigated. This study experimentally analyzes a steel-reinforced DSCW-to-RC foundation anchorage joint under monotonic uniaxial tension loading. Seven 1:3 scale specimens were tested to examine the effects of varying lap-spliced bar diameter, steel plate thickness, and stud bolt spacing. Crack propagation, load-displacement response, and reinforcement strain were measured. The results characterize two potential failure modes: ductile steel yielding and brittle stud shearing. Steel strains developed linearly up to yielding, demonstrating uniform transmission of tensile loads. Increased plate thickness and decreased stud spacing enhanced capacity. To mitigate sudden shear failures, the number and strength of studs must exceed the expected tensile demand. New design recommendations are proposed, including minimum stud bolt shear strength and the use of confining tie bars. This study provides an improved understanding of the behavior of DSCW-to-RC foundation lap-spliced connections, enabling resistance to axial demands while avoiding brittle failure modes. The experimental data will inform future analytical models and design provisions for these critical structural joints.

Whip-Bezier: A C1-continuous hardening law for efficient direct and inverse identification

In 3D constitutive models, the hardening law is an essential model ingredient that has a first order effect on the predicted stress–strain response. In most phenomenological plasticity models, the hardening law coincides with the stress–strain curve for monotonic uniaxial loading. When identifying the hardening law for large strains through hybrid experimental–numerical approaches, the numerical properties of the hardening law play an important role. Here, we propose a novel piecewise-defined hardening law based on a composition of quadratic Bezier curve segments. The Whip-Bezier formulation preserves C1 continuity and achieves a parametrization with less parameters than its piecewise-linear counterpart. Both the possibility of identifying the hardening parameters in a decoupled optimization (e.g. from in-plane torsion experiments) and the use of a fully-coupled identification scheme (e.g. from notched tension experiments) are detailed. When contrasted with widely-used analytical expressions, the Whip-Bezier model consistently demonstrates enhanced performance with increasing number of parameters. This improvement comes with minimal statistical variance and reduced dependence on the initial optimization guess. Furthermore, the fitting quality is at least equivalent to that of the Swift-Voce hardening law with the same number of parameters.

Static Unified Inelastic Model: pre- and post-yield dislocation-mediated deformation

Modelling dislocation glide over the initial part of a stress–strain curve of metals received little attention up to now. However, dislocation glide is essential to ones understanding of the fundamental relationship between inelastic deformation and the evolution of the dislocation network structure. Therefore, we present a model of dislocation-driven deformation under static loading conditions.We reproduce repeated cyclic uniaxial tensile tests on Interstitial-Free and Low-Alloy steels. The elastic mechanical behaviour is described by isotropic linear elasticity, pre-yield anelastic mechanical behaviour by a dislocation bow-out model with dissipation, and the post-yield evolution of dislocation network structure by a statistical storage model. We hypothesise that when the local anelastic compliance is lower than the global plastic compliance, deformation is mechanically recoverable, and vice versa. This hypothesis is corroborated with the classical Taylor relation. We report the relation between stable and unstable dislocation glide using this prototypical modelling framework.We find four structural variables, that are based on dislocation physics, to describe the stress–strain curve: total dislocation density, average dislocation segment length, dislocation junction formation rate, and average dislocation junction length. Firstly, we quantify the dislocation network evolution during uniaxial monotonic loading, and verify work-hardening by dislocation junction formation and a Taylor-type equation for flow. Finally, we present a semi-empirical relation for the evolution of the dislocation network structure. Which allows us to: refine the physical interpretation of the Taylor relationship, and rationalise experimental observations on apparent modulus degradation by thermomechanical processing. Both these findings circumvent the limitations of current, physics-based hardening models.

Investigating Optimal Confinement Behaviour of Low-Strength Concrete through Quantitative and Analytical Approaches.

Reinforced concrete is used worldwide in the construction industry. In past eras, extensive research has been conducted and has clearly shown the performance of stress–strain behaviour and ductility design for high-, standard-, and normal-strength concrete (NSC) in axial compression. Limited research has been conducted on the experimental and analytical investigation of low-strength concrete (LSC) confinement behaviour under axial compression and relative ductility. Meanwhile, analytical equations are not investigated experimentally for the confinement behaviour of LSC by transverse reinforcement. The current study experimentally investigates the concrete confinement behaviour under axial compression and relative ductility of NSC and LSC using volumetric transverse reinforcement (VTR), and comparison with several analytical models such as Mander, Kent, and Park, and Saatcioglu. In this study, a total of 44 reinforced-column specimens at a length of 18 in with a cross-section of 7 in × 7 in were used for uniaxial monotonic loading of NSC and LSC. Three columns of each set were confined with 2 in, 4 in, 6 in, and 8 in c/c lateral ties spacing. The experimental results show that the central concrete stresses are significantly affected by decreasing the spacing between the transverse steel. In the case of the LSC, the core stresses are double the central stress of NSC. However, increasing the VTR, the capacity and the ductility of NSC and LSC increases. Reducing the spacing between the ties from 8 in to 2 in center to center can affect the concrete column’s strength by 60% in LSC, but 25% in the NSC. The VTR and the spacing between the ties greatly affected the LSC compared to NSC. It was found that the relative ductility of the confined column samples was almost twice that of the unrestrained column samples. Regarding different models, the Manders model best represents the performance before the ultimate strength, whereas Kent and Park represents post-peak behaviour.

Effects of Polyethylene Ground Plastic Waste Aggregate for Concrete Mixing Proportion

In recent times, the production of polyethylene ground plastics has increased markedly in the Philippines. However, current levels of their usage and disposal generate several environmental problems. Recycling is one of the most important actions that are being made to reduce these impacts. The present study used polyethylene ground plastic wastes to investigate their possible use as plastic aggregate in concrete application. The shredded plastic wastes were used in concrete with partial replacement of ½ kg and 1kg by volume of conventional coarse aggregate. Three types of concrete specimens including one without plastic aggregate were used in the study for comparison. All the concrete specimens were tested for their different mechanical properties after a curing period of 28 days. Various physical properties of all aggregates and fresh concrete properties were also tested in the laboratory, these include pound per square inch (psi), Mega Pascal (MPa), Kilo Newton (KN), and the type of fracture. The test for psi, MPa, and kN resulted that concrete mixtures with 1kg ground plastic produced the best result among the three samples having 3150 Psi, 21.7 MPa, and 395.7 KN, respectively. Moreover, the specimens were loaded under a monotonic uniaxial compressive load up to failure by using MATEST hydraulic testing machine with the indicator of kN. The result showed that both standard mixtures of concrete and the standard mixture of concrete with ½ kg polyethylene ground plastic have a comparison infraction that has a result of an SW-Shear Wedge of Type 5, while the standard mixture of concrete with 1kg polyethylene ground plastic has a conical type of a fracture. Based on the several tests conducted, it is concluded that the standard concrete mixture with 1kg polyethylene ground plastic provided the best result compared to other specimens. Furthermore, the use of polyethylene ground plastic waste in the standard concrete mixture provides some advantages like on reduction of plastic wastes, prevention of environmental pollution, and energy saving.

Buckling analysis of gusset plates with bolted connections using finite element modeling

Gusset plates connect lateral bracing to a building by fixing two perpendicular edges into the corners of a frame. This means that along the length of a gusset plate the cross sectional area is not uniform. For these reasons, stress distribution through a gusset plate is complex and difficult to predict. This has motivated design methods based upon approximate yield force analysis for gusset plates. The Whitmore width method (1952) is a widely adopted method used to size the yielding area of gusset plates in tension or those that do not buckle in compression. When considering buckling, international design codes prescribe equations that calculate strength curves that reduce the yielding capacity based on slenderness. However, these design code methods are based on column buckling behavior and are not specific to gusset plates. This study uses finite element modeling to study the development of yielding and buckling behavior in gusset plates with bolted connections. In total 184 variations of gusset plate geometries were modelled in Abaqus®. The simulated testing assumed an initial imperfection and applied a monotonic uniaxial load. Upon comparing results to current design methods, it was found that the Whitmore width is generally un-conservative in predicting initial yielding of gusset plates. By using the Thornton method with modifications based on FEA observations of gusset plate behavior, a new yield area and compressive strength curve suitable for gusset plates is proposed. These changes improved accuracy and safety in the design of gusset plates without adding complexity to the design process.

A new simple method for calculating notch root stress and strain of plane problems subjected to monotonic loading up to general yielding

In the present study, a new method for calculation of notch-root stress and strain is proposed. This novel method couples Neuber’s rule and incremental ESED method. A numerical procedure for solving the equation is presented. Also, the advantages and disadvantages of the numerical procedure are discussed. The coupling method is simple, and its accompanying numerical solution is easy to handle and straightforward. The proposed method is based on the total strain energy density, and strain energy density increment of the actual and elastic problem. Three cases of monotonic uniaxial loading in isotropic homogeneous plates with different material properties, namely nonlinear hardening obeying Ramberg–Osgood behavior, bilinear behavior, and elastic-perfectly plastic behavior, are investigated. The results show that, up to general yielding, the present method offers better accuracy compared to the previous methods. It is also observed that for the particular case of linear hardening, the difference of calculated stress and strain at the notch-root, compared to FEM, is less than 1%.

Experimental and numerical investigations of reinforced concrete columns confined internally with biaxial geogrids

Geogrids are geosynthetic materials that have been proven effective for stabilization and strengthening applications in infrastructure, such as: reinforcement and stabilization of pavement layers, reinforcement of embankments and soil walls, in addition to soil improvement. The main aim of this study is to investigate the feasibility of using biaxial geogrids as a replacement of ordinary transverse steel reinforcement in columns. Using geogrids as confining material in reinforced concrete columns offers advantages over steel stirrups in that they are less laborious to install and are more durable. The study presents results of experimental and analytical investigations of the behavior of small-scale reinforced concrete columns of 500 mm height subjected to monotonic uniaxial compressive loading. The main test variables include confining material (steel stirrups or geogrids), number of geogrids layers, and the aspect ratio (height to diameter) of the column. Strain gauges were installed on the geogrids to determine the displacement fields of the geogrid elements. Axial displacement and axial load were measured to assess the overall load-displacement behavior, stiffness, ultimate strength, and ductility of the confined column specimens. Analysis of the results revealed that the ductility and energy absorption capacity of concrete column specimens are substantially enhanced without any significant effect on the ultimate load capacity when internally confined by biaxial geogrids. Two distinct analytical models were developed to predict the load-displacement behavior, one for unconfined plain concrete specimens, and the other for columns with transverse reinforcement using biaxial geogrids. The models provided satisfactory predictions of the stress–strain response when the analytical and experimental results were compared.

A comparative study of the dynamic fragmentation of non-linear elastic and elasto-plastic rings: The roles of stored elastic energy and plastic dissipation

We develop a comparative analysis of the processes of dynamic necking and fragmentation in elasto-plastic and hyperelastic ductile rings subjected to rapid radial expansion. For that purpose, finite element simulations have been carried out using the commercial code ABAQUS/Explicit. Expanding velocities which range between 25 and 600 m/s have been investigated. The elasto-plastic material and the hyperelastic material are modelled with constitutive equations which provide nearly the same stress-strain response during monotonic uniaxial tensile loading, and fracture is assumed to occur at the same level of deformation energy. The computations have revealed that, while the number of necks nucleated in the elasto-plastic and hyperelastic rings is similar, the mechanisms which control their development are significantly different. In the elasto-plastic rings several necks are arrested due to the stress waves which travel the specimen after the localization process has started, and thus the number of fractures in the ring is significantly lower than the number of incepted necks. On the contrary, these stress waves do not stop the development of any neck in the hyperelastic rings. The elastic energy released from the sections of the ring which are unloading during the localization process fuels the development of the necks. Hence, for the whole range of investigated velocities, the proportion of necks that develop into fracture sites is much greater for the hyperelastic rings than for the elasto-plastic ones. The comparison between the numerical results obtained for both materials brings to light the roles of elastic unloading and plastic dissipation in multiple necking and fragmentation processes.

Ductile fracture of notched aluminum alloy specimens under elevated temperature part 2 – Numerical modelling and fracture criterion

Paper presents the results of the numerical modelling of axisymmetric specimens with circumferential notches made of aluminum alloy EN-AW 2024 T3 under elevated temperature. A range of notch rood radii (rK = 0.5, 2, 4, 8, 30 mm) is considered. The specimens underwent monotonic uniaxial loading at elevated temperature 20, 100, 200 and 300 °C. Stress and strain fields in whole specimens were calculated using finite element analysis (FEM). Axisymmetric finite element mesh model built of four-node elements with a bilinear shape function was used in simulations. The aim of these calculations were to determine the location of maximum stress and plastic strain in the specimen depending on the notch radius and the elevated temperature. Significant attention was paid to influence on distributions of stresses and plastic strains under uniaxial loading, elevated temperature and notch radius. It has been shown that the location of maximum stresses and plastic strains depends only on the notch radius where their value depends both on the notch radius and on the temperature. The main aim of these research was to develop new ductile fracture criterion for notched specimens taking into account elevated temperature and uniaxial loading. In this criterion assumed that the fracture initiation occurs when the normal stress on this physical plane reaches the critical value, depending on the isotropic damage state variable ω, generated by plastic flow of the material (depending on the temperature).

A meso-mechanical constitutive model of bulk metallic glass composites considering the local failure of matrix

Referring to the existing experimental investigation, a meso-mechanical constitutive model is constructed to describe the deformation and failure of bulk metallic glass composites under the monotonic uniaxial tensile and compressive loading conditions. Firstly, a free volume based constitutive model considering the failure mechanisms of bulk metallic glass and a unified visco-plastic model are employed for the bulk metallic glass matrix and toughening phase, respectively. To effectively reflect the local failure occurring in the bulk metallic glass matrix of the composites, a new two-leveled homogenization method is developed by extending the traditional Mori-Tanaka's method. Then, the algorithmic tangent operators for both of bulk metallic glass matrix and toughening phase are derived; the numerical integration algorithm of proposed model is also developed. Finally, the effectiveness of proposed model is validated by predicting the deformation and failure of bulk metallic glass composites under the monotonic tension and compression, respectively. Comparison of predicted results and corresponding experimental ones demonstrates that the proposed model can predict the deformation and local failure of bulk metallic glass composites well.

The Effect of Pre-Damaged Level on Repair Damaged Columns by Using Steel Straps Tensioning Technique

To date, repair of damaged columns has become increasingly more significant. The failure of columns structure contributes to the serious consequences in structural stability. Most of the existing repairing techniques are based on lateral passive confining pressure. However, this passive-type of confinement is ineffective in restoring the performance of damaged concrete columns. In this regards, active confinement was selected in this study to repair damaged concrete columns which can actively confine concrete in this study. Steel strapping tensioning technique (SSTT) allows pre-tensioning low-cost recycled steel straps around the damaged column was chosen herein to represent active confinement. A total of 12 columns were prepared and loaded axially to certain degree of their respective ultimate strength. Hence, a pre-damage level of the columns was developed. Then, the damaged columns repaired by using mortar and confined with SSTT. Finally, the repaired columns were then tested under monotonic uniaxial load. The structural performances of the confined repaired columns were compared with those of the repaired columns without confinement. It is expected that as the concrete compressive strength increases, the effectiveness in restoring the load carrying capacity of the damaged column becomes more significant.

Fabrication of nanocomposites with silica nanoparticles

Functionalization of silica nanoparticles is needed as to improve the mechanical performance of epoxy nanocomposites. Previous experience showed that direct dispersion of commercially available silica nanofillers does not improve significantly the mechanical properties of resulting nanocomposites. Different methods of fabrication are presented along with comments on the possibilities to improve the quality of obtained specimens. Both functionalized and unfunctionalized silica nanoparticles were added in three epoxy resins. The considered filling fraction was in most cases 0.1, 0.3 and 0.5 wt%. The obtained nanocomposites were subjected to monotonic uniaxial loading at room temperature. The static mechanical properties were not significantly changed regardless the filler type or percentage and type of epoxy resin.

Behaviour of Epoxy Silica Nanocomposites Under Static and Creep Loading

Abstract Specific manufacturing technologies were applied for the fabrication of epoxy-based nanocomposites with silica nanoparticles. For dispersing the fillers in the epoxy resin special equipment such as a shear mixer and a high energy sonicator with temperature control were used. Both functionalized and unfunctionalized silica nanoparticles were added in three epoxy resins. The considered filling fraction was in most cases 0.1, 0.3 and 0.5 wt%.. The obtained nanocomposites were subjected to monotonic uniaxial and creep loading at room temperature. The static mechanical properties were not significantly improved regardless the filler percentage and type of epoxy resin. Under creep loading, by increasing the stress level, the nanocomposite with 0.1 wt% silica creeps less than all other materials. Also the creep rate is reduced by adding silica nanofillers.

Compressive behaviour of concrete columns confined with steel-reinforced grout jackets

Abstract This paper investigates the compressive strength of concrete columns confined with a new jacketing system using high strength steel reinforced fabrics embedded in an inorganic matrix (SRG). A comprehensive experimental programme was conducted on 52 cylindrical columns with SRG jackets and 15 control specimens under monotonic uniaxial compression load. The test specimens were designed to investigate the influence of different design parameters including the density of the fabric (1, 1.57, 4.72 cords/cm), number of layers (1, 2), overlap length (24, 36 cm), bonding agent (4 different types of mortar) and the concrete strength (16–30 MPa). The test results highlight the efficiency of the proposed method, where one-layered and two-layered SRG jackets could increase the strength capacity of the unconfined specimens by up to 122% and 193%, respectively.

Localization of cracks in cementitious materials under uniaxial tension with electrical resistance tomography

This paper explores the feasibility of using electrical resistance tomography (ERT) for detecting damages or cracks on the engineered cementitious composites (ECC) under monotonic uniaxial tension loading. Two types of electrode arrays, unilateral planar electrodes array (UPEA) and bilateral edge electrodes array (BEEA) were developed and equipped in ERT system for ECC specimens and an electrode switching module (EMS) was designed to enforce the adjacent driver pattern of sixteen electrodes attached to the surface of ECC specimens. A constant and low frequency electric current (1μa, 1.5kHz) is applied onto the ECC specimen via some electrode pairs, and AC voltages were measured synchronously using the rest of electrode pairs. All these data were input into the inverse program to analyze and obtain the internal resistance distribution in the studied specimens. The capabilities of difference ERT to locate the cracks in ECC was estimated using (1) finite element models with given single crack and multiple cracks for image reconstruction, and (2) image reconstruction of real cracks in ECC plates under uniaxial tensile loading. The results showed that difference ERT could be used to detect the position and approximate range of the cracks produced in ECC and the performance of BEEA was better than that of UPEA.

Effect of different treatments on the flexural strength of fully versus partially stabilized monolithic zirconia

Statement of problemRecent monolithic zirconia materials used for indirect restorations are predominantly fully stabilized zirconia with claims of enhanced optical properties. These restorations may behave differently from the conventional partially stabilized zirconia restorations, which may negatively affect some of the core properties required for restoration success. PurposeThe purpose of this in vitro study was to evaluate and compare the effects of staining, airborne-particle abrasion, and artificial aging on the flexural strength of fully and partially stabilized zirconia material. Material and methodsEach partially stabilized monolithic zirconia (PSZ) and fully stabilized zirconia (FSZ) material and a zirconia core material (control) were prepared as bar-shaped specimens (2×2×25 mm) and divided into 6 groups (n=8/subgroup): regular sintering, vacuum sintering, stained, airborne-particle abrasion, artificially aged regular sintering, and artificially aged vacuum sintering. Critical load to fracture was determined for all groups by using monotonic uniaxial loading in accordance with International Organization for Standardization standard 6872. Data were analyzed using univariate analysis of variance, followed by the Tukey honest significant difference post hoc test (α=.05). ResultsThe control and PSZ (1034 and 1008 MPa) displayed a significantly higher (P<.05) flexural strength than FSZ (582 MPa). Airborne-particle abrasion significantly (P<.05) enhanced the strength of the control and PSZ (1413 and 1227 MPa) but significantly (P<.05) reduced the flexural strength of the FSZ (442 MPa). Staining, artificial aging, and vacuum sintering had no significant effects on any of the groups. ConclusionsFully stabilized zirconia may behave differently from conventional PSZ, especially with regard to airborne-particle abrasion, which may weaken the FSZ. The strength of PSZ is approximately double the strength of FSZ. Both of the zirconia materials showed resistance to artificial aging.