Longitudinal Tensile Research Articles

A novel dynamic constitutive micromechanical model to predict the strain rate dependent mechanical behavior of glass/epoxy laminated composites

In the present research, a novel dynamic constitutive micromechanical (DCM) model was developed to predict the strain rate dependent mechanical behavior of laminated glass/epoxy composites. The present model is an integration of the generalized strain rate dependent constitutive model as a constitutive model for the neat polymer, the plasticity model of Huang as a micromechanical model, and dynamic progressive failure criteria. This model is able to predict the longitudinal and transverse tensile and in-plane shear behaviors of unidirectional glass/epoxy composites with arbitrary fiber volume fractions at arbitrary strain rates. The present model can also predict the stress-strain behavior of laminated composites with different layups and fiber volume fractions at arbitrary strain rates. A comparison between the results predicted by the present model and the available experimental data showed that the model predicts the strain rate dependent mechanical behavior of glass/epoxy composites with very good accuracy.

Analysis of the transverse compressive behavior of Kevlar fibers using microscopic scale approach

During the ballistic impact process of fabrics, yarns are locally subjected to both longitudinal tensile and transverse compressive loading. This paper presents a microscopic numerical investigation of the transverse compressive behavior of a single and bulk aramid fibers. Interactions with friction between single fibers in a yarn have been taken into account. Numerical calculations were performed in the case of a transverse compression using the assumption of plane strain and validated by experimental data. Effects of friction and representative volume size were also discussed. It can be highlighted that using a numerical homogenization technique, the variation of the transverse mechanical effective property versus fiber volume fraction has been determined based on the microscopic transverse behavior of bulk aramid fibers. Finally, power relationships describing effective transverse Young's modulus E¯ and apparent strain ε¯ versus the normalized fiber volume fraction have been proposed and discussed. This effective homogenized material allows the development of homogenized Kevlar yarns and fabrics in the further works of homogenized approaches.

Flexural behavior of hybrid GFRP - concrete railway sleepers

Abstract This paper aims to present the flexural behavior of hybrid GFRP (glass fiber reinforced polymer) concrete beams as sleepers to railway application. It was tried to obtain sleepers with adequate mechanical resistance, not susceptible to corrosion, durable and lighter than the sleepers in prestressed concrete. Pultruded fiberglass and polyester resin profiles were filled with high strength concrete and polyolefin fiber in the following proportions by volume: 1% and 2.5%. The beams were 1.06 meters long and had a 76 mm x 76 mm x 6 mm cross section, corresponding to a reduced model in a 1: 2.64 scale of a 2.80 meters long sleeper. In the bending tests, the load was applied at the center of the sleeper, as provided in the Brazilian standard NBR 11709 (2015) and American standard AREMA (2016). During the tests the applied load, the vertical deflection and the longitudinal tensile and compression deformations were measured in the center of the span. The influence of fiber addition on the strength, rupture mode and flexural modulus of elasticity of the hybrid beams was analyzed. Finally, the hybrid sleeper performance was compared to that of the prestressed concrete monoblock sleeper. The results obtained were satisfactory, indicating that the proposed hybrid sleeper is a constructively and technically feasible alternative.

Considerations on longitudinal dynamic effects of unbraked vehicle in passenger train composition – parametric study

The study investigates the trains’ longitudinal dynamic evolutions in certain unusual situations that may be encountered, even rarely, in railway operation. It is about the case of operating passenger trains having in componence a vehicle with isolated braking system. This is a state that, according to regulations, is generally not acceptable, but there are circumstances that can conduct to exceptions. Our purpose is to find out by numerical simulations the influence that certain parameters, such as the number of vehicles of the train, the weight of locomotive and the position of the unbraked vehicle, have on the longitudinal dynamics of passenger trains during braking actions. The numerical simulations were performed for trains in classical composition, meaning a locomotive hauling 3 up to 19 passenger vehicles, thus covering virtually all the current situations encountered in operation. In simulations there were considered all the possible placements of the unbraked vehicle within the train body. The main outcomes, submitted to a comprehensive analyse, are the maximum in-train forces and the position in long of the train of the most affected couplers by longitudinal dynamic compression (buff) and tensile (draft) forces. The time dependency of in-train forces is also discussed.

High strength Kevlar fiber reinforced advanced textile composites

A state of art on characterization of Kevlar fibers and Kevlar fiber reinforced polymer (KFRP) composites is presented to enunciate the limits of further researches in regard of its applicability with the optimized design in today’s high-tech era. A proper characterization is very important for enhancing material properties in various applications such as defense, industrial, marine and aerospace. In this review work, research works performed on the mechanical impact and deformation behavior of Kevlar fiber and KFRP composites have been focused. Kevlar fibers possess high fracture toughness and high strength to weight ratio, of high-performance reinforcement in polymer textile composites. Researchers using different modeling approaches such as homogeneous isotropic and orthotropic material model along with the effect of different parameters as fabric weaving pattern, matrix material, and composite fabrication techniques, working and loading conditions are discussed in detail. Due to anisotropic nature of Kevlar fibers; KFRP composites have high ratio of longitudinal tensile to compression strength whereas the compression strength is considerably found to increase after fiber surface treatment. The purpose of this study is to provide the reader with an overview of different strategies applied with the experimental and numerical investigations of high strength Kevlar fibers and KFRP composites at micro/meso/macroscale.

Behaviour of concrete filled glass fibre-reinforced polymer tubes under static and flexural fatigue loading

Abstract Concrete-filled glass fibre-reinforced polymer tubes (CFFTs) have reportedly been considered for industrial applications such as fender piling for marine structures and bridge girders. Even though previous investigations of the flexural fatigue behaviour of circular sectioned CFFTs have been reported in the literature, no such study has been carried out for square or rectangular sectioned tubes. In order to address this research gap, an experimental programme was carried out to investigate the flexural fatigue behaviour of square sectioned CFFTs, considering fatigue deformation cycles equal to 75%, 80%, 85% and 90% of the deformation corresponding to the static flexural failure of the tested CFFTs. The used glass fibre-reinforced polymer (GFRP) tubes contained reinforcements at the longitudinal direction and ±45° to the longitudinal axis of tubes. They were also specified to have much larger longitudinal tensile and compressive strength compared to typical rectangular GFRP tubes. Self-compacting concrete was used for the core-infill of the tested CFFTs. In total, eight static flexural tests and sixteen flexural fatigue tests were conducted under displacement-control fatigue loading using two loading arrangements, namely three-point and four-point bending. All CFFTs beams subjected to the fatigue loading failed due to buckling of the compression flange of CFFT. It was observed that the number of cycles to failure for the employed fatigue deformation ranges were quite low and decreased with increasing the amplitude of fatigue deformation. The bending stiffness of the tested specimens was observed to decrease as the fatigue loading progressed. It was also found that the amount of dissipated energy in a given cycle and the rate of stiffness degradation increases with an increase in the amplitude of fatigue deformation, especially for specimens tested under four-point bending. Furthermore, the bending stiffness at failure for the specimens tested under four-point bending was found to be approximately 80–90% of its initial value.

Effects of Cross-Sectional Size and Shape on the Longitudinal Tensile and Anchoring Properties of CFRP Cables

AbstractCarbon fiber–reinforced polymer (CFRP) is very suitable for use as a prestressed cable and can replace conventional steel cables in cable roofs. In engineering practice, the anchoring lengt...

Micromechanical modeling of the effects of adiabatic heating on the high strain rate deformation of polymer matrix composites

Fiber reinforced polymer matrix composites are increasingly being used to fabricate energy-absorbing aerospace structural components susceptible to impact loading, such as jet engine containment structures subjected to blade-out events. The development and certification of such structures necessitates a detailed understanding of the dynamic behavior of the constituent materials, particularly the strain rate, temperature, and pressure dependent polymer matrix, and their complex interaction. As the rate of deformation increases, the thermodynamic condition transitions from isothermal to adiabatic. The conversion of plastic work to heat causes local adiabatic heating in the polymer matrix, but the rapid nature of impact events does not allow sufficient time for heat to dissipate; ballistic impact events can therefore be regarded as fully adiabatic. Local adiabatic heating can significantly affect the high rate deformation response if thermal softening effects outweigh strain and strain rate hardening effects and therefore, must be explicitly modeled at the appropriate length scale. In this paper, an existing isothermal viscoplastic strain rate and pressure-dependent polymer constitutive formulation is extended to nonisothermal conditions by modifying the inelastic strain rate tensor components to explicitly depend on temperature based on the Arrhenius equation for nonisothermal processes. A methodology based on shifting neat resin dynamic mechanical analysis data is utilized to determine the polymer elastic properties over a range of strain rates and temperatures. Temperature rises due to the conversion of plastic work to heat are computed, assuming adiabatic conditions. It is demonstrated that the modified polymer constitutive model is capable of capturing strain rate and temperature dependent yield as well as thermal softening associated with the conversion of plastic work to heat at high rates of strain. The nonisothermal polymer constitutive model is then embedded within the Generalized Method of Cells micromechanics framework to investigate the manifestation of matrix thermal softening, due to the conversion of plastic work to heat, on the high strain rate response of a T700/Epon 862 unidirectional composite. Adiabatic model predictions for high strain rate composite longitudinal tensile, transverse tensile, and in-plane shear loading are presented. Results show a substantial deviation from isothermal conditions; significant thermal softening is observed for matrix dominated deformation modes (transverse tension and in-plane shear), highlighting the importance of accounting for local adiabatic heating in the polymer matrix in the high strain rate analysis of polymer matrix composite structures.

Impact of Mining Subsidence on Natural Gas Pipeline Failures

The main goal of the paper is to present the influence of ground deformations, caused by mining subsidence, on natural gas pipelines. There are also presented characteristic examples of the gas pipelines failures in mining areas in Poland. Failures of buried natural gas pipelines pose a threat to people and the environment due to gas leaks. The main reasons of the leaks are corrosion of steel pipelines, mechanical damage as a result of construction works and unsealing of joints as well as expansion joints. In mining areas, the gas pipelines are influenced by ground deformations. Mining extraction induces subsidence, horizontal displacements, horizontal strains and curvatures of the subsurface ground layer where natural gas pipelines are buried. The horizontal strains are of significant importance for the considered issue. The mining-induced ground deformations cause displacements of pipelines as well as additional longitudinal tensile and compression loads. The load values depend on the soil-pipe friction coefficient, pipeline depth and pipeline section length subjected to horizontal strains. The load conditions also change in the transverse direction of pipelines. In Polish mining areas distribution gas pipelines are constructed with steel and polyethylene pipes. Transmission gas pipelines are constructed with steel pipes. The steel gas pipelines usually are equipped with built-in expansion joints to protect them and to transmit ground deformations. The polyethylene gas pipelines are flexible and are able to transmit mining ground deformations but polyethylene pipes can be used up to 1,0 MPa nominal pressure in natural gas systems. Mining extraction causes additional failures of the gas pipelines despite their above mentioned capacities. The failures occur most frequently in the steel gas pipelines, particularly in old ones. The main causes of gas leaks are wall breaks, mostly near welded areas, wall buckling and sealant damage of expansion joints. Mining deformations can also induce the buckling of polyethylene pipelines. Therefore, in mining areas additional inspections of the natural gas network are needed to detect the leaks early.

Studies on the weldability, mechanical properties and microstructural characterization of activated flux TIG welding of AISI 321 austenitic stainless steel

The presence of titanium in AISI 321 austenitic stainless steel, mitigates the corrosion when deployed in specific applications such as boiler shells, aircraft exhaust manifolds and process equipment. Using Commercial flux purchased from Edison Welding Institute (EWI), studies were conducted to note the effect of Activated Tungsten Inert gas (A-TIG) welding on the surface morphology of type 321 austenitic stainless steel welds and compared with conventional TIG welding. A thin flux layer was applied to the surface of the 6 mm thick plate, followed by a conventional TIG welding process. The bead on trial results shows that compared with the TIG welding process, the flux causes the weld depth to increase, weld bead width to decrease and weld area to increase. This incredible depth of penetration (DOP) has been accomplished by the mechanisms of reversal of Marangoni flow and Arc constriction. From various experimental trials, arc length of 3 mm, welding current of 220 Amps and welding speed of 120 mm min−1 were found to be optimal and subsequently used as input parameters to produce a good quality A-TIG welded butt joint. The welded joint is subjected to transverse and longitudinal tensile and bend tests, charpy impact toughness tests, microhardness, optical microscope, x-ray diffraction analysis, ferrite number measurement and Scanned electron fractography. The welded joint exhibited improved tensile strength, bend and charpy impact toughness and hardness. The weld metal microstructure was observed to be austenite, delta-ferrite and TiC intermetallic compounds (Titanium carbides). The XRD pattern indicates that austenite and ferrite phases are present in both base and weld metal. The results of Fischer Feritscope FMP30 (ferrite measurement) show that the content of delta-ferrite in the weld metal (5.9 FN) is much higher than the parent metal (1.2 FN) and shows excellent mechanical properties in the A-TIG welded joint. Scanned electron fractography indicates that the failure of weld metal and base metal occurs in the ductile mode of fracture.

Mechanics of the reciprocal effects of bending and torsion during 3D bending of profiles

Profiles with circular cross-sections can be geometrically described by the shape of the bending line. To achieve 3D bending lines with kinematic bending processes, a continuous change of the bending plane is needed, resulting in bending force vectors that change direction accordingly. These force vectors generate a bending moment in the forming zone and, hence, longitudinal tensile and compressive stresses. For profiles with non-circular cross-sections the orientation of the cross-section along the bending line needs to be controlled additionally. This can be achieved by applying a specific torque to the bending process and, thus, introducing desired shear stresses into the forming zone. Until now, this fundamental aspect of 3D profile bending has not been studied in a coherent fashion. To take into account the reciprocal effects of the various stresses applied to the forming zone and their effect on the bending moment and, thus, on springback, a comprehensive analytical process model was set up. The model is validated by experimental investigations performed using the Torque Superposed Spatial (TSS) profile bending machine and by comprehensive numerical investigations. Analyses were performed during plane bending as well as during bending superposed with torsion. The investigations show that the applied bending force and torque not only result in stress superposition, but actually also affect the development of shear strains over the cross-section of the profile. Similar to the longitudinal strains, the shear strains decrease linearly from the intrados and extrados of the profile to the neutral axis. Considering this newly observed behavior in the analytical process model, the absolute bending force deviation was reduced by a factor of four down to 7.6%.

Microstructural Evolution and Mechanical Properties of CSEF/M P92 Steel Weldments Welded Using Different Filler Compositions

In the present investigation, P92 steel weld joints were prepared using a shielded metal arc welding (SMAW) process for two different fillers, E911 and P92. A comparative study was performed on the microstructural evolution, tensile strength, microhardness, and Charpy toughness across the P92 steel weldments in the as-welded and post-weld heat-treated (PWHT) conditions. The PWHT was performed at 760 °C for 2 hours. To study the effect of the different filler metals and PWHT on the mechanical properties, longitudinal and transverse tensile tests were carried out at room temperature for a constant cross-head speed of 1 mm/min. In the longitudinal direction, the tensile strength of the P92 steel welds was measured as 958 ± 35 and 1359 ± 38 MPa for the E911 and P92 filler, respectively. In the as-welded condition, the transverse tensile specimens were fractured from the fine-grained heat-affected zone or inter-critical heat-affected zone (FGHAZ/ICHAZ) and, after PWHT, the fracture location was shifted to over-tempered base metal from the FGHAZ/ICHAZ. After the PWHT, the tempering reaction resulted in lowering of the hardness throughout the weldment. After PWHT, the Charpy toughness of the weld fusion zone and heat-affected zone (HAZ) of the E911 filler weldments was measured as 66 ± 5 and 142 ± 8 J, respectively. The minimum required Charpy toughness of 47 J (EN1557: 1997) was achieved after the PWHT for both E911 and P92 filler.

Effect of interlayers on softening of aluminum friction stir welds

Effects of the zinc, copper and brass interlayers were studied on the microstructure evolution and mechanical properties of the wrought aluminum friction stir welds. Optical and scanning electron microscopes (SEM) as well as X-ray diffraction (XRD) analysis were used for investigation of the distribution, dissolution and reactions of the interlayers, grain structure in the stir zone and fracture surfaces. Longitudinal and transverse tensile and microhardness tests were also carried out in order to evaluate the mechanical properties of the welds. The results showed that without insertion of the interlayer, the joint efficiency (ratio of the weld strength to the aluminum base metal strength) was ~60%. While zinc and copper interlayers had no significant effect on the joint efficiency, insertion of the brass interlayer increased the joint efficiency up to ~90%. Microstructural observation indicated that brass interlayer was relatively well distributed inside the stir zone and Al2Cu and Al4Cu9 intermetallic compounds were formed due to the solid-state reactions between the aluminum matrix and brass particles during welding leading to the increase in the weld strength. In the case of the zinc interlayer, no intermetallic compound was detected inside the weld zone and zinc was dissolved in the aluminum matrix to form a solid solution. Moreover, the joint welded using copper interlayer suffered from lack of distribution of the detached copper particles. Fracture analysis after tensile test showed that insertion of the interlayers generally changed the fracture location from the advancing side towards the retreating side due to the formation of a composite structure and increase in the strength of the advancing side.

Automated optimization of steel reinforcement in RC building frames using building information modeling and hybrid genetic algorithm

Abstract Design of steel reinforcement is an important and necessary task for designing reinforced concrete (RC) building structures. Currently, steel reinforcement design is performed manually or semi-automatically using computer software such as ETABS, with reference to building codes. These approaches are time consuming and sometimes error-prone. Recent advances in building information modeling (BIM) technology allow digital 3D BIM models to be leveraged for supporting different types of engineering analyses such as structural engineering design. With the aid of BIM technology, steel reinforcement design could be automated for fast, economical and error-free procedures. This paper presents a BIM-based framework using the developed three-stage hybrid genetic algorithm (GA) for automated optimization of steel reinforcement in RC frames. The methodology framework determines the selection and alignment of steel reinforcement bars in an RC building frame for the minimum steel reinforcement area, considering longitudinal tensile, longitudinal compressive and shear steel reinforcement. The first two stages optimize the longitudinal tensile and longitudinal compressive steel reinforcement while the third stage optimizes the shear steel reinforcement. International design code (BS8110) and buildability constraints are considered in the developed optimization framework. A BIM model in Industry Foundation Classes (IFC) is then automatically created to visualize the optimized steel reinforcement design results in 3D thereby facilitating design communication and generation of construction detailing drawings. A three-storey RC building frame is analyzed to check the applicability of the developed framework and its improvement over current design approaches. The results show that the developed methodology framework can minimize the steel reinforcement area quickly and accurately.

Mechanical properties and microstructure of potato peels

ABSTRACTPotato peel, as the outermost tissue of the fruit, playing a role of protection and fresh keeping on the pulp tissue, is crucial for the design of potato harvesting machines. In this study, two types of potato ‘Yangyu 4’ and ‘Helan 14’ were selected to conduct friction, tensile and tear tests on their peel. Longitudinal and transverse tensile tests were conducted on the peels of two potato cultivars using an electronic universal testing machine, and tear tests were carried out on peels as well. The static friction coefficient for different materials, stress-strain curves and tear force-deformation curves of the peels were obtained and the tensile strength, elastic modulus, failure strain tear strength of the peels were measured. The results showed that the maximum value of the static friction coefficient against metallic materials was and against rubber materials, respectively. The maximum values of the tensile strength, elastic modulus, fracture strain, tear strength were 1.648 MPa, 0.388 MPa, 4.5%, 0.326 kN·m-1, respectively. Scanning electron microscopy images show that many compact and regular polygonal similar-grain grid structures distributed onty the epidermis surface and microcrack basically did not exist on the peel. The spherical micro-convex structures arranged closely and linearly at the boundary of the grid structure. Hierarchical structure surface with spherical micro-convex structures was one of the reasons for its outstanding friction coefficient. The bearing capacity of the peel depended on the number and distribution of grid structures on the surface, and the size and shape of the epidermal cells.

Field Measurement and Modeling of Vertical and Longitudinal Strains from Falling Weight Deflectometer Testing

AbstractThis study investigates longitudinal tensile and vertical compressive strains at the bottom of the hot mix asphalt (HMA) layer subjected to a falling weight deflectometer during different s...

Mechanical characterization of pseudoelastic shape memory alloy hybrid composites

Shape memory alloys (SMAs) are embedded in fiber reinforced plastic (FRP) composites material to achieve properties like higher toughness, shape morphing, variable stiffness etc. Pseudoelastic SMAs are mostly used in improving the energy absorbing capability of composites subjected to impact loading. Pseudoelastic SMA material has the property of absorbing higher strain energy without failure as compared to other engineering materials. Embedding SMA in FRP composites may affect its in-plane properties. This paper deals with study on SMA hybrid GFRP (Glass Fiber Reinforced Plastic) composites to find out the effect of embedding SMA in composites on the mechanical properties such as longitudinal tensile and compressive strength, transverse tensile strength and compressive strength and in-plane shear strength. Experimental results show that longitudinal compressive strength of shape memory alloy hybrid composites (SMAHCs) increases by approximately 30% over pristine composites. There is a marginal change in values of longitudinal tensile strength and in-plane shear strength in SMAHCs as compared to pristine composites whereas there is reduction observed in transverse tensile and compressive strength in SMA hybrid GFRP composites as compared to pristine GFRP composites.

Modeling and simulation of the effective strength of hybrid polymer composites reinforced by carbon and steel fibers

The present study describes the modeling and simulation of the effective strength of hybrid composites reinforced by carbon and steel fibers. The numerical simulations are performed within the framework of a finite element analysis. The macroscopic effective material properties are determined from microscopic properties using a homogenization and a representative volume element (RVE) approach. An elastic–plastic model is used to describe the mechanical behavior of the steel fibers and the epoxy resin, while the carbon fibers are modeled as a linear elastic material. The nonlinear stress–strain curves are determined under macroscopic longitudinal and transversal tensile as well as under shear loads. Moreover, 2D and 3D failure envelopes are computed. By using hexagonal-, square- and micrograph-based RVEs, the influences of fiber arrangements and different volume fractions of the carbon and steel fibers are investigated. Finally, the simulation results for tensile loads in fiber direction are compared with the experimental results of comparable topologies made of steel and carbon fiber reinforced plastics. The modeling and computational approach used in this study correlates with the experimentally determined, effective properties of hybrid composites in the tensile test.

Experimental investigation of composite beams reinforced with GFRP I-beam and steel bars

This paper presents results of an experimental study on the flexural behaviour of a composite beam, which is reinforced with longitudinal tensile steel bars as well as glass fibre reinforced polymer (GFRP) pultruded I-beam encased in concrete. Five beam specimens, including one traditional reinforced concrete (RC) beam and four composite beams, were cast and tested under four-point bending. The variables involved in the composite beams include the type of longitudinal tensile bars (steel bars and GFRP bars) and the location of the I-beam in the cross-section (middle and a shift of 30mm towards the tension region). The test results presented in this study show that the proposed composite beams have a very ductile response due to the existence of the tensile steel bars, and the yield point of the composite beam is controlled by the tensile steel bars. The ultimate load of the proposed composite beam in this study is higher than the traditional RC beam in this study, and the ultimate load is governed by the encased I-beam. When GFRP bars were used to replace the tensile steel bars to reinforce the composite beams, the brittle failure of GFRP bars caused lack of ductility of the beam members, and both the stiffness and ultimate load were reduced significantly. Compared with steel bars, the slip between the concrete and the I-beam was also increased when GFRP bars were used. The different location of the I-beam has little effect on the flexural response.

The reciprocal effects of bending and torsion on springback during 3D bending of profiles

Abstract Profiles with circular cross-sections can be geometrically described by the shape of the bending line. To achieve 3D bending lines with kinematic bending processes, a continuous change of the bending plane is needed, resulting in bending force vectors that change in direction accordingly. These force vectors generate a bending moment in the forming zone and, thus, longitudinal tensile and compressive stresses. For profiles with non-circular cross-sections, the orientation of the cross-section along the bending line needs to be additionally controlled. This can be achieved by applying a specific torque to the bending process and, thus, introducing desired shear stresses into the forming zone. Up until now, this fundamental aspect of 3D profile bending has not been regarded in a coherent fashion. To take into account the reciprocal effects of the stresses applied to the forming zone and their effect on the bending moment and, thus, on springback, a comprehensive analytical process model was set up. The model is validated by experimental investigations performed using the TSS profile bending machine and comprehensive numerical investigations. Analyses were performed during plane bending as well as bending superposed with torsion. The investigations show that the applied bending force and torque not only result in stress superposition but actually also affect the development of shear strains over the cross-section of the profile. Similar to the longitudinal strains, the shear strains decrease linearly from the intrados and extrados of the profile to the neutral axis. Considering this newly observed behavior in the analytical process model, the bending moment prediction is in accordance with the experimental and numerical results.