Axial Tensile Research Articles

Numerical Identification of Meso Length-Effect and Full-Field Edge-Effect of 3D Braided Composites

A study is conducted with the aim of developing two numerical models, meso-scale model and fiber embedded matrix model, for evaluating the length-effect and full-field edge-effect of 3D braided composites. Also, for the validation of fiber embedded matrix model, a series of digital image correlation measurements are conducted along the axial directions. The results show that the predicted mechanical behaviors of the tensile and compressive samples are essentially sensitive to the RVC number. Moreover, the proposed fiber embedded matrix method is capable of accurately predicting the cut-edge effect on the full-field mechanical behaviors of 3D braided composites when subjected to the axial tensile and compressive loading, validated by the comparison of the full-field displacement and strain fields.

Strength and failure characteristics of sandstone containing two circular holes filled with two types of inclusions under uniaxial compression

Plate shaped sandstones containing two fabricated circular holes that were filled with gypsum and high-strength concrete respectively were prepared for studying the effects of ligament length L ligament incline angle α, as well as filling modes on their strength properties and failure modes. The results show that the initial cracks can be categorized as wing crack, axial tensile crack and curved tensile crack. The failure modes of ligaments can be categorized as mode of single inclined crack, mode of single axial crack and mode of two parallel cracks. The final failure modes of all specimens can be categorized as the tension-shear mixed failure and shear failure. The strength of inclusions shows little influence on the final failure modes of specimens, while the failure modes vary with L and α. When α is a fixed value, the peak strength σ c and elastic modulus E c of tested specimens increase firstly with increasing L and reaches to the maximum value at L of 16 mm, then declines. When L is a fixed value, σ c declines firstly and then turns to increase as α increases to 75° from 45°, while E c increases linearly. The axial stress σ p performs the similar variation trends with those of σ c versus increasing L and α when ligaments fail.

Hygrothermal aging effects on axial behaviour of pultruded web–flange junctions and adhesively bonded build-up bridge members

Premature local failure of web/flange junctions of the majority of unstiffened commercially produced pultruded fiber-reinforced polymer composites profiles is inescapable due to lack of fiber continuity at the resin-dominated junction zones. This paper focuses on evaluating both short- and long-term behavior of such junctions when subjected to axial tensile stresses. In this study, the axial mechanical behavior of web/flange junctions of pultruded bridge deck components before and after hygrothermal aging effect is investigated. In the experimental phase, axial tensile tests were performed on six different types of pultruded web–flange junctions to assess axial characteristics of each web/flange junction type. In order to evaluate the hygrothermal behavior of such junctions, axial tensile tests were conducted on web/flange junction specimens that were exposed to both fresh water and artificial seawater environments at temperatures of 40℃, 60℃, and 80℃. Several controlling parameters affecting both strength and stiffness of pultruded fiber-reinforced polymer junctions were identified and discussed that include: (i) Junction's web and flange thicknesses, (ii) fillet radius, and (iii) variation of hygrothermal exposure environments. Results of this study indicated that the axial tensile capacity of a pultruded profiles is increased as the thickness of both web and flange increases. Also, it was found that the larger fillet radius of the pultruded fiber-reinforced polymer profile may contribute to a larger axial tensile capacity of pultruded profiles. However, due to variable size and geometry of the resin-rich junction zones and the common manufacturing defects in the form of folded fabric and other fibers misalignment effects, it is difficult to generalize the preceding results. Experimental results also showed that the degradation of web/flange junctions axial tensile strength increases when junctions are exposed to higher temperatures. Also, it was found that the axial tensile characteristics for junctions specimens exposed to freshwater environment are slightly different than those that were exposed to artificial seawater environments.

Measurement of the Mechanical Properties of the Human Kidney

The kidney plays an important role by filtering of all the blood in the body. Mechanical loading as a result of accident or any kind of trauma can disrupt the normal function of the kidney. Since the abdominal injuries these days are on the rise, understanding the mechanical response of the kidney, as one of the most important organs in the abdomen, is of great interest to design of protective equipment as well as preventive measures. Therefore, the precise reliable mechanical properties of the human kidney are a crucial tool for the biomechanical analyses of such conditions. However, so far almost all the reported results on the mechanical properties of the kidney are related to the animals and there is a paucity of knowledge on the mechanical properties of the human kidney. Hence, this study was aimed at experimentally measuring the axial and transversal mechanical properties of the human kidney under the tensile loading. To do that, the kidney of 20 human cadavers was excised during the autopsy and histologically analyzed to extract the mean angle of collagen fibers. Thereafter, the samples were cut and subjected to a series of axial and transversal tensile loadings. The results revealed the tensile elastic modulus of 180.32 ± 11.11 kPa (Mean ± SD) and 95.64 ± 9.39 kPa under the axial and transversal loadings, respectively. Correspondingly, the maximum/failure stresses of 24.46 ± 3.14 kPa and 31.00 ± 5.06 kPa were observed under the axial and transversal loadings, respectively. The kidney showed a significantly (p<0.01, post hoc Scheffe method) higher elastic modulus under the axial loading compared to the transverse one. In addition, a significantly (p<0.05, post hoc Scheffe method) higher maximum/failure stress was observed under the transverse loading compared to the axial one. The findings of the current study have implications not only for understanding the mechanical properties of the human kidney tissue under axial and transversal tensile loadings, but also for providing a raw data for both the doctors and engineers to be used for diagnosis and simulation purposes as well as tissue engineering.

Axial Tensile Stress–Strain Characterization of Bi-2212 Round Wire With Different Heat Treatments

The China Fusion Engineering Test Reactor is a new tokamak device whose magnet system includes toroidal field (TF), central solenoid (CS), and poloidal field (PF) coils which are made up of cable-in-conduit conductor (CICC). The maximum field of CS and TF will reach around 15 T, which is much higher than that of present reactors. In this case, the high-temperature superconducting material Bi-2212 is considered as one potential magnet material for CICC because it has an outstanding conductor-carrying capacity at 4.2 K in magnetic field, especially for that with high-pressure heat treatment. However, Bi-2212 phase is a ceramic structure, which is sensitive to strain. The mechanical property is important for its application. In this paper, the axial tensile measurements on Bi-2212 round wires with different heat treatments were performed at room temperature, 77 K and 4.2 K, respectively. It was found that the wires with high pressure heat treatment had higher mechanical strength than that with normal pressure. The compared results were given, and SEM of cross sections for tested samples was also made and analyzed.

Measurement of the mechanical properties of the human gallbladder

Gallbladder is a small organ of the body which is located in the right side of the liver. It is responsible of storing the bile and releasing it to the intestine. The gallbladder can subject to the mechanical deformation/loading as a result of the cholecystitis, cholesterolosis of the gallbladder, etc. However, so far the mechanical properties of the human gallbladder have not been measured. This study was aimed at conducting an experimental study to measure the mechanical properties of the human gallbladder under the axial and transversal tensile loadings. To do that, the gallbladder tissue of 16 male individuals was excised during the autopsy and subjected to a series of axial and transversal loadings under the strain rate of 5 mm/min. The amount of elastic modulus as well as the maximum/failure stress of the tissues were calculated via the resulted stress–strain diagrams and reported. The results revealed that the axial and transversal elastic modulus were 641.20 ± 28.12 (mean ± SD) and 255 ± 24.55 kPa, respectively. The amount of maximum stresses was also 1240 ± 99.94 and 348 ± 66.75 kPa under the axial and transversal loadings, respectively. The results revealed a significantly higher axial stiffness (p < .05, post hoc Scheffe method) compared to the transversal one. These findings have implications not only for understanding the axial and transversal mechanical properties of the human gallbladder tissue, but also for providing a diagnosis tool for the doctors to have a suitable threshold value of the healthy gallbladder tissue.

Experimental investigation of the effects of adhesive defects on the single lap joint strength

For robust design of the joints in the engineering structures, it is necessary to determine the stress and strain under a certain load and predict the failure potential. Adhesive joints are susceptible to defect and separation, especially the joints with high overlap area. The aim of this study is the experimental investigation on the influences of the size and shape of 2D and 3D defects on the ultimate shear strength of the adhesive single lap joints. So, square, triangular and circular defects with different sizes are artificially embedded into the Araldite 2015 adhesive layer of the Aluminum 2024-T3 joints. The artificially defective samples are examined under the axial tensile tests according to ASTM D1002-01 standard. In the case of the single lap joints with 3D defects, there is an approximately linear decrease in the joint strength as the defect area increases. However, when 2D defects are applied in adhesive joint, a non-linear decrease in the joint strength is observed. Actually, the joint strength decreases gradually when the defect area/overlap area is smaller than 30%. The decline rate in the joint strength for bigger defect is more sever, indicating that the edges of the overlap area become more important as the local strains exceeding the limiting values in this zone. The survey about the defect shape show that the least decline in the strength of single lap joints occurs with circular defects. The greatest disparity in reducing the strength compared to the other 2D and 3D defects is approximately 11% and 8%, respectively. Based on the experimental results, functions are proposed to estimate the ultimate strength in defected samples with respect to defect-free samples.

The synchronous improvement of strength and plasticity (SISP) in new Ni-Co based disc superalloys by controling stacking fault energy

It is a great challenge to improve the strength of disc superalloys without great loss of plasticity together since the microstructures benefiting the strength always do not avail the plasticity. Interestingly, this study shows that the trade-off relationship between strength and plasticity can be broken through decreasing stacking fault energy (SFE) in newly developed Ni-Co based disc superalloys. Axial tensile tests in the temperature range of 25 to 725 °C were carried out in these alloys with Co content ranging from 5% to 23% (wt.%). It is found that the ultimate tensile strength (UTS) and uniform elongation (UE) are improved synchronously when microtwinning is activated by decreasing the SFE at 650 and 725 °C. In contrast, only UTS is improved when stacking fault (SF) dominates the plastic deformation at 25 and 400 °C. These results may be helpful for designing advanced disc superalloys with relatively excellent strength and plasticity simultaneously.

EFFECTS OF RESIDUAL RUST ON STRENGTH RECOVERY OF CORRODED STEEL PLATE REPAIRED WITH PATCH PLATE

In Japan, there have been found a lot of corrosion damages recently in steel bridges aged for fifty or more years. If the strength of a steel structure is decreased by serious corrosion damages, the structure must be repaired to ensure its safety. In order to supplement the strength loss of a steel member with local corrosion, steel plate bonding method is often adopted, where the corroded area is covered with steel plate bonded by adhesive. In this case, surface preparation is the most important issue to bond the cover plates completely. In this method, surface preparation is the most important issue to bond the cover plates completely. However, it is quite difficult to completely remove rust and wastes in the fieldwork of surface preparation. Thus, this paper presents recovery effect of local corroded steel plate by steel plate bonding method when rust is not completely removed. Specimens are rectangular steel plates with irregular surface which imitated local corrosion in the center of plate. Then rust is also imitated rather than actual one to quantitatively evaluate the recovery effect. Axial tensile tests were conducted for these specimens repaired with patch plate. Then, the size of patch plate and amount of rust were changed and investigated how these differences affect the peeling off of the patch plate.

Design of Elastic Screw Fasteners under Tensile Load

This paper presents an equivalent stress approach in the design of screw fasteners under tensile load. Design equations are formulated for sizing and verifying screw fastener selection. It considers axial tensile, direct shear, bending, and torsional stresses and combines them as appropriate into equivalent or effective stresses. The equivalent or effective stresses are compared with screw fastener material strength capabilities such as proof, yield, fatigue, and tensile strengths for failure assessment. Design factors are derived for assessing design adequacy the screw fastener. For elastic screw fasteners, these stresses must each be in the elastic range for the screw material. When the load is removed, elastic screw fasteners regain their original size and shape, behaving like springs. Two illustrative design examples are used to demonstrate both design verification and sizing tasks. Design verification was performed in the first example and the static yield design factors are found to be 0.77 and 0.68 for the preload and service load, respectively. These values are less than unity, representing a case of under-design in static yield failure modes. Without changing the specification of the screw fastener, the preload tension was reduced by 62.76%, and the static yield design factors changed to 1.42 and 1.12 for the preload and service load, respectively. This shows that the under-design condition resulted from high preload tension. When the screw pitch is changed from coarse to fine series, the design factors are worse off in fatigue stress resistance but indicated some improvement in static stress resistance. This suggests that fine pitch threads is not better than coarse pitch threads in fatigue stress capacity when direct shear and bending stresses are considered in Example 1. Both design sizing and verification are performed in Example 2. Design sizing suggests a screw fastener ( ) of slightly larger size than the previous solution ( ). Design verification indicates the previous solution and new solution has a minimum static yield design factor of 0.93 and 1.09, respectively for the service load. This suggests that the screw fastener of the previous solution may yield in service, if implemented. The new solution has a higher design factor in this failure mode and presents less risk of failure. From the illustrative examples presented, it seems that ignoring direct and bending stresses in screw fastener design can lead to under-design in some failure modes.

Influence of uniaxial tension and compression on shear strength of concrete slabs without shear reinforcement under concentrated loads

Under the shear load, reinforced concrete structures may be simultaneously subjected to the axial tensile or compressive forces due to shrinkage in restrained members, earthquake, tornado, and so on. Until now, no experiment addressing the effect of the uniaxial load on the shear resistance of reinforced concrete slab has been reported in the literature. All the experimental tests found in the literature were conducted on panel and beam (or wide beam) specimens. The current shear design provisions with axial load (ACI 318 and Eurocode 2) were developed based solely on panel and beam tests and not slab tests. Therefore, the current shear design codes applied to slab structures under the effect of axial forces urgently need revision. The present research studies the shear strength tests of slabs under the concentrated load simply supported on four sides. The effect of the tension/compression forces on the shear capacity was studied on full-scale slabs without shear reinforcement, a design similar to the slabs used in nuclear buildings, under a concentrated load near support. Experimental tests were conducted to quantify the shear capacity and the associated failure modes with the influence of axial forces. In this study, a series of seven tests on seven full-scale slabs measuring 4m×2.6m×0.3m is presented. The experiments were used to evaluate the pertinence of Eurocode 2 in terms of shear in reinforced concrete slabs with axial load, to compare these results to the AFCEN ETC-C code used for nuclear buildings, and to compare them to the ACI 318 code. The results showed that the axial tension forces equal to 0.28fctm (average concrete tensile capacity) reduced the shear capacity up to 30% in the concrete slab experiments conducted.

Influence of concrete strength and steel fibre geometry on the fibre/matrix interface

Abstract The main objective of the research described in this paper was to evaluate how the concrete compressive strength and the geometry of the steel fibres influence the behaviour of the fibre/matrix interface. With this aim, three different concrete matrices were designed with 20, 60 and 100 MPa, and two types of steel fibres were adopted (Dramix ® 3D and Dramix ® 5D). Specific pull-out specimens were produced and three sets of axial tensile tests were defined with different fibres (3D fibres, and 3D and 5D fibres with trimmed ends). A numerical model was calibrated and used to expand the scope of results obtained from the experimental tests. It can be concluded that the concrete compressive strength strongly influences the fibre/matrix strength. In the set with untrimmed 3D fibres, higher strengths were reached due to the hook shaped endings, for all concrete strengths, varying between 64% and 72% of the total load. For fibres with straight endings, increasing both diameter and length lead to higher adhesion and friction strengths.

Nonlinear finite element analysis of failure modes and ultimate strength of flexible pipes

Designs of flexible pipe utilized in offshore dynamic riser applications need to be subjected to strength assessment over the entire length in relation to the dynamic motion of the connected floater. Such assessment includes many uncertain factors including soil properties, internal pressure, ocean metadata and others. Failure of flexible pipe, moreover, leads to serious financial loss and environmental degradation. Thus, flexible pipe failure modes and safety need to be evaluated in terms of ultimate strength under various loads.Ultimate strength assessment of flexible pipe is quite complicated and time-consuming compared with that of a steel catenary riser, due to the composite materials, geometric complexity and the contact mechanism between layers The material nonlinearity and large deformation, moreover, render stable convergence of nonlinear analysis to a solution problematic. This paper proposes practical and stable methods of ultimate-strength assessment using 8-layered and 5-layered 3D FE models subjected to axial tensile and compressive loads, respectively. In the 5-layered model, four inner layers (carcass, pressure sheath, pressure armour, and anti-friction tape) are replaced by one equivalent pressure layer which plays a role of withstanding pressure applied together with the axial compression. It aims to improve the convergence of nonlinear analysis by simplifying the interactions between layers. For each analysis, the failure mechanisms and the interactions between layers are investigated in detail with incremental loading. The effect of initial imperfection, i.e. ovalizations are also examined. In the compressive strength analysis, the influence of various external pressure are additionally studied.

Stress wave propagation in Boron-Nitride nanotubes

The propagation of axial stress waves in Boron-Nitride nanotubes of different chirality and length under adiabatic conditions has been studied using molecular dynamics (MD) simulations. The velocities of the axial stress waves are found using three methods - (i) direct MD simulations, (ii) harmonic approximation of the nanotubes, and (iii) one-dimensional (1-D) wave equation. The MD simulation results indicate a small dependence of the wave velocities on the nanotube chirality and the excitation frequency – in armchair and zigzag nanotubes waves travel faster than that in chiral nanotubes, and wave velocities decrease with an increase in the frequency of excitation. The wave speed obtained from the harmonic approximations is ≈20–25% higher than that found from the MD simulations. Likewise, the frequencies of vibrations from the two approaches differ by 15–20% for most of the cases. The computation of the wave speed from 1-D equation requires a prior knowledge of the elastic modulus and the nanotube wall thickness. The values of these parameters are found from MD simulation results – axial tensile tests provide an estimate of the wall thickness scaled elastic modulus and the transverse vibration data relates the standard deviation of the tip displacement with material properties of the nanotube. The wave speed predicted from the 1-D wave equation agrees with that obtained from the MD simulations at low excitation frequencies. The contribution of the anharmonicity to the dynamics during wave propagation is found by matching the response of the anharmonic Fermi-Pasta-Ulam chain with the MD simulation results.

Non-destructive Assessment of the Axial Stress State in Iron and Steel Truss Structures by Dynamic Measurements

This paper is concerned with the inverse identification of the stress state in axially loaded slender members of iron and steel truss structures using measured dynamic data. A methodology is proposed based on the finite element model updating coupled with nature-inspired optimization techniques, in particular the particle swarm optimization. The numerical model of truss structures is calibrated using natural frequencies and mode shapes from vibration tests, as well as additional information of the axial forces in selected truss members based on the experimentally identified modal parameters. The results of the identification are the axial forces or corresponding stresses in truss structures and the joint rigidity in relation to pinned and rigid conditions. Attention is given to several examined aspects, including the effects of the axial tensile and compressive forces on the dynamic responses of trusses, mode pairing criteria, as well as modeling assumptions of joints and the use of a joint rigidity parameter. Considering the pairing of modes, it is performed by adapting an enhanced modal assurance criterion that allows the selection of desired clusters of degrees-of-freedom. Thus, information extracted from the measurements related to specific modes is utilized in a more beneficial way. For modeling of joints, the numerical model of a truss structure includes rotational springs of variable stiffness to represent semi-rigid connections. Moreover, a fixity factor is introduced for practical estimation of the joint flexibility. The effectiveness of the proposed methodology is demonstrated by case studies involving simulated and laboratory experimental data.

Design of a self-contained breathing apparatus (SCBA) using a carbon fibre reinforced polymer and filament winding

The design of a self-contained breathing apparatus (SCBA), which is an extremely important device for firefighting on board of ships, covers not only in-service loadings, but also a proper selection of materials, manufacturing processes, as well as the specification of other construction details, such as hydrostatic test parameters, among others.The work developed and presented in this manuscript sought to verify the feasibility and the advantages of using composite materials in a SCBA subjected to high internal pressure (300bar, 30MPa), instead of other metallic material currently in use. Hence, a carbon fibre reinforced polymer (CFRP) and the filament winding technique were considered in the SCBA redesign. Analytical formulas, as well as engineering standards and advanced finite element analysis (FEM) were used to analyse two types of SCBA commonly used on board of ships.Five valid axial tensile tests were performed in samples of CFRP using a DARTEC 100kN servo hydraulic machine according with standard ASTM D3039/D 3039M (2002) in order to determine the mechanical properties of the material, and a displacement transducer or strain gages were used to determine strains induced in the composite during experimental axial tensile tests, Then, several FE numerical simulations were carried out in order to verify the compliance of a redesigned SCBA with the functional requirements, and the main manufacturing parameters were also determined. Furthermore, experimental internal pressure tests were carried out in a pressure vessel similar to the redesigned SCBA. The results of FE simulations and experimental tests were compared and conclusions could be drawn.

Effect of axial tensile and compressive loads on transport properties of cement mortar

Effect of axial tensile and compressive loads on transport properties of cement mortar

Macro- and micromechanical behaviors of poly(lactic acid)–hydroxyapatite electrospun composite scaffolds

It was demonstrated that the macro- and micromechanical behaviors of electrospun composite scaffolds based on PLA and HA can be simultaneously studied using 3D digital image correlation strain measurements coupled with an axial tensile test. It was proven that the addition of a small quantity (2%) of HA particles into PLA electrospun scaffolds decreased their mechanical properties by approximately 40 and 60% at the micro- and macroscales, respectively; nevertheless, when this amount was increased beyond 2% of HA, the composites recovered their stiffness, showing Young’s moduli ranging between 400 and 600 MPa. Hence, the mechanical responses of PLA–4% HA and PLA–6% HA electrospun scaffolds were conveniently enhanced with the addition of hydroxyapatite nanoparticles. The micromechanical measurements were able to capture the microstrain mechanism between electrospun nanofibers and the effect of HA nanoparticles on their mechanical response. This methodology could be a powerful tool for developing scaffolds for specific applications in tissue engineering.

EFFECT OF SURFACE PREPARATION GRADE ON REPAIR BY MEANS OF COVER PLATES AND ADHESIVE

There are a lot of corroded steel bridges, which have to be prolonged its life in Japan. Corroded members in these bridges generally have local corrosion damages, and are often repaired by covering on the corroded area with steel plates in order to rehabilitate the strength. Recently, adhesive such as epoxy resin is often used for bonding the cover plates made of steel or CFRP, even though high-tensile bolts or welding have been adopted conventionally. In this case, surface preparation is the most important issue to bond the cover plates completely. However, complete removal of rust and wastes are quite difficult in the fieldwork of surface preparation. This paper presents recovery effect of local corrosion damage by means of covering method used by adhesive when the rust is not completely removed. Axial tensile tests were conducted for rectangular steel plates of 1,100mm x 100mm x 12mm with 400mm length of corrosion-surface-unevenness on the both surfaces, and the defects of surface preparation are made by putting tape paper at the damaged area. Then various sizes of the repair plates are bonded to consider the influence to repairing. From the test results, the ultimate strength decreased 7-10% compared with non-rust state when the defect area rate was about 30%.

Pull-out behaviour of wood bolt fully grouted by PS-F slurry in rammed earth heritages

ABSTRACTThis article presents a laboratory and field investigation of pull-out resistance of wood bolts in rammed earth heritages. The laboratory testing involved axial tensile tests of four grout specimens prepared in specially designed moulds using PS-F (Potassium Silicate solution-Fly ash) slurry to investigate the performance of anchors. The field testing involved pull-out tests of three wood anchors installed in rammed earth heritages by gravity grouting. Experiments reveal that the failure mode is the pull-out of bolt from grout and average skin friction resistance of bolt–grout interface is approximately 0.34MPa. Load–displacement curves and elastic–residual displacement derived from cyclic loading indicate such anchor system has strong ductility with small elastic deformation and large residual deformation. Bond collapse firstly occurs at the loaded end and then propagates towards the full bonded length. Bond stress distribution is not uniform along the bonded length. Maximum bond stress distributes at the range from 0.3 m to 0.4 m. Emergence of compressive strain in the interface reveals such anchor system enjoys the advantages of both tensile and compressive anchor types, which significantly differs from results from other regular bolts. The research conclusion makes scientific senses to traditional material and craft in rammed earth heritages.