Axial Tensile Tests Research Articles

Experimental and theoretical behavior of crack spacing of specimens subjected to axial tension and bending

AbstractCrack spacing has been identified as an important parameter in predicting the crack widths in reinforced concrete (RC) structures. An experimental program has been conducted to investigate the crack spacings when reinforced concrete beams are subjected to both axial tension and flexure. The stochastic nature of cracking behavior makes the experimental program complicated. A large sample size of the crack spacing data was recorded, in order to give a statistical overview. Recent studies in the literature were used to verify the experimental results. The existing crack spacing prediction models have been developed based on different theoretical approaches, namely bond‐slip, no‐slip, and combined approaches. In this study, Eurocode 2, Model Code 2010, Japanese Code, Eurocode 2 with German Annex and Beeby's crack spacing models were selected, as they represent each theoretical approach. Experimental results of this study and from selected literature were compared with the aforementioned prediction models. Japanese Code gave better predictions for axial tensile tests. For the four‐point bending test, all the calculation models gave good agreement with the results, except for Eurocode 2 with German Annex.

Effects of melatonin on the passive mechanical response of arteries in chronic hypoxic newborn lambs

Chronic hypoxia is a condition that increases the cardiovascular complications of newborns gestated and born at high altitude (HA), over 2500 m above sea level (masl). A particularly complex pathology is pulmonary arterial hypertension of the neonate (PHN), which is increased at HA due to hypobaric hypoxia. Basic and clinical research have recognized that new treatments are needed, because current ones are, in general, palliative and with low effectiveness. Therefore, recently we have proposed melatonin as a potential adjuvant treatment to improve cardiopulmonary function. However, melatonin effects on the mechanical response of the arteries and their microstructure are not known. This study assesses the effects of a neonatal treatment with daily low doses of melatonin on the passive biomechanical behavior of the aorta artery and main pulmonary artery of PHN lambs born in chronic hypobaric hypoxia (at 3600 masl). With this purpose, ex-vivo measurements were made on axial stretch, tensile and opening ring tests together with a histological analysis to explore the morphometry and microstructure of the arteries. Our results show that the passive mechanical properties of the aorta artery and main pulmonary artery of lambs do not seem to be affected by a treatment based on low melatonin doses. However, we found evidence that melatonin has microstructural effects, particularly, diminishing cell proliferation, which is an indicator of antiremodeling capacity. Therefore, the use of melatonin as an adjuvant against pathologies like PHN would present antiproliferative effect at the microstructural level, keeping the macroscopic properties of the aorta artery and main pulmonary artery.

Polycrystalline modeling of the behavior of neutron-irradiated recrystallized zirconium alloys during strain path change tests

During normal operating conditions, zirconium alloy nuclear fuel cladding tubes experience various biaxial loadings with complex strain path histories. Experiments have been conducted on neutron-irradiated thin cladding tubes in order to study the response to changes in the loading path. These tests consist of alternate internal pressure tests and axial tensile tests. During the internal pressure test steps, the flow stress exhibits significant cyclic strain softening, while axial tensile tests exhibit a smaller degree of cyclic strain softening. TEM analyses of the tested samples have revealed that the observed mechanical behavior can be attributed to clearing of irradiation-induced defect by gliding dislocations. The cyclic strain softening observed for internal pressure tests is due to clearing of defects by dislocations gliding in the basal planes. The smaller degree of cyclic strain softening in tensile tests is due to clearing of defects by dislocations gliding in the prismatic and pyramidal planes. A polycrystalline model has been developed to simulate these tests. This model is able to reproduce many features of the complex behavior of the material and provides a better understanding of the role of the clearing of defects and the contribution of kinematic hardening on the behavior of neutron-irradiated recrystallized zirconium alloys.

Assessment of the Mechanical Properties of ESD Pseudoplastic Resins for Joints in Working Elements of Concrete Structures.

Concrete structure joints are filled in mainly in the course of sealing works ensuring protection against the influence of water. This paper presents the methodology of testing the mechanical properties of ESD pseudoplastic resins (E-elastic deformation, S-strengthening control, D-deflection control) recommended for concrete structure joint fillers. The existing standards and papers concerning quasi-brittle cement composites do not provide an adequate point of reference for the tested resins. The lack of a standardised testing method hampers the development of materials universally used in expansion joint fillers in reinforced concrete structures as well as the assessment of their properties and durability. An assessment of the obtained results by reference to the reference sample has been suggested in the article. A test stand and a method of assessing the mechanical properties results (including adhesion to concrete surface) of pseudoplastic resins in the axial tensile test have been presented.

Mechanical characterization of PVA hydrogels' rate-dependent response using multi-axial loading.

The time-dependent properties of rubber-like synthesized and biological materials are crucial for their applications. Currently, this behavior is mainly measured using axial tensile test, compression test, or indentation. Limited studies performed on using multi-axial loading measurements of time-dependent material behavior exist in the literature. Therefore, the aim of this study is to investigate the viscoelastic response of rubber-like materials under multi-axial loading using cavity expansion and relaxation tests. The tests were performed on PVA hydrogel specimens. Three hyperelasitc models and one term Prony series were used to characterize the viscoelastic response of the hydrogels. Finite element (FE) simulations were performed to verify the validity of the calibrated material coefficients by reproducing the experimental results. The excellent agreement between the experimental, analytical and numerical data proves the capability of the cavity expansion technique to measure the time-dependent behavior of viscoelastic materials.

Experiments and progressive damage analyses of three‐dimensional five‐directional braided composite joints for propeller

AbstractIn this article, experiments and numerical simulation on the tensile loading properties of three‐dimensional five‐directional braided composites are studied. Herein, axial tensile loading tests were performed on braided composite and aluminum joints for propeller. A repeated unit cells model was established to analyze the micromechanical properties of the braided joint, a progressive damage model was established to evaluate the damage in the joint. In contrast to aluminum joint, which exhibited a tensile failure mode in only one direction, the braided joint exhibited both longitudinal and transverse damage failure modes, of which the transverse damage was the primary failure mode. The load‐displacement curves and damage morphology of the numerical simulation were in a good agreement with the experimental results.

A Preisach Model for Monotonic Tension Response of Structural Mild Steel with Damage

This paper presents the new type of Preisach model that describes the elastoplastic behavior of structural mild steel under axial monotonic tension load with damage. Newly developed model takes into account elastic region, horizontal yield plateau, plastic hardening region, and softening region due to material damage under tension. In order to study the monotonic behavior of structural mild steel and find suitable material properties for the model, monotonic axial tensile tests up to the failure are carried out. Tests are conducted on specimens of the three most common types of European structural steel S235, S275, and S355. The basis of the model represents a mathematical description of material single crystal monotonic axial behavior. In the multilinear mechanical model, a drop in stress, after achieving ultimate stress under tension is achieved by a negative stiffness element. The good agreement with experimental results is accomplished by parallel connection of infinitely many single crystal elements, forming the polycrystalline model. The model represents a good solution for common engineering practice due to its geometrical representation in form of Preisach triangle.

The evaluation of failure mode behavior of CFRP/Adhesive/SPCC hybrid thin laminates under axial and flexural loading for structural applications

The failure mode behavior and the mechanical performance in terms of stress-strain of Carbon Fiber Reinforced Plastic - Steel Plate Cold Commercial (CFRP-SPCC) hybrid thin laminates are investigated in this study through axial tensile and flexural tests. Four different adhesives were used. Materials were characterized using Differential Scanning Calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). Surface behavior was monitored in real time and after completion (final failure) with an optical microscope during the tensile test. The results from DSC and FTIR show that the materials undergo complete curing. The results from the tensile test indicate that by adding SPCC in hybrid laminates, the premature failure of CFRP laminates can be delayed up to 58.5%. The result shows the strain at failure increases from 1.85% of CFRP laminates to 2.1% of hybrid laminates, which equals an increased rate of more than 13%. The flexural tests demonstrate that hybrid laminates have a higher strain value compared to CFRP laminates. With the addition of SPCC layers, the failure mode is shifted from premature fiber breakage to adhesive breakage followed by final failure with fiber breakage originating from the CFRP laminates.

Static and dynamic mechanical behavior of engineered cementitious composites with PP and PVA fibers

Engineered cementitious composites (ECC) reinforced with oiled polyvinyl alcohol (PVA) fibers becomes more and more attractive in both research and engineering communities, while the PVA fibers-reinforced ECC (PVA-ECC) is of high cost due to the usage of the PVA fibers. One way to reduce the cost is to mix other economical fibers like polypropylene (PP) fibers with the PVA fibers. To prove the feasibility of hybrid PP and PVA fibers-reinforced ECC (PP-PVA-ECC), this paper presents a pilot study on static and dynamic properties (compression, tensile and impact resistance) of the PP-PVA-ECC and compared with those of PVA-ECC. PP-PVA-ECC specimens with three hybrid fiber volume ratios (0.5% PP+1.0% PVA, 1.0% PP+1.0% PVA, 1.5% PP+1.0% PVA) and PVA-ECC specimens with four fiber volume ratios (1.0%, 1.5%, 2.0% and 2.5%) were prepared. The axial static compression, tensile and drop-weight impact tests on the PP-PVA-ECC and the PVA-ECC with corresponding fiber volume ratios were conducted. The compression, tensile and impact performances of PP-PVA-ECC were studied and compared with those of PVA-ECC. The results indicated that the post-peak compression toughness, tensile strength, ultimate tensile strain, impact strength of PP-PVA-ECC increased significantly with the volume ratio of PP fibers. Results also showed that the PP-PVA-ECC performed slightly worse than the PVA-ECC with a given fiber volume ratio. The experimental evidences presented in the current study demonstrate the feasibility and plausible future of the novel hybrid PP-PVA-ECC.

Self-expanded piles: A new approach to unconventional piles development

In onshore and offshore fields of ocean engineering, piles are used as foundation systems for various structures. Piles are classified into different types depending on their materials, geometries, and particularly, installation methods, which have advantages or limitations. Companies and engineers have developed a new group of piles, because of necessity to improve their performance in terms of increasing the bearing capacity, reducing impacts of traditional installation procedures, implementing by low- torque power equipment, and utilizing them in widely different ground conditions, including in a marine environment. In the present study, three different models of a new pile with an expander body are introduced to increase the shaft and pile-toe diameters and its self-expansion in the embedment depth under the titles of the Bubble pile (BP), Self-Expanded pile (SEP) and Wing pile (WP). The main subject of this research is to achieve increased bearing capacity, reduced installation effects, and decreased required installation torque. The frustum-confining vessel of Amirkabir University of Technology (FCV-AUT) was employed for this purpose. Up to 14 axial compressive and tensile load tests were carried out on different model piles on sand collected from Anzali shore located on the northern coast of Caspian Sea in Iran, with relative densities of 45% to 50% within FCV-AUT. Comparing the performance of introduced pile with traditional pile corresponding to the same characteristics, the results indicated a significant increase in the axial bearing capacity and reduced disturbance effect of the pile. Also, a lower installation torque of the SE pile was required compared to the helical pile. The test results also demonstrated that the new pile could resist considerable compressive and uplift loads, and could be a possible alternative to traditional piles in the onshore sector.

Mechanical behavior of AL/CFRP single-lap joint subjected to combined thermal and constant loading

ABSTRACT This research aimed to investigate the effect of constant loading coupled with elevated temperature on the mechanical behavior of single-lap joints (SLJs) with aluminum alloy (AL) and carbon fiber-reinforced plastic (CFRP). The aging tests of adhesive and AL/CFRP SLJs were completed under the combined thermal and constant loading environment. Then, the quasi-static axial tensile tests were accomplished. The results showed the insignificant effect of temperature condition on the strength degradation behavior of SLJ; whereas constant loading coupled with temperature condition exhibited a significant influence. Meanwhile, the results also showed that the adhesive and SLJ had the same trend in strength degradation: the failure strength increased with the prolonged aging time under the temperature-only condition, whereas the failure strength increased first and then decreased with prolonged aging time under the combined thermal and constant loading environment.

Particle-toughened interlayers enhance mechanical response of composite laminates

Toughened composite materials, where the toughening agents are micro-particles dispersed within the interlayer resin rich regions, provide enhanced delamination resistance. This delay in delamination promotes intralaminar micro- and macro-cracking, thus providing superior toughness. In this paper, a thorough study of damage accumulation was conducted to identify and quantify failure mechanisms in the ±45∘ laminate axial tensile test. Progression of damage accumulation was captured with digital image correlation techniques, in-situ inspection with high-resolution cameras and interrupted tests at different loading stages. Detailed cross-section microscopy of specimens were used to observe progression of crack formation, density of cracks formed and crack branching at the toughened interfaces.

Experimental assessment of damage-thermal diffusivity relationship in unidirectional fibre-reinforced composite under axial tensile test

The influence of damage on thermal properties is an important issue for the design of reliable ceramic matrix composites for high temperature applications. This work is devoted to the experimental study of this influence on SiC/SiC minicomposite. This single tow reinforced composite is appropriate to investigating the damage mechanisms and thermal behavior. Relationships between the properties of constituents (fibre/matrix/interface) and behavior of the assembly can be established. Nevertheless, the literature review showed that no experimental study has focused on the thermal behavior during mechanical tests. Lock-in thermography was used to measure the thermal diffusivity during tensile tests on minicomposites while acoustic emission technique allowed monitoring damage. In this work, it is demonstrated that the evolution of the thermal diffusivity competes favorably with acoustic emission and Young's modulus as a reliable indicator of matrix damage.

Design and analysis of shockless smart releasing device based on shape memory polymer composites

In this paper, a new releasing device with the advantages of non-pyrotechnic, shockless, re-settable, and simple structured are presented. A sandglass-like mechanism is designed and it is made of carbon fiber reinforced epoxy-based shape memory polymer (SMP) and its composite (SMPC). The SMPC active element is the outer part, while the inner part is made of metal with a sandglass-like profile. The active element is designed to change shape and accomplish a separation between the mating parts of the release mechanism with no impact. The actuation of the SMPCs parts is not an instant but duration, so that the considerable preload will be released gently and with no impacting shock. Some basic mechanical tests for SMP and SMPC plate specimens were done to determine the basic mechanical properties of the epoxy-based SMP and SMPC. The locking-compression test, axial tensile test and relaxation test were conducted to determine the mechanical properties of the smart releasing device. The recovery experiment of the device was also applied and the scanning electron microscope (SEM) was used to observe the morphologies of the SMPC cylinders of the smart releasing devices before and after releasing.

Failure mechanisms in carbon fiber reinforced plastics (CFRP) / aluminum (Al) adhesive bonds subjected to low-velocity transverse pre-impact following by axial post-tension

The present study aimed to explore the effects of impact surface and impact energy on the residual characteristics of the carbon fiber reinforced plastics (CFRP)/aluminum (Al) adhesive bonded joints. The adhesive specimens were manufactured in the hot pressing machine with specific curing temperature and curing pressure of the adhesive. In the experiments, a transverse low velocity pre-impact was carried out first and then followed by the axial (longitudinal) tensile test. The results divulged that CFRP, as an impact surface, could generate better structural integrity and decrease loss of joint strength in comparison with the aluminum impact surface. The mechanism for alternating residual tensile strength resulting from transverse impact load was the combined effect of both damage and mechanical interlocking effectiveness. The residual tensile strength and failure displacement decreased with increasing impact energy except for the joint strength impacted onto the aluminum surface at 10 J due to the prominent mechanical interlocking effect. The strain evolution paths in the adherends at the overlap region presented the different forms when impacted onto the different surfaces. In the tensile tests, the fracture surfaces for the joints with impacting on the aluminum surface can be classified as shear failure zone, annular failure zone and mixed failure zone, while the fracture surfaces for the joints with impacting onto the CFRP surface classified to be shear failure zone and crossed impact zone. This study is expected to provide systematic understanding on crashing behavior of adhesive joints with dissimilar materials for multiple impacts from different directions.

Centrifuge modelling of a helical anchor under different cyclic loading conditions in sand

Helical foundations used in transmission towers, wind turbines, solar panel systems and other similar structures must exhibit adequate performance under cyclic loading. Although a number of studies on the cyclic behaviour of helical anchors has increased, the available observations are still incomplete in terms of providing conclusive recommendations for practical applicability. To address this need, cyclic and monotonic axial tensile load tests were conducted on a single-helix model anchor in very dense dry sand in a centrifuge. The cyclic tests were carried out with different load amplitudes and with the number of cycles varying between 1000 and 3000. After the cyclic tests, the post-cyclic tensile capacity was evaluated by way of monotonic loading tests. Two different displacement regimes were observed during cycling, with a noticeable development of cumulative permanent displacements in the first approximately 100 cycles. In most of the tests, a stable cyclic response and a slight reduction in the post-cyclic capacity were observed. Additionally, the effect of the cyclic loading sequence was evaluated by way of two additional tests in which the cyclic loading was applied with different amplitudes in different orders. The results indicated that the order of the cyclic sequences influences the displacement response and the losses in the post-cyclic capacity.

Impact of thermal and chemical treatment on the mechanical properties of E110 and E110G cladding tubes

Abstract The mechanical and corrosion behavior of the Russian zirconium fuel cladding alloy E110, predominantly used in VVERs, has been investigated for many decades. The recent commercialization of a new, optimized E110 alloy, produced on a sponge zirconium basis, gave the opportunity to compare the mechanical properties of the old and the new E110 fuel claddings. Axial and tangential tensile test experiments were performed with samples from both claddings in the MTA EK. Due to the anisotropy of the cladding tubes, the axial tensile strength was 10–15% higher than the tangential (measured by ring tensile tests). The tensile strength of the new E110G alloy was 11% higher than that of the E110 cladding at room temperature. Some samples underwent chemical treatment – slight oxidation in steam or hydrogenation – or heat treatment – in argon atmosphere at temperatures between 600 and 1000 °C. The heat treatment during the oxidation had more significant effect on the tensile strength of the claddings than the oxidation itself, which lowered the tensile strength as the thickness of the metal decreased. The hydrogenation of the cladding samples slightly lowered the tensile strength and the samples but they remained ductile even at room temperature.

Evaluation of corrosion characteristics and corrosion effects on the mechanical properties of reinforcing steel bars based on three-dimensional scanning

Non-uniform corrosion of steel reinforcing bars is the main cause of structural failure in civil engineering. However, the accurate measurement of the critically corroded cross-sectional area, or the pit shape, is difficult owing to conventional limitations on detection. To accurately represent the corrosion morphology and better understand the corrosion effects on the tensile responses of deformed steel bars, a three-dimensional model of a corroded steel bar was reconstructed using a three-dimensional (3D) laser scanner. Based on the elicited 3D profiles, the corrosion factors-including the corrosion uniformity-the average, and maximum cross-sectional areas and their relationships, were identified in this study. The statistical analyses indicated that the number of corroded pits and their depths increased when the corrosion rate increased, and that decreases of the critical cross-sectional areas were linearly related to the average mass loss. Axial tensile tests of corroded steel bars were also carried out. The tensile test results showed that both the yield and the ultimate loads linearly decreased with increases in corrosion loss. Corresponding decreases in ductility were also observed. Compared with the degradation in the strength, the non-uniform corrosion had a considerable effect on the loss of ductility. The relationships between the mechanical parameters and the corrosion factors were established on the basis of the experimental results, and compared with the available prediction models. It was found that fractures originated at the locations of the critically corroded pit, and brittle fracture gradually occurred at the weakest location of the corroded steel bar, evidenced by concomitant increases in corrosion loss. Numerical simulations were carried out to clarify the critical section, the effect of pit corrosion on the concentration of stress, and the tensile response of the corroded steel bar, based on the 3D model reconstructed using scanning.

Mechanical properties and bond strength degradation of GFRP and steel rebars at elevated temperatures

Fiber reinforced polymer (FRP) rebars have recently been gaining popularity in the construction industry all around the world while steel rebars have been widely used so far. FRP bars, which have higher tensile strength compared to steel rebars with the same nominal diameter under normal conditions, are composed of resin matrix and fibers. In this study, mechanical and bonding properties of glass fiber reinforced polymer (GFRP) and steel rebars subjected to elevated temperature effects were investigated throughout a correlative comparison. Axial tensile tests and pull-out tests of these materials were performed subsequent to exposing them into elevated temperature effects in the range of 23–800 °C. Severe effects on the tensile properties of bare steel bars were observed after 600 °C, while this critical limit is 300 °C for bare GFRP bars. Test results show that bond strength degradation is almost linear for both type of rebars, however, 600 °C is also the critical temperature regarding the serious deterioration on concrete. Additionally, an empirical modeling approach on the bond strength degradation of rebars at elevated temperatures was proposed and it was found that comparison results have quite promising consistency based on the modeling process.

Simulation of temperature rise within a rolling tire by using FE analysis

A simulation method is proposed to predict temperature rise within a dynamic rolling tire. The friction heat from tire-road contact and the internal heat generated by hysteresis loss caused by rubber deformation are considered in the simulation model. A systematic process was developed to calculate the heat generation rate by using dissipated energy, and it was applied to the simulation model by establishing user subroutines. An axial tensile test was conducted for the rubber specimen, and the obtained stress-strain curve was applied to the simulation model based on the first-invariant Marlow model. The reliability of the simulation method was verified by comparing the tensile simulation and test results. A simplified 3D finite element tire model was developed, and simulations were performed in dynamic rolling conditions. Heat was generated because of friction and internal deformation. The temperature distribution within the tire, which was derived using the model, indicates that the proposed simulation method is reliable.