Results Of Tension Tests Research Articles

Formation of Al15Mn3Si2 Phase During Solidification of a Novel Al-12%Si-4%Cu-1.2%Mn Heat-Resistant Alloy and Its Thermal Stability

The formation of Al15Mn3Si2 phase in Al-12Si-4Cu-1.2Mn (wt.%) alloy during solidification was investigated by adopting CALPHAD method and microstructural observation by optical microscopy, SEM–EDS, TEM–EDS/SAD and XRD analysis; SEM fixed-point observation method was applied to evaluate its thermal stability. As-cast microstructural observation consistently demonstrates the solidification sequence of the studied alloy predicted by phase diagram calculation. Based on the phase diagram calculation, SEM–EDS, TEM–EDS/SAD and XRD analysis, as well as evidences on Al-Si-Mn-Fe compounds from the literature, the primary and eutectic Mn-rich phases with different morphologies in the studied alloy are identified to be Al15Mn3Si2 that has a body-centered cubic (BCC) structure with a lattice constant of a = 1.352 nm. SEM fixed-point observation and XRD analysis indicate that Al15Mn3Si2 phase has more excellent thermal stability at high temperature than that of CuAl2 phase and can serve as the major strengthening phase in heat-resistant aluminum alloy that has to face a high-temperature working environment. Results of tension test show that addition of Mn can improve the strength of Al-Si-Cu alloy, especially at elevated temperature.

Experimental study of thermo-mechanical behavior of a thermosetting shape-memory polymer

The thermo-mechanical behavior of shape-memory polymers (SMPs) serves for the engineering applications of SMPs. Therefore the understanding of thermo-mechanical behavior of SMPs is of great importance. This paper investigates the influence of loading rate and loading level on the thermo-mechanical behavior of a thermosetting shape-memory polymer through experimental study. A series of cyclic tension tests and shape recovery tests at different loading conditions are performed to study the strain level and strain rate effect. The results of tension tests show that the thermosetting shape-memory polymer will behave as rubber material at temperature lower than the glass transition temperature (Tg) and it can obtain a large shape fix ratio at cyclic loading condition. The shape recovery tests exhibit that loading rate and loading level have little effect on the beginning and ending of shape recovery process of the thermosetting shape-memory polymer. Compared with the material which is deformed at temperature higher than Tg, the material deformed at temperature lower than Tg behaves a bigger recovery speed.

On strain measurement of smart GFRP bars with built-in fiber Bragg grating sensor

A smart glass fiber reinforced polymer (SMFRP) reinforcing bar with a fiber Bragg grating (FBG) sensor was fabricated using a pultrusion technique, while ribs were formed to improve bonding between concrete and SMFRP. Then, strain of SMFRP bars were measured for a uniaxial tension test of an SMFRP bar, and a four-point bending test of concrete beams reinforced with SMFRP bars. The results of a uniaxial tension test illustrate that the strain obtained from an FBG sensor agrees well with that obtained from electrical resistance strain gauge (ERSG). Additionally, concrete beams reinforced with SMFRP bars were fabricated, and actual flexural test were performed while the strain of with an FBG sensor was compared with that of ERSG. The experimental results demonstrate that SMFRP bars can be used as reinforcement of concrete member while providing deformation information. Furthermore, SMFRP bars may provide stronger durability and smart monitoring to reinforced concrete members under corrosive environments during a service life.

Composite Properties and Micromechanical Analysis of Highly Ductile Cement Composite Incorporating Limestone Powder

This paper presents the results of an experimental study on the effect of limestone powder on the compressive strength, tensile behavior, and micromechanical parameters of a highly ductile cement composite incorporating limestone powder. Four mixtures were determined according to the replacement ratio of cement with limestone powder. A series of experiments including compressive strength, uniaxial tension, single fiber pullout, and matrix toughness tests were performed. Test results showed that the strength (compressive, initial cracking, and tensile strength) decreased, and that the tensile strain capacity increased, with an increase of the replacement ratio of cement with limestone powder. Micromechanical tests and analysis supported the uniaxial tension test result.

Analysis and Optimization of Parameters for Friction Stir Welding

Aluminium welding cannot be done by conventional process because temperature characteristics of material will be changed. To overcome this drawback, friction stir welding process is done. In friction stir welding two Aluminium plates or sheets are joined together and cylindrical shouldered tool with profile threaded and straight threaded H 13 is used. The trial experiments are conducted using Friction Stir Welding (FSW) on commercial AA2014. Practical results of tension test are compared with simulation results of tension test in LSDYNA.

Ultra-low cycle fatigue life of aluminum alloy and its prediction using monotonic tension test results

Ultra-low cycle fatigue (ULCF) life of ductile metal is closely correlated with monotonic tension coupon test results. This paper aims to propose a novel approach to evaluate crack initiation of aluminum alloy under ULCF loading only with monotonic tension coupon test results. ULCF tests on 15 specimens made of aluminum alloy 6061-T6 were conducted, and numerical analyses using a previously proposed cyclic void growth model indicated that the ULCF life of aluminum can be greatly underestimated by the model. A new fracture model based on the concept of different dislocation structures is thus proposed, which classifies damage into kinematic hardening correlated and isotropic hardening correlated. A material constant is employed to consider the relatively low damage induced by the kinematic hardening compared with the isotropic hardening one. The newly proposed fracture model can well simulate the instants of crack initiation for the specimens. A process to evaluate the ULCF life of aluminum alloy based on both monotonic coupon test results and simple numerical analysis is presented.

Tensile behavior of tailor rolled blanks with longitudinal thickness transition zone: Introducing a new tensile specimen

In this study, a new design for tensile specimens made from tailor rolled blanks (TRB) with longitudinal thickness transition zone (TTZ) has been proposed. To this end, an additional lateral wedge angle is introduced to obtain a uniform stress field along the gauge length, which enables one to study the tailored properties of TRBs via stress-strain curves without considering the effects of geometrical inhomogeneities. Parallel finite element simulations were carried out to study the stress and strain fields resulted from different geometries of tensile specimens. The results were then used to obtain stress triaxiality factors to analyze the deformation prior to failure. In addition, a mathematical model was developed to study the contribution of different parts of TTZ to the total deformation. The results of uniaxial tension test along with results of simulation revealed that the deformation is controlled by the side with lower load-bearing ability in the new-developed tensile specimen. Furthermore, it was concluded that the conventional tensile specimens are more appropriate to study the effect of thickness changes on the elongation of TRBs. However, the presented tensile specimens can be used to study the strength of TRBs. Finally, the fracture mechanisms were investigated utilizing SEM and optical observations.

Experimental study on durability of strengthened corroded RC columns with FRP sheets in tidal zone of marine environment

The main objective of this paper was to illuminate the effect of marine environmental condition on durability of reinforced concrete (RC)-corroded columns strengthened with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) layers. Small-scale columns were prepared and corroded by an accelerated corrosion process. After strengthening, compressive strength tests were carried out on control and weathered specimens. In this research, a marine simulator was designed and constructed similar to the tidal zone of marine environment in south of Iran which was selected as a case study in this research. Mechanical properties of wrapped specimens were studied after placing them inside the simulator for 3000 hours. Marine environment decreased ultimate strength by 4.5% and 26.3% in CFRP and GFRP-wrapped columns, respectively. In some corroded-columns, strengthening was carried out after replacing damaged cover by self-compacted mortar. In this method, by confining with one layer of CFRP and GFRP, 4.2% and 22.4% reduction in ultimate strength was observed, respectively, after exposure. Furthermore, the elastic-brittle behavior has been verified in this retrofit method. Also results of tension tests revealed, the ultimate tensile strength was degraded by 2% and 28.8% in CFRP and GFRP sheets, respectively, after applying marine exposure.

Mechanical behaviour of a polyvinyl alcohol fibre reinforced engineered cementitious composite (PVA-ECC) using local ingredients

A polyvinyl alcohol fibre reinforced engineered cementitious composite (PVA-ECC) using local ingredients is developed, aiming for a reduced cost and a tensile strain capacity matching that of steel reinforcement for commonly used reinforced concrete structures. Experiments are conducted to determine mechanical behaviour of the composite. In addition, a finite element model is developed to simulate the flexural behaviour of PVA-ECC beams, and experimental results are used to calibrate the model. The material models of the PVA-ECC under compression and tension are calibrated using experimental results of uniaxial compression and tension tests. Furthermore, a theoretical relationship on the tensile strength between specimens with two-dimensional and three-dimensional fibre distribution is derived, and accuracy of the simulation is improved by using the theoretical ratio. Agreement between the computed results and the experimental data demonstrates the effectiveness of the finite element model.

On a Procedure for the Determination of the Mechanical Characteristics of Materials in the Case of Tensile Test of Specimens at Elevated Temperatures

The paper presents a procedure for the determination of the mechanical characteristics of materials for modern aircraft gas-turbine engines on the basis of results of uniaxial tension tests under elevated temperature conditions. The procedure permits one to allow for measurement errors, which arise from the misalignment of the load chain and temperature effect when using strain gauges of modern testing systems. The evaluation of the procedure is illustrated for the uniaxial tension of specimens of EI962 alloy (11Kh11N2V2MF).

Literature Survey and Experimental Study on the Direct Tension Test on Rocks

Abstract Direct tension tests are indispensable for obtaining an accurate understanding of the deformation and failure characteristics of rocks in tension. For this technical note, the authors collected original papers published in international journals and surveyed the previously reported methods and results of direct tension tests on rocks. Some important factors affecting the strength and stress–strain curve are discussed, such as the shape, size, anisotropy, and water content of the specimen; the loading rate; and the confining pressure. The relationship between the results of the direct tension tests and those of other tests also is discussed. Although various types of testing apparatuses have been adopted in direct tension tests on rocks, the dependence of test results on the apparatuses has not been investigated. In this study, direct tension tests were conducted using various testing apparatuses in seven laboratories. The results of the direct tension tests showed that direct tensile strengths were not dependent on the type of test apparatus used or whether a flexible linkage system was used. The results of the tuff in this study showed that the coefficient of variation of the direct tensile strengths is smaller than that of the Brazilian tensile strengths. Moreover, the results revealed that the coefficient of variation of the direct tensile strengths is comparable to that of the uniaxial compressive strengths of the tuff. The authors noted that to obtain the stress–strain curve from the pre-failure region to the post-failure region, it is necessary to conduct a test with a high-stiffness machine and without a flexible linkage system. This technical note summarized the results of the standardization activity by the authors in the Japanese Geotechnical Society.

Stress relaxation of AA5182-O aluminum alloy sheet at warm temperature

Abstract Uniaxial tension and the subsequent stress relaxation tests at 25, 100, 200 and 300 ° C were conducted for AA5182-O aluminum alloy sheet with the thickness of 1mm in order to observe the temperature and strain rate dependency on its flow stress and stress relaxation. From the tension test results, it was observed that the stress-strain curves at 25 and 100 ° C were almost the same while the flow stress decreased with the increase of temperature. On the other hand, stress dropped at 100 ° C during relaxation even if almost no relaxation was found at 25 ° C. The degree of stress drop was pronounced more with the increase of temperature and the stress almost disappeared at 300 ° C. To reveal the relaxation mechanism, relaxation test followed by subsequent tension were performed at 100, 200 and 300 ° C. The re-yield stresses during subsequent tension at 100 and 200 ° C decreased compare to its flow stress at the end of pre-tension test (start of relaxation), while the stress did not changed at 300 ° C. The obtained results implies that the dominant mechanism of relaxation is grain boundary slide rather than dynamic recovery.

The shear behaviour of pine wood in the Arcan test with the digital image correlation

The Arcan shear test is used together with the digital image correlation to study the shear stress-strain relationship for pine wood in the symmetry plane LR . The relationship of shearing perpendicular to the grain direction is shown by the straight line below the proportional limit and the nonlinear curve beyond it describing hardening up to the ultimate limit. Subsequent failure modes are shown during the load increase. Additionally, some results of the off-axis tension tests, as well as the uniaxial tension tests, with the mechanical and electric resistance strain gauges are presented to determine and compare the shear modulus from both methods of testing.

Cyclic and Biaxial Deformation Behavior for Bake-hardenable Steel Sheet

Abstract It is well known that bake hardening treatment on the bake-hardenable steel sheets leads to the increase of yield strength and appearance of yield point phenomena under uniaxial tension deformation. On the other hand, strain paths during forming process and the subsequent dent resistance are usually not monotonic nor uniaxial, so that more investigation under complex strain path and stress state are essential in order to establish its constitutive model and achieve an accurate prediction of dent resistance by numerical simulation. In the present study, the effects of bake hardening treatment on various pre-strain paths and secondary deformations after bake hardening treatment were observed. From the obtained results, the yield drop phenomena did not appear and the Bauschinger effect was observed in cyclic deformation with bake hardening treatment. On the other hand, the yield drop and the subsequent yield plateau followed by workhardening was observed in equi-biaxial tension test as similar to the result of conventional uniaxial tension test result with bake hardening treatment.

Failure investigation of the crankshaft of diesel engine

In this work the failure, stress and modal analysis of the crankshaft of diesel engine was performed. Visual examination of damaged part showed that the fatigue beach marks were observed on the fracture. Results of additional investigation using the scanning electron microscope revealed the presence of micro-cracks in crack origin area. In next part of experimental investigations the specimens were cut from damaged shaft. Results of tension test showed that mechanical properties of the steel used for the crankshaft manufacturing is in the range defined by the standard. In order to explain the reason of premature crankshaft damage, the finite element method was utilized. In first step the numerical model of crankshaft with the connecting rods was prepared. The boundary conditions were next defined on bearing journal surfaces. The complex load cases were also defined in order to model the real engine loadings. Results of nonlinear stress analysis performed for the crankshaft model showed that during work of engine with a maximum power the high stress area was located in another zone than the crack origin. This result was a reason for extension of investigation on the dynamic problems. In last part of the study the numerical modal analysis was performed for the crankshaft. In this analysis both the frequencies and modes of free vibration were obtained. Results of modal analysis showed that during second mode of free vibration the high stress area was located in the crack origin zone. Based on results of performed investigations it was concluded that the main reasons of premature failure are resonant vibrations of the crankshaft.

Spiral cracking pattern in asphalt materials

The present work for the first time reports observations and modeling to characterize three-dimensional spiral-shaped fracture patterns in a bi-axially stressed layer of asphalt material bonded to an aluminum substrate. Five different asphalt materials with different fracture characteristics are investigated. A logarithmic spiral model was found to mathematically represent the 3D helix-shaped cracks observed. A spiral tightness parameter is proposed for the characterization of spiral fracture patterns in asphalt. Results of acoustic emission and compact tension tests are also presented and employed in the evaluation of observed spiral cracks. The shape of spirals are found to be influenced by the fracture properties of the asphalt materials tested and appear to be independent of the thickness and shape of the test sample. The embrittlement temperature and fracture energy of tested asphalt materials were found to correspond to the characteristic parameters of spiral cracks.

Homogeneous and Heterogeneous Solid State Self-Healing System

The solid state self-healing system was obtained by employing a thermosetting epoxy resin, into which a thermoplastic is dissolved. The aim of this study is to investigate the homogeneous and heterogeneous solid state self-healing system by using thermoplastics comprised of poly(bisphenol-A-co-epichlorohydrin) (PDGEBA), polyvinyl chloride (PVC), polyvinyl alcohol (PVA), polyethylene (PE) and polypropylene (PP) as healing agents. PDGEBA produced homogenous resin blend which undergone random molecule diffusion healing process. A heterogeneous resin blend composed of 8 wt.% PVC, PVA PE, and PP, yielding a “bricks and mortar” morphology wherein the epoxy phase exists as a matrix (mortar) interpenetrated with a percolating thermoplastic (bricks). The healing process in heterogeneous resin blend is attributed to volumetric thermal expansion of healing agent above its melting point in excess of epoxy brick expansion. Healing was achieved by heating the fractured resins to a specific temperature; above their glass transition temperature ( Tg) which obtained from dynamic mechanical analysis (DMA) in order for diffusion process and thermal expansion to occur. The thermal properties and bonding formed in the epoxy resins were characterized by means of Fourier Transform Infrared Spectroscopy (FTIR) and dynamic mechanical thermal analysis (DMTA). Izod impact test and compact tension test were conducted to demonstrate details self-healing capability of different specimens. Results of Izod impact test are in agreement with the result of compact tension test. Under compact tension test, the healable resin with PDGEBA has the highest healing efficiency of 60% followed by PVC, PP, PE, and PVA with 39%, 37%, 28% and 21% of average percentage healing efficiencies in three healing cycle respectively. Morphological studies using optical microscope verified the fracture-healing process and morphological properties of the resins.

Prediction of Failure Mode in Hole Clinching of Al Alloy and Advanced High-Strength Steel

Common joining methods used in automotive industry are welding, adhesive bonding, friction stir welding, mechanical fastening, self-piercing rivets, mechanical clinching and so on, for multi-material designed automotive bodies. Among different joining methods, mechanical clinching which achieves geometrical interlocking by plastic deformation has several advantages such as no need of additional joining elements and fast joining. But mechanical clinching is difficult to join a ductile material with a high-strength or low ductility material. Therefore the hole clinching as a new mechanical clinching process has been proposed to join these material combinations. In the hole clinching process, as punch force is applied to a upper sheet (a ductile material), it is indented into hole of lower sheet (low ductile material) on die and then interlocked by plastic deformation. It is very important for a successful design of hole clinching to predict the failure mode such as neck fracture and button separation and the strength of hole-clinched joint. For this an analytical approach was carried out for the hole clinching process of Al6061 and DP980. Tool geometry used in hole clinching was designed by the predicted failure mode. Preliminary finite element simulation was performed to validate the geometrical interlocking and joinability. The predicted failure mode and strength were verified by the results of cross tension test.

Experimental and numerical investigation of low-temperature performance of modified asphalt binders and mixtures

Thermal cracking is the prevalent type of distress experienced by asphalt pavements in cold regions. It is widely assumed that when thermal stresses induced in the pavement exceed the tensile strength of the asphalt surface layer, cracking occurs; however, the role of thermal fatigue should not be ignored. To better describe the low-temperature (LT) performance properties of modified asphalt binders, a new parameter, normalised tensile stress (NTS), was defined in this research. NTS values were compared with bending beam rheometer (BBR), direct tension (DT) and semi-circular bending (SCB) fracture test results. The m-value parameter of the BBR test specifies the type of asphalt binder. This classification changes as the loading time changes and is only valid in the linear viscoelastic range. It showed limited sensitivity to changes in the material properties of modified asphalt binders that showed superior LT damage resistance. In contrast, the results from the DT, SCB and NTS parameters were sensitive to the changes. The results of SCB testing and NTS parameters were in agreement with the existing field data. It was also found that the use of sulphur as a cross-linking agent improved the storage stability of styrene butadiene styrene (SBS)-modified asphalt binder and decreased the amount of SBS required to yield a comparable result by about 50%. In contrast to what has been reported by some investigators, the use of polyphosphoric acid as a cross-linking agent intensified the phase separation of bitumen and SBS, and somewhat reduced the efficacy of SBS modification with regard to LT performance.

Damage development in woven carbon fibre thermoplastic laminates with PPS and PEEK matrices: A comparative study

In this work, we investigate the effect of the matrix on the mechanical performance of woven carbon fibre composites. More specifically, composites with the same 5-harness satin carbon fabric reinforcement and different thermoplastic matrices, PPS and PEEK, are compared in various mechanical tests (tensile, interlaminar fracture toughness and compression-after-impact tests). The results of tension tests show the influence of the matrix type on the development of cracks in yarns. The cracks in carbon fabric/PEEK composite appear later than in carbon fabric/PPS composite. Their density is also lower. A correlation between cumulative acoustic emission energy and transverse crack appearance in tensile tests is shown. The most evident difference is demonstrated for the Double Cantilever Beam tests and End Notch Flexure tests. The interlaminar fracture toughness for both mode I and mode II is more than 1.5 times higher for carbon fabric/PEEK laminates as compared to carbon fabric/PPS ones. The higher fracture toughness of carbon fabric/PEEK results in its higher residual compressive strength after impact (∼25%). Thus, the study concludes that the performance of textile composites is highly sensitive to the performance of the matrix. Matrices that have higher strength, ductility and fracture toughness lead to structural composites with lower crack densities, better performance in the bias direction, higher resistance to delaminations and higher residual strength after impact.