The effect of polyethylene glycol (PEG) modification on the corrosion behavior under tensile deformation of hydroxyapatite-coated Mg-3mass% Al-1mass% Zn (HAp-AZ31) was examined in Hanks’ solution. ...Slow strain rate tensile (SSRT) and rapid straining electrode (RSE) tests and electrochemical impedance measurements were performed. In SSRT tests, PEG-modified HAp-AZ31 showed 1.4 times longer elongation to failure than HAp-AZ31. In RSE tests, the PEG modification showed little effect on cracking of HAp coating, while it reduced corrosion propagation from the cracks by half. The improvement in tensile elongation of HAp-AZ31 with PEG is attributed to the inhibition of corrosion propagation from coating cracks.
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•Improvement of elongation to failure of HAp-AZ31 with PEG and SPA modification.•PEG modification reduces corrosion propagation from cracks in HAp coating.•SPA modification reduces crack initiation in HAp coating and corrosion propagation.•PEG present at the interface prevents delamination of HAp coating.•Mechanical properties of coatings dominate corrosion behavior under deformation.
Free-standing microtensile specimens were extracted from the substrate and the interdiffusion zone of a MCrAlY coated nickel-based single-crystal superalloy. Testing of these specimens was conducted ...at elevated temperatures, up to 1100°C under controlled atmosphere, to assess the tensile and thermal expansion properties of the interdiffusion zone materials. These properties were measured and found to lie between the properties of the substrate and those of the coating. The poor mechanical strength of the interdiffusion zone evidenced its non-load bearing contribution to the system for uniaxial creep loading at high temperature representative of service conditions. It was also shown that the fabrication process of MCrAlY coated nickel-based superalloy affects the mechanical properties of the system due to the presence of voids and non-adherent grit-blasting particles within the interdiffusion zone.
•Local tensile and thermal expansion properties of a coated system are measured.•The interdiffusion (ID.) weakens the local tensile properties of the substrate.•Voids and grit-blasting particles are highly present in the interdiffusion zone.•Voids and grit-blasting particles favor the early fracture of the ID. zone.
Gas Tungsten arc welding (GTAW) process was employed for welding of Inconel 718 with two different shielding gases, namely argon (Ar) and argon with a 5 vol% hydrogen mixture (ArH) and two fillers ...viz., ERNiCrMo-10 and ERNiCrMo-4. The effects of gas composition and filler wires on the laves phase formation were studied in detail. The results revealed that hydrogen addition through ArH shielding gas mixture resulted in better grain refinement in the welds than pure Ar. The hydrogen addition induced a steep thermal gradient in the weld, which lowered the segregation of elements like Niobium (Nb) and Molybdenum (Mo) at the interdendritic regions. The laves phase formation in Mo-rich filler addition welds was minimized due to restriction of Nb segregation by Mo at the interdendritic region. Tensile test results indicated that the strength and ductility of the joints of both autogenous and filler added welds of Ar were higher than the ArH shielded welds. In the case of filler added welds, higher Mo content filler exhibited better tensile properties in both shielding gas combinations due to solid solution strengthening of Mo. Nano-sized hydrogen assisted cracks observed in ArH autogenous welds caused a reduction of strength and ductility.
•The gas mixture of Ar (95%) plus H2 (5%) with Mo rich fillers was employed for welding of Inconel 718.•Hydrogen addition induced steep temperature gradient in weld; thus the size of the laves phase got reduced.•Autogenous weld exhibited low tensile strength due to hydrogen assisted cracking.•Molybdenum addition improves the tensile properties of welds.
Stress relaxation, which occurs during holding at the bottom dead center in press forming, affects press formability. Because holding at the bottom dead center is completed within several seconds, it ...is important to predict the stress relaxation behavior of the first few seconds after the start of holding. The purpose of this study is to propose a model, the material parameters of which are obtained from tensile tests, to predict the stress decreasing behavior in the early stage of stress relaxation in steel sheets. We constructed the model by modifying the Kocks-Mecking model based on the following assumptions: Stress relaxation at room temperature is due to the slip motion of dislocations, which indicates that the plastic strain rates at the start of stress relaxation are same as those in the previous tensile process. In this study, it was assumed that the change in microstructure during stress relaxation is negligible; hence material parameters remain constant during stress relaxation. The measured and predicted stress relaxation behaviors for various strain rates during the tensile process were compared. It was observed that an increase in the plastic strain rate during the tensile process accelerated stress relaxation. The proposed model was able to predict this phenomenon. However, the relative error between experimental results and the model increased as the stress relaxation progressed mainly owing to dynamic strain aging. Therefore, the proposed model is applicable in the condition when effect of dynamic strain aging is negligible.
Tensile tests of bonded, bolted, and hybrid braided CFRP joints were conducted using an MTS tester. Twenty-four groups of specimens were designed with four stacking sequences and two lapping ...patterns. The strain data around the bolt holes were recorded using a dynamic acquisition device. The macroscopic and microscopic failure modes obtained by SEM were analysed. The strength, stiffness, and bolt load distributions with different variables were investigated to determine the mechanical properties of the CFRP joints. The results show that the load–displacement curves for S1, S2, and S4 are approximately linear before fracture; the curve for S3 is nonlinear. Bolts 1 and 2 near the loading side have large strain values; bolts 3 and 4 have smaller strain values. The failure modes include adhesive debonding, fibre fracture, net-section failure, tearing failure, and bolt fracture. Hybrid joints exhibit a combination of failure modes with single joint failure. The SLJ exhibits better strength and stiffness than the SSBJ. The strength of bonded joints with high-performance adhesives can be greater than that of hybrid joints, and is related to the stacking sequence and lapping pattern. Bolt load distribution is a dynamic process. With addition of an adhesive layer, there is greater balance between the four bolts, which can effectively reduce fluctuation of the load distribution.
•Tensile tests of bonded, bolted, and hybrid joints with different lapping patterns.•Four stacking sequences designed using braided CFRP.•Strain data recorded around each bolt hole.•Analysis of macro and micro failure mode of bonded, bolted, and hybrid joints.•Bolt load distribution discussion for four-bolted and hybrid joints.
Nowadays, adhesively bonded joints are frequently employed in engineering designs as they enable the manufacture of joints with great strength while remaining light. These joints used in aviation ...sectors, where lightness and reliability are important, are generally designed to join metal-metal, metal-composite and composite-composite adherends. The surface roughness of the adherends with its degree and the way the adhesive interacts with the surface are the most crucial parameters in these applications. In the current work, surface roughness and normal stress strength of nano-composite adhesive in butt joint subjected to tensile loading were investigated. DP460 liquid structural epoxy from 3 M was used as adhesive, AA2024-T3 aluminum alloy as adherend, Graphene-COOH and Carbon Nanotube-COOH as nanostructures while sandpaper and sandblasting methods were used for introducing roughness to the adherend surfaces. A two dimensional axisymmetric FE model was developed to get an insight about the joint failure. When the failure load obtained from experiments was examined, an increasing trend in maximum force values was noticed with an increase in surface roughness, but this increase in joint strength decreased when the surface roughness increased to very high values. In addition, minimum surface roughness reduces the adhesive's adhesion to the surface, thus reducing the normal stress strength of the joint. When 1 % Graphene-COOH nanostructure was added to the adhesive, the ultimate normal stress of the joints increased from 9 % to 21 %. However, when the same percentage of Carbon Nanotube-COOH was added, the increase was from 27 % to 62 %. Different normal stress values of the joints were obtained using by sanding and sandblasting methods even though the roughness resulting from the two treatments was similar.
•A new optimal regression process for acquiring the weld material properties is proposed by using tensile and hardness test data.•The regression function for the hardness distribution with local ...softening of weld zone is proposed.•The change in material properties resulting from the change in hardness showed a similar tendency in the two materials used in this study.•The weld material properties of two different pipes were estimated, and showed great accuracy compared to the finite element results and tensile test in terms of load-displacement curve.
A new method is proposed to obtain the coefficients of plastic constitutive laws of weld metal via tensile test and hardness test. In this method, a general expression between hardness ratio and flow stress model coefficients is established. The predicted flow stresses for the differential areas are integrated over the entire section of tensile specimen to predict the tensile load. The optimal regression coefficients that minimize the difference between the predicted and experimental loads are derived using the Nelder-Mead simplex direction search algorithm. The constraint for the diffuse necking strain is applied in the convergence procedure to avoid the ‘mystical’ material property shown as non-unique solution. The material constants obtained from the proposed method are independent of the width of tensile specimen. The difference of tensile loads between finite element analysis results using the determined material constants and the experiment was less than 8 %. As the derived material constants were shown to be consistent and reliable, the methodology can be applied to general line welded parts.
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•Crushable aggregates with the real geometry shape are generated by using clump-cluster method.•Flat-Joint Model is adopted as the constitutive law.•A concrete meso-scale modeling framework is ...proposed based on discrete element method (DEM).•The effects of aggregate strength on dynamic tensile properties and damage behavior of high strength concrete are quantitatively studied.
The dynamic mechanical behavior of high-strength concrete is sensitive to aggregate properties, thus an accurate description of the effect of aggregate strength on the dynamic tensile mechanical properties of high-strength concrete is essential to evaluate the structural stability of concrete. In this paper, a concrete meso-scale modeling framework was proposed based on discrete element method (DEM). The meso-scale model considered the three-dimensional meso-structure of concrete (coarse aggregate, mortar and interfacial transition zone), and the crushable aggregate model with realistic morphological characteristics was generated by the “clump-cluster” method. Based on this, the effects of aggregate strength on dynamic tensile properties and damage behavior of high strength concrete were quantitatively studied by splitting tensile test. The simulation results reveal the influence of aggregate strength and strain rate on the tensile properties of concrete at both macroscopic and mesoscopic levels, including dynamic deformation behavior, microcracks propagation mode and the proportion of different kinds of microcracks at different loading stages. The results show that the aggregate strength plays an important role in the dynamic tensile properties of concrete. The failure behavior of concrete and the damage degree of different components under dynamic tensile loading are influenced by the ratio of aggregate strength to mortar strength.
•Aluminum silicon (AlSi) and aluminum (Al) films are subject to fatigue test.•Adding silicon (Si) increases mechanical characteristics in Al film.•Fatigue crack propagation in AlSi film is 10 times ...slower than that in pure Al film.•AlSi film's fatigue crack propagates in a zigzag way while detouring Si segregation.
This paper focuses on investigating the differences in fatigue fracture between sputtered aluminum silicon (AlSi) alloy and pure aluminum (Al) films by means of pulsating-tension cyclic loading tests. AlSi alloy film with 1.0 wt% (wt%) silicon (Si) and pure Al film are prepared at a substrate temperature of 450 ℃ and 260 ℃, respectively, by dc magnetron sputtering. After annealing those films at 490 ℃ under a hydrogen and nitrogen atmosphere for 1 hour, the tensile test specimens are prepared using semiconductor fabrication technologies. Quasi-static tensile tests measure the mean yield strength of 52 MPa and 33 MPa for AlSi and Al films, respectively, which are used as reference stress values for fatigue tests. During fatigue tests, a crack is introduced at the one-side edge of pure Al film specimen and propagates straightly to the other side, whereas a zig-zag crack is observed in AlSi alloy film. The crack propagation rate for AlSi film is around one-tenth of that for pure Al film. The mechanism of fatigue crack propagation is discussed based on element mapping results by energy dispersive X-ray analysis.
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•Molecular dynamics study for sintering process of nano-scale tungsten carbide (WC) with various heating rate.•High surface energy shows the surface diffusion sintering mechanism at ...higher temperature for nano tungsten carbide.•Slower heating rate (i.e. 2.5 K/ps) shows higher necking and shrinkage with respect to high heating rate (4.63 K/ps).•Higher temperature and sintering time show higher diffusion of atoms during sintering.•Slower heating rate possess higher tensile strength as compared to high heating rate.
In the present research paper, atomistic simulation at microscopic level has been performed for sintering of nanocrsytalline tungsten carbide particles. The sintering parameters like dihedral angle, neck width, and shrinkage ratio have been evaluated during sintering. The Radial Distribution Function (RDF) and Mean Square Displacement (MSD) for atoms have been simulated in order to understand the crystal structure properties and diffusion behaviour of the atoms. The solid state sintering (heating in range of0.6-0.8Tm) has been performed at two different heating rates i.e. 2.5 K/ps and 4.63 K/ps for various size of particles i.e. (2 – 8 nm). The sintering behaviour for 4 nm size particle has been analysed. It has been found that neck width in case of slower heating rate is 33 Å, which is more than the higher heating rate. Besides this, the maximum dihedral angle of 1120 has been found during sintering which lies in the range of solid state sintering of the nano scale powders. The diffusivity coefficient calculated during various sintering rate has been found to be 5.25×10-14m2/s and 1.05×10-13m2/s. In order to check the tensile properties of sintered particle, uniaxial tensile test simulations have been performed at strain rate of 1010 s−1. The maximum strength of 4235 MPa and 3690 MPa has been achieved by slow and fast heating rate sintered particles respectively. The tensile strength variation with respect to temperature has also been studied during the sintering process. This Molecular Dynamic (MD) study in turn has laid the platform for setting of the optimum parameters during sintering of WC powders at nano scale level.
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