•An improved shear modified GTN model is proposed for ductile fracture prediction of materials under different stress states;•The damage parameters are calibrated using a FE inverse calibration ...method incorporating the Latin hypercube design, Kriging approximate model and NLPQL optimization method;•Influence of each damage parameter on damage evolution under different stress states is analyzed by a unit cell model;•Reasonable identification results are obtained for the aluminum alloy 6061 using the proposed method;•The mechanism of deformation and failure are studied using fracture morphology analyses and damage analyses using FE simulation in microscale and macroscale perspectives.
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To solve the problem that the original GTN model cannot accurately simulate ductile fracture of material under low stress triaxiality, many scholars have made shear improvement to it, but these shear modified GTN models have their own advantages and disadvantages and the parameters are difficult to be determined. An improved shear modified GTN (ISMGTN) model containing two independent damage mechanisms is proposed for ductile fracture prediction of materials under different stress states. The shear damage parameters, tensile damage parameters and the hardening parameters are identified using a FE inverse identification method incorporating the Latin hypercube design, Kriging approximate model and NLPQL optimization method performed in the optimization software ISIGHT. Influence of each damage parameter on damage evolution under different stress states is analyzed by a unit cell model. Accuracy of the ISMGTN model and feasibility of the damage parameters identification method are verified by performing them on a material aluminum alloy 6061 with 0°, 30° and 60° shear tests, plate tensile tests, and notched tensile tests. Additionally, fracture morphology analyses of the fractured specimen and contour plots of the effective tensile damage and effective shear damage from the FE analysis using the identified parameters are performed to study possible mechanism of deformation and failure in microscale and macroscale perspectives, respectively, and a good consistence is obtained.
A key criterion in the selection process for turfgrass breeding is effective wear tolerance, indicating the plant's capacity to endure forces that may impact leaves, stems, crowns, and roots. In this ...study, the correlation between mechanical and chemical traits and the wear tolerance of 37 cultivars belonging to seven turfgrass species was examined. Mechanical properties and fiber characteristics of wide range of turfgrass cultivars were determined and compared for the first time. The evaluation of turf wear tolerance (described as turf cover index, TCI) was conducted through a three-year field trial using a Brinkman traffic simulator. Tensile tests were conducted to determine biomechanical parameters. According to the TCI, the most wear-resistant cultivars were those of Lolium perenne, Most of these cultivars demonstrated a TCI below 0.1. The cultivar 'Nira' was the most resistant, with a TCI of − 0.285. The least resilient cultivars belonged to Festuca ovina and Festuca rubra, all exhibiting TCI values above 0.6. Agrostis stolonifera and Agrostis capillaris were characterised by lower cellulose and acid detergent fiber content but high hemicellulose content. The opposite result was determined for Festuca rubra and Festuca ovina. The highest hemicellulose ratio was obtained for Poa pratensis. Lolium perenne was characterised by relatively high content of cellulose, lignin and hemicellulose. Cultivars of Festuca arundinace distinctly differed from other cultivars, demonstrating higher mechanical resistance with an average force-to-break of 3.73 N. Cultivars of Agrostis stolonifera and Agrostis capillaris reached force-to-break values up to 1.0 N. The relationships between TCI and fiber composition of turfgrass leaves were significant for crude fiber, NDF and hemicellulose content. Thus higher NDF and hemicellulose content resulted in higher force-to-break and work-to-break parameters.
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•The most wear-resistant cultivars were those of Lolium perenne.•Least resilient cultivars belonged to Festuca ovina and Festuca rubra.•Lolium perenne was characterised by high content of cellulose, lignin and hemicellulose.•Higher NDF and hemicellulose content resulted in higher mechanical resistance.
•The interfacial bond performance of the UHPC-NSC is sufficient for rehabilitation of concrete structures.•Proper surface treatment and moisture degree are the major factor for the bond capacity of a ...UHPC-to-NSC interface.•The bond strength of the UHPC-NSC interface can be evaluated by using the cohesion and friction coefficient.
Ultra-high performance concrete (UHPC) is suitable for the durable rehabilitation and strengthening of deteriorated normal strength concrete (NSC) structures due to its excellent characteristics, such as superior compressive strength, high tensile capacity, and extremely low permeability. However, a successful repair depends on whether the UHPC-NSC interface can provide good bonding performance under various applied loads and working conditions throughout its service life. In this study, the bond characteristics between the NSC substrate and UHPC layer were investigated by applying slant shear, splitting tensile, and direct tensile tests, and the interfacial bond strength and corresponding failure modes were observed. Seven studied factors, the roughness of substrate surface, UHPC age, moisture degree of substrate, curing condition of UHPC, strength of NSC substrate, bonding agent and expansive agent were included to explore their influences on the bond strengths, and the UHPC-NSC interfacial bonding enhancement mechanism. Results indicated that the UHPC overlay achieved superior interfacial bond performance for the rehabilitation of concrete structures, with the appropriate surface roughness and substrate wetness. The UHPC-NSC composite samples met the minimum requirements of the interfacial bond strengths specified in ACI 546-06 and achieved an “excellent” bonding quality. Furthermore, the friction coefficient for calculating interfacial bond strength was back-calculated according to the results obtained from the corresponding direct tensile and slant shear tests.
In this work, mode I fracture parameters of steel fibre reinforced self-compacting concrete (SFRSCC) were derived from the numerical simulation of indirect splitting tensile tests. The combined ...experimental and numerical research allowed a comparison between the stress–crack width (σ–w) relationship acquired straightforwardly from direct tensile tests, and the σ–w response derived from inverse analysis of the splitting tensile tests results. For this purpose a comprehensive nonlinear 3D finite element (FE) modeling strategy was developed. A comparison between the experimental results obtained from splitting tensile tests and the corresponding FE simulations confirmed the good accuracy of the proposed strategy to derive the σ–w law for these composites. It is concluded that the post-cracking tensile laws obtained from inverse analysis provided a close relationship with the ones obtained from the experimental uniaxial tensile tests.
In recent years, additive manufacturing has gained importance, especially since the full melting of the raw material in the selective laser melting process enables the fabrication of directly ...deployable components. However, the multiple directional dependencies involved result in an anisotropic material behavior. The raw material under investigation in this study was the precipitation-hardenable AlSi10Mg alloy, with the main focus on the positioning and inclination effects, which were studied on six characteristic orientations. In addition, the superimposed effects based on the surface condition and thermal post-treatments were taken into account. The examination contained: comprehensive tensile tests with strain gauges, detecting strains in two directions; detailed surface hardness investigations in various conditions; and micro-section investigations. Major direction dependencies were revealed and the tensile strength and the surface hardness results, coupled with annealing procedures, exhibited consistent results, explaining the encountered findings. The Young’s modulus varied between 62.5GPa to 72.9GPa with the Poisson’s ratio fluctuating between 0.29 and 0.36. Regarding the tensile strength, the UTS ranged from 314MPa to 399MPa with breaking elongations spanning from 3.2% to 6.5% in the non-heat-treated condition.
Additive manufacturing is a one of the most promising technology nowadays that offers the advantages not only in building products of complex shapes but also of complex materials. A complex structure ...is characteristic for Functionally Graded Composites, which basics, principles and applicability have been widely investigated over the last years. The present study is focused on the detailed investigation of mechanical and structural properties of FGC consisting of stainless steel 316L and Inconel 718 processed by Blown Powder Directed Energy Deposition system. Mechanical properties within single layers and over layers transitions were investigated with the use of tensile tests and fracture toughness tests. Metallographic and fractographic investigations were carried out. Metallographic investigation revealed the differences in the interfaces between single material layers, nucleation processes and subsequent growth of the grains of the used materials. It has been shown that the formation of transition region between deposited single material layers is dependent on the order of material deposition since different deposition parameters are used for certain material. Evaluation of the tensile properties showed that the mechanical properties of a single material layers are in very good agreement regardless of the deposition height. However, the types of interfaces considering to the results of fractographic observations affect the tensile performance of the Functionally Graded Composite. The fracture toughness test results demonstrate changes in the mechanism of crack propagation at the interface between materials with respect to the type of transition. Furthermore, the material layers interfaces turned out to be the weakest points of the Functionally Graded Composite.
•A great continuation of the Inconel's grains is observed when deposited on 316 L.•316 L grains show rare crystallographic traceability when deposited on the IN718.•Tensile properties are in very good agreement regardless of the deposition height.•Material layers interfaces are the weakest points of the functionally graded material.•The crack propagation mechanism in FGC is dependent on interface type.
The mechanical properties and tensile deformation mechanism of Ti-6.5Al-3.5Mo-1.5Zr-0.25Si alloy (TC11) with different percentages of primary α phase (αp) were studied by conventional and interrupted ...tensile tests, respectively. The results show that the strength of TC11 alloy increases with the increase of the percentage of αp. During tensile deformation, TC11 alloy with different percentages of αp exhibits similar behavior. The deformation mechanism in αp transforms from single slip to multiple slip. While, the microcracks first initiate at the interface of two phases, propagate along it, and then propagate through the transformed β phase (βt) and finally through αp. Finally, a method for predicting the strength of TC11 alloy considering the sizes of αp and βt is proposed.
The present work investigates the influence of hydrogen on the mechanical properties of four multiphase high strength steels by means of tensile tests on notched samples. This was done by performing ...mechanical tests on both hydrogen charged and uncharged specimens at a cross-head displacement speed of 5 mm/min. A considerable hydrogen influence was observed, as the ductility dropped by 8–60%. In order to demonstrate the influence of diffusible hydrogen, some parameters in the experimental set-up were varied. After tensile tests, fractography was performed. It was found that hydrogen charging caused a change from ductile to transgranular cleavage failure near the notch with a transition zone to a fracture surface with ductile features near the centre.
•The effect of hydrogen charging on four high strength steels is evaluated by tensile tests.•TRIP lost 60% of its ductility, DP 54% and FB 37% at a deformation speed of 5 mm/min.•HSLA steel did not suffer from hydrogen embrittlement at a deformation speed of 5 mm/min.•The fracture surface of the H-charged samples showed brittle transgranular cleavage failure.•Decreasing the deformation speed to 0.05 mm/min increased the hydrogen embrittlement.
•Cu/Al-Al2O3 composites were fabricated by a combination of pressureless infiltration casting and cold roll bonding methods.•The addition of whiskers resulted in strength increment and elongation ...reduction in Cu/Al-Al2O3 composites.•A large number of deep and shallow dimples appeared on fractured surfaces.
In this research, the Cu/Al-Al2O3 laminar composites were manufactured by pressureless infiltration casting and roll bonding processes. The effect of alumina content on microstructure, tensile properties and oil painting pigment was studied. The SEM images showed that the whiskers were aligned along rolling direction. By increasing the alumina content, the interfaces between Cu and Al-Al2O3 became wavier. The increase of whiskers improved the yield and ultimate strengths while reduced the elongation. Also, the fracture surfaces of composites indicated smaller dimples in composites with high whiskers’ content. Deeper dimples appeared near whisker cluster due to the debonding between Al and Al2O3. By increasing alumina content, the composites also experienced more oil painting penetration as a result of porosities near whiskers.
The hydrogen effect on a X65 carbon steel was investigated by tensile tests under both ex-situ and in-situ hydrogen charging conditions. The fractured samples were characterized and compared using a ...combination of scanning electron microscopy, electron backscattering diffraction, and energy-dispersive spectroscopy. The work highlights that the in-situ hydrogen charging is a necessity for investigation of hydrogen detrimental effects on the studied material, where a pronounced reduction in fracture elongation, the evolution of secondary cracks on gauge surface, and the corresponding brittle fractography were thoroughly characterized after in-situ testing. The reason resides in the rapid hydrogen outgassing effect, which was proved by Fick's law-based diffusion models. Then the interrupted tensile tests were performed to track the crack initiation and propagation behavior. The results show that the majority of cracks initiated at the interfaces of MnS and Al2O3 inclusions or between inclusions and matrix, which attributes to the elevated stress concentration around the inclusions. Moreover, the cracks were found to propagate along the {110} slip planes.
•Ex-situ and in-situ H charging method was compared on a X65 carbon steel.•In-situ H charging is more suitable for investigation of hydrogen embrittlement.•H-induced cracks initiate at non-metallic inclusions due to stress concentration.•H-induced cracks propagate in transgranular manner along the {110} planes.
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