Mechanical Properties Of Specimens Research Articles

Microstructure Homogeneity and Mechanical Properties of Large-Size As-Cast High Nb Containing TiAl Alloy Ingot

The high Nb containing TiAl alloy with a nominal composition of Ti–44Al–8Nb–0.2W–0.2B–0.1Y was fabricated by a Vacuum Arc Remelting furnace. The microstructure and mechanical properties of specimens located in different sites of the ingot were investigated. Owing to the influence of melting process and electrode fabricating method, the morphologies and phase containing of this near lamellar structure in the top, middle, and bottom parts of ingot were different. The subtle difference in microstructure strongly influenced the room and high-temperature tensile properties in turn. However, the dominant influence factor of the mechanical properties was the defects at the bottom of this large-size ingot, though the bottom had the finest grain size.

Influence of random pore defects on failure mode and mechanical properties of SiC ceramics under uniaxial compression using discrete element method

To investigate the relationship between micro-defects in ceramic materials and macro mechanical properties and behaviours, a computational model of SiC ceramics with randomly oriented elliptical pores was established using the discrete element method (DEM). The effects of pore defect content and its aspect ratio on the failure mode, stress-strain curve and mechanical properties of specimen were investigated under uniaxial compression. The effective Young's modulus which was obtained from DEM simulations was compared with the predictions of Mori-Tanaka scheme (MTS) and Self-Consistent scheme (SCS) at various pore defect densities. The results showed that the compressive strength and crack initiation stress decrease nonlinearly as the pore defect content increases. Furthermore, the smaller the aspect ratio of the elliptical pore defects was, the more obvious the weakening trend was. As the pore defect content increases, the failure mode of the specimen changed from brittle fracture to tensile-shear mixing and then to axial splitting. The stress-strain curves showed a certain “softening” period during the loading process. The effective Young's modulus obtained from the DEM simulations coincides with the approximations of MTS and SCS at low pore densities. However, when the pore defect density became larger, the DEM simulation results were slightly lower than the theoretical results of the Mori-Tanaka scheme, which only considers the weak interaction between defects.

Hygroscopic ageing of nonstandard size sandwich composites with vinylester-based composite faces and PVC foam core

Abstract This paper aims to assess the hygroscopic behaviour of nonstandard size sandwich composites constituted of thick Electronical-Chemical Resistance (ECR) glass fibre reinforced vinylester composite faces bonded to closed-cell Polyvinyl Chloride (PVC) foam core in the service environment as a reference and basis for materials selection. In order to exhibit the change of sandwich composites properties in realistic environment, the specimens fabricated by Vacuum Infusion Moulding Processing (VIMP) were immersed in two humid conditions: seawater with 30 °C (SWL) and purewater with 80 °C (PWH) for 1680 h. The moisture uptake and various mechanical properties of specimens, including the flatwise tension strength, flatwise compressive strength, in-plane shear strength, shear strength using short beam bending and edgewise compressive strength were tracked periodically. The results from water absorption measurement indicate that the specimens immersed in two humid conditions reach saturation levels after immersion of 1008 h, and non-Fickian and Fickian diffusion occur simultaneously. The characterization on mechanical properties was mainly placed on the variation of PVC foam core and faces-core interface properties, and corresponding results reveal that the moisture absorption has insignificant effects on the PVC foam core properties but appreciably affects the composite faces and face-core interface properties, especially for the specimens immersed in PWH.

Tensile behavior of half grouted sleeve connection at elevated temperatures

Half grouted sleeve connection is widely used in joining rebars in precast concrete structures. However, its mechanical behaviors at elevated temperatures remain to be a topic with little research. This paper presents experimental results of 12 half grouted specimens and 12 single rebars under static tension at different temperatures. The tensile properties of half grouted sleeve connection were found to be directly affected by the temperature, and some characteristics are different from that of the rebar. The results showed that the half grout sleeves exhibited two types of failure, namely rebar fracture and rebar pullout due to bonding failure. The mechanical properties of specimens were similar to that of single rebars. When the temperature elevated, the failure mode and rebar breakpoint location may change. The bonding length that would be sufficient at room or low temperature, becomes insufficient at 600 °C. Suggestions about the bond length are given to avoid rebar pull out from the grout due to bond failure at elevated temperature.

Orthodontic bonding and debonding induces structural changes but does not alter the mechanical properties of enamel

BackgroundThe purpose of the study is to investigate the effect of the bonding procedure on the mechanical properties of human enamel.MethodsA total of 20 extracted human premolars were included in this study, with the half of each tooth acting as its own internal control. Embedded and horizontally cut specimens were prepared, and two bucco-orally zones were separated. The first enamel zone of each tooth remained untreated. The opposing zone was subjected to simulated bonding and debonding, including etching with 37% phosphoric acid, bonding with primer and flowable composite resin, and subsequent removal of the composite with an adhesive removal bur. The properties tested were (a) elemental composition by energy-dispersive X-ray analysis, (b) mechanical properties of specimens by instrumented indentation testing (Martens hardness, elastic modulus, and elastic index), (c) enamel morphology by low-vacuum scanning electron microscopy, and (d) molecular composition by Raman microspectroscopy. Statistical analysis was performed by one-way mixed-effects analysis of variance at a = 0.05.ResultsNo significant differences could be found in the mechanical properties (Martens hardness, elastic modulus, and elastic index) and elemental composition of intact and treated enamel, with the possible exception of Si traces, which were found only in the latter. Raman analysis revealed no differences between the two surface states while shallow grooves and parallel lines were found on the surface of treated enamel by SEM analysis.ConclusionsUnder the limitations of the conditions of the study, there were no mechanical properties’ alterations on enamel subjected to orthodontic bonding.

Development of an optimum mix design method for self-compacting concrete based on experimental results

The main objective of this study is to develop an optimum mix design method for self-compacting concrete (SCC) based on experimental results. For this purpose, mix design of self-compacting concrete is formulated as an optimization problem. Given the importance of manufacturing costs of concrete, the total cost of one cubic meter of self-compacting concrete is considered as the objective function in the optimization problem, which must be minimized. Limitation of the 28-day compressive strength and slump flow of self-compacting concrete are considered as the main inequality constraints. To ensure that sum of concrete components makes unit volume, an equality constraint is considered. To formulate the self-compacting concrete mix design optimization problem based on experimental data, forty-two different mix designs of self-compacting concrete are presented and three cylinder specimens are made and tested for each of them. Two mathematical models are developed to estimate the strength and the slump of the concrete and used to define the main constraints in the mix design optimization model. The concrete specimens are prepared in a construction site in Sanandaj in Iran. Considering importance of sand grading on the compressive strength of self-compacting concrete, stone powder is used to improve sand fineness modulus. The sequential quadratic programming is employed to solve the optimal mix design problem of self-compacting concrete based on proposed model. In order to verify the proposed method, the mix design problem is solved for several case studies and then the final optimal mix designs are made in laboratory and mechanical properties of specimens are evaluated. The results show that the proposed method satisfies the mechanical characteristics of the self-compacting concrete, besides minimizing the cost of the concrete and automating the mix design process.

Evaluation of microstructure and mechanical properties of aluminum AA7022 produced by friction stir extrusion

Friction stir extrusion (FSE) is a process in which a sample is produced through the heat generated by the friction between die and materials, and the extrusion pressure. The extruded sample could be wire, tube, rod or another form. The wired samples were produced of aluminum alloy AA7022 at different rotational speeds and extrusion forces, and impacts of these two parameters were studied. The samples produced at higher rotational speeds and lower forces had a far better surface quality and less surface cracks were seen on them. The optical microscopy and scanning electron microscopy (SEM) were used to examine the microstructural properties of samples and the mechanical properties of specimens were studied by micro hardness and compression tests. Using X-ray diffraction technique and Rietveld method, the average crystallite size and micro-strain and dislocation density of samples were calculated and the yield strength of each sample was estimated by Taylor Equation. The average crystallite size and grain size were increased and the mechanical properties and dislocation density were decreased with the rise of rotational speed. Increasing the extrusion force to a certain level caused increase in yield strength of material. The experimental yield strength of compression test and Taylor’s yield strength were compared with each other and had a good conformity.

Development and application of an environmentally friendly ductile alkali-activated composite

This paper presents a development of a ductile alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) based composite as an environmentally friendly material for structural concrete application. For this purpose, polyvinyl alcohol (PVA) fibres and sand aggregate were combined with alkali-activated paste. Workability, setting time, mechanical properties and failure mode of PVA fibres in the mixture were studied by slump test, Vicat needle test, flexural and compression tests, and Scanning Electron Microscopy (SEM) imaging, respectively. Although the mixture sets in a short period of time (less than 30 min), the workability was good and the developed fibre reinforced composite was used for a large scale application in a canoe. Casting a large volume (45 l compared to 3 l, as initially designed) did not affect the workability and the setting time of the mixture. Mechanical properties of specimens coming from “small” (3 l) and “large” (45 l) batches were tested at different ages (up to 120 days) and compared. It was shown that their flexural and compressive strength are similar, i.e. not affected by the upscaling. Furthermore, it was shown that the mixture with PVA fibres exhibits deflection hardening behaviour even with aggregate particles as large as 4 mm, although single crack localization led to failure. The SEM images of fractured surfaces indicated that combined fibre pull-out and fibre rupture occurred, with the latter one causing the final failure. The developed mixture, additionally reinforced with the plastic fiberglass mesh, was used in the 5.8 m long and 16 mm thick canoe for the student competition, which for the very first time, was constructed without the use of Ordinary Portland cement (OPC). The upscaling was successful and the results show the potential of fibre-reinforced alkali-activated FA and GBFS composite to be used as a durable and resistant material suitable for the structural application in thin shell elements, exemplified by the canoe. Such an application and a low risk project was suitable to gain the necessary experience and confidence with this innovative, “concrete like”, material for which no codes or regulations are available. Furthermore, similar applications are the first step for larger scale structural applications, like structural elements in the building industry, bridges and other civil engineering structures.

Effects of date palm fibres on the mechanical behaviour of stabilised earth blocks: case study on Ksar of Kenadsa, province of Bechar (South-West Algeria)

In the field of construction based on raw clay, there is an active search for less costly stabilising materials, where exploitation of natural resources for construction has become a major concern due to the common problems of degradation of stabilised earth blocks such those used in Ksour constructions. However, despite the technical, economic and ecological advantages reported using the stabilised earth blocks (SEBs), they remain associated with numerous disadvantages due to the lack of research data in this field. This study contributes to a better understanding of the SEBs used in the Kenadsa site, specifically, which are characterised by a mixture of vegetation fibres such as date palm fibres. An analysis is conducted to studying the mechanical properties of specimens prepared from clay collected on the site and mixed to different amounts of fibres and to two different types of stabilisers (cement and/or lime).

The Effect of Carbon Nanotubes on the Mechanical Properties of Wood Plastic Composites by Selective Laser Sintering.

Wood-plastic composites (WPCs) made by selective laser sintering (SLS) approach of 3D printing offer many advantages over single polymer materials, such as low cost, sustainability, and better sintering accuracy. However, WPCs made via SLS are too weak to have widespread applications. In order to increase the mechanical properties of WPCs, a novel type of WPCs containing 0, 0.05, 0.1 and 0.15 wt % carbon nanotubes (CNT), 14 wt % wood fibers, 86 wt % polyether sulfone (PES) was manufactured via SLS. The experimental results showed that the addition of small amount of CNTs can significantly increase the mechanical properties of the wood/PES composite material. The tensile strength, bending strength, and elasticity modulus were 76.3%, 227.9%, and 128.7% higher with 0.1 wt % CNTs than those without CNTs. The mechanical properties of specimens first increased and then decreased with the addition of CNTs. The SEM results of the specimens’ fracture morphology indicate that the preferable bonding interfaces between wood flour grains and PES grains were achieved by adding CNTs to the composites. There are two reasons why the composites possessed superior mechanical properties: CNTs facilitate the laser sintering process of WPCs due to their thermal conductivities, and CNTs directly reinforce WPCs.

Effect of Thin Polymer Coatings on the Mechanical Properties of Steel Plates

The influence of powder coatings based on an epoxide polyester mixture on the mechanical properties of the plates made of rolled sheet steel is studied. The influence of 100-μm-thick coatings on the mechanical properties of specimens 0.7–1.5 mm thick is considered. The bending and tensile tests performed at room and elevated temperatures show that the thin coatings weakly affect the mechanical properties of the plates. In particular, the stiffness of the coated plates during tension and bending remains almost the same despite the fact that the elastic modulus of the coated plates is always slightly lower than Young’s modulus of steel because of an increased specimen thickness determined with allowance for the presence of a coating. The influence of the coatings is substantial in compressive stability tests. Under supercritical deformation conditions, the bearing capacity of the coated plates decreases substantially, and their critical stability load on the loss of stability falls by 20–30% (depending on the substrate thickness). This effect can be explained by the influence of the residual thermal stresses that appear in the specimens during coating deposition.

Influence of Powder Surface Contamination in the Ni-Based Superalloy Alloy718 Fabricated by Selective Laser Melting and Hot Isostatic Pressing

The aim of this study was to gain a deep understanding of the microstructure-mechanical relationship between solid-state sintering and full-melting processes. The IN718 superalloy was fabricated by hot isostatic pressing (HIP) and selective laser melting (SLM). Continuous precipitates were clearly localized along the prior particle boundary (PPB) in the HIP materials, while SLM materials showed a microstructure free of PPB. The mechanical properties of specimens that underwent SLM + solution treatment and aging were comparable to those of conventional wrought specimens both at room temperature and 650 °C. However, a drop was observed in the ductility of HIP material at 650 °C. The brittle particles along the PPB were found to affect the HIP materials’ creep life and ductility during solid-state sintering.

Fracture evolution and failure behaviour of marble specimens containing rectangular cavities under uniaxial loading

To analyse the fracture coalescence behaviour around hole-like flaws in rock, rectangular cuboid marble specimens containing a single rectangular cavity or two rectangular cavities with different layouts were tested under uniaxial compression. Failure characteristics of specimens and strain concentration regime (SCR) evolution on specimen surfaces were measured by means of acoustic emission (AE) and digital image correlation (DIC) techniques respectively. Numerical simulations were further conducted on specimens with the same specimen and cavity dimensions using the discrete element method (DEM), and the inclination angle between centroids of two cavities with respect to the horizontal direction was varied to investigate its influence on failure modes and mechanical properties of specimens. Results showed that both cavity number and layout have a significant influence on mechanical behaviour of marble specimens. The existence of two cavities leads to more degradation of mechanical properties than a single cavity. For specimens with two cavities, the strength first decreases and subsequently increases with increasing inclination angle, and the specimen with two vertically aligned cavities has the maximum strength. Four failure modes were observed in specimens, namely splitting failure, shear failure, mixed tensile/shear failure, and surface spalling. In addition, absorbed energy per unit volume e was introduced to characterise the fragmentation of different groups of specimens. Specimens containing cavities absorbed less energy per unit volume, and thus were less fragmented after failure.

Research on Compatibility of Wheat Straw and Portland Cement

Straw burning has become a serious risk for environment and security. It is very urgent to develop and research materials to utilize straws. The compatibility between straw and portland cement is a problem to be resolved for application of straw fiber in cement-based materials. In the experiment, samples of cement-based composites with untreated straw fiber and pretreated straw fiber were prepared and mechanical properties of specimens were tested. The compatibility between straw fiber and portland cement can be improved through pretreatment process that consists of dipping straw fiber in 4% NaOH solution for 12 hours, then rinsing and drying. In this process, substances in fiber harmful to cement hydration are leached furthest. The negative influences of straw fiber on setting and hardening of cement paste are eliminated. The pretreatment can optimize the mechanical properties of the composite. The strength of composite is not linearly relative to cement-to-water ratio, instead, there exists an optimal water-to-cement ratio, i.e. 0.60. The strength of cement-based straw fiber composite prepared in this ratio reaches maximum.

A novel fixing method for Mg-based specimens used in the in-vitro immersion test

PurposeThe aim of this paper is to predict the in-vivo degradation behaviour of Mg-based implants through in-vitro immersion test.Design/methodology/approachA novel placement mode arming to mimic the in-vivo situation was investigated in this work. Specimens were mounted on bones and then immersed in dynamic Hank’s solution.FindingsThe degradation behaviour of the specimen’s two sides is unequal. The bottom side which clings to the bone was isolated from solution in the early stage. During the late immersion period, there was crevice corrosion appearing on the bottom side. Weight loss and mechanical properties of specimens were also affected by the placement mode.Research limitations/implicationsPlacement mode reported here have guiding significance for degradation behaviour of bio-implants in the clinical study.Social implicationsPlacement mode reported here have guiding significance for degradation behaviour of bio-implants in the clinical study.Originality/valueA novel placement mode arming to mimic the in-vivo situation was investigated in this work, which was better fit the actual in vivo immersion situation.

Investigating of the Microstructure and Mechanical Properties of Al-Based Composite Reinforced with Nano-Trioxide Tungsten via Accumulative Roll Bonding Process

In the present investigation, an Al/WO3p metal matrix nanocomposite was fabricated by accumulative roll bonding (ARB) technique. Microstructural evaluation and mechanical properties of specimens were studied by Field Emission-Scanning Electron Microscopy, X-ray Diffraction, microhardness and tensile test. Several factors that affect uniform distribution of reinforcing particles were investigated. At the initial stages of ARB process particle free zones as well as particle clusters were observed in the microstructure of the composite. After 12 ARB cycles, a nanocomposite with a uniform distribution of nanoparticles was produced. It was shown that the tensile strength of the ARBed composite enhanced with the increasing number of ARB cycles. After the first cycle, a significant increase was observed in the tensile strength of nanocomposite in 2.0 percent volume of WO3p, from 89 MPa to 128 MPa (almost 1.4 times increase in strength). After the final cycle, the tensile strength value increased to 205 MPa (that is almost 2.3 times increase in strength) due to the strain hardening and grain refinement. The X-ray diffraction results showed that Al/WO3p nanocomposite with the average crystallite size of 41 nm was successfully attained after 12 cycles of the ARB process. Finally, observations revealed that the fracture mode in Al/WO3p nanocomposite was of type shearing ductile fracture with elongated shallow dimples.

경화 거동에 따른 다기능 구조 전해질의 전기적 기계적 특성 연구

최근에는 이온 전도도의 감소없이 높은 기계적 물성을 가진 구조 복합재를 개발하기 위하여 에폭시 매트릭스를 기반으로 하여 전해질을 함유한 다기능성 구조 전해질에 대한 연구가 활발히 진행 중이다. 구조 전해질의 최적 함량 및 소재 선정에 대해서는 많이 연구되고 있는 반면, 경화 거동에 따른 특성 분석에 관한 연구는 더디게 진행되고 있기 때문에 본 연구에서는 구조 성능과 에너지 저장 성능을 동시에 가진 고체 전해질을 함유한 에폭시 기반의 구조 전해질을 다양한 경화 시간 및 온도에 따라 제조하고 기계적 특성 및 이온 전도도 특성을 측정하였다. 그리하여 전해질의 열 분해가 일어나지 않는 온도 범위 내에서 에폭시가 충분히 경화할 수 있는 경화 조건을 통해 115 MPa와 <TEX>$6{\times}10^{-5}S/cm$</TEX>의 값을 동시에 가지는 구조 전해질을 얻었다. Recently, many research groups have studied on the epoxy-based multifunctional electrolyte to develop the structural composite bearing high mechanical properties without sacrificing the ionic conductivity at the same time. The studies on the optimal content and material selection for structural electrolyte have been published, while its curing behavior has not much analyzed yet. In this study, epoxy-based structural electrolyte containing solid electrolyte was prepared by varying the curing temperature and time. In addition, the ionic conductivities and mechanical properties of specimens were measured. We also find out the optimal hardening condition where the epoxy domain enables to be hardened within the range of temperature at which the thermal decomposition of electrolyte does not occur. Finally, we propose the multifunctional structural electrolyte showing achievable electrical and mechanical properties (282 MPa and <TEX>$9{\times}10^{-6}S/cm@25^{\circ}C$</TEX>).

Monitoring of seawater immersion degradation in glass fibre reinforced polymer composites using quantum dots

Abstract In this paper, a simple and innovative method is proposed to monitor the effects of seawater ageing in glass fibre reinforced polymer (GFRP) composites using quantum dots (QDs). The cadmium sulfide (CdS) QDs modified with 3-(trimethoxysilyl)-1-propanethiol (MPS) were firstly synthesized, and then the modified CdS QDs were labeled on the glass fibre by chemical bond. GFRP composites with QDs at the interface between the fibre and matrix were obtained. The sigle-fibre-fragment tests of specimens were done to verify the modified CdS QDs did not affect the interfacial bonding of the matrix and fiber. The effects of seawater ageing on the adhesion behaviour between the fibre and the matrix of QD/GFRP hybrids were investigated based on confocal fluorescence microscopy images. After 6 months of immersion in seawater, the glass transition temperature ( T g ), tensile strength, and flexural strength of specimens decreased 2.5%, 13.8%, and 9.8%, respectively. Furthermore, the thermal and mechanical properties of specimens can be calculated by the fluorescence intensity quantificationally.

Performance recovery concerning the permeability of concrete by means of a microcapsule based self-healing system

This paper presents work toward the development of self-healing materials that hold promise for permeability healing of concrete or other cementitious composites. To achieve this innovative system, Urea-formaldehyde/Epoxy microcapsule was designed and synthesized by an in-situ polymerization method, using epoxy resin E-51 as the curing agent and urea-formaldehyde resin as the shell material. The viability of microcapsule and the influence of microcapsules on mechanical properties of specimens were investigated first. The breakage of microcapsules upon cracking and the crack-healing results were verified by SEM/EDS. Self-healing capacity was evaluated by crack-healing effect and chloride permeability. The experimental results shown that the chloride diffusion coefficient decreased from 8.15 to 6.53 ( × 10−12 m2 s−1) after 28-day healing. The healing efficiency of permeability increased to a maximum level of 19.8%. It was also noticed that several factors such as the amount of microcapsules, particle size, healing age, curing temperature and pre-load level have great influences on the self-healing efficiency.

Experimental investigation of size effect on mechanical properties of carbon fiber reinforced polymer (CFRP) confined concrete circular specimens

The mechanical properties of concrete have significant size effect. Size effect of carbon fiber reinforced polymer (CFRP) confined concrete specimens should be investigated further. In this study, the uniaxial compressive tests of CFRP confined concrete cylinders in different sizes (70mm, 100mm, 150mm, 190mm, 310mm) under different confinement (CFRP of one layer, two layers and three layers) were conducted. Four parameters were obtained, including interception strength, uniaxial compressive strength, strain of turning point and peak strain. From the test results, it can be found that the uniaxial compressive strength of unconfined concrete cylinders has apparent size effect which accords with the Weibull size effect law. Under different ratios of CFRP confinement, the CFRP confined concrete cylinders have apparent size effect. The stress-strain model proposed by Lam and Teng fails to interpret how size effect acts on the mechanical properties of specimens. Thus, based on the stress-strain model proposed by Lam and Teng, a modified stress-strain model with the consideration of size effect was established.