Papers by Keyword: Mechanical Behaviour

Abstract: The mechanical behaviour of materials is influenced by processing and thermomechanical exposure. In safety-sensitive industries there is a need to make predictions on the envelope of safe use beyond proven constitutive equations. Microstructural simulations, such as crystal plasticity modelling, can model features like grain size, morphology and texture. However, they are computationally demanding and it can be hard to translate measured microstructures into meaningful or representative statistical distributions. Surrogate models incorporate machine learning regression and statistical methods to emulate the response of a complex model. As they are much faster, they can model the response over a wide range of material parameters, permitting sensitivity analysis and uncertainty quantification. Preferred orientation (texture) can be challenging to incorporate into surrogate models as accurate representations can require a lot of parameters. In this study, reduced-order representations of crystallographic texture are presented to represent the bulk response of a polycrystal volume element. These representations are used as inputs to a gaussian process regression (GPR) model that is used to predict the macroscopic stress-strain response of a polycrystal for different crystallographic textures. The GPR acts as a surrogate model of the underlying crystal plasticity model and allows an inherent quantification of the model epistemic uncertainty and the uncertainty related to unobserved effects not captured by the texture parameterization. Incorporation of the surrogate model into finite element coding will be used as an application of the method.

Abstract: The joining of metals and polymer-based materials has a very high interest for many industrial sectors, as it allows to achieve components combining the specific characteristics of each material class. Additive manufacturing technologies could boost the production of these joints, allowing the controlled deposition of a polymeric material over the metal substrate. The present research is aimed to study the feasibility of a joint concept that can be used to produce aluminium/polymer-based material joints through a 3D printing-supported technique. The innovative joint concept, which is based on an interlocking mechanism promoted by a deposited pin, was compared to two conventional concepts. The innovative joint concept allows the production of samples with good mechanical behaviour, in which the failure occurs outside the material overlapping zone. This design is very suitable to be tested for the production of dissimilar material joints.

Abstract: This investigation inspects the concurrent influence of steel fibers with different materials such as Fly Ash(FA), Silica Fume(SF) and aggregates on the mechanical behaviour of geopolymer concrete (GPC) mixes. A range of 8 to 16 molar NaOH molarities variation was observed in the experimental work. Sodium hydroxide molar (NaOH) and sodium silicate solution (NaOH) were utilised as alkaline activators in proportions of 1, 1.5, and 2 (Na₂SiO₃/NaOH). Steel crimped fibers having aspect ratio of 60 were added in the geopolymer concrete. Geopolymer concrete properties considering type of fly ash, the quantity of fly ash, silica fume, the content of fine aggregate and coarse aggregate, effect of sodium hydroxide concentration, content of sodium silicate solution and inclusion of 0.2% of steel fibers in the geopolymer concrete are analyzed.

Abstract: Foamed cellular concrete (FCC) is a type of lightweight concrete. Traditionally, it has been used for insulation and void filling. However, in the last years, the possibility of obtaining high strength FCC has motivated the study of its structural use. The novelty and uniqueness of this article is to provide a review of the most important aspect of FCC including component materials, design and mix elaboration, physical properties and mainly, its mechanical behaviour. Also, in order to achieve a global understanding of the material and its characteristics, advances regarding its physical properties are collected: density, porosity, thermal, acoustic and water insulation, durability, fire resistance and drying shrinkage. Then mechanical properties such as elastic modulus, compressive, tensile, bending and shear behaviour, are analysed. The literature review also aims to evaluate the influence of using inert and active mineral additions, fibers and chemical additives to improve its mechanical and physical properties. Based on the work done, research needs have been identified: there are no prediction models for stress-strain behaviour with complete curves for FCC in compression nor in traction, the performed numerical modelling is scarce, use and effect of chemical additives is a not far studied, long-term tests are scarce or nil, the evaluation of resistance in different aggressive environments has not been sufficiently evaluated.

Abstract: The objective of this research is to evaluate the temperature dependent strengthening mechanism of 0.5 wt.% carbon nanofiber reinforced glass fiber/epoxy (CNF-GE) as a function of environmental temperature. Flexural response of the CNF-GE composite has been studied at 30°C, 70°C and 110°C temperatures and compared over control glass fiber/epoxy (GE) composite. When flexural test was conducted at room temperature, CNF-GE composite exhibited about 29% improvement in strength, over control GE composite. With increase in environmental temperature, the extent of strength enhancement continued to decrease and at 110°C, the strength of the CNF-GE composite was found to be about 12% lower than control GE composite. Visco-elastic properties of CNF-GE and control GE composites have also been studied in the temperature range of 40 to 200°C.

Abstract: The exceptional and distinctive properties of the allotropes of carbonaceous nanomaterials like carbon nanotubes and graphene have attracted many researchers and engineers to enhance the performance of fibrous polymeric composites. This article extrapolates the synergetic impact of carbon nanotube (CNT) and multi-layered graphene (MLG) reinforcement onto the mechanical performance of glass fiber/epoxy composites. Magnetic stirring and ultra-sonication process have been carried out under optimized parameters for incorporation of CNT-MLG into the epoxy polymer. Incorporation of 0.1wt% of carbon nanotube to the glass fiber/epoxy composites enhances a flexural strength of 10% and addition of 0.1 wt. % of multi layered graphene to the glass fiber/ epoxy composites enhances a flexural strength of 6% when differentiated with neat GE. Embodiment of 0.1 wt. % CNT and MLG to the glass fiber/epoxy composites in three different ratios like 1:1, 1:2 and 2:1 showcases a 13%, 12.25% and 14.7% enhancement in the flexural strength respectively with respect to the neat glass fiber/epoxy composites when tested at room temperature. Among them, the ratio 2:1(CNT: MLG) contributes higher strength due to the combined action of high aspect ratio of CNT and higher specific surface area of multi-layered graphene thus, facilitating efficient stress transfer from matrix to the reinforcements. Thermal characterizations have been carried out using differential scanning calorimetry (DSC). The fractography of the samples is examined through the scanning electron microscope.

Abstract: Multiple use of pan concentrate from placer deposits directly in technical process without prealltoment of pure components could become one of promising directions in the field of receiving wide range of multicomponent metal and ceramic powdered materials. In this paper as the object of comparative examination, we present the hemimethylated plating made of exploited experimentative flux cored wires based on industrial Ni-Cr-B-Si system powder modified with rare-earth elements of concentrated complex from Tomtor mineral assets Republic of Sakha (Yakutia). The structure of received plating is heterogeneous and has oxidation coating as boundaries. According to the data of the phase shift analysis plating predominantly consist of Fe-Ni austenitic alloy phases with the Cr, Si carbide and Cr boride precipitation strengthening, plating generally consist of Al2O3, Cr2O3 и Fe2O3 oxide. The research of the plating ultimate composition testifies the equable allocation of main and alloying elements, local location of some elements in the structure of the plating. Microhardness of flux cored wire plating substantially depends on composition and fabricated structure. It has been established that the introduction of rare earth elements provided the formation of strengthening phase with the high hardness of plating resulting in wear resistance increase.

Abstract: Cold-formed steel (CFS) is a popular steel-based material for building such as roof truss system and wall frame panel. CFS with a variety of shapes, cross-sections and thickness produce a lot of advantages such as ease of production, corrosion resistance and high strength to weight ratio. Connection of the CFS sections between them uses screw, bolt and nut, rivet or weld. But, the detail information for the connector in standard either by Eurocode 3 or American Iron and Steel Institute (AISI) is still incomplete especially methods for testing and also lack in the basic knowledge of testing for the connector or combination of connectors. The connector that was used in this study was a self-drilling screw. The objective of the study is to provide the mechanical behaviour information of self-drilling screws from shear and pull-out tests. Both tests utilised Universal Testing Machine with 100 kN capacity to determine the ultimate load and load-deformation behaviour of the self-drilling screws with different numbers. As a result, the ultimate load of the specimen was found to increase with increasing number of the self-drilling screws for shear and pull-out connection tests.

Abstract: Polypropylene (PP), nylon and polyvinyl alcohol (PVA) micro-fibres with different geometries were used at 1 vol. % dosage to investigate rheological and mechanical properties of cementitious composites to be used for thin overlays. Slump-flow and visual stability index methods were used to characterise the rheological properties. Single crack tension and bending studies were carried out to evaluate the tensile and bending strength, as well as the post-cracking behaviour. The results show that fibre geometry (L/d ratio and specific surface area) has a pronounced influence on the fresh state rheological properties of the cementitious composites. The results also surprisingly indicated that the nylon fibres are able to significantly increase the pre-cracking tensile and bending strength. All tested composites showed tensile strain softening and insignificant deflection hardening after cracking and a major strength loss. The results indicate single crack tension method to be the most appropriate for evaluation of mechanical properties of cementitious composites used for thin overlays.

Abstract: The paper addresses the development of advanced welding technologies with two and three solid wires for joining of HSLA API-5l X70 (High-strength low-alloy) steel plates with thickness of 19.1 mm. The experiments were performed using a multi-wire Submerged Arc Welding (SAW) system that was developed for welding of steels with solid, tubular and cold wires, in different combinations. The main goal of the research was to assess the mechanical performances of the welded joints achieved by multi-wire SAW technology and then to compare them with the single wire variant, as reference system. The welded samples were firstly subjected to NDT control by examinations with liquid penetrant, magnetic particle, ultrasonic and gamma radiation, with the aim of detecting the specimens with flaws and afterwards to reconsider and redesign the corresponding Welding Procedure Specifications (WPS). The defect-free welded samples were subjected to tensile, Charpy V-notch impact and bending testing in order to analyse and report the mechanical behaviour of API-5l X70 steel during multi-wire SAW process. The experimental results were processed and comparatively discussed. The challenge of the investigation was to find the appropriate welding technology which responds simultaneously to the criteria of quality and productivity. Further research on metallurgical behaviour of the base material will be developed, in order to conclude the complete image of the SAW process effects and to understand how the multi-wire technologies affect the mechanical and metallurgical characteristics of the API-5L X70 steel used in pipelines fabrication.