Papers by Keyword: Mechanical Testing

Abstract: There is an emerging need to upgrade historic masonry buildings and infrastructures which are most vulnerable to earthquakes. An objective of a long-term research program at Perugia University, Italy was developing design criteria for masonry reinforcement using a new class of materials, using Composite Reinforced Mortars (CRM). These are typically made of fiberglass meshes embedded into a cementitious or lime mortar, which offers higher sustainability features, in terms of vapour permeability and compatibility with masonry, lower costs, and better performance at high temperatures, compared to more traditional steel rebar jacketing or epoxy-bonded composites. These design criteria have been based on a comprehensive experimental and numerical research plan that included a study of the influence of reinforcing material, coating and wall thickness, and associated masonry strength and elastic properties, and the interaction of different stress states on bond behavior at interface masonry-to-coating. A design equation suitable for ultimate load design has been developed. Finally, analytical models regarding the lateral capacity of shear walls are briefly discussed.

Abstract: Oil shales have unstable mechanical and chemical properties, which makes their extraction for characterization and conventional mechanical testing uneasy and complex. Most often, mechanical property measurements are usually taken from core samples that are costly to extract and test using conventional testing methods. This paper presents a focused study carried out on oil shale cuttings obtained from the sidewalls of two different wellbore depths in the Niger Delta area of Nigeria. Using the X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) characterization techniques, the morphology of these shales was studied. The results obtained clearly showed the composition, bonding and variations in the morphology of the studied shale samples. Furthermore, the heterogeneity associated with these shales across varied depths were revealed. An efficient and less expensive technique compared to conventional testing methods, instrumented indentation testing (IIT) was carried out to obtain essential mechanical parameters of the shale specimen. These properties are important parameters in determining the hydrocarbon storage space of shale formations, wellbore stability, and optimization of hydraulic fracturing which is necessary for efficient drilling operations.

Abstract: The aim of this work is a development and characterization of a sustainable product from solid waste from civil construction. Morphology of collected waste has been analyzed by SEM/EDS. Residues have been macerated, mixed in different proportions with cement and water, and made into rectangular boxes. Mechanical test has been carried out by flexing three points on specimens, absorbing water and analyzing fracture by SEM. Morphology of samples have shown a heterogeneous and porous mass, with particles of different sizes, few agglomerates, and presence of organic material. Resistance to average rupture of samples has been obtained in MPa, characteristic of concrete for structural application. For CDR to be used in sustainable ceramics, it is recommended to improve a process of comminution and homogenization to guarantee reproducibility of lots and technological product properties. This being so, a mockup has been developed proposing a hollow element type product, Cobogó style, indicating potential of using civil construction waste as a sustainable product.

Abstract: Natural fiber reinforced polymer composites have become more attractive due to their high specific strength, light weight and environmental concern. However, some limitations such as low modulus and poor moisture resistance were reported. This paper presents the role of halloysite nanotubes (HNTs) on physico-mechanical properties of bidirectional silk and basalt fiber reinforced epoxy (SF-BF/Ep) hybrid composites. Vacuum bagging and ultra-sonication method were used for the fabrication of hybrid composite slabs. The effect of HNT loadings (1.5, 3 and 4.5 wt. %) on physico-mechanical characteristics like density, hardness, flexural and impact properties of SF-BF/Ep composites were determined according to ASTM standards. Experimental results revealed that the incorporation of HNTs improves the mechanical properties. The impact strength of SF-BF/Ep is predominant at 3 wt. % HNT loading where the impact strength surges to 568.67 J/m, which may render HNT filled SF-BF/Ep desirable for various toughness-critical structural applications. The test results demonstrated that SF-BF/Ep-3HNT coded composites exhibited improved mechanical properties among the all composites.

Abstract: This work shows the mechanical design and the FE analyses performed for an innovative naval Antenna Unit for signal interception application: more than twenty electromagnetic sensors operating from HF up to Ka band and microwave modules are integrated in a unique structure designed for a top mast installation (i.e. for naval platform). The number of constraints in terms of weight and electromagnetic transparency calls for the employment of composite materials such as glass, aramidic and carbon epoxy prepregs. Primary structures was modelled by using FE codes: both orthotropic and isotropic models have been implemented as well as non-linear contacts and bolted joints. The mast-mounted installation requires high mechanical stiffness and strength but the exposure to saline environment needs many manufacturing issues to be respected. In particular, the selection process of suitable materials and the sealing manufacturing procedures to protect them from the external agents was reported. Another key feature of the presented design concerns the electromagnetic compatibility requirement: to avoid electromagnetic emissions (EMC) generated by antenna’s internal units and to protect antenna sensors by external platform’s emitters, an appropriate stacking sequence was chosen for composite laminates with a prepreg copper mesh.

Abstract: This research aims at studying the mechanical properties of industrial hemp fibers and promoting their use as a reinforcing composite material for strengthening of civil engineering structures. Natural hemp fibers are of great interest due to the following advantages they have: low cost, high strength-to-weight ratio, low density and non-corrosive properties. The use of plant fiber composite materials has increased significantly in recent years because of the negative reduction impact on the environment. For example, the tendency to use renewable resources and their possibility for recycling. They cause fewer health and environmental problems than synthetic fibers. Natural fibers, in addition to environmental aspects, have advantages such as low densities, i.e. have low weight, interesting mechanical properties comparable to those of synthetic fiber materials, and last but not least, low cost. Composites based on natural plant fibers can be used to reinforce or repair reinforced concrete structures, as shown by research on flax fiber composites. These concretes specimens strengthened with biocomposite materials have very good resistance to bending and significantly increase the rigidity of the structure. The results show that the hemp fiber reinforcement has significant effects on the strengthening and increase in flexural strength from 8% to 35 %.

Abstract: Polybenzimidazole (PBI) nanofiber membranes were prepared using electrospinning potential of 15 kV and 0.2 ml/h flow rate at different PBI concentrations (6.5 and 7.5 w/v%) with the solvent mixture ratio (DMAc:DMF) of 1:1 and 2:1, respectively. This study investigated the properties of the polymeric solution and the effects of solvent ratio and concentration on morphology, hydrophobicity and mechanical properties of PBI nanofiber membranes. The solvent mixture ratio and spinning solution properties are not significantly different than the effect of polymer concentration on the viscosity. The viscosity and surface tension of spinning solutions increases with an increase in the concentration of PBI. It was observed that the average diameter of nanofibers was 75 and 97 nm for 6.5 and 7.5 w/v% PBI spinning solution, respectively. Moreover, the contact angle values range from 111 to 125°. This observation reflects that the nanofiber membranes are hydrophobic. Another finding is that the nanofiber membranes with 7.5 w/v% of PBI showed excellent mechanical properties with the maximum stress value of 4.20 ± 0.29 MPa. The finding also shows that the polymer concentration on the spinning solution influences the structure and morphology of the nanofibers. On the other hand, the solvent mixture ratio does not have any significant impact on the nanofiber membranes properties.

Abstract: Beta titanium alloys have several attractive features; this has resulted in this group of alloys receiving much attention since 1980’s. Among the attributes which distinguish them for their superiority over other structural materials are (i) high strength to which they can be heat treated, resulting in high strength to weight ratio (ii) high degree of hardenability which enables heat treatment in large section sizes to high strength levels (iii) excellent hot and cold workability, making them as competitive sheet materials etc. The standard heat treatment consists of solution treatment in beta or alpha plus beta phase field followed by aging. However, certain aging treatments can render the materials in a state of little or no ductility; the designer has to be aware of this behaviour and has to keep away from such treatments while working with the materials. Such unfavourable aging treatments may adversely affect not only the static properties such as reduction in area and elongation in a tensile test, but also dynamic properties such as impact toughness. Results of fractographic studies are in line with those of mechanical testing. The authors would present the foregoing analysis, based primarily on the wide-ranging researches they carried out on beta titanium alloy Ti15-3 and to some extent data published by researchers on other grades of beta titanium alloys. An attempt is made to explain the mechanisms underlying the embrittlement reactions that take place in beta titanium alloys under non-optimal aging treatments.

Abstract: An Al-3Mg (wt. %) alloy was studied after equal channel angular pressing and subsequent cold rolling. The mechanical behavior of the alloy in the temperature range from 223 K to 373 K (from –50°C to 125°C) at strain rates 2.1×10^–1 – 5.2×10^–5 s^–1 was investigated. The analysis of stress-strain curves was performed to determine the conditions of manifestation of the Portevin – Le Chatelier (PLC) effect in investigated alloy. The deformation curve at a temperature of 298 K (25°C) and a strain rate of 1×10^–3 s^–1 is characterized by instability of plastic flow in contrast to the deformation curves obtained under other studied strain rate/temperature conditions. Stress oscillations at the necking stage were observed at high temperatures (>323 K (50°C)) and lower strain rates (1×10^–4 s^–1 and 5.2×10^–5 s^–1) forming the left border of the PLC effect domain. In general, deformation curves are characterized by the absence of stress serrations during the uniform elongation.

Abstract: Biobased products have been widely used to prevent damage to the environment. In this context, the use of composites reinforced with natural fibers, replacing synthetics ones, has motivated several researches in last years. The objective of the present work was to characterize composites prepared with unsaturated polyester resin and untreated sisal fibers by tensile and flexural tests. The untreated sisal fibers reinforcement was investigated using 25 g and 50 g masses. The fibers were randomly arranged into the resin to mold composite boards, using the compression molding technique without heating, in a curing process at 25°C for 48 hours. The results indicated that composite with 50 g presented better tensile strength (49%), flexural strength (71%) and flexural modulus (137%). The increase of fibers content improved the mechanical behavior of the composite. In addition, the use of natural fibers replacing a portion of petroleum-based resin can increase the sustainable concept of the products and reduce manufacturing costs, because it can be used less resin.