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The structural components made of polymer composites in aviation, automobile, and marine applications are subjected to various environmental conditions throughout their design service life. Furthermore, the examination of the effect of various ageing environments on moisture absorption and mechanical behaviour is essential to protect the structures from premature and catastrophic failures. This study evaluates the influence of three different ageing conditions, namely, ambient (25°C), sub-zero (−10°C), and humid (40°C and 60% relative humidity) on the mechanical properties of hybrid interply basalt-aramid/epoxy composites. The compression molding process was adopted to fabricate the specimens and the specimens were aged in a distilled water environment for a period of 180 days. The aged specimens were subjected to static and dynamic mechanical tests viz. tensile, flexural (3-point bending), short-beam shear (SBS), and Charpy impact tests to study the behaviour, and then results were compared with the unaged specimens. Fourier Transform Infrared Spectroscopy (FTIR) was also performed to analyze the chemical changes within the composites due to the ageing process. It was witnessed that moisture absorption rate increases with - increase in ageing period and attains a state of saturation between 1.8% and 5.44% depending on the ageing conditions. Investigations revealed that moisture absorption has an unfavourable effect on the mechanical performance of the composites. The retention of mechanical strengths of aged composites is in the order of Unaged > Sub-zero > Humid > Ambient. Fractured tensile specimens were analyzed for microscopic observation using Scanning Electron Microscope (SEM) to study the damage morphology. Matrix decomposition, matrix cracks, and interfacial debonding were the major failure modes observed in aged composites.

Recovery of useful products from spent rubber materials can potentially turn waste into an immense and continuous source of valuable carbon black (CB). In this study, recovered residue from oil extraction (OER) was used as a CB filler substitute after subjecting the untreated samples to different material characterization techniques. These include SEM imaging, XRD and BET Analysis, as well as thermogravimetry. Using a specific tire formulation with target threshold tensile strength, the OER was then substituted for the standard commercial CB in increasing ratios. The effects of size, structure, purity and morphology of OER on rubber compound processability and mechanical properties were then investigated. Static and dynamic mechanical tests that involve the use of universal testing machine, Mooney Viscometer and Rubber Process Analyzer were performed to determine the most effective filler amount of OER as a commercial CB substitute.

The tensile strengths of individual multiwalled carbon nanotubes (MWCNTs) were measured with a \"nanostressing stage\" located within a scanning electron microscope. The tensile-loading experiment was prepared and observed entirely within the microscope and was recorded on video. The MWCNTs broke in the outermost layer (\"sword-in-sheath\" failure), and the tensile strength of this layer ranged from 11 to 63 gigapascals for the set of 19 MWCNTs that were loaded. Analysis of the stress-strain curves for individual MWCNTs indicated that the Young's modulus E of the outermost layer varied from 270 to 950 gigapascals. Transmission electron microscopic examination of the broken nanotube fragments revealed a variety of structures, such as a nanotube ribbon, a wave pattern, and partial radial collapse.

A three-dimensional variational formulation is used to obtain a plate bending element which includes the thickness change of the plate. The nodal degrees of freedom for the four-node element are the deflection w, the rotations θx and θy, and the thickness change H. Bilinear functions of the in-plane coordinates ξ and η are used for the approximation of the deflection, the rotations and the thickness change. Integration in thickness direction is performed analytically. One key feature of the element is that the three-dimensional constitutive equations for the six stresses have not to be modified. Using eight enhanced strain terms, a well performing plate bending element is obtained.

Abstract A purely flexural structural analysis is carried out for a thin solid circular plate, deflected by a static central transverse concentrated force, and simply supported along an edge arc, the remaining part of its periphery being free. This problem is modelled in terms of a Fredholm integral equation of the first kind, where the kernel is expressed analytically, and where the unknown function is the reaction force along the support. The initial equation is then modified into a new Fredholm integral equation of the first kind, which implicitly respects the condition imposed on the plate edge deflections by the rigidity of the support, but which has still to be coupled with the translational and rotational equilibrium conditions. By showing that a certain operator is a contraction mapping, it is demonstrated that this new integral equation coupled only with the translational equilibrium condition possesses a unique solution expressed in terms of a smooth function with square root singularities at the support ends. It is also shown that this unique solution, when expressed via Chebyshev polynomials, does not fulfil the rotational equilibrium condition, apart from the limit case when the plate is axisymmetrically supported. It is concluded that, in the framework of the purely flexural plate theory, the title problem does not possess any smooth solution with square root singularities at the ends. An approximate solution is nevertheless computed with the collocation method, by accepting limited undulations of the plate periphery.

A non-destructive forced resonance technique was used to assess the damage development in SiC fibre reinforced glass matrix composite materials subjected to cyclic thermal shock. Both elastic modulus and internal friction measurements were conducted. The thermal shock tests involved quenching the specimens from high temperatures (590-710°C) to room temperature in a water bath. Damage in theform of matrix microcracks was induced by quenchingfrom 620 and 660°C, and the extent of damage increased with the number of thermal shock cycles. After a certain number of shocks, this damage was detected by a decrease in the Youngs modulus and a simultaneous increase in the internal friction. The non-destructive dynamic forced mechanical resonance technique employed was shown to be more sensitive than a destructive three point flexural technique for detecting crack development in the early stages of thermal shock damage. The technique was also used to confirm the occurrence of a crack healing process in the thermally shocked specimens: after an annealing heat treatment for 12 h at 550°C, the initial values of Young's modulus and internal friction were recovered. This was attributed to crack closure due to viscous flow of the glass matrix.

This study is aimed at examining and comparing several friction force models dealing with different friction phenomena in the context of multibody system dynamics. For this purpose, a comprehensive review of present literature in this field of investigation is first presented. In this process, the main aspects related to friction are discussed, with particular emphasis on the pure dry sliding friction, stick–slip effect, viscous friction and Stribeck effect. In a simple and general way, the friction force models can be classified into two main groups, namely the static friction approaches and the dynamic friction models. The former group mainly describes the steady-state behavior of friction force, while the latter allows capturing more properties by using extra state variables. In the present study, a total of 21 different friction force models are described and their fundamental physical and computational characteristics are discussed and compared in details. The application of those friction models in multibody system dynamic modeling and simulation is then investigated. Two multibody mechanical systems are utilized as demonstrative application examples with the purpose of illustrating the influence of the various frictional approaches on the dynamic response of the systems. From the results obtained, it can be stated that both the choice of the friction force model and friction parameters involved can significantly affect the simulated/modeled dynamic response of mechanical systems with friction.

The efficiency of four silicon elastomers as damping materials was studied in high rate (2.9 m/s) instrumented impact testing. The measurements were done on injection molded PP specimens. Dynamic effects could be efficiently reduced by all four silicon rubbers. Mechanical damping leads to smooth force versus deflection correlations, which considerably facilitates the determination of valid fracture mechanics characteristics. Damping does not influence the maximum force measured during fracture, KIc is independent of rubber type and thickness. Since the damper consumes considerable energy, GIc is significantly modified by damping, the effect depends both on the viscoelastic properties and the thickness of the damper. The approach proposed earlier for the correction of energy could be applied in all cases where a load versus deflection trace void of oscillations was registered. Similarly to KIc, corrected GIc values proved to be completely independent of the conditions of damping, i.e. the type and thickness of the damper. The parameters of the non-linear constitutive equation which was used to describe the deformation behavior of the damper could not be related to properties determined by simple measurements (hardness, modulus, rebound elasticity, etc.).

Integrity assessments of Magnox nuclear reactors with steel pressure vessels quantify the temperature margins between the operating temperature of the plant, at any given location, and the onset of upper-shelf temperature. The onset of upper-shelf temperature can be estimated from the fracture toughness properties of each material used in the construction of the pressure vessels. Although start-of-life fracture toughness properties of the materials have been measured, such properties are not available for the neutron-irradiated and thermally aged condition. One of the main effects of neutron irradiation and temperature experienced during service is to increase the ductile-to-brittle transition temperature (DBTT), which can be represented in terms of temperature shifts. In the irradiation surveillance schemes for the Magnox reactors, these temperature shifts can be inferred from Charpy impact energy data which have been measured regularly during the service life. Since Charpy impact energy data are inherently scattered, it is necessary to optimize the interpretation of the data by statistical processing. A recent analysis undertaken by Moskovic et al. concluded that Bayesian analyses are best suited to address the problem. In this overview, we consider the requirements of such analyses and the various options available. We then consider the method proposed by Moskovic et al. with respect to the requirements of the inputs to the integrity assessment and the validity of this approach. In this method of analysis, the distribution of all possible values of model coefficients is established by judging the various possible combinations of these model coefficients in relation to the likelihood of the observed data. Analysis of artificially generated data has been used to compare the effectiveness of Bayesian analyses with those used traditionally.