Key Engineering Materials Vols. 577-578

Abstract: The application of infrared thermography to obtain the external surface temperature during the application of cyclic loading, allows to evaluate the dynamic behavior of an element and to determine the fatigue limit. In this contribution, the reliability of the fatigue limit provided by the Risitano et al. and Canteli et al. methodologies is investigated in order to check their validity for practical applications. With this aim, an experimental program on aluminium specimens (AL 2024) under load control using a stress ratio minus one is performed. The fatigue limit for AL 2024 is derived, first from the Wöhler curve and then, compared with both Risitano et al. and Canteli et al. methodologies.

Abstract: The stress intensity factor and the T-stress describing the near-crack-tip fields for selected specimen shapes of a test geometry based on wedge splitting and three point bending tests with several variants of boundary conditions are computed using finite element software ANSYS. The test configuration in question is expected to be a convenient alternative to classical fracture tests (especially the tensile ones) for investigation of the quasi-brittle fracture of building materials, when low constraint is requested. These specimens are investigated within the framework of two-parameter fracture mechanics; near-crack-tip stress field parameters are determined and compared with those of the wedge splitting test due to their shape similarity. The sensitivity of the values of these parameters to the boundary conditions is also shown. Suitable choice of the shape of the specimens is discussed.

Abstract: The role of stress state on the fracture properties of a quasi-brittle material are explored using reactor core Gilsocarbon graphite. The objective of the experiment was to study the initial propagation of cracks. Cruciform specimens have been tested by a biaxial flexural loading method. Pre-slots of 10 mm width and up to a quarter of the depth of the specimen were introduced at the centre of the specimen by electric discharge machining. The slots are located between two through-thickness holes, which are designed to guide crack propagation. A loading jig has been designed and built that allows a range of biaxial loading states to be applied by variation of the length of the loading arms. Clip gauges are used to measure the crack mouth opening displacements. Preliminary tests have studied the fracture of specimens under different loading conditions.

Abstract: Recently, the development need of environmental and fuel efficient aircrafts has been emphasized as an eco-friendly requirement in response to high oil prices. Accordingly, it is necessary to develop the next-generation eco-friendly and high fuel efficiency engine technology to enhance the fuel efficiency and aerodynamic performance of aircrafts for the purpose of reducing carbon dioxide emission amount prior to collecting and dealing with air pollution substances being discharged. In this study, development of the turboprop propeller blade for turboprop engine including aerodynamic and structural design and analysis was performed. The proposed propeller will be used as a candidate propeller for a regional aircraft which has been developed in Korea. Because the propeller for the target aircraft must endure the high bending and twisting moment loads during the flight operation, the high stiffness and strength carbon/epoxy composite material is used as a major structure materials. As a design procedure for the present study, firstly the structural design load is estimated through the aerodynamic load case analysis, and then flanges of spars from major bending loads and the skin from shear loads are initially sized using both the netting rule and the rule of mixture. In order to investigate the structure safety and stability, the structure analysis is carried out by finite element analysis using commercial code, MSC. NASTRAN. In addition, because the propeller should be safe against the bird strike, the bird strike phenomenon is analyzed using a commercial code, ANSYS.

Abstract: Advanced polymeric materials, such as ultra-high molecular weight polyethylene (UHMWPE) are used in lightweight body armour because of their combination of good impact resistance with light weight. However, a broader use of such materials is limited by the complexity and cost of the manufacturing processes and the lack of experimental data on their behaviour and failure evolution under high strain-rate loading conditions. The current study deals with an investigation of the internal heat generation during the tensile testing of UHWMPE and polymer nano-composite blends at various strain rates. A 3D finite element (FE) model of the tensile test is developed and validated with the experimental work. An elastic-plastic material model is used with adiabatic heat generation. The temperature and stresses obtained with the FE analysis are found to be in a good agreement with the experimental results for UHMWPE materials. The model can be used as a simple and cost effective tool to predict the thermo-mechanical behaviour of parts made from these materials under various loading conditions.

Abstract: An accurate 1D model of post-buckling deformation of a thin sub-laminate of layered composite is develloped using nonlinead theory of slender plate. The strain energy realize rate at delamination propagation is obtained via the elliptical integrals. A model of fracture buckled sub-laminate is implemented and used for general analysis of progressive damage of composite

Abstract: The placing of anti-washout underwater concrete for the increasing construction of offshore foundations of long-span bridges at relatively deep sea is accompanied with significant loss of the quality of concrete as well as of the durability and reliability of the structure due to limitations brought by the workability of the high-pressure pump and the performance of the anti-washout agent. Therefore, the improvement of the performance of the underwater anti-washout agent and the development of high fluidity anti-washout underwater concrete exhibiting improved packing ability and fluidity should be implemented. Accordingly, this study focuses on the concrete for foundations applied in the RCD (Reverse Circulation Drill) method. The adequate mix proportions of a high fluidity anti-washout underwater concrete satisfying a design compressive strength of 35 MPa, slump flow larger than 600 mm and with less than 50 mg/ℓ of suspended solids is derived and the corresponding characteristics are evaluated.

Abstract: One of the main issue in a FEM analysis is to determine and minimizing discretization errors. This kind of errors assume a critical importance especially where the solution, in terms of displacement and stress, quickly changes inside the finite element. This issue can be overcame adopting a very refined element discretization in those regions.Hence, for this kind of simulations, it is common practice to use global-local methods rather than adopt a refined discretization over the entire domain. Indeed, global-local methods allow to define very refined elements distributions in some regions of interest, which can be coupled with coarser element distributions in the rest of the domain.A global-local approach based on the superposition technique is presented in this work. This approach allows the coupling of two different meshed domain by superimposing the refined local mesh on the global mesh for the region of interest. The coupling takes place without introducing multi-point constraints or transition regions; the mesh continuity and the well-conditioning of the stiffness matrix are satisfied by appropriate boundary conditions. This approach allows to obtain accurate solutions in the areas of interest while keeping the computational time within satisfactory limits. Several numerical applications are presented which allow to assess the effectiveness of the proposed approach for 3D linear static simulations.

Abstract: The analysis of sphere nonlocal elasticity is carried out by using the improved point collocation method. The approach is based on the Eringen’s model and two and three dimension problems are transformed to one dimension problems considering the polar symmetry. One dimension second order differential equation in terms of radial displacement is derived with domain integral. Due to the excellent accuracy of the point collocation method to one dimension differential equation using the radial basis function interpolation, the numerical solutions can be used as benchmarks. This approach can be easily extended to dynamic nonlocal elasticity and plasticity for sphere.

Abstract: Pipeline working environment is characterised by corrosive conditions, able to develop hydrogen formation. The presence of atomic hydrogen localized in correspondence of crack tip, where the plastic strain reaches the maximum value, is responsible for life reduction. For this reason, it is important to estimate and predict the mechanical properties decay, in terms of toughness and crack propagation, when steel is in contact with hydrogen. Aim of this study is to develop FE models of two carbon, low-alloyed steels used in pipelines applications: X65 and F22. A complex model including three simulations steps is presented. It considers the combined effect of plastic strain and hydrogen concentration on the material toughness. The results of the model are validated by a comparison with experimental tests carried out on the two low-alloyed steel.