Procedia Structural Integrity最新文献

The article describes a new accelerated technique for estimation of cyclic stress-strain curves of cyclically stable materials based on a full-field measurement of strain during low-cycle testing on a large amplitude of loading. Any optical method suitable for capturing the strain contours on the curved part of the specimen during cyclic loading is applicable in the approach developed. In this study, the digital image correlation method is used to measure the deformation on the curved part of the specimen. The technique is presented on chosen results of low-cycle fatigue tests performed on AlSi10Mg printed with selective laser melting technology. Proportional loading cases were performed in tension-compression and pure torsion. The case of non-proportional loading was realized in the form of 90 degree out-of-phase tests. The stress-strain behavior is evaluated using a standard procedure and an accelerated technique with a good correlation for the three loading cases.

One of the most challenging issues for additive manufactured materials is fatigue endurance. Engineering components often operate under complex, variable amplitude loadings, in which existing technological imperfections promote fatigue cracks growth and damage of elements eventually. In this study the effects of different variable-amplitude strain levels on fatigue life, 18Ni300 steel was tested. The work presents various behaviours of the material depending on the load level.

This paper introduces an FFT-based homogenisation approach designed to mitigate the computational demands associated with conventional numerical methods for thin plate structures. The periodic Lippman-Schwinger is proposed equation as an approach to solve the governing equation of both Classical and First-order plate models in cell problems, achieving an explicit solution by Green's function obtained from the Fourier space. The paper provides comprehensive details on the developed method, its algorithmic implementation, and its potential application demonstrated through two case studies focused on complex plate structures. The findings reveal a significant alignment with the results derived from Finite Element Method (FEM), with an added advantage of marked time efficiency observed within the FFT-based approach.

The material development is an expensive process, especially considering composite materials as their microstructure can be very complex. Particle reinforced composites in particular can consist of particles with complicated shapes. Traditionally ellipsoid approximations are used to reduce shape complexity, which comes at the drawback of neglecting the influence of the particles shape onto the composite mechanical properties. The computational method as proposed in this work employs particle swarm optimization in combination with the FE method to create spherical equivalents, which reduces the complexity but also stores the particle shape information. The proposed method can minimize the development cost of new particle reinforced composite materials, while increasing the spectrum of evaluated material features.

One method of treating diabetic foot ulcers (DFU), especially superficial and deep ulcers, is by using a wound scaffold in the form of a hydrogel. Sericin derived from silkworm cocoons is a promising hydrogel material candidate. Sericin protein is a part of silk that is rarely used but has the potential for biocompatibility, biological activities, and is easy to process. One of the drawbacks of sericin hydrogels is their lower mechanical properties. Therefore, sericin was composited with PVA through the freeze-thaw technique to obtain a hydrogel with good stability. Sericin/PVA hydrogel was prepared with variations in solution concentration and the ratio of PVA and sericin. It resulted in the hydrogel with interconnected pore structures. Hydrogel-based wound dressings are often chosen for the treatment of DFU in combination with herbal extract. Moringa oleifera leaves extract was embedded into sericin/PVA hydrogel as a substance to heal DFU. In this study, the morphological and structural properties of sericin/PVA hydrogels were evaluated. The micro-CT imaging analysis was done to confirm hydrogel structure and calculate its porosity percentage. The compression test and hyperelasticity validity test were done to validate the hyperelastic material model.

Many literature contributions deal with the evaluation at FE post-processing stage of the interlaminar normal stress distribution in moderately thick single or doubly curved laminates subject to flexure, based on through-the-thickness equilibrium relations. Most of the contributions, however, discuss test cases in which the principal directions of the load-induced elastic curvatures are aligned with the principal directions of the initial curvature; this condition is not general. In the present work, a simple post-processing methodology for the recovery of the interlaminar tensile stress is presented.

The procedure retrieves the Interlaminar Tensile Stresses (ILTS) distribution in a doubly curved laminate modelled through common wise quadrilateral shell Finite Elements and is based on customary FE sub-model which inputs are the displacements and rotation calculated on the shell structure. At the moment the sub-model can't retrieves Interlaminar Shear Stresses but can be further enhanced to do it.

In this paper the methodology is successfully applied to an open thin walled profile in torsion test case, in which the principal directions of elastic curvature are strongly misaligned with the principal directions of initial curvature.

This work proposes a novel methodology for the automatic multi-objective optimisation of sensor paths in Structural Health Monitoring (SHM) sensor networks using Archived Multi-Objective Simulated Annealing (AMOSA). Using all of the sensor paths within a sensor network may not always be beneficial and could impair damage detection accuracy. Knowing which paths to include, and which to exclude, can require significant prior expert knowledge, which may not always be available, and may not result in optimal path selection. Therefore, this work proposes a novel automatic procedure for optimising sensor paths to maximise coverage level and damage detection accuracy, and minimise overall signal noise. This procedure was tested on a real-world large composite stiffened panel with many frames and stiffeners. Compared to using all of the available sensor paths, the optimized network exhibits superior performance in terms of detection accuracy and overall noise. It was also found to provide 35% higher damage detection accuracy compared to a network designed based on prior expert knowledge. As a result, this novel procedure has the capability to design high-performing SHM sensor path networks for structures with complex geometries, but without the need for prior expert knowledge, making SHM more accessible to the engineering community.

Recently, the electronic personal mobility has been focused for sustainable development goals. The synthetic leather is used as rider suit of personal mobility for comfort. But, the damage of rider suit using synthetic leather will be occurred under outdoor exposure environment. So, this study was examined the effect of outdoor exposure environment on tensile property of synthetic leather (front: polyurethane, back: polyester) for durability of raider suit of personal mobility. The maximum test time of outdoor exposure test was one month (start time: July 2022, test place: Japan (Hino, Tokyo)). The outdoor exposure test was conducted based on Japanese Industrial Standard (JIS) Z 2381. The test surface was front side. Before and after outdoor exposure tests, static tensile tests of synthetic leathers were conducted based on JIS K 6552. Test temperature and humidity were room temperature and 65%RH, respectively. As a result, tensile property of synthetic leather decreased after outdoor exposure test. Generally, the tensile property of polyurethane decrease with an increase of test time. The constituent material on surface of synthetic leather was probably degraded by ultraviolet irradiation. Therefore, tensile property of synthetic leather for personal mobility was mainly affected by ultraviolet irradiation under outdoor exposure environment.

For linear elastic fracture mechanics, the variational technique with a path independent contour integral is used to determine the stress intensity factors (SIFs) for functionally graded materials (FGMs) under static and dynamic loads in this work. Utilizing the interpolation of the Chebyshev polynomials and the finite block method (FBM) to deal with two-dimensional fracture problems. The Quadratic form block is transformed from Cartesian coordinates to normalized coordinates with 8 nodes by technology of mapping. The new equilibrium equations in terms of displacements are derived in a normalized coordinate system. All coefficients of the Chebyshev polynomials are determined by considering the governing equations, boundary conditions and connecting conditions of the two blocks. The accuracy and convergence of the FBM with Chebyshev polynomials are illustrated through several examples and comparison has been implemented with analytical solutions and different numerical approaches.

This work proposed multi-scale modelling to predict the micromechanical properties of semi-crystalline polymers. Semi-crystalline polymers are usually spherulitic crystal structure, which is, however, not completely radially symmetric. In the initial stage of spherulite growth, its structure is manifested as multilayer wafers with a certain orientation namely sheaf structure. The size and orientation of sheaf structure are affected by various processing parameters. Previous research considered spherulite as completely radially symmetric structures, ignoring the effects of structures anisotropy on mechanical properties. In this work, the microstructure of single spherulite was first modelled with different initial orientations. The crystal plasticity constitutive model together with the Arruda-Boyce model was used to describe the micromechanical behaviors of the crystalline lamellae and amorphous lamellae, respectively. Based on the deformation behaviors of single spherulite, the Voronoi tessellation was then used to characterize the multi-spherulites, the evolution of inhomogeneous plastic deformation and inter-lamellae deformation was observed under tension. Achieving the cross-scale analysis from micro-modeling to meso-modeling. The results shown by this work improve the understanding of the micromechanical properties of semi-crystalline polymers, which, in turn, provides theoretical guides to improve their fracture resistance in manufacturing.