117,352 research outputs found
The influence of cracks on chloride penetration in concrete structures - Part I: Experimental evaluation
Get PDFDetermination of the Singularity Order at the Interface between Two Dissimilar Materials in a Simple Lap Joint
No full textInfluence of cracks on chloride penetration in mortar specimens subjected to cyclic treatment
No full textChloride-induced steel corrosion is worldwide one of the major causes of deterioration of reinforced concrete structures, producing loss of structural strength and stability. One of the most aggressive exposure conditions for concrete is marine environment together with the drying and wetting conditions by tidal and splash action. In such an aggressive environment the presence of cracks has a great influence on chloride ingress. In this paper both the experimental and the numerical results of the influence of artificial cracks on chloride penetration in mortar specimens are presented. The experimental results were obtained using chloride penetration tests on mortar specimens of different sizes, with and without artificial cracks, subjected to a cyclic treatment. Numerical results were obtained using transient finite element analysis by simulating chloride mass diffusion with COSMOS/FFE realized with the hear transfer modulus T, which was replaced by the total concentration C, and the thermal conductivity KX, replaced by diffusion coefficient D. Comparisons between the results on chloride penetration concluded that the numerical ones obtained using the mass transfer modulus agree fairly well with the experimental ones. In addition the influence of crack length on chloride ingress was presented
The influence of cracks on chloride penetration in concrete structures. Part II: Numerical simulation
Get PDFStatic and fatigue behavior of 3D printed smooth and notched PLA and short carbon fibers reinforced PLA
No full textAdditive manufacturing (AM) offers various advantages, such as geometrical design freedom and highly tailored components. Among the AM technologies, fused deposition modeling (FDM) is one of the most commonly used methods for polymers. In this work, we analyze the fracture behavior of both smooth and notched specimens made from two different materials: polylactic acid (PLA) and short carbon fiber (CF) reinforced PLA. The experimental research revealed poorer static and fatigue properties for the PLA-CF specimens, regardless of the geometry. These poorer mechanical properties could be attributed to several factors, including higher porosity and poorer adhesion between filament layers. To assess the static and fatigue behavior influenced by the component geometry, the averaged strain energy density (SED) method was considered. After determining the characteristic length, R0, for both static and fatigue conditions, the data has been summarized in terms of averaged SED values. This method predicts the critical loads for different geometries and materials considered with an average error of ± 7 %. Additionally, a SED-based fatigue curve, independent of the geometry, has been determined for both materials
Size-effect independence of particleboard fracture toughness
No full textThe present paper aims to prove the size-effect independence of particleboard (PB) fracture toughness when the Modified Two-Parameter Model (MTPM), recently proposed by some of the present authors, is used to measure such a parameter. Firstly, three-point bending (TPB) tests on single-edge notched specimens characterised by three different values of thickness are performed for a commercial particleboard. By exploiting such experimental data, the value of the fracture toughness is analytically determined through the MTPM. Then, a fracture toughness index is defined by taking into account the dependence of fracture toughness on the material density. Finally, the mean value of such an index is compared with that obtained from the results (available in the literature) related to a previous experimental campaign performed on the same commercial PB
The application of the Theory of Critical Distances to non-homogeneous materials
Get PDFThe Theory of Critical Distances (TCD) has undoubtedly represented a breakthrough in the brittle failure assessment of engineering materials containing defects, crack, or notches. The basic idea on which the simplest formulation of the TCD is based is to evaluate an effective stress at a characteristic distance from the tip of the defect/crack/notch and compare it with an inherent fracture strength. Is the critical distance related to the material (micro) structure? Whereas a correlation was already proved for homogeneous materials, the current attention to nonhomogeneous ones has brought the question back to the fore. The goal of the present work is therefore twofold: (i) to extend the use of the TCD, through the simple yet effective Point Method (PM), for the static failure assessment of inhomogeneous materials, such as cellular, biological, and additively manufactured (AM) materials; and (ii) to look for a correlation between critical distance and internal (micro) structure
Finite Fracture Mechanics and Cohesive Crack Model: Size effects through a unified formulation
Get PDFFinite Fracture Mechanics and Cohesive Crack Model can effectively predict the strength of plain, cracked or notched structural components, overcoming the classical drawbacks of Linear Elastic Fracture Mechanics. Aim of the present work is to investigate size effects by expressing each model as a unified system of two equations, describing a stress requirement and the energy balance, respectively. Brittle crack onset in two different structural configurations is considered: (i) a circular hole in a tensile slab; (ii) an un-notched beam under pure bending. The study is performed through a semi-analytical parametric approach. Finally, theoretical strength predictions are validated with experimental results available in the literature for both geometries, and with estimations by the point criterion in the framework of Theory of Critical Distances
Fracture toughness of a rigid polyurethane foam: experimental and numerical investigation by varying the specimen sizes
Get PDFIn the present paper, the fracture toughness of a polyurethane (PUR) foam (manufactured by Necumer GmbH, Germany, under the commercial designation Necuron 651) is experimentally and numerically investigated in order to examine its dependence on the specimen sizes. As a matter fact, to the best knowledge of the present authors, such an analysis is still missing in the technical literature. To perform the experimental campaign, notched PUR foam beams, with different geometrical sizes, are tested under three-point bending loading, and the Modified Two-Parameter Model (recently proposed by some of the present authors) is employed to measure the fracture toughness. Subsequently, such an experimental campaign is numerically simulated by applying a micromechanical model, implemented in a non-linear finite element homemade code. Finally, the results obtained are compared with some experimental data available in the literature, related to the same PUR foam
Static and fatigue behavior of 3D printed PLA and PLA reinforced with short carbon fibers
No full textFabrication based on additive manufacturing (AM) process from a threedimensional (3D) model has received significant attention in the last few years. The present paper presents the mechanical characterization of 3D printed specimens based on fused deposition modelling (FDM), which is one of the most commonly used AM methods. Tensile and fatigue tests were performed to characterize the quasi-static mechanical response and to evaluate the fatigue performance of FDM thermoplastic materials, respectively. The materials used to manufacture the specimens were polylactic acid (PLA) and PLA reinforced with short carbon fibers (CF). Good correlations were obtained between fatigue resistance and tensile strength for each type of material. It was also observed that the samples reinforced with CF present both lower tensile and fatigue properties. The poorer properties of PLA-CF specimens could be attributed to several reasons such as higher porosity and poorer adhesion between filament layers compared to the PLA counterparts
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