Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Code development for the computational analysis of crack propagation in structures
Get PDFIn this study, the main objective was the creation of a code, which gives the capability to a Finite Element Analysis Program with no built-in crack study tools, to study the propagation of a crack, in a cracked surface. For this purpose, the Finite Element Program FEMAP 11.3.2 with solver the NX NASTRAN has been used, and the proposed code was created, using the Application Program Interface (API) of the program. The Linear Elastic Fracture Mechanics (LEFM) theory has been applied to the code, and can predict, if the crack will propagate, the trajectory of the crack, as well as the number of cycle loads required for the propagation of the crack, for given boundary conditions and loads. Finally, the Stress Intensity Factors (SIF) produced by the program, were compared with results from analytical method. Also, experimental results have been used, for the verification of the results of the trajectory of the propagation, and the cycle loads.
 
Modeling of mechanical behavior of cork in compression
Get PDFThe present work consists of a contribution in modeling the mechanical behavior of cork in compression. For this purpose, compression tests are performed in the non-radial direction on high density reproduction cork samples. Cork shows stress-strain curves, typical of cellular materials, characterized by an elastic slope followed by an important plateau corresponding to buckling of cells; and finally hardening due to the densification of the material. Two behavior models are proposed to represent this behavior. A trilinear model in which each slope represents one of the three domains and whose parameters are identified directly from the stress-strain curves. A more nonlinear model corresponding to a third-order polynomial whose parameters are identified by means of a polynomial regression. Test-model comparisons reveal little relevance of the results given by the trilinear model whereas a very good consistency is observed for the results given by the nonlinear model
Thermally active interphase inclusion in a smooth contact conditions with transversely isotropic half-spaces
Get PDFAn exact solution of the stationary thermoelasticity problem about interfacial circular absolutely rigid inclusion, which is in the smooth contact conditions in a piecewise homogeneous transversely homogeneous space, is constructed. The task with the help of the constructed discontinuous solution, by the method of singular integral relations, is reduced to a system of singular integral equations (SIE). An exact solution has been built for the specified SIE, as a result, dependences of translational displacement of the inclusion on temperature, the resultant load, main moment and thermomechanical characteristics of transversely isotropic materials have been obtained
Crack coalescence and strain accommodation in gypsum rock
Get PDFGypsum is a soft rock with low strength and high propensity to plastic deformation. Its mechanical properties are relevant in a wide range of technical application (e.g. tunnel excavation, stability assessment of underground quarries, oil and gas accumulation). The micro-mechanisms involved in the deformation of gypsum rock have for long time interested the scientific world and are still not completely understood. The peculiar crystallographic structure of this bi-hydrate salt, with water molecules layered in the salt structure, favours the development of plastic structures in the rock.
The present work proposes an experimental investigation of strain accommodation mechanisms in gypsum rock, reporting data referred to uniaxial and triaxial stress conditions. The rock strain was studied with a multiscale approach, with the comparison of results from DIC and microstructural analyses
Strain-gradient effect on the crack tip dislocations density
Get PDFIn this study, the influence of a material’s plastic properties on the crack tip fields and dislocation density behavior is analytically and numerically analyzed using the conventional mechanism-based strain-gradient plasticity (CMSGP) theory established using the Taylor model. The material constitutive equation is implemented in a commercial finite element code by a user subroutine, and the crack tip fields are evaluated with novel parameters in the form of the intrinsic material length, characterizing the scale over which gradient effects become significant. As a consequence of the strain-gradient contribution, FE results show a significant increase in the magnitude of the stress fields of CMSGP when the material length parameter is considered. It is found that the density of geometrically necessary dislocations (GND) is large around the crack tip, but it rapidly decreases away from the crack tip. On the contrary, the density of statistically stored dislocations (SSD) is not as large as geometrically necessary dislocations around the crack tip, but it decreases much slower than GND away from the crack tip. A couple effect of material work hardening and the crack tip distance is identified
Longitudinal fracture analysis of inhomogeneous beams with continuously varying sizes of the cross-section along the beam length
Get PDFAnalyses of longitudinal fracture behavior of inhomogeneous beams which have continuously varying sizes of the cross-section along the beam length are carried-out. Beams of a rectangular cross-section are studied. It is assumed that beams exhibit continuous (smooth) material inhomogeneity along the width and height of the cross-section. A longitudinal crack located arbitrary along the beam height is analyzed. First, a cantilever beam with linearly varying width and height along the beam length is considered. The material of the beam has non-linear elastic mechanical behavior. The external loading consists of one bending moment applied at the free end of the lower crack arm. The fracture behavior is analyzed in terms of the strain energy release rate assuming that the modulus of elasticity is distributed continuously in the beam cross-section. The balance of the energy is considered in order to derive the strain energy release rate. A solution to the strain energy release rate is obtained also by considering the complementary strain energy for verification. The longitudinal fracture behavior of the inhomogeneous non-linear elastic cantilever beam configuration is studied also for the cases when the variation of the width and height of the cross-section is described by sine and power laws.  
Comparison of mechanical performance between friction-stir spot welded and adhesive bonded joints
Get PDFThe main objective of this study is to compare the mechanical strength of friction stir spot welded (FSSW) joints and adhesive bonded single lap ones. The present study aims to compare the morphology and strength of welded and adhesive bonded joints. The welded joints were done by friction stir spot welding and the adhesive bonded ones by the use of the adhesive Araldite 420 A/B. The produced joints were subjected to morphology and microstructure analyzes, microhardness tests, tensile-shear tests and local strain analyzes. The welded joints have higher strength than adhesive-bonded joints. However, this difference is insignificant, around 5%, which is covered by the standard deviation. The connection by FSSW proves to be an alternative to adhesive bonded joints, offering the same strength, but with the connection at isolated points, inducing local stress concentration
Thermal Effect on Bond Strength of Rubberized Concrete Filled Steel Tubular Sections
Get PDFThis study aims to assess the effect of high temperature on the bond strength of Concrete Filled Steel Tubular (CFST) sections incorporating crumb rubber particles as partial replacement of fine aggregates in concrete core. High daily temperatures; as in hot countries; was considered as well. Push out tests were conducted on 72 CFST specimens with five different concrete mixes. Prior to these tests, 210 concrete specimens were tested to obtain the mechanical properties of rubberized concrete under high temperature gradients. Some of the tests; on CFST sections or concrete specimens; were tested at the desired high temperature, and some others were tested after cooling down. The main variables considered were the crumb rubber replacement ratio, type of CFST section (circular or square) and temperature gradient. The test results indicated that high temperature reduces the bond strength between steel tube and rubberized concrete core with small percentage of rubber replacement. Recovery in bond strength was observed when the specimens were cooled down. Circular sections showed higher bond strength and ductility on its square counterpart
Glass/epoxy fiber orientation effects on translaminar fracture toughness under Mixed mode(I/II) load using FPB specimen
Get PDFTo study glass/epoxy fiber orientation effects on translaminar fracture toughness under Mixed mode(I/II) load using asymmetric Four Point Bend specimen. Fracture toughness values for different fiber-oriented glass/epoxy laminates under Mixed modes are compared with unidirectional glass/epoxy laminates. Specimens were fabricated using hand layup technique with (0/45)° and (0/90)° fiber oriented glass fiber. The experimental study was conducted for 6 crack positions varying from 0 to 1 with an increment of 0.2 for Four Point Bend specimen. The specimens were tested under universal testing machine to obtain peak loads and further evaluate fracture toughness. The experimental test results show fracture toughness can be increased by orienting the fiber in the laminate. Fracture toughness is highly dominating for (0/90)° fiber-oriented laminates compared to 0° and (0/45)° glass/epoxy laminates
A coupled elastoplastic damage model for brittle rocks: elastoplastic damage model for brittle rocks
No full textBrittle rock contains an important plastic deformation, which causes microcracks when coupled with stress-induced damage. A new coupled elastoplastic damage model is established in order to discuss the damage behaviors found in brittle rock, based on theoretical analysis and experiments. Micromechanic considerations determine the effective elastic properties of anisotropic damaged geomaterials. An energy-based damage criterion is used to deduce the damage initiation and the damage evolution law of the brittle rocks. Moreover, the non-linear unified strength criterion is modified. It takes anisotropic damage and the effects of intermediate principal stress into account, in order to determine both the yield and plastic potential functions. The non-associated plastic flow rule is utilized. The consistency condition of plastic and damage is applied in the coupled process. The damage evolution rule and the coupled plastic damage of brittle rock are conceived within the framework of irreversible thermodynamics. By comparing the simulations and the experimental data from limestone that was subjected to various loading paths, a strong connection between the numerical simulations and experimental data is therefore obtained. The numerical results show that the new model is able to describe the main features of the mechanical properties observed in brittle rock