Papers by Keyword: Damage Mechanics

Abstract: Medium-Mn steel (MMnS) is a promising candidate of the third generation of advanced high strength steels (AHSS), which can provide superior tensile properties. To consider the edge crack issues, the local formability, as an indicator of fracture resistance, of the MMnS needs to be quantitatively evaluated for their potential application to industries. Thus, the local formability of two different MMnS is evaluated by the forming limits at fracture using the damage mechanics approaches and compared with a DP1000 steel in this study. Despite the superior tensile properties, the local formability of the investigated MMnS is worse than the DP1000, which is characterized by the fracture strain under different stress states. Therefore, for the assessment of their potential application in automotive industries, it is recommended that more attention should be paid to the local formability and fracture resistance of these advanced high strength steels.

Abstract: In this study, the Interlaminar shear strength (ILSS) and flexural properties for five different laminate orientations [0°, 45°, [45°/-45°/45°]_s, [±45°/0°/90°]_s and 90°] of unidirectional carbon fiber reinforced plastic (CRP) and glass fiber reinforced plastic (GRP) composites are investigated. The different approach is used by applying the tensile load on notched specimens for measuring the inter-laminar shear strength. The theoretical flexural properties are obtained using the classical laminate theory [CLT]. The good agreement is obtained between the theoretical model and experimental results. The results indicate that the flexural strength and stiffness are higher for 0° laminate whereas flexural strain is higher for [45°/-45°/45°]_s laminates as compared to other laminates. The scanning electron microscopy is used to observe the fracture surface of all laminate orientations of CRP and GRP composites.

Abstract: In this paper, a thermodynamically consistent formulation for the analysis of creep fracture and fatigue is presented. The model is described via two potential functions, the specific Helmholtz free energy and the complementary dissipation potential. Isotropic damage variable is used to describe the degradation of the material. In addition, the use of creep parameters, like Monkman-Grant and Larson-Miller parameters are discussed and their relation to the proposed model are derived. Developed model is implemented as a user subroutine to the commercial finite element code ANSYS and an example case of practical interest is shown.

Abstract: Low velocity impacts induce concurring failure phenomena in unidirectional fiber reinforced composites. Hence a refined methodology able to predict the different failure modes and their interaction is mandatory to correctly predict the damage onset and evolution. Indeed, intra-laminar damage and inter-laminar damage often take place concurrently, causing a significant strength reduction up to composite structure collapse. In this paper, a numerical study is proposed which, by means of non-linear explicit FEM analysis, aims to completely characterize the composite reinforced laminates damage under low velocity impacts by introducing a user defined material model in the FEM code ABAQUS. The proposed 3-D numerical investigation allowed to obtain an exhaustive insight on the different phases of the impact event considering the damage formation and evolution.

Abstract: In this paper, we focus on the numerical simulation of degradation of concrete structures subject to External Sulfate Attack (ESA). A diffusion-reaction model is used to describe the diffusion of sulfates inside the material and the reaction with the reactive constituents of the cement paste (calcium aluminates). The mechanical analysis is based on a new bi-phase chemo-elastic model with chemical and mechanical damage. The results obtained with the proposed approach are compared with experimental data on a reduced scale tunnel lining structure subject to ESA.

Abstract: The non-linear response of solids is an expression of irreversible processes that originate in microdefects, which are understood as initial material damage. This work aims to analyze the degradation of the mechanical properties of medium density polyethylene through continuum damage mechanics using Digital Image Correlation (DIC). With this technique, displacement and strain fields are obtained throughout the specimen gauge length and therefore optical gauges in any region of interest can measure the strain. Mechanical testing with successive loading and unloading were performed in order to obtain the actual magnitude of the material stiffness in certain strains. Finally, through the damage versus strain diagrams, the results showed that the damage in medium density polyethylene increases from a certain deformation.

Abstract: The investigation of fiber-reinforced composite laminates mechanical response under impact loads can be very difficult due to simultaneous failure phenomena. Indeed, as a consequence of low velocity impacts, intra-laminar damage as fiber and matrix cracking and inter-laminar damage, such as delamination, often take place concurrently, leading to significant reductions in terms of strength and stability for composite structure. In this paper a numerical study is proposed which, by means of non-linear explicit FEM analysis, aims to completely characterize the composite reinforced laminates damage under low velocity impacts. The numerical investigation allowed to obtain an exhaustive insight on the different phases of the impact event considering the damage formation and evolution. Five different impact locations with the same impact energy are taken into account to investigate the influence on the onset and growth of damage.

Abstract: Development and application of composite materials in modern industry are very dynamic. Composite materials seem to be replacing steel and aluminium ones. Composites are a cheaper solution, with similar mechanical strengths. Generally, there are two types of joints in composite structures: mechanical and adhesively bonded ones. The aim of the study was to determine the feasibility of riveted joints in composites materials. Static tensile test method was used. In the test there was used one type of glass fabric (Interglas 92140) from which two types of composite samples were prepared. In each sample there was used the same type of fiber with the same fiber orientation – 3 layers. Samples had dimensions of 220x100 mm and thickness of approximately 1.5 mm. They were connected to each other with aluminium rivet nuts (from 1 to 3) and placed in a metal frame with a screw connection which was made of screws with nominal thread pitch M5. Screws were tightened with constant torque. It was to provide an axial force to the sample during the tensile test. The frame was placed between cross-bars of tensile machine INSTRON 8516. The samples were stretched at a speed of 0.05 mm/s at a distance up to 20 mm. During the tensile test displacement of the samples and pull force were registered. Depending on the fiber orientations and number of rivet nuts composite damage models were described. On the basis of the results the possibility of usage of aluminium rivet nuts connections in composite materials was determined.

Abstract: A cohesive zone damage-healing model (CZDHM) derived based on the laws of thermodynamics for self-healing materials is presented. The well-known nominal, healing, and effective configurations of classical continuum damage mechanics are extended to self-healing materials. A new physically-based internal crack healing state variable is proposed for describing the healing evolution within the crack cohesive zone. The effects of temperature, crack-closure, and resting time on the healing behavior are discussed. Numerical examples are conducted to show the various novel features of the formulated CZDHM.

Abstract: In this study, a planar spring lattice model is used to study the evolution of damage variable d_L in disordered media. An elastoplastic softening damage constitutive law is implemented which introduces a cohesive length scale in addition to the disorder-induced one. The cohesive length scale affects the macroscopic response of the lattice with the limiting cases of perfectly brittle and perfectly plastic responses. The cohesive length scale is shown to affect the strength-size scaling such that the strength increases with increasing cohesive length scale for a given size. The formation and interaction of the microcracks is easily captured by the inherent discrete nature of the model and governs the evolution of d_L . The proposed method provides a way to extract a mesoscale dependent damage evolution rule that is linked directly to the microstructural disorder.