Key Engineering Materials Vols. 577-578

Abstract: This paper aims at revealing the relationship between fractographic parameters of the mortar-mortar interface and the mechanical properties of such interface in terms of flexural strength and fracture energy. The FEM simulation was conducted where 8 cases of the combination of material properties were applied for all 7 interface models. The fractographic parameters evaluated on each interface model were six. Among them, both Sd (standard deviation of the height) and RL (ratio of the real length of the crack path to the projected length) are closely related to the mechanical properties.

Abstract: In the range of linear elastic fracture mechanics, the critical loading assessment of structures made of two dissimilar materials is usually based on the assumptions of the prevailing normal mode of loading. However, in engineering practice there are cases of loading and failure close to the shear mode of loading. The aim of the work is to study the stress distribution in the vicinity of a bi-material notch subjected to a combination of normal and shear modes of loading. Then the stability criteria use knowledge of common fracture mechanics properties for normal I and shear II modes of loading. The assessment of crack initiation conditions is shown on a specimen with two different bi-material notches under loading of a varying direction.

Abstract: This research focus on the characterization of banana and abaca reinforced composites obtained by rotational molding process. These composites were fully characterized by means of DSC and mechanical tests (tensile, flexural, impact and DMA), as well as by optical microscopy. Tests presented in this paper aim to the observation of failures occurred in composites, in comparison with those observed in pure polyethylene. This equipment consists in a microtensile tester, equipped with an optical microscope, a camera and specific software for images capture. Tests have been carried out with test samples obtained from rotomoulded parts, at a rate of 1000 μm/min. Differences between both types of fiber have been observed, showing different compatibility of these fibers with the polymeric matrix; treated fiber also shows different failure process. Banana and treated abaca fibers break in the PE matrix, while pull-out effect was observed for abaca fiber.

Abstract: Research activities on gigacycle fatigue properties of materials have recently focused on the influence of specimen size used for ultrasonic fatigue tests. In order to increase the volume of material subjected to the maximum stress (risk volume) a new specimen shape with a Gaussian profile is proposed. An approximation of the Gaussian profile with an arc of circle is presented in the paper, in order to simplify the Gaussian specimen manufacturing process. The effect of the approximation is evaluated analytically and through a finite element analysis.

Abstract: In this paper, the crack propagation behavior of naturally initiated small crack in in low-carbon/medium-nitrogen 316 stainless steel under thermo-mechanical fatigue loading was investigated. The experimental results indicated that the importance of the investigation of small crack propagation behavior because the information on the basis of physically long crack growth rate provides a dangerous evaluation on reliability to actual components. The small crack exhibits high growth rate under the In-phase TMF loading because of irreversible creep and plastic strains. However, the growth rates of small crack under the Out-of-phase TMF loading were lower because the effect of creep deformation became negligible in such condition.

Abstract: Gas hydrates are known to form plugs in pipelines. Gas hydrates are crystalline compounds that form when hydrocarbons such as methane come in contact with water under thermodynamical opportune conditions, as high pressure and low temperature. Hydrates, like any obstruction in a pipeline, reduce flow, increase back pressure in the system and increase the differential pressure across the obstruction. When the line section is obstructed by a plug, the differential pressure can put the hydrate in movement and quickly accelerate it up to a speed approaching that of sound; in this case, the moving mass can cause serious mechanical damages at downstream locations where the plug can also meet restrictions or obstacles such as valves, elbows or tees. In this paper a real case of a gas pipeline failure, due to the presence of a moving mass of methane hydrate, has been investigated by considering an analytical and numerical modeling of the motion of the hydrates, as well as of their impact against the pipes.

Abstract: In this work, a parametric numerical investigation on the plastic zone size and shape at the crack front of a through crack in a plate is presented. The thickness of the plate, the size of the crack and the applied remote load values are considered as parameters. The obtained results allow assessing the limits of the linear elastic fracture mechanics in presence of an extensive material yielding at the crack front and the relationship between the plastic zone size and other parameters of the elastic-plastic fracture mechanics theory is highlighted.

Abstract: Numerical model for fatigue crack propagation within the framework of finite element smeared crack analysis is presented. It concentrates on modeling of fatigue behavior of material under tensile load which causes initiation and growth of cracks in concrete. The fatigue material model is an extension of existing static three-dimensional fracture-plastic material model, and as such it has been implemented into the ATENA Finite Element software package. The developed model has been used to model experiments with high-cycle loading of three point bending concrete specimens tested by collaborating institutions. Analysis results are compared to the measurements.

Abstract: Composite corners are generally tested under four point-bending to identify Inter-Laminar Tensile Strength design values. Hereafter several lay-ups have been defined in order to characterize very different damage evolution processes. Damage monitoring has been performed with the help of Digital Image Correlation, Acoustic Emission and Fast Video Recorder. The different processes leading to final failures have been identified. A deterministic continuous composite material model is used to investigate these phenomena. Initiation and evolution up to saturation and fracture are implemented for various damage mechanisms and for delamination. A first comparison between experiments and numerical simulations is presented.

Abstract: Three-dimensional (3D) elastic stress distributions in the vicinity of overlap corners of single-lap joints are investigated. A detailed 3D finite element (FE) model is carried out to study the intensity of the in-plane and out-of-plane stress distributions along the plate width direction. The effects of adhesive thickness and Poisson's ratio are also studied. The FE results show the presence of coupled modes at the overlap corners of the joint. In particular, sharp increment of out-of-plane fracture mode very near the lateral free surface of the joint is worth noting.