Failure mechanism under tensile loads in CFRP 0-90º cross-ply laminates containing voids

The failure mechanism of a voided CFRP 0-90° cross-ply laminate under tensile loads applied in one direction was studied in this Final Degree Project. For this purpose, voided coupons were manufactured for being tested and a FEA was done. In both investigations, voids were placed in 90º and 0º direction, in order to understand the void location influence. On the one hand, the behaviour of the voided laminates was investigated through a FEM in order to preview the stress distribution within the material. On the other hand, voided specimens where manufactured by applying blowing agent in between the inner layers. These specimens were tested by a quasi-static step wise tensile test where data showing its real behaviour was collected. Specimens were X-rayed after each step of the test in order to investigate the failure mechanism of the composite. Data from the test was studied so that relations such as strength of the laminates, crack density per stress, void length per first crack at the void and void area per first crack at the specimen could be characterized

Monitoring and failure mechanism interpretation of an unstable slope in Southern Switzerland based on terrestrial laser scanner

We present the application of terrestrial laser scanning (TLS) for the monitoring and characterization of an active landslide area in Val Canaria (Ticino, Southern Swiss Alps). At catchment scale, the study area is affected by a large Deep Seated Gravitational Slope Deformation (DSGSD) area presenting, in the lower boundary, several retrogressive landslides active since the 1990s. Due to its frequent landslide events this area was periodically monitored by TLS since 2006. Periodic acquisitions provided new information on 3D displacements at the bottom of slope and the detection of centimetre to decimetre level scale changes (e.g. rockfall and pre-failure deformations). In October 2009, a major slope collapse occured at the bottom of the most unstable area. Based on the comparison between TLS data before and after the collapse, we carried out a detailed failure mechanism analysis and volume calculation.

Failure mechanism of reinforced concrete structural walls with and without confinement

This paper presents the results of cyclic loading tests on two large-scale reinforced concrete structural walls that were conducted at Purdue University. One of the walls had confinement reinforcement meeting ACI-318-11 requirements while the other wall did not have any confinement reinforcement. The walls were tested as part of a larger study aimed at indentifying parameters affecting failure modes observed to limit the drift capacity of structural walls in Chile during the Maule Earthquake of 2010. These failure modes include out-of-plane buckling (of the wall rather tan individual reinforcing bars), compression failure, and bond failure. This paper discusses the effects of confinement on failure mode. Distributions of unit strain and curvature obtained with a dense array of non-contact coordinate-tracking targets are also presented.

Failure mechanism of the all-polyethylene glenoid implant

Fixation failure of glenoid components is the main cause of unsuccessful total shoulder arthroplasties. The characteristics of these failures are still not well understood, hence, attempts at improving the implant fixation are somewhat blind and the failure rate remains high. This lack of understanding is largely due to the fundamental problem that direct observations of failure are impossible as the fixation is inherently embedded within the bone. Twenty custom made implants, reflecting various common fixation designs, and a specimen set-up was prepared to enable direct observation of failure when the specimens were exposed to cyclic superior loads during laboratory experiments. Finite element analyses of the laboratory tests were also carried out to explain the observed failure scenarios. All implants, irrespective of the particular fixation design, failed at the implant-cement interface and failure initiated at the inferior part of the component fixation. Finite element analyses indicated that this failure scenario was caused by a weak and brittle implant-cement interface and tensile stresses in the inferior region possibly worsened by a stress raiser effect at the inferior rim. The results of this study indicate that glenoid failure can be delayed or prevented by improving the implant/cement interface strength. Also any design features that reduce the geometrical stress raiser and the inferior tensile stresses in general should delay implant loosening.

Internal instability as a possible failure mechanism for layered composites

Funding Financial support of part of this research by The Royal Society, The Royal Society of Edinburgh, The Royal Academy of Engineering and The Carnegie Trust for the Universities of Scotland is gratefully acknowledged.

Identification of lift-off mechanism failure for salt drill-in drilling fluid containing polymer filter cake through adsorption/desorption studies

Drilling fluid`s contact with the productive zone of horizontal or complex wells can reduce well productivity by fluid invasion in the borehole wall. Salted drilling drill-in fluid containing polymers has often been applied in horizontal or complex petroleum wells in the poorly consolidated sandstone reservoirs of the Campos basin, Rio de Janeiro, Brazil. This fluid usually consists of natural polymers such as starch and xanthan gum, which are deposited as a filter cake on the wellbore wall during the drilling. Therefore, the identification of a lift-off mechanism failure, which can be detachment or blistering and pinholing, will enable formulation improvements. increasing the chances of success during filter cake removal in open hole operations. Likewise, knowledge of drill-in drilling fluid adsorption/desorption onto sand can help understand the filter cake-rock adhesion mechanism and consequently filter cake lift-off mechanism failures. The present study aimed to identify the lift-off failure mechanism for this type of fluid filter cake studying adsorption/desorption onto SiO(2) using solutions of natural polymers, lubricants, besides the fluid itself. Ellipsometry was employed to measure this process. The adsorption/desorption studies showed that the adsorbed layer of drilling fluid onto the walls of the rock pores is made up of clusters of polymers, linked by hydrogen bonds, which results in a force of lower cohesion compared to the electrostatic interaction between silica and polymers. Consequently, it was found that the most probable filter cake failure mechanism is rupture (blistering and pinholing), which results in the formation of ducts within the filter cake. (C) 2009 Elsevier B.V. All rights reserved.

Failure assessments of corroded pipelines with axial defects using stress-based criteria: Numerical studies and verification analyses

Conventional procedures used to assess the integrity of corroded piping systems with axial defects generally employ simplified failure criteria based upon a plastic collapse failure mechanism incorporating the tensile properties of the pipe material. These methods establish acceptance criteria for defects based on limited experimental data for low strength structural steels which do not necessarily address specific requirements for the high grade steels currently used. For these cases, failure assessments may be overly conservative or provide significant scatter in their predictions, which lead to unnecessary repair or replacement of in-service pipelines. Motivated by these observations, this study examines the applicability of a stress-based criterion based upon plastic instability analysis to predict the failure pressure of corroded pipelines with axial defects. A central focus is to gain additional insight into effects of defect geometry and material properties on the attainment of a local limit load to support the development of stress-based burst strength criteria. The work provides an extensive body of results which lend further support to adopt failure criteria for corroded pipelines based upon ligament instability analyses. A verification study conducted on burst testing of large-diameter pipe specimens with different defect length shows the effectiveness of a stress-based criterion using local ligament instability in burst pressure predictions, even though the adopted burst criterion exhibits a potential dependence on defect geometry and possibly on material`s strain hardening capacity. Overall, the results presented here suggests that use of stress-based criteria based upon plastic instability analysis of the defect ligament is a valid engineering tool for integrity assessments of pipelines with axial corroded defects. (C) 2008 Elsevier Ltd. All rights reserved.

Structural analysis of Turtle mountain (Alberta) using digital elevation model: Toward a progressive failure

In 1903, the eastern slope of Turtle Mountain (Alberta) was affected by a 30 M m3-rockslide named Frank Slide that resulted in more than 70 casualties. Assuming that the main discontinuity sets, including bedding, control part of the slope morphology, the structural features of Turtle Mountain were investigated using a digital elevation model (DEM). Using new landscape analysis techniques, we have identified three main joint and fault sets. These results are in agreement with those sets identified through field observations. Landscape analysis techniques, using a DEM, confirm and refine the most recent geology model of the Frank Slide. The rockslide was initiated along bedding and a fault at the base of the slope and propagated up slope by a regressive process following a surface composed of pre-existing discontinuities. The DEM analysis also permits the identification of important geological structures along the 1903 slide scar. Based on the so called Sloping Local Base Level (SLBL) an estimation was made of the present unstable volumes in the main scar delimited by the cracks, and around the south area of the scar (South Peak). The SLBL is a method permitting a geometric interpretation of the failure surface based on a DEM. Finally we propose a failure mechanism permitting the progressive failure of the rock mass that considers gentle dipping wedges (30°). The prisms or wedges defined by two discontinuity sets permit the creation of a failure surface by progressive failure. Such structures are more commonly observed in recent rockslides. This method is efficient and is recommended as a preliminary analysis prior to field investigation.

Numerical modeling of the failure mechanisms in Si thin film anode for Li-ion batteries

In recent times, the demand for the storage of electrical energy has grown rapidly for both static applications and the portable electronics enforcing the substantial improvement in battery systems, and Li-ion batteries have been proven to have maximum energy storage density in all rechargeable batteries. However, major breakthroughs are required to consummate the requirement of higher energy density with lower cost to penetrate new markets. Graphite anode having limited capacity has become a bottle neck in the process of developing next generation batteries and can be replaced by higher capacity metals such as Silicon. In the present study we are focusing on the mechanical behavior of the Si-thin film anode under various operating conditions. A numerical model is developed to simulate the intercalation induced stress and the failure mechanism of the complex anode structure. Effect of the various physical phenomena such as diffusion induced stress, plasticity and the crack propagation are investigated to predict better performance parameters for improved design.

Serrated yielding and the localized shear failure mode in aluminium alloys

A study has been made of serrated yielding in two commercial Al-Zn-Mg alloys in the as-quenched condition. The different serration types produced in the two alloys and the shear failure mechanism observed in both notched-bend and tensile testing are related to the mechanisms of dynamic strain ageing occurring during the test. An estimate of 19.7 kJ/mole for the activation energy for exchange of a solute atom and a vacancy in Al-6.2 wt% Zn, 2.5 wt% Mg has been made. © 1981.

Failure Mechanisms and Local Scour at Coastal Structures induced by Tsunamis

On March 11 2011, an exceptionally large tsunami event was triggered by a massive earthquake offshore, the northeast coast of Japan, which affected coastal infrastructure such as seawalls, coastal dikes and breakwaters in the Tohoku region. Such infrastructure was built to protect against the Level 1 tsunamis that previously hit the region, but not for events as significant as the 2011 Tohoku tsunami, which was categorized as a Level 2 tsunami [Shibayama et al. 2013]. The failure mechanisms of concrete-armoured dikes, breakwaters and seawalls due to Level 2 tsunamis are still not fully understood by researchers and engineers. This paper investigates the failure modes and mechanisms of damaged coastal structures in Miyagi and Fukushima Prefectures, following the authors' post-disaster field surveys carried out between 2011 and 2013. Six significant failure mechanisms were identified for the coastal dikes and seawalls affected by this tsunami: 1) Leeward toe scour failure, 2) Crown armour failure, 3) Leeward slope armour failure, 4) Seaward toe and armour failure, 5) Overturning failure, and 6) Parapet wall failure, in which leeward toe scour being recognized as the major failure mechanism in most surveyed locations. The authors also propose a simple practical mathematical model for predicting the scour depth at the leeward toe of the coastal dikes, by considering the effects of the tsunami hydrodynamics, the soil properties and the type of structure. The key advantage of this model is that it depends entirely on quantities that are measurable in the field. Furthermore this model was further refined by conducting a series of hydraulic model experiments aimed to understand the governing factors of the leeward toe scour failure. Finally, based on the results obtained, key recommendations are given for the design of resilient coastal defence structures that can survive a level 2 tsunami event.

Effect of hole drilling at the overlap on the strength of single-lap joints

Bonded unions are gaining importance in many fields of manufacturing owing to a significant number of advantages to the traditional fastening, riveting, bolting and welding techniques. Between the available bonding configurations, the single-lap joint is the most commonly used and studied by the scientific community due to its simplicity, although it endures significant bending due to the non-collinear load path, which negatively affects its load bearing capabilities. The use of material or geometric changes in single-lap joints is widely documented in the literature to reduce this handicap, acting by reduction of peel and shear peak stresses at the damage initiation sites in structures or alterations of the failure mechanism emerging from local modifications. In this work, the effect of hole drilling at the overlap on the strength of single-lap joints was analyzed experimentally with two main purposes: (1) to check whether or not the anchorage effect of the adhesive within the holes is more preponderant than the stress concentrations near the holes, arising from the sharp edges, and modification of the joints straining behaviour (strength improvement or reduction, respectively) and (2) picturing a real scenario on which the components to be bonded are modified by some external factor (e.g. retrofitting of decaying/old-fashioned fastened unions). Tests were made with two adhesives (a brittle and a ductile one) varying the adherend thickness and the number, layout and diameter of the holes. Experimental testing showed that the joints strength never increases from the un-modified condition, showing a varying degree of weakening, depending on the selected adhesive and hole drilling configuration.

Numerical and Experimental Analysis of Balanced and Unbalanced Adhesive Single-Lap Joints between Aluminium Adherends

The single-lap joint is the most commonly used, although it endures significant bending due to the non-collinear load path, which negatively affects its load bearing capabilities. The use of material or geometric changes is widely documented in the literature to reduce this handicap, acting by reduction of peel and shear peak stresses or alterations of the failure mechanism emerging from local modifications. In this work, the effect of using different thickness adherends on the tensile strength of single-lap joints, bonded with a ductile and brittle adhesive, was numerically and experimentally evaluated. The joints were tested under tension for different combinations of adherend thickness. The effect of the adherends thickness mismatch on the stress distributions was also investigated by Finite Elements (FE), which explained the experimental results and the strength prediction of the joints. The numerical study was made by FE and Cohesive Zone Modelling (CZM), which allowed characterizing the entire fracture process. For this purpose, a FE analysis was performed in ABAQUS® considering geometric non-linearities. In the end, a detailed comparative evaluation of unbalanced joints, commonly used in engineering applications, is presented to give an understanding on how modifications in the bonded structures thickness can influence the joint performance.

Análisis mecánico de albañilería arqueológica de adobe bajo cargas de compresión uniaxial: El caso de Huaca de la Luna

This article presents an experimental and numerical study for the mechanical characterization under uniaxial compressive loading of the adobe masonry of one of the most emblematic archaeological complex in Peru, 'Huaca de la Luna' (100-650AD). Compression tests of prisms were carried out with original material brought to the laboratory. For measuring local deformations in the tests, displacement transducers were used which were complemented by a digital image correlation system which allowed a better understanding of the failure mechanism. The tests were then numerically simulated by modelling the masonry as a continuum media. Several approaches were considered concerning the geometrical modelling, namely 2D and 3D simplified models, and 3D refined models based on a photogrammetric reconstruction. The results showed a good approximation between the numerical prediction and the experimental response in all cases. However, the 3D models with irregular geometries seem to reproduce better the cracking pattern observed in the tests.

Numerical Assessment of the out-of-plane response of a brick masonry structure without box behaviour

This paper presents the assessment of the out-of-plane response due to seismic loading of a masonry structure without rigid diaphragm. This structure corresponds to real scale brick masonry specimen with a main façade connected to two return walls. Two modelling approaches were defined for this evaluation. The first one consisted on macro modelling, whereas the second one on simplified micro modelling. As a first step of this study, static nonlinear analyses were conducted to the macro model aiming at evaluating the out-of-plane response and failure mechanism of the masonry structure. A sensibility analyses was performed in order to assess the mesh size and material model dependency. In addition, the macro models were subjected to dynamic nonlinear analyses with time integration in order to assess the collapse mechanism. Finally, these analyses were also applied to a simplified micro model of the masonry structure. Furthermore, these results were compared to experimental response from shaking table tests. It was observed that these numerical techniques simulate correctly the in-plane behaviour of masonry structures. However, the