Prediction Of Failure Modes Research Articles

Numerical and Experimental Analysis of Flexural Properties of Bamboo Tali Laminate Composite

This research was done to evaluate flexural properties (flexural strength, flexural modulus, and failure mode) of Bambu Tali (Gigantochloa Apus) composite. Lycal 1101 was used as matrix. Two types of laminate were tested in four point bending, unidirectional (00/00) s and symmetric cross ply (00/900) s. Results were then compared with numerical simulation using MSC PATRAN-NASTRAN to determine flexural strength and failure mode prediction for both specimens. All specimens were manufactured using cold press manufacturing method. Results show there was around 28% reduction in flexural strength from unidirectional specimen to symmetric cross ply. Numerical simulation results on failure mode prediction show good agreements with actual four point bending test.

Investigation on failure modes for pin joints made from unidirectional glass–epoxy nanoclay laminates

AbstractIn the present work the effect of the nanoclay on the bearing strength and failure mode of the pin joints was investigated both experimentally and numerically. Geometric parameters, i.e. the distance from the free edge of specimen to the diameter of the first hole (E/D) ratio and width of the specimen to the diameter of the holes (W/D) ratio were investigated. The E/D and W/D ratios were varied from 1 to 5. Tsai–Wu failure criterion with characteristic curve method and progressive damage analysis was used for the prediction of failure modes. Results showed that bearing strength and failure mode were considerable affected by the wt% of nanoclay and the geometric parameters. A good agreement was obtained between experimental and numerical predictions.

Mechanical design and analysis of direct-plated-copper aluminum nitride substrates for enhancing thermal reliability

Direct-plated-copper (DPC) aluminum nitride (AlN) substrate with a high thermal conductivity can provide a good alternative to conventional aluminum oxide (Al2O3) substrate for better heat dissipation in the high-power module applications. However, the DPC AlN substrate suffers AlN crack initiating at the edge corner of Cu film during thermal cycling, due to the higher thermal expansion coefficient mismatch with copper material. This study is to resolve the AlN crack problem of DPC AlN substrate during thermal cycling and further to provide important parameters for mechanical design for ensuring good thermal reliability. Prior to the analysis, the out-of-plane deformation measurement of a Cu-AlN bi-material plate subject to the solder reflow heating and cooling is conducted for evaluating the material property of the plated Cu film and residual stresses induced from the manufacturing and solder reflow process. The results show the hysteresis and Bauschinger-like behaviors for the Cu-AlN plate during the solder-reflow heating and cooling. It is also found from the validated finite element simulation that the Cu-film wedge angle, length, and thickness significantly affect the maximum 1st principal stress of AlN during thermal cyclic loading, and the predicted failure mode and location based on the maximum 1st principal stress is consistent with experimental observation. The other factors, such as single-side and double-side Cu-film (sandwich-structure-alike) substrates, length difference of Cu films, and the nonlinear property of Cu film will be presented and discussed in detail as well.

Tensile Behaviour of Galvanised Grade 8.8 Bolt Assemblies in Fire

In structural fire engineering, the importance of bolt assemblies is often overlooked. Connection design uses the temperature-dependent bolt strength-reduction factors prescribed in Eurocode 3, despite the existence of two distinct failure modes under tension; necking of the bolt shank, and thread-stripping. While literature exists to predict failure modes at ambient temperature, there is no method for failure mode prediction for elevated temperatures where ductility is critical to avoid collapse. Galvanised M20 structural bolt assemblies and bolt material from a single batch have been tested under tension at a range of temperatures and strain-rates typical of those experienced in fire. Turned-down bolt test data produced stress-strain curves characteristic of different microstructures at ambient temperature, despite a tempered-martensitic microstructure being specified in the standards. The failure modes of bolt assemblies were found to be dependent on the as-received microstructure at ambient temperature. At elevated temperatures, however, only thread-stripping was observed.

Failure criterion for graphene in biaxial loading—a molecular dynamics study

Molecular dynamics simulations are carried out in order to develop a failure criterion for infinite/bulk graphene in biaxial tension. Stresses along the principal edge configurations of graphene (i.e. armchair and zigzag directions) are normalized to the corresponding uniaxial ultimate strength values. The combinations of normalized stresses resulting in the failure of graphene are used to define failure envelopes (limiting stress ratio surfaces). Results indicate that a bilinear failure envelope can be used to represent the tensile strength of graphene in biaxial loading at different temperatures with reasonable accuracy. A circular failure envelope is also introduced for practical applications. Both failure envelopes define temperature-independent upper limits for the feasible combinations of normalized stresses for a graphene sheet in biaxial loading. Predicted failure modes of graphene under biaxial loading are also shown and discussed.

A three dimensional implicit finite element damage model and its application to single-lap multi-bolt composite joints with variable clearance

A three-dimensional, implicit, finite element composites damage model is developed, and applied to a problem involving highly complex, three-dimensional loading, i.e. a single-lap, multi-bolt, composite joint, having variable clearances. The model extends a previous model, adding Puck’s criteria to allow delamination-like, transverse cracking-like or mixed mode failures to be simulated. Plasticity is also added for non-reversible strains in the undamaged parts of the matrix, and a mesh independence strategy is incorporated. A back-up strategy for when the Newton–Raphson method fails to converge, adds significantly to model robustness. The model is implemented in a commercial, implicit solver and demonstrates excellent robustness, being capable of following damage progression from onset, through bearing failure at the holes, to catastrophic, net-tension failure. The predicted failure modes and loads are in good agreement with experiment. The effect of clearance on secondary bending, and consequently on damage progression, is demonstrated. The current model shows better capability than our previous model for predicting matrix damage near the hole, which will be important for future fatigue modelling studies.

Deformation gradient tensor decomposition for representing matrix cracks in fiber-reinforced materials

A new method is presented for the representation of matrix cracks in continuum damage mechanics (CDM) models for fiber-reinforced materials. The method is based on the additive decomposition of the deformation gradient tensor into ‘crack’ and ‘bulk material’ components, analogous to the additive strain decomposition of the smeared-crack approach. The potential improvements to the accuracy of CDM models that utilize the presented method are demonstrated for a single element subjected to simple shear deformation and for a unidirectional open-hole tension specimen. The presented method avoids load transfer across matrix cracks and eliminates the prediction of spurious secondary failure modes that occurs when conventional strain-based CDM models are used in geometrically nonlinear finite element analyses involving large shear deformations.

Harpoon technology development for the active removal of space debris

This paper presents the results of preliminary empirical testing and numerical modelling carried out to demonstrate the effectiveness of using a harpoon in an ADR application. Empirical testing involving the impact of blunt and conical shaped steel tips into 3mm Al plate showed that the ballistic limit varies in proportion to the tip circumference, with conical shapes resulting in a higher relative ballistic limit due to the additional energy required for petaling. The creation of secondary debris was also monitored. It was found that blunt shapes created a plug during penetration as a result of shearing around the periphery of the projectile, whilst conical tips resulted in minor spalling and fragmentation. Preliminary oblique impact testing with conical and blunt tips showed that the ballistic limit increases with obliquity at a greater rate for blunt tips than conical ones.Impact testing of 3mm Al plate with conical projectiles at low temperatures showed a more brittle fracture mode when compared with targets impacted at room temperature. As such, the fragmentation and spalling evident in room temperature targets was absent. The energy required to perforate the cooled plates also increased.Impact testing of Al panel obstructed with fixed heat pipes showed that the harpoon could successfully penetrate a target panel with such an obstruction due to shearing of the pipe flange.Testing of two lock on mechanisms showed that both a spring activated and integrated toggle could reliably open upon impact. This testing also used a tensile testing machine to show that both designs could withstand the force expected during deorbiting manoeuvres after impact with Al H/C panels.A parametric simulation comparing the diameter of conical tips with ballistic limits showed a good agreement with the predictions of De Marre’s formula for normal impact. This suggests that the ballistic limit of plates impacted by conical projectiles can be successfully extrapolated with limited experimental data. A SPH solver, which is better suited to modelling impact into brittle materials, was used to model impact into CFRP targets. This showed that the debris formed by conical tips was less coherent and had a higher terminal velocity than that produced by blunt tips. As a result of conducting these simulations, it was shown that numerical modelling can provide an accurate prediction of impact speeds required for a conical projectile to perforate Al plate, excellent prediction of impact failure modes, and good predictions of debris likely to be created during the impact process.Finally, preliminary studies of harpoon impact into low mass targets with up to 3 DOF showed that the harpoon was still able to penetrate such targets under simulated μ-gravity conditions.

Failure mode prediction and energy forecasting of PV plants to assist dynamic maintenance tasks by ANN based models

In the field of renewable energy, reliability analysis techniques combining the operating time of the system with the observation of operational and environmental conditions, are gaining importance over time.In this paper, reliability models are adapted to incorporate monitoring data on operating assets, as well as information on their environmental conditions, in their calculations. To that end, a logical decision tool based on two artificial neural networks models is presented. This tool allows updating assets reliability analysis according to changes in operational and/or environmental conditions.The proposed tool could easily be automated within a supervisory control and data acquisition system, where reference values and corresponding warnings and alarms could be now dynamically generated using the tool. Thanks to this capability, on-line diagnosis and/or potential asset degradation prediction can be certainly improved.Reliability models in the tool presented are developed according to the available amount of failure data and are used for early detection of degradation in energy production due to power inverter and solar trackers functional failures.Another capability of the tool presented in the paper is to assess the economic risk associated with the system under existing conditions and for a certain period of time. This information can then also be used to trigger preventive maintenance activities.

A criterion for failure mode prediction of angle-ply composite laminates under in-plane tension

As the failure of fibre-reinforced angle-ply composite laminates involves basic features of failure of general laminates, its understanding and prediction are of fundamental importance. In this paper, a criterion for predicting the failure mode of angle-ply laminates under in-plane tension is presented. The criterion is able to predict the two different modes of the final failure of angle-ply laminates found in previous experiments: the pull-out of the internal layer due to transverse cracks and delaminations with no fibre breakage, and a single crack across the width of the laminate. The theoretical results demonstrate that the final failure mode of an angle-ply laminate is determined by the value of a failure factor which is related to the thickness and strength of the lamina, the width and ply angle of the laminate, and the interface strength. The pull-out failure occurs when the failure factor is greater than one, and the single cracking occurs when it is less than one. The criterion also shows that the final failure of angle-ply laminates exhibits size effects both in the thickness direction and the width direction. Moreover, the criterion is extended and applied to general angle-ply laminates. The theoretical predictions agree with experimental results.

Reliability Prediction of Failure Modes due to Pressure inSolid Rocket Case

In this paper, an efficient technique is developed to predict failure probability of three failure modes(case rupture, fracture and bolt breakage) related to solid rocket motor case due to the inner pressure during the mission flight. The overall procedure consists of the steps: 1) design parameters affecting the case failure are identified and their uncertainties are modelled by probability distribution, 2) combustion analysis in the interior of the case is carried out to obtain maximum expected operating pressure(MEOP), 3) stress and other structural performances are evaluated by finite element analysis(FEA), and 4) failure probabilities are calculated for the above mentioned failure modes. Axi-symmetric assumption for FEA is employed for simplification while contact between bolted joint is accounted for. Efficient procedure is developed to evaluate failure probability which consists of finding first an Most Probable Failure Point(MPP) using First-Order Reliability Method(FORM), next making a response surface model around the MPP using Latin Hypercube Sampling(LHS), and finally calculating failure probability by employing Importance Sampling.

Transient Thermal Analysis and Viscoplastic Damage Model for Life Prediction of Turbine Components

This paper reports the process and computer methodology for a physics-based prediction of overall deformation and local failure modes in cooled turbine airfoils, blade outer air seals, and other turbomachinery parts operating in severe high temperature and high stress environments. The computational analysis work incorporated time-accurate, coupled aerothermal computational fluid dynamics (CFD) with nonlinear deformation thermal-structural finite element model (FEM) with a slip-based constitutive model, evaluated at real engine characteristic mission times, and flight points for part life prediction. The methodology utilizes a fully coupled elastic-viscoplastic model that was based on crystal morphology, and a semi-empirical life prediction model introduced the use of dissipated energy to estimate the remaining part life in terms of cycles to failure. The method was effective for use with three-dimensional FEMs of realistic turbine airfoils using commercial finite element applications. The computationally predicted part life was calibrated and verified against test data for deformation and crack growth.

LIMIT STATE EVALUATION OF STEEL-REINFORCED CONCRETE ELEMENTS BY VON MISES AND MENÉTREY–WILLAM-TYPE YIELD CRITERIA

An advanced version of a recently developed numerical limit analysis procedure for the prediction of peak loads and failure modes of steel-reinforced concrete elements is proposed. The modified procedure allows to take into account possible yielding of reinforcement thus capturing the actual behavior at the collapse of both steel and concrete. This implies a finite element (FE) modeling of the reinforced concrete (RC) elements in which concrete is governed by a Menétrey–Willam-type yield criterion, with cap in compression, while steel bars are governed by a von Mises yield criterion. The peak load of a wide range of RC structures whose behavior at ultimate state is dominated either by the concrete crushing or by the steel bars yielding is then predicted with a very good accuracy.

Numerical modelling of concrete-filled steel box columns incorporating high strength materials

In this paper, an accurate finite element model which accounts for the effects of initial local imperfections and residual stresses is developed for the nonlinear analysis of high strength steel box columns infilled with high strength concrete. The inelastic behaviour of the steel box and the concrete core is modelled using an elastic–plastic model with linear hardening and a concrete damaged plasticity model, respectively. In addition, an extensive numerical analysis based on a wide range of width-to-thickness ratios, yield stresses of steel tubes and compressive strengths of concrete core was also carried out to propose a new empirical equation for estimating the confining pressure on the concrete. The predictions of ultimate strengths, behaviour and failure modes are compared with experimental results to verify the accuracy of the present model. Parameter studies indicate that both the Eurocode EC4 and Australian Standard AS 5100 approaches can be safely extended to predict the ultimate strength of concrete-filled steel columns with high strength materials.

Evaluation of uncertainties in determining the seismic vulnerability of historic masonry buildings in Slovenia: use of macro-element and structural element modelling

The effect of uncertainties regarding modelling choices and knowledge of specific structural configurations on the seismic vulnerability evaluation of masonry buildings in Slovenia were studied using two case studies: a set of damaged buildings from the rural area of NW Slovenia hit by earthquakes in 1998 and 2004 and the urban buildings from the historic city centre of Ljubljana. Two modelling strategies were applied—failure mechanisms analysis by means of macro element methodology (MEM) and non-linear response analysis by means of structural element modelling. The accuracy in predicting failure modes by MEM ranged between 50 and 80 % of the stock of building in rural area. The most critical failure mechanisms were due to out-of-plane loading. Given the uncertainties associated with the data relative to the urban architecture stock, the MEM analysis was carried out considering different hypotheses, leading to a range of 30–70 % damaged buildings, for 475 years return period, with diverse failure mechanisms and ultimate capacity depending on specific structural assumptions. For one building of rural architecture already damaged during previous earthquake in 2004, where due to the extensive in-situ campaign the influence of uncertainties were minimised, direct comparison of the effectiveness of both methods were investigated. MEM assessment yields more conservative results in respect to non-linear approach and thus may be an efficient tool for the design of strengthening measures for heritage buildings to prevent damage in lower intensity events with higher probability of occurrence.

Development of a steel component combustion model for fires involving pure oxygen systems

Pure oxygen systems pose significant fire and explosion risk to equipment, operations, and personnel if a loss of oxygen containment occurs. In industrial oxygen systems, combustion of metal can be initiated by a variety of ignition sources. The combustion of process vessel walls, components, or piping can result in loss of containment of pressurized oxygen. Automatic shutdown and isolation systems are designed to detect loss of containment, incipient loss of containment due to process parameters (e.g., pressure drop), or internal fire conditions. The effectiveness of these isolation systems is dependent upon the speed with which they activate after the initiating event.The prediction of failure modes and time scales can be an important tool in the design, operation, and maintenance of industrial high purity oxygen systems. Modeling of metal consumption in oxygen fueled fires requires consideration of multiple ignition mechanisms. Previously published experimentation has been motivated by the need to compare the relative burn resistance of metals and nonmetals under a variety of operating conditions, but has not produced a tool to inform the potential for loss of containment in oxygen systems based on the different ignition mechanism failure modes.This work aims to develop a series of theoretical models using experimental results and kinetic relationships in order to predict loss of containment in piping for industrial systems for combinations of different failure modes. Using this type of analysis, process designers can make informed decisions on the design of high purity oxygen systems, the timescale required by emergency shutdown systems, and schedules for routine maintenance and inspection. © 2014 American Institute of Chemical Engineers Process Saf Prog 33: 299–304, 2014

Deformation and failure mechanisms of sandwich beams under three-point bending at elevated temperatures

Quasi-static three-point bending tests at different temperatures were carried out for sandwich beams with aluminum face sheets and closed-cell aluminum foam core. The deformation and initial failure behaviors were explored and of the three potential failure modes, i.e. core shear, indentation and face yielding, only the latter two were observed in the experiments at different temperatures. Failure mechanism maps which illustrate the dominant initial failure mode for practical beam designs were constructed for different test temperatures based on the modified Gibson model. It was found that upon increasing the temperature, the incidence of face yield mode increases and the incidence of core shear mode decreases. The theoretical predictions of the initial failure modes and limit loads according to the modified Gibson model are found to be in good agreement with the experimental results at different temperatures.

Progressive Failure Analysis of Pin-Loaded Unidirectional Carbon-Epoxy Laminated Composites

In this study, a research was carried out to determine the failure modes and failure loads at pinned joint unidirectional laminated carbon/epoxy composite plates. To evaluate the effects of joint geometry and fiber orientation on the failure loads and failure modes, parametric studies were performed experimentally and numerically. A numerical study was performed by using 3D APDL codes with ANSYS fem software and Hashin Failure Criteria was used for predicted failure mode and failure load. The experimental and numerical results showed that the failure loads of composite plates were increased with increasing E/D and W/D ratios.

Predictions of High Strain Rate Failure Modes in Layered Aluminum Composites

A dislocation density-based crystalline plasticity formulation, specialized finite-element techniques, and rational crystallographic orientation relations were used to predict and characterize the failure modes associated with the high strain rate behavior of aluminum layered composites. Two alloy layers, a high strength alloy, aluminum 2195, and an aluminum alloy 2139, with high toughness, were modeled with representative microstructures that included precipitates, dispersed particles, and different grain boundary distributions. Different layer arrangements were investigated for high strain rate applications and the optimal arrangement was with the high toughness 2139 layer on the bottom, which provided extensive shear strain localization, and the high strength 2195 layer on the top for high strength resistance The layer thickness of the bottom high toughness layer also affected the bending behavior of the roll-bonded interface and the potential delamination of the layers. Shear strain localization, dynamic cracking, and delamination are the mutually competing failure mechanisms for the layered metallic composite, and control of these failure modes can be used to optimize behavior for high strain rate applications.

Prediction of Failure Modes during Deep Drawing of Metal Sheets with Nickel Coating

To optimize the process parameters, it is necessary to exactly predict failure modes during deep drawing of coated metal sheets, where two main failure forms are fracture and wrinkling. In this paper, finite element simulations based on continuous damage mechanics were used to study the failure behavior during a cylindrical deep drawing of metal sheets with nickel coating. It is shown that taking the effect of blank holder force into account, these two failure modes can be predicted. The simulation results are well consistent with that obtained from experiments.