Sliding contact on the interface of elastic body and rigid surface using a single block Burridge-Knopoff model

Burridge and Knopoff proposed a mass-spring model to explore interface dynamics along a fault during an earthquake. The Burridge and Knopoff (BK) model is composed of a series of blocks of equal mass connected to each other by springs of same stiffness. The blocks also are attached to a rigid driver via another set of springs that pulls them at a constant velocity against a rigid substrate. They studied dynamics of interface for an especial case with ten blocks and a specific set of fault properties. In our study effects of Coulomb and rate-state dependent friction laws on the dynamics of a single block BK model is investigated. The model dynamics is formulated as a system of coupled nonlinear ordinary differential equations in state-space form which lends itself to numerical integration methods, e.g. Runge-Kutta procedure for solution. The results show that the rate and state dependent friction law has the potential of triggering dynamic patterns that are different from those under Coulomb law

Comparison of Equivalent Stress Methods with Critical Plane Approaches for Multiaxial High Cycle Fatigue Assessment

Several equivalent stress methods and more advanced critical plane criteria are compared in terms of their performance in fatigue life estimations under uniaxial and biaxial loadings in which the effect of phase is investigated. For this purpose a MATLAB code is written which transforms the multiaxial cyclic stress state into a uniaxial cyclic stress to use with the equivalent stress based methods. For critical plane approaches the program searches a damage parameter on all material planes. The maximum damage parameter is then compared with a material allowable obtained from uniaxial fatigue tests for life estimation. In addition, various methods for calibration of the material coefficient k and prominent stress history enclosure methods to calculate the shear stress amplitude are also studied for determining their effect on the performance of critical plane approaches. (C) 2017 The Authors. Published by Elsevier B.V

Dynamic Frictional Sliding Modes between Two Homogenous Interfaces

Dynamic frictional sliding behaviour between two homogenous Homalite blocks is studied. The blocks are initially held together using a constant compressive stress. The sliding motion is initiated by impacting one of the blocks with an external object. The resulting sliding modes are inspected. Initiation of fretting is examined by studying the opening stresses in the interface

Strength Analysis of a Composite Turbine Blade Using Puck Failure Criteria

The strength analysis of an existing 5-meter composite wind turbine blade using Tsai- Wu and Puck failure criteria is presented. Finite element analysis is performed on the blade under static flap wise loading. ANSYS APDL scripting language is used to implement Puck failure criteria and degradation rules for the progressive failure analysis of the blade. Evaluation and visualization of Tsai-Wu inverse reserve factors and Puck failure exposures in the blade is done with the help of the Ansys ACP/Post module. The results of this study indicate that the blade is not able resist extreme load case and needs to be redesigned. Root and trailing edge of the blade have the highest risk of failure initiation. Linear analysis using Tsai-Wu and Puck failure criteria is compared with the nonlinear analysis using progressive Puck failure criteria. It is concluded that progressive analysis is necessary for a more realistic simulation of blade failure mechanisms. Results of the analysis will be used to calibrate structural test set-up of the blade

Simulation of Drop-Weight Impact Test on Composite Laminates using Finite Element Method

This study presents the simulation of standard drop-weight impact test on a [0/90/0]s composite laminate. For this purpose, a three-dimensional virtual test setup is developed in ABAQUS/Explicit finite element tool. Hemispherical impactor and specimen fixture are modeled as rigid bodies. Composite plate is modeled as a 3-D deformable solid and discretized using a biased mesh for computational efficiency. For simulation of ply damage in the composite laminate, a continuum damage mechanics based damage model is developed and implemented into the analysis via a user-written subroutine VUMAT. Delamination damage is simulated by inserting cohesive elements at the interfaces of plies having different orientations. Results show that the initial failure mechanism in the 3-D low-velocity impact event is the matrix cracking in the lowermost plies independent from the stacking sequence of the laminate. Furthermore, the simulation accurately predict that delaminated regions expand mainly in the same direction as of the fibers of the lower adjacent layer in accordance with the bending stiffness mismatching concept. (c) 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the 1st International Workshop on Plasticity, Damage and Fracture of Engineering Materials organizer

Advanced Elasticity

At the end of the course, the student should be able to design and analyze aerospace engineering components subject to different types of loading. In particular, the objective is to introduce the student to i) the methods of stress, deformation and stability analysis in the design of aerospace engineering components, ii) failure theories, fatigue analysis and thermal stress analysis in the design process, iii) the use of computer tools to solve problems in mechanics. Independent learning, professionalism and applications to real engineering applications and problems will be stressed throughout

Dynamic failure of curved CFRP composite laminates under quasi static loading

In aerospace and wind energy industries, new advances in composite manufacturing technology and high demand for lightweight structures are fostering the use of composite laminates in a wide variety of shapes as primary load carrying elements. However, once a moderately thick laminate takes highly curved shape, such as an L-shape, Interlaminar Normal Stresses (ILNS) are induced together with typical Interlaminar Shear Stresses (ILSS) on the interfaces between the laminas. The development of ILNS promotes mode-I type of delamination propagation in the curved part of the L-shaped structure, which is a problem that has recently raised to the forefront in in-service new composite wind turbines. Delamination propagation in L-shaped laminates can be highly dynamic even though the loading is quasi-static. An experimental study to investigate dynamic delamination under quasi-static loading is carried out using a million fps high-speed camera. Simulations of the experiments are conducted with a bilinear cohesive zone model implemented in user subroutine of the commercial FEA code ABAQUS/explicit. The experiments were conducted on a 12-layered woven L-shaped CFRP laminates subjected to shear loading perpendicular to the arm of the specimen with a free-sliding fixture to match the boundary conditions used in the FEA. A single delamination is found to initiate at the 5th interface during a single drop in the load. The delamination is then observed to propagate to the arms at intersonic speed of 2200m/s. The results obtained using cohesive zone models in the numerical simulations were found to be in good agreement with experimental results in terms of load displacement behavior and delamination history. These results are the first conclusive evidence of intersonic delamination in composite materials triggered under quasistatic loading

Malzeme Arayüzlerinde Ve Arayüzlere Yakın Bölgelerdeki Çatlak Davranışının Fotoelastik Yöntem İle İncelenmesi

Bu çalışmanın ana amacı değişik malzeme arayüzlerinde ve arayüze yakın bölgelerdeki çatlak davranışının fotoelastik yöntem ile incelenmesidir. Bu amaç doğrultusunda değişik malzeme arayüzleri ve arayüzlere yakın bölgelerde numuneler üzerinde açılacak olan çentiklerdeki gerilim siddet katsayısının fotoelastik görüntüleme yöntemi kullanılarak (stress intensity factor) öngörülecektir