Four-point combined DE/FE algorithm for brittle fracture analysis of laminated glass

AbstractA four-point combined DE/FE algorithm is proposed to constrain the rotation of a discrete element about its linked point and analyze the cracks propagation of laminated glass. In this approach, four linked points on a discrete element are combined with four nodes of the corresponding surface of a finite element. The penalty method is implemented to calculate the interface force between the two subdomains, the finite element (FE) and the discrete element (DE) subdomains. The sequential procedure of brittle fracture is described by an extrinsic cohesive fracture model only in the DE subdomain. An averaged stress tensor for granular media, which is automatically symmetrical and invariant by translations, is used to an accurate calculation of the averaged stress of the DE. Two simple cases in the elastic range are given to certify the effectiveness of the combined algorithm and the averaged stress tensor by comparing with the finite element method and the mesh-size dependency of the combined algorithm and the cohesive model is also investigated. Finally, the impact fracture behavior of a laminated glass beam is simulated, and the cracks propagation is compared with experimental results showing that the theory in this work can be used to predict some fracture characteristics of laminated glass

Light-weight design of vehicle roof panel for stiffness and crash analyses

Vehicle crashworthiness refers to proper designing of the vehicle structure to reduce the risk of death and injury during the vehicle accidents. In the recent years, due to the enforcement of new EU normative, the interest of all the car manufacturers in producing lightweight vehicles is progressively increased as the combustion engine optimization has already used most of the improvements they had and the residual ones are becoming more and more difficult and costly. Based on this auto industry’s interest, lightweight materials such as composite have absorbed lots of attention due to their superior characteristic of high stiffness to weight ratio. In this thesis, efforts have been made to present a broad research on the light-weight design of vehicle roof panel for stiffness and crash analyses. The first part of the analyses belongs to the vehicle chassis static and dynamic stiffness analyses via the finite element code with the specific focus on substituting the steel roof panel with the lightweight materials of aluminum and composites. The structural response of the vehicle roof panel, made of different solutions, in full frontal crash with respect to NHTSA standard has been investigated at the second step. The effects of increasing the vehicle roof panel thickness at the both steps have been tested and compared for different solutions. At the third step an innovative design solution for the vehicle roof structure has been developed and tested in rollover crash analysis. In order to perform this task, After determining the performance of tubes made of steel, composite and composite foam-filled solutions under the three points bending test and proving the efficiency of composite-foam design; the same idea is implemented on the vehicle roof panel during the roof quasi-static crush test. Besides the composite solutions, the sandwich design consists of composite face-sheets and foam core are tested in the roof crushing test based on the FMVSS 216 standard. After assessment of the sandwich roof panel in crushing test, the geometrical optimization of the foam core is implemented to determine the optimum design with respect to vehicle strength-to-weight ratio and mass reduction percentages. Besides different foam core configurations that have been tested, the final optimization have been implemented using the foam core with various densities and also the optimum face-sheets thickness has been determined. At the last chapter, challenges of vehicle composite roof panel assembly have been discussed. Results in the case of stiffness and frontal crash analyses at step one and step two proved that although the composite solutions have lower energy absorption capacity in comparison with the steel one, they have large contribution to the weight reduction of the vehicle roof panel and still stays in the acceptable range of structural performance. Using the new design of sandwich solutions in roof crushing test have proved that while theses designs have reduced the vehicle roof panel weight by 68%, they have the same structural performance as the steel solution and could be considered as interesting solutions. Evaluating the behavior of the vehicle roof structure made of different solutions with various configurations under distinct analyses of stiffness and crashworthiness will help to improve the vehicle roof structure performance

Harmonised method to validate the impact resistance performance of composite passenger railway carbodies

PhD ThesisThe pursuit to become a better and more efficient transportation mode and the need of renovation has led the railway industry to search for new technologies. An example to such reform is the ongoing efforts to implement new lightweight materials into the railway vehicles as primary load bearing structures, which can help to reduce energy consumption, maintenance costs, and to increase passenger and line capacity. Composite materials are promising candidates in this respect and this thesis addresses a railway specific risk namely flying object strike, which requires attention when composites are in use especially in high speed rail operation, consequently providing detailed analysis on impact behaviour of composite materials for rail specific applications. This thesis shows for the first time an approach to harmonise and unify different railway standards into a single method for small object strike against composite rail vehicles. The original and essential contribution of this study is a cost effective and practical method for the rail industry that removes the necessity of high velocity impact experiments. Quasi-static punch tests (QSPT) were carried out with glass fibre reinforced laminates and foam core sandwich materials incorporating such laminates. It has been shown that the failure modes experienced in a high velocity impact can be mimicked via QSPT method. A numerical model was developed and was validated with QSPT experiments. Following, the numerical model was used to perform high-velocity impact simulations in a velocity range that is relevant with rail service while considering the strain rate effects. Lastly, various standards for impact risks against railway vehicles were investigated from proposed methodology perspective, and discussed whether they can be harmonized into the presented assessment method. The results showed that the proposed methodology has considerable potential to be preferred over costly high velocity impact experiments. The analysis of the energy transfer characteristics, contact forces, impact velocity change of the projectile, and structural damage showed that the proposed method can be used alone instead of various existing standards, providing a significant reduction in sample size as well as avoiding the costly high-velocity impact experiments, hence resulting in substantial cost savings.Anadolu University of Turkey and Council of Higher Education of Turke

A New Centering Table For Encapsulated Glass Positioning

With the progress of the society, people`s living standard is increasing. More and more cars (more than 72 million) are produced and utilized all over the world. This makes a large number of quarter windows which located on the back-side window of a vehicle are urgently needed. Encapsulated glass is widely adopted for a quarter window for various advantages. Positioning by centering table is one of the most important procedures during the fabrication of encapsulated glass for the quarter window. The existing centering table has a lot of disadvantages such as poor flexibility and precision, which results in failure in production such as damage or low quality. Developing a centering system for positioning encapsulated glass with high efficiency and precision becomes very significant for the industry. In this thesis, I designed a new centering table that used a new column base structure and pins for tightness. This new centering table has a high precision while still maintain the flexibility of the table that makes the centering table can be applied to encapsulated automotive glass with other sizes and shapes

Investigation on the impact damage of glass using the combined finite/discrete element method

Glass and laminated glass are widely used for structural members in industry. To investigate how they fracture under impact as well as the subsequent fragmentation, the combined finite-discrete element method (FEM/DEM) was employed in this thesis. The mode I fracture model was extended for glass by changing the strain softening curve to a bilinear-like exponential decay shape. Analysis based on this model was performed and numerical examples in both 2D and 3D were investigated. Parametric study was carried out and conclusion was reached that the tensile strength, fracture energy and thickness are the top three parameters in improving the performance of monolithic glass under impact. Two mixed mode I + II fracture models (the elasto-plastic fracture model and the scaling model) were developed for the glass and the interface in laminated glass. The elasto-plastic model reached some similarity with the Mode I model, while some modification is needed for the scaling model. Results on laminated glass from the FEM/DEM were compared and verified with that from FEM, DEM and experiments. Parametric study on the laminated glass was performed, showing better capacity in energy absorption over monolithic glass

Experimental approaches for assessing time and temperature dependent performances of fractured laminated safety glass

Laminated glass is for a few decades a well-known product in the construction industry for conferring safety performances to glazing units. Besides to the safeguarding of persons, laminated glass products are contributing to a variety of other safety performances, in case of accidental or attack situations leading to breakage of or crack propagation in the glass panes of a laminated glass unit. The ultimate residual load-bearing capacity of a damaged element can be resumed to one critical load-transfer mechanism, in the form of interlayer ligaments bridging the glass fragments. The characterization for design purposes of the mechanical properties of the interlayer involved in this load-transfer mechanism through the ligament appears however far from obvious. This results from specificities on the one hand of adhesive polymer components and on the other of design and control processes in the building industry. These specificities are mainly related to two aspects : firstly to the time- and temperature dependent behaviour of interlayer materials and their possible sensitivity to ageing effects, and secondly to initially vaguely defined intended fields of use, especially when non-conventional structural applications are within the considered application scope. The combination of these two aspects raises constraints for the development of experimental methods, test configurations and assessment strategies for laminated glass products. This research proposes analysis grids to get an overview of the constitutive elements of application scopes and of the possibilities and limitations for experimental assessment, with purpose to distinguish and estimate different types of border effects. These are used to evaluate the representativeness and the robustness of different test methods and test configurations, corresponding to different experimental scales. An incremental experimental approach has been developed for investigating the time- and temperature dependent performances of damaged laminated glass elements, on the basis of tests on pre-cracked specimens of small dimensions. The assessment of the residual load-bearing capacity of damaged elements used in structural applications was the main focus of these investigations. This research highlights the need for adapting experimental assessment approaches to characterize properties of laminated glass products for design purposes with respect to their post-fracture performances, in comparison with other construction materials. It also explains specific difficulties for obtaining quantitatively meaningful results and the challenges for harmonizing experimental assessment strategies for different applications and products made with a same type of interlayer material

Impact simulation of bird strike on semi-spherical transparencies: application to observation bubbles in the C-295 aircraft

Conflicts between birds and aircraft have increased in the last years since traffic volume and bird population have spread. Although it seems an insignificant event,up to 2009, EASA sets in 242 fatalities and 90 hull losses because of these incidents and this is why Canadian customers are concerned by this increment and have demanded a specific certification for the spotter windows bubbles of C-295 aircraft. This concern has motivated the aim of this research promoted by Airbus Defence and Space. The purpose of this research is the numerical simulation of bird impact on semi-spherical transparencies similar to observation bubbles in the C-295 aircraft in order to obtain a rst approach of the structural behaviour under this fact. The study is divided into three stages: - Firstly, the characterization of the bird is performed against rigid at metallic targets. Experimental data coming from CRAVHI project and analytical interpretation based on Willbeck's theory have been used to validate the results. - Secondly, the characterization of the transparency is achieved, and although the lack of experimental results complicated the labour, some researches and analytical results have been used to find a suitable model.Two analyses on at transparencies have been carried out in parallel, a monolithic transparency and a laminated model (similar to spotter windows and cabin windshields respectively). - Finally, the semi-spherical bubble has been modelled. The explicit numerical simulation code \Visual Environment", formerly PAM-CRASH, has been used for the simulation of these impacts. The results show the high dependence of acrylic materials on strain rates and the need to take it into consideration in the modelization of the finite element model. Moreover, the results expressed in terms of ballistic limits show that the current spotter window monolithic design would not fail in case of a bird striking the bubble until speeds about 50 m/s, making the advantages of laminated model (in terms of weight reduction and limit speed increment) of interest for further works.Ingeniería Aeroespacia