Arlindo Silva

Numerical evaluation of failure mechanisms on composite specimens subjected to impact loading

Abstract Composite panels are in common use, especially in aeronautic and aerospace structures due to their high strength/weight and stiffness/weight ratio. The out-of-plane impact loading is considered potentially dangerous mainly because the damage may be left undetected and because the loading itself acts in the through-the-thickness direction of the laminated composite panel. This direction is the weakest in the composite since no fibres are present in that direction. The impact loading can lead to damage involving three modes of failure: matrix cracking, delamination and eventually fibre breakage for higher impact energies. Even when no visible impact damage is observed at the surface on the point of impact, matrix cracking and delamination can occur, and the residual strength of the composite is considerably reduced. The objective of this study is to determine the mechanisms of the damage growth of impacted composite laminates when subjected to impact loading. For this purpose a series of impact tests were carried out on composite laminates made of carbon fibre reinforced epoxy resin matrix. An instrumented drop-weight-testing was used together with a C-scan ultrasonic device for the damage identification. Two stacking sequences of two different epoxy resins and carbon fibres, representative of four different elastic behaviours with a different number of interfaces were used. A numerical evaluation of these specimens was also carried out, using static analysis only. Results showed that the delaminated area due to impact loading depends on the number of interfaces between plies. Two failure mechanisms due to impact were identified, which are influenced by the stacking sequence and by the thickness of the panels.

Creativity enhancement in a product development course through entrepreneurship learning and intellectual property awareness

Product development is the set of activities starting with the perception of a market need and ending in the production and sale of a new product satisfying that need. Broadly speaking, it is a process that should follow a structured methodology, if a certain level of effectiveness and efficacy is envisaged. In the Portuguese industrial environment, there is, in general, a weak perception of this methodology. Even when this perception exists, it is hardly integrated with the companys culture and related processes. In university engineering degrees curricula, there is very little integration of interdisciplinary knowledge that leads to a global understanding of what engineering and product development integrated with entrepreneurship issues should be. This work presents an integrative approach to bridge this gap between industry and university by the teaching of a course on product development and entrepreneurship, at a graduate level. Special attention is given to innovation and creative thinking during concept development, through the introduction of a structured method to promote it, and to the appeal of intellectual property rights to motivate innovative thinking among students. Teaching product development integrated in an entrepreneurship framework promotes students skills in what it takes to start a new business and makes them feel comfortable in executing the idea-to-product viability evaluation in a business perspective.

Mechanical Behavior of Sandwich Structures using Natural Cork Agglomerates as Core Materials

Cork is a material of great value to the Portuguese economy. Unfortunately, its use is still restricted to traditional areas, with the agglomerate form in particular not being used to its full potential. The objective of this article is to analyze the viability of using cork-based material as core materials in sandwich structures in aeronautical and aerospace applications. The use of cork-based material is proposed because of its isolation properties (both thermal and acoustic) and there is no significant performance loss, when compared with the currently used materials. It presents other advantages, as well as, less wastage of energy in manufacturing and a better environmental integration, both in the transformation stage and in the end of life recycling stage. The objective of this work is to study the mechanical behavior of different sandwich specimens, with carbon/epoxy faces, and cores of different cork agglomerates and their comparison with the results obtained with similar specimens using current material cores. Experimental shear tests and three-point bending tests were carried out and the evolutions of the load— displacement curves of the different cork agglomerates/sandwiches were analyzed and discussed. The obtained results show that significant room for improvement still exists in use of cork-based core materials.

Natural fibre-reinforced composite parts for automotive applications

In this paper, we conduct a brief revision of the state-of-the-art on vegetable fibre-reinforced composite applications in the automotive industry. We then present some results for the dynamic characterisation of an auto part made of jute fibres and an equivalent one made of traditional glass fibres, where the increase in damping is most evident. An inverse characterisation method based on the free vibration response of composite plate specimens is also applied to estimate damped material parameters in vegetable fibre-reinforced composites. The obtained results are compared with the ones obtained with equivalent specimens made of glass fibre and future application of this technique to the study of environmental parameters on the material properties is proposed.

Teaching Design in the First Years of a Traditional Mechanical Engineering Degree: Methods, Issues and Future Perspectives.

Engineering design is known as an answer to an ill-defined problem. As any answer to an ill-defined problem, it can never be completely right or absolutely wrong. The methods that universities use to teach engineering design, as a consequence of this, suffer from the same fate. However, the accumulated experience with the ‘chalk and talk’ teaching tradition has led to a reality in which the employers of fresh graduates are not happy with the engineers they are getting. Part of their complaints are related with the inability of recently graduate engineers to work in problems where the boundaries are not well defined, are interdisciplinary, require the use of effective communication and integrate non-technical issues. These skills are mostly absent from traditional engineering curricula. This paper demonstrates the implementation of engineering design perspectives enhancing some of the aforementioned skills in a traditional mechanical engineering curriculum. It emphasises in particular a design project that is tackled in a sequence of conventional courses with a focus that depends on the course objectives and disciplinary domain. This transdisciplinary design project conveys the idea (and effectively implements it concurrently) that design is multidisciplinary.

Eco-composite: the effects of the jute fiber treatments on the mechanical and environmental performance of the composite materials

In this study, untreated and treated jute fiber composites were investigated as candidates to replace glass fibers as reinforcement to produce structural composites with better environmental performance. The surface of the jute fibers was modified by drying and bleaching/drying treatments to improve the wetting behavior of the apolar polyester, improving the mechanical properties of the composites. The mechanical characterization of the composites was obtained according to the ASTM standards (D-3039/D-790) and dynamic mechanical analysis. The environmental characterization was obtained by life-cycle assessment method. The treatment characterization was obtained by horizontal attenuated total reflectance infrared spectroscopy and thermogravimetry. Finally, jute composites were compared with glass composites and results show that the jute fiber treatments imply a significant increase of the mechanical properties of the composites without damaging their environmental performances.

Exploring the Use of Cork Based Composites for Aerospace Applications

Aerospace components are characterized by having high strength to weight ratios in order to obtain lightweight structures. Recently, different types of sandwich components using composite materials have been developed with the purpose of combining the effect of reinforced face-sheets with low weight core materials, such as honeycombs and foams. However, these materials must combine damage tolerance characteristics with high resistance under both static and dynamic loads. Cork composites can be considered as an alternative material for sandwich components since cork is a natural material with some remarkable properties, such as high damage tolerance to impact loads, good thermal and acoustic insulation capacities and excellent damping characteristics for the suppression of vibrations. The experiments carried out in this investigation were oriented in order to optimize the specific strength of cork based composites for sandwich components. Static bending tests were performed in order to characterize the mechanical strength of different types of cork agglomerates which were obtained considering distinct production variables. The ability to withstand dynamic loads was also evaluated from a set of impact tests using carbon-cork sandwich specimens. The results from experimental tests showed that cork agglomerates performance depends on the cork granulate size, the type of reinforcing elements and the bonding procedure used for the cohesion with the matrix material.

Handbook of research on trends in product design and development: technological and organizational perspectives

The Handbook of Research on Trends in Product Design and Development: Technological and Organizational Perspectives provides a snapshot of the current issues, trends, challenges, and future perspectives of product design and development, which is an area of growing interest and increasingly recognized importance for industrial competitiveness and economic growth. Product design and development is affecting not only industry, but society in general, as new and innovative products shape our way of life. This handbook is unique in that it explores product design and development not only from a technological standpoint, but from a sociological perspective, as well. It includes contributions from 58 experts in 15 countries.

Development of green composites reinforced with ramie fabrics: Effect of aging on mechanical properties of coated and uncoated specimens

Bio-polymers have already penetrated in a great number of industries such as packaging and automotive in which they typically target the eco-minded consumers. Following that lead, novel green composites were prepared by resin transfer molding (RTM) and tested. Mechanical properties of ramie/bio-polyester composites were investigated in different fiber loadings. The results indicate that the flexural strength can be increased up to 138 % while tensile strength improved up to 31 %. The Young’s and bending moduli have also been increased up to 26 and 79 % respectively by the presence of the fiber fabrics. Environmental degradation tests have been performed on a set of coated and uncoated specimens. It is envisaged that an appropriate coating on the composite surfaces can preserve the durability properties under the range of exposure conditions examined by this study.

Mechanical bending behaviour of composite T-beams

Abstract A study of the design and mechanical behaviour of co-cured T-beams subjected to very high loading is presented. The T-beams were made by press moulding from pre-pregs of uni-directional glass or carbon fibre and glass fabric reinforced high performant epoxy matrix. Each type of beam was instrumented with strain gauges in the web and flange in order to carry out experimental four point bending tests. Analytical and numerical studies were also performed to compare experimental versus numerical and analytical results and to establish the suitability of a simplified bending theory for statically determinate composite beams constructed from laminated composite panels. The maximum carrying loads in the beam layers were evaluated experimentally and analytically using the Tsai-Wu failure criterion. Results showing the suitability of the simplified beam theory are presented and discussed.