A.M. Amaro

Residual Strength after Low Velocity Impact in Carbon-Epoxy Laminates

The aim of present work is to study the influence of low energy impacts on residual strength of carbon-epoxy laminates. Experimental tests were performed on [0,90,0,90]2s and [0,90]8 laminates using a drop weight-testing machine. The influence of the laminate stacking sequence is analysed under 1.5 J, 2 J, 2.5 J and 3 J impact energies, corresponding to a 0.91 ms-1, 1.05 ms-1, 1.18 ms-1 and 1.29 ms-1 of impact velocity, respectively. The impacted plates were inspected by CScan to evaluate the size, shape and position of the delaminations through the thickness of the plate. The same plates were inspected by C-Scan before the impact, to evaluate the eventual presence of defects produced during the manufacturing process. The residual flexural strength showed that the [0,90,0,90]2s laminates have better performance than the [0,90]8 ones. The explanation is related with the lower flexural stiffness of the antisymmetric lay-up relatively to the symmetric one.

Introduction to Finite Element Method

As discussed in Chap. 1, mechanic problems are governed by a set of partial differential equations that are valid in a certain domain and they needed to be solved for evaluating the stress condition of mechanical components. Although analytic methods can be employed to solve linear problems involving partial differential equations, its use to analyze complex structures may be a difficult or, even, an impossible task. Thus, in this chapter, Hamilton’s principle, which one of the most powerful energy principle, is introduced for the FEM formulation of problems of mechanics of solids and structures. The approach adopted in this chapter is to directly work out the dynamic system equations, after which the static dynamic equations can be easily obtained by simply dropping out the dynamic terms

UFe6Ge6: a new ternary magnetic compound

Abstract The ternary intermetallic magnetic compound UFe6Ge6 was studied by single crystal X-ray diffraction and 57Fe Mossbauer spectroscopy; the magnetic properties were also investigated. UFe6Ge6 was found to melt congruently at c. 950 °C and to crystallize in space group P6/mmm, with cell parameters a = 5.126 8(4) A , c = 4.050 7(5) A , V = 92.204 7(13) A 3 , Z = 0.5 and a YCo6Ge6 type structure that was solved by single crystal X-ray diffraction to a final R = 0.059 (Rw = 0.071). Magnetization measurements suggest two transitions: one at 322(5) K reminiscent of an antiferromagnetic ordering and another ferromagnetic at 230(10) K. According to 57Fe Mossbauer spectroscopy there is a transition at 322(5) K associated with the ordering of the Fe moments which do not undergo any noticeable reordering at lower temperatures. Thus the transition at 230 K is tentatively attributed to the ordering of the U-sublattice.

Influence of the specimen thickness on low velocity impact behavior of composites

Abstract In this work, the influence of specimen thickness on low velocity impact behavior of carbon-epoxy composite laminates is studied. Plates with different thicknesses were tested under low velocity impact using a hemispherical impactor. The internal damage was mainly constituted by delaminations which were evaluated through the inspection of the impacted plates by the ultrasonic C-scan technique. It was observed that delaminations increase with plate thickness. In order to better understand the physical phenomenon explaining this result, a progressive damage model was used to simulate composites behavior under low velocity impact. In this context, a three-dimensional numerical analysis considering interface finite elements, including a cohesive mixed-mode damage model, which allows simulating delaminations onset and growth between layers, was performed. Good agreement was obtained between experimental and numerical analysis, which validated the proposed procedure. In addition, the proposed numerical methodology allowed identification of physical phenomena related to the influence of plate thickness on delamination size.

Interfacing system dynamics and multiobjective programming for regional water resources planning

A preliminary planning methodology is presented. This approach relies upon a strategy identification mechanism, a system dynamics model to simulate the behaviour of the identified strategies and multiobjective programming formulations to evaluate them. An application to regional water resources planning in the Guadiana basin is included to illustrate the methodology.

Mechanical Properties of Epoxy Nanocomposites Using Alumina as Reinforcement - A Review

Polymers and their composites find use in many engineering applications as alternative products to metal-based ones and, nowadays, have wide technical applications. One of the most used composite materials is the epoxy resins (EP), which is a thermoset polymer matrix. After cure, this material displays some excellent mechanical, thermal, electrical and chemical properties. For these reasons, it has been widely used for a wide range of automotive and aerospace applications, as well as for shipbuilding or electronic devices. However, EP has poor resistance to crack propagation and is brittle. So, in recent years, a considerable amount of research has been carried out to improve the performance of the toughness of EP. The most common studied technique consist to reinforce the EP matrix with rigid nanoparticle fillers, such as alumina, silica, mica, talc, organoclays, nanoclays, carbon nanotubes, TiO2, among others. Among these nanofillers type, nanosize alumina particles has not been widely studied. However, recent studies have reported that the use of functionalized nanosize alumina particles as nanofiller can significantly improve the properties of the nanocomposite, even with low contents. These results, combined with the low cost of the alumina, show that the reinforcement of EP with alumina nanoparticles is a viable solution. In this paper, an attempt is made to review and highlight some recent findings and also some trends to show future directions and opportunities for the development of polymer nanocomposites reinforced with alumina nanoparticles.

Effect of different acid solutions on glass/epoxy composites:

Composite materials are exposed to a range of hostile environments with consequent degradation in terms of mechanical properties. However, the bibliography is not sufficient to establish a full knowledge about the effect of hostile environments on mechanical properties. This work intends to study the response to flexural and to low velocity impact of a glass fibre/epoxy composite after immersion in two different acid solutions, hydrochloric acid and sulphuric acid. These solutions affect significantly the flexural and impact strength, however, the hydrochloric acid was responsible for the worst results. The maximum load and elastic energy decreases with the impacts. On the other hand, the maximum displacement and damaged area showed an inverse tendency.

Engineering Computation of Structures: The Finite Element Method

This book presents theories and the main useful techniques of the Finite Element Method (FEM), with an introduction to FEM and many case studies of its use in engineering practice. It supports engineers and students to solve primarily linear problems in mechanical engineering, with a main focus on static and dynamic structural problems. Readers of this text are encouraged to discover the proper relationship between theory and practice, within the finite element method:Practice without theory is blind, but theory without practice is sterile. Beginning with elasticity basic concepts and the classical theories of stressed materials, the work goes on to apply the relationship between forces, displacements, stresses and strains on the process of modeling, simulating and designing engineered technical systems. Chapters discuss the finite element equations for static, eigenvalue analysis, as well as transient analyses. Students and practitioners using commercial FEM software will find this book very helpful. It uses straightforward examples to demonstrate a complete and detailed finite element procedure, emphasizing the differences between exact and numerical procedures.

A new magnetic intermetallic compound: UFe6Ga6

Abstract A new intermetallic magnetic compound, UFe6Ga6, has been obtained by induction melting of the stoichiometric elements. It melts congruently at about 1020°C and crystallizes with the orthorhombic ScFe6Ga6-type structure. Magnetization measurements on the polycrystalline material indicate ferromagnetic behaviour below 515 K. A value of 10.5 μB/f.u. at 5 K was obtained for the spontaneous magnetization in a free powder sample.

UFe2Zn20: a new uranium intermetallic compound

Abstract A new uranium intermetallic compound, UFe 2 Zn 20 , was prepared and characterized by single-crystal X-ray diffraction, 57 Fe Mossbauer spectroscopy and magnetization measurements. It crystallizes in the cubic Fd3m space group ( a =14.0998(9) A) and is isostructural with CeCr 2 Al 20 ( R =0.045, W R 2 =0.12). Mossbauer spectra, taken between 5 K and room temperature, consist of a symmetric quadrupole doublet with narrow lines, confirming an ordered structure with the iron on only one crystallographic site and showing no magnetic ordering transition above 5 K, in good agreement with magnetization measurements.