Gustavo R. Dias

MPCVD diamond tool cutting-edge coverage: dependence on the side wedge angle

Abstract Microwave plasma CVD usually produces uniform diamond coatings and high-quality diamond films. However, abnormal deposits appear near the sample edges — the so-called ‘edge effect’. Wedge-shaped silicon nitride inserts with 30°-, 60°-, 75°- and 90°-edge angles were vertically and horizontally exposed to MPCVD diamond coating to systematically study this effect. Finite element method (FEM) analysis was used to simulate the temperature distribution on such geometries. Diamond morphology and quality were assessed by SEM and micro-Raman techniques. The edge effect, a consequence of plasma concentration and thermal phenomena in this experimental set-up (activation by electromagnetic gas discharge), is more accentuated on samples that are vertically wedge-oriented towards the plasma. A grain-size gradient is established along the exposed surface, steeply increasing at the hot edge. An extreme effect occurs in the sharpest wedge samples, avoiding diamond growth at the edge.

Hyperelastic modelling of cork-polyurethane gel composites : non-linear FEA implementation in 3D foot model

The CPGC – Cork-Polyurethane Gel Composite is a material that is mechanically characterized by non-linear elastic behaviour at large deformations. The non-linear behaviour can be modelled by hyperelastic constitutive models based on strain energy functions enabling a structured phenomenological framework for CPGC material modelling. The CPGC is a promising material for human comfort enhancement and dynamic damping/control applications. This paper presents the experimental methodology used for the CPGC evaluation of material parameters used in the hyperelastic models and the finite element model build-up. A 3D foot FEA model is presented in order to evaluate the performance of the hyperelastic model in a real case situation and the mechanical performance of shoe insoles, namely, trough the monitoring of the contact pressure values at the insole/foot interface.

Finite Element Modelling of Thermoplastic Matrix Composite Gas Cylinders

Continuous glass/polypropylene (GF/PP) commingled fiber tapes were employed to produce wrapped pressure gas vessels for domestic applications by using filament winding. The vessel structural-wall was built using a hybrid solution consisting in a very thin steel liner over wrapped by the filament wounded GF/PP commingled fiber tape layers. FEM analysis was used to evaluate if the composite gas pressure vessel based on the hybrid solution (steel liner + glass fiber reinforced thermoplastic) is capable to withstand the following pressure requirements: the metallic liner, alone, a minimum burst pressure of 4MPa and whole hybrid composite vessel minima internal test and burst pressures of 3 MPa and 6.75 MPa, respectively. Finally, gas pressure vessel prototypes manufactured in industrial cycle conditions were submitted to burst pressure tests to prove that they accomplish all European standard strength requirements.

A numerical and experimental study of the material properties determining the crushing behaviour of pultruded GFRP profiles under lateral compression

The present work aims at determining the critical material properties that can be used to tailor the crush behaviour of pultruded GFRP (Glass Fibre Reinforced Polymer) box-beams, as can be found in, for example, roadside furniture such as guard-rails. For this purpose, the mechanical behaviour and energy absorption mechanisms of the constituent pultruded box-beam sections subjected to lateral compressive loading, the dominating load case in composite structures when used as roadside furniture, have been studied. The analysed pultruded profiles consist of E-glass fibre reinforcements with two different lay-up configurations in a polyester matrix. The lateral crushing of profile sections is experimentally evaluated and further numerically studied using commercially available tools, applying readily available models incorporated in the software, in analogy to common practice in designing structures, to identify design and material parameters for improving the fracture behaviour of pultruded GFRP profiles. From the analyses, it is shown that the junctions between flanges and webs are the weakest points of box-beam sections: here, high shear stress concentrations in combination with occurring matrix failure lead to further damage such as delamination and tearing. This behaviour is well-described using the Hashin damage model within ABAQUS. Predicted failure behaviour corresponds with observed experimental results, whereas the material stiffness is underestimated. It is shown that the out-of-plane properties (transverse tensile and shear strength) are the dominant parameters affecting the overall performance.

Combining experimental and computed data for effective SHM of critical structural components

A highly effective Structural Health Monitoring, SHM, system for aerospace applications must be, besides highly reliable, a low complexity and low weight solution.1,2 This can be achieved with a reduced number of sensors, which normally implies a low resolution mapping of the monitored variables and, consequently, a weakness on the diagnosis and prognosis procedures. To overcome these difficulties, the physical information from the sensing network can be complemented with a virtualization of the representative geometry and physics of the structural system. This article proposes an integrated procedure to analyze structural health of critical system, combining experimental data from a sensor network with a computational model of the structural system. This approach involves vibration-based monitoring and diagnostic. The SHM technology is applied to a reinforced carbon fiber plate having different damage levels. This flat plate with z-shaped stiffeners is instrumented with accelerometers. The location of sensors is optimized for maximum detection capability using computer simulations (Abaqus®) and a custom developed algorithm. Computational simulations of the vibration behavior of the monitored structural component are also performed to validate the damage diagnosis concept and analyze the sensitivity of the method in damage detection. Furthermore, the data from sensors are compared with the simulation results. The method is able to detect, locate and assess the damage severity, becoming a power tool for damage diagnosis of structural components. Finally, a SHM platform that allows the combination of physical and virtual data for damage diagnostic, PRODDIA®, is presented.

Visualization of Injection Moulding Process

A special tool-transparent mould designed to visualize the melt flow inside the cavity is used in this research. The aim of the work is to assess the polymer melt behavior under different processing conditions-close to industrial, in conventional and two materials non-conventional injection moulding techniques. The mould is designed with two injection locations and has possibility to change the geometry of the cavity in order to investigate the melt behavior in differently shaped cavities. Visual access in the mould is allowed by the sapphire windows, surrounding the cavity. For image acquisition a high speed video camera NAC 1000 is used. Materials used in the research are three polypropylenes with different flow index. Results are obtained for conventional injection moulding, two material monosandwich and two material biinjection moulding. Apart from visualization, instrumentation of the mould allows to be obtained PT data for each processing condition. Results from conventional injection moulding are compared with MPI5.0 simulations.

Influence of the Interaction Potential Parameters on the Mechanical Response of Simulated Semi-Crystalline Polymeric Materials

The tensile deformation of a semi-crystalline lamellar structure was simulated using coarse-grain molecular dynamics. Interactions between statistical segments are described by Lennard-Jones potentials, with two types of interactions (primary and secondary bonds) defined for the amorphous and crystalline phases. The choice of the correct interaction potentials in coarsegrain simulations requires an understanding of the influence of each interaction potential parameter on the mechanical response. The present paper reports results from that study, following a design of experiments approach. It was found that the apparent modulus is mainly determined by the width of the secondary bond potential. The yield stress and the extent of deformation of the material at a fixed force level are influenced both by the width of the secondary bond potential and the depth of the potential well of the amorphous region. Thus, the tensile mechanical properties and behaviour of the specific lamellar structure under study seems to be mainly determined by the secondary interactions in the amorphous region.

Deformation of the lamellar structure in semi-crystalline polymers studied by computer simulations

Abstract Yield in a semi-crystalline polymer involves the disruption of the crystalline phase in an irreversible deformation process. In a semi-crystalline polymer, the crystalline lamellar regions are bridged together by inter-lamellar amorphous layers, which act as a loading transfer medium. The deformation of both phases is, therefore, to some extent inter-related. In this work we adopted a continuous mechanic approach (neglecting atomic/molecular interactions) of the lamellar deformation of semi-crystalline polymers in the sense that we simulated the mechanical response of a lamellar structure (two lamellae interconnected by amorphous regions) in a finite element analysis. The use of computer simulations allows studying independently the effect of each relevant morphological parameter on the mechanical response. Several simulations were performed considering isolated variations of the following morphological parameters: i) mechanical behaviour of the amorphous material; ii) thickness of the crystalline regions; iii) length of the amorphous regions; iv) number of amorphous regions connected with a crystalline lamella; v) relative angle between the crystalline and the amorphous regions; vi) mode of loading (tension and compression). The thickness of the crystalline lamellae is evidenced as the most significant factor affecting the tensile response of the lamellar structure, followed by the mechanical behaviour of the amorphous phase. The connection angle between amorphous and crystalline regions and the number of amorphous regions bridging adjacent crystalline lamellae play only a minor role. The length of the amorphous regions has a negligible influence. As expected, the lamellar structure shows also distinct behaviours under distinct loading modes, tensile loading showing the highest stresses.