Rinze Benedictus

Recent development in aluminium alloys for aerospace applications

Abstract Driven by the increasing requirements from aircraft producers, Hoogovens Aluminium Rolled Products GmbH, together with Hoogovens Research & Development, has enhanced the property combinations of their aircraft materials. For these types of material, optimised processing routes as well as new alloy chemistries have been investigated. Whilst retaining the strength levels required by the aerospace industry, new processing routes offer major improvements in ductility, toughness, fatigue performance and in reduction of residual stress in large dimension plate and sheet products. A further goal of investigating new alloy chemistries is the trend towards new joining techniques such as welding and brazing for aircraft structures. These new joining techniques require different property combinations compared to the conventional aerospace alloys. In parallel to these improved processing routes and new alloy developments, new ultrasonic inspection techniques have been developed, which are able to predict fatigue performance and residual stress in thick plate products.

Experimental and Numerical Investigation of Metal Type and Thickness Effects on the Impact Resistance of Fiber Metal Laminates

The impact response of fiber metal laminates (FMLs), has been investigated with experiments and numerical simulations, which is reported in this article. Low-velocity impacts were carried out to study the effects of metal type and thickness within FMLs. Glare5-3/2 laminates with two aluminum layer thicknesses and a similar FML containing magnesium sheets were impacted by drop weight tests. Also, a major part of this study was to accomplish a dynamic non-linear transient analysis to study the impact response of FMLs using the commercial finite element (FE) analysis code ABAQUS. By reviewing different approaches of modeling constituents of an FML, it is shown that the appropriate selection of elements has more significant role than failure criterion to predict acceptable results for this type of laminate and loading. The good agreement obtained between experimental and numerical results verifies the possibility of relatively simpler simulation by FE-analysis to predict overall response of FMLs under impact loading.

Mechanics of Tailor Welded Blanks: An Overview

Taking advantage of high-tech welding methods, a concept is formed in sheet metal forming community. The so-called tailor-welded blanks (TWBs) are sheet metals that are welded together prior to forming. This technology dates back to the 80’s, and numerous studies are conducted in order to explore different aspects of it. This review paper concerns with mechanics of TWBs. The paper is divided into three major chapters. The first chapter is devoted to mechanical properties of TWBs. Tensile testing, tensile properties, and hardness of TWBs are covered in this chapter. The second chapter deals with the formability of TWBs. The formability testing methods, effect of different parameters on the formability of TWBs, material flow phenomena, control of material flow, stress and strain distributions, and springback behavior are covered in the second chapter. The third chapter is focused on failure and fracture of TWBs. Failure modes and failure criteria are the principal topics of this chapter.

Fiber/Metal composite technology for future primary aircraft structures

This paper discusses the structural and material considerations for fiber/metal composite technology for future primary and secondary aircraft structures. Based on these considerations and the experience obtained so far with fiber/metal laminates in primary aircraft structures, the potential field of further development of fiber/metal composite technology will be explained. It is concluded that a composite technology approach, in which both metals and fibers are combined to form a tailored structural material, can lead to significant weight reduction in future structural applications.

Damage evolution in GLARE fibre-metal laminate under repeated low-velocity impact tests

An experimental study was performed on the repeated low-velocity impact behaviour of GLARE. Damage evolution in the material constituents was characterised with successive number of impacts. Records were correlated with visual inspection, ultrasound C-scan and chemical etching. The stiffness of the plate varied when cumulating the number of impacts. Damage accumulation was limited thanks to the synthesis of unidirectional composite and metal. The glass/epoxy plies with high elastic tensile strength could withstand several impacts before perforation despite delamination growth in the vicinity of the impacted area. The damage tolerant aluminium layers prevented the penetration of the projectile and avoided the expansion of delamination. This efficient mechanism preserved the structural integrity of GLARE until first aluminium cracking at the non-impacted side. Among the different failure modes, plate deformation absorbed most of the impact energy. The findings will support the development of a generic quasi-static analytical model and numerical methods.

A comparative evaluation between flat and traditional energy directors for ultrasonic welding of CF/PPS thermoplastic composites

Energy directors, responsible for local heat generation in ultrasonic welding, are neat resin protrusions traditionally moulded on the surfaces to be welded. This study evaluates an alternative energy directing solution for ultrasonic welding of thermoplastic composites based on the usage of a loose flat layer of neat resin at the welding interface, referred to as ‘flat energy director’. Analysis of dissipated power, displacement of the sonotrode, welding energy and time as well as weld strength compared to more traditional energy directing solutions showed that flat energy directors, which significantly simplify ultrasonic welding of thermoplastic composites, do not have any substantial negative impact in the welding process or the quality of the welded joints.

On the prediction of cure-process shape deviations in fibre metal laminates

An investigation of the fabrication-induced distortions in fibre metal laminates is presented using finite-element modelling and experiments. Cooling down is considered as the main source of distortion. Four fibre metal laminate panels are manufactured and their curvature is measured using digital image correlation and linear variable differential transformer. The curvatures are the response of the non-symmetric lay-up to different parameters like stacking order and number of composite or metal layers. Acceptable agreement between model and experiment in predicting the geometry shows that the laminate shape can be predicted with reliability. A large displacement model should be used for large shape deviations in laminates with high level of non-symmetry. Fibre metal laminates may have single or multi-stable configurations after removal from the layup tool. This phenomenon is analysed and parameters and modelling considerations are investigated to obtain a method to predict the final configuration. Further modelling and experimentation are needed to improve the quality of the predictions with increasing complexity of the component.

Thermoelectric power in carbon nanotubes and quantum wires of nonlinear optical, optoelectronic, and related materials under strong magnetic field: Simplified theory and relative comparison

We study thermoelectric power under strong magnetic field (TPM) in carbon nanotubes (CNTs) and quantum wires (QWs) of nonlinear optical, optoelectronic, and related materials. The corresponding results for QWs of III-V, ternary, and quaternary compounds form a special case of our generalized analysis. The TPM has also been investigated in QWs of II-VI, IV-VI, stressed materials, n-GaP, p-PtSb2, n-GaSb, and bismuth on the basis of the appropriate carrier dispersion laws in the respective cases. It has been found, taking QWs of n-CdGeAs2, n-Cd3As2, n-InAs, n-InSb, n-GaAs, n-Hg1?xCdxTe, n-In1?xGaxAsyP1?y lattice-matched to InP, p-CdS, n-PbTe, n-PbSnTe, n-Pb1?xSnxSe, stressed n-InSb, n-GaP, p-PtSb2, n-GaSb, and bismuth as examples, that the respective TPM in the QWs of the aforementioned materials exhibits increasing quantum steps with the decreasing electron statistics with different numerical values, and the nature of the variations are totally band-structure-dependent. In CNTs, the TPM exhibits periodic oscillations with decreasing amplitudes for increasing electron statistics, and its nature is radically different as compared with the corresponding TPM of QWs since they depend exclusively on the respective band structures emphasizing the different signatures of the two entirely different one-dimensional nanostructured systems in various cases. The well-known expression of the TPM for wide gap materials has been obtained as a special case under certain limiting conditions, and this compatibility is an indirect test for our generalized formalism. In addition, we have suggested the experimental methods of determining the Einstein relation for the diffusivity-mobility ratio and the carrier contribution to the elastic constants for materials having arbitrary dispersion laws.

Signal processing in optical coherence tomography for aerospace material characterization

Abstract. Based on a customized time-domain optical coherence tomography (OCT) system, a series of signal processing approaches have been designed and reviewed. To improve demodulation accuracy and image quality, demodulation approaches such as median filter, Hilbert transform, and envelope detector were investigated with simulated as well as experimental data. Without noise, the Hilbert transform has the best performance, but after considering the narrow-band noise in the modulated signal, the envelope detector was selected as the ideal demodulation technique. To reduce noise and enhance image contrast, digital signal processing techniques such as a bandpass filtering and two-dimensional median filtering were applied before and after the demodulation, respectively. Finally with integration of the customized OCT setup and designed signal processing algorithms, aerospace materials, such as polymer coatings and glass-fiber composites, were successfully characterized. The cross-sectional images obtained clearly show the microstructures of the materials.

Quality assessment of aerospace materials with optical coherence tomography

The increasing demand of the aerospace industry for new functional materials requires appropriate methods for quality assessment. It is a new challenge nowadays to characterize materials with microstructure quickly, accurately, and nondestructively. Optical coherence tomography (OCT) is a contactless and non-destructive technique for obtaining the internal structure of turbid materials. In the past 20 years it has been continuously developed and nearly exclusively applied for biomedical imaging of tissues while OCT-based methods for non-biomedical investigation tasks, e.g. within the field of non-destructive testing for material inspection, are rarely reported. Therefore, here we demonstrate and evaluate the suitability of OCT for the assessment of aerospace materials, e.g. coatings, and glass fibre composites. A well-designed OCT system was built using a broad bandwidth light source with centre wavelength of 1550 nm. 2D galvanometer scanners and an optical delay line incorporated in the system make cross-sectional imaging available. Finally in combination with appropriate image processing, the thickness of thin films and the microstructure of materials can be determined for quality assessment.