Bioinspired low-frequency material characterisation

New-coded signals, transmitted by high-sensitivity broadband transducers in the 40–200 kHz range, allow subwavelength material discrimination and thickness determination of polypropylene, polyvinylchloride, and brass samples. Frequency domain spectra enable simultaneous measurement of material properties including longitudinal sound velocity and the attenuation constant as well as thickness measurements. Laboratory test measurements agree well with model results, with sound velocity prediction errors of less than 1%, and thickness discrimination of at least wavelength/15. The resolution of these measurements has only been matched in the past through methods that utilise higher frequencies. The ability to obtain the same resolution using low frequencies has many advantages, particularly when dealing with highly attenuating materials. This approach differs significantly from past biomimetic approaches where actual or simulated animal signals have been used and consequently has the potential for application in a range of fields where both improved penetration and high resolution are required, such as nondestructive testing and evaluation, geophysics, and medical physics

Sensor material characterisation for magnetometer application

Pengukuran dan gangguan medan magnet arus terus dan arus ulang-alik memerlukan penderia medan magnet yang mempunyai kepekaan yang tinggi dan stabil. Untuk menghasilkan penderia tersebut, ciri-ciri bahan magnet yang baik telah dikenalpasti. Beberapa jenis bahan magnet yang berbeza telah digunakan untuk mengkaji ciri-ciri dan kesannya terhadap medan magnet. Teras gelang yang diperbuat daripada bahan-bahan magnet tersebut direkabentuk dengan dimensi yang sama bagi membolehkan perbandingan dibuat dengan mudah. Selain itu, rod tunggal dan berkembar juga telah digunakan sebagai teras penderia fluxgate, untuk melihat prestasi setiap jenis penderia tersebut. Kedua-dua penderia tersebut telah diuji dengan menggunakan dua sumber bahan magnet iaitu bar magnet tetap dan solenoid dengan diameter dawai yang berbeza. Isyarat keluaran bagi setiap penderia fluxgate seterusnya diproses bagi mengenalpasti hubungannya dengan ketumpatan medan magnet

Material Characterization and Real-Time Wear Evaluation of Pistons and Cylinder Liners of the Tiger 131 Military Tank

Material characterisation and wear evaluation of the original and replacement pistons and cylinder-liners of Tiger 131 is reported. Original piston and cylinder-liner were operative in the Tigers’ engine during WWII. The replacement piston and cylinder-liner were used as substitutes and were obtained after failure in two hours of operation in the actual engine. Material characterisation revealed that the original piston was aluminium silicon hypereutectic alloy whereas the replacement piston was aluminium copper alloy with very low silicon content. Both original and replacement cylinder-liners consisted of mostly iron which is indicative of cast iron, a common material for this application. The replacement piston average surface roughness was found to be 9.09 μm while for replacement cylinder-liner it was 5.78 μm

Numerical and experimental studies of multi-ply woven carbon fibre prepreg forming process

Woven carbon fibre prepreg is being increasingly used in high-performance aerospace and automotive applications, primarily because of its superior mechanical properties and formability. A wide range of forming simulation options are available for predicting material deformation during the prepreg forming process, particularly change in fibre orientation. Development of a robust validated simulation model requires comprehensive material characterisation and reliable experimental validation techniques. This paper presents experimental and numerical methods for studying the fibre orientation in multi-ply woven carbon fibre prepreg forming process, using a double-dome geometry. The numerical study is performed using the commercial forming simulation software PAM-FORM and the material input data are generated from a comprehensive experimental material characterisation. Two experimental validation methods are adopted for fibre shear angle measurement: an optical method for measuring only the surface plies, and a novel CT scan method for measuring both the surface plies and the internal plies. The simulation results are compared against the experimental results in terms of fibre shear angle and the formation of wrinkles to assess the validity of the model

Unbound material characterisation with Nottingham asphalt tester

The resilient modulus (MR) of unbound materials is a required input in most of the mechanistic-based pavement analysis and design process and has a significant effect on the projected pavement performance in the mechanistic– empirical pavement design guide programme or AASHTOWare DARwin. The Iowa Department of Transportation (DOT) recently acquired a servo-hydraulic dynamic loading materials test system known as the Nottingham asphalt tester (NAT). The Iowa DOT NAT is a hybrid servo-hydraulic machine designed for testing not only hot-mix asphalt performance properties but also unbound materials’ MR (although this has not been verified so far). The primary objectives of this research are to update and verify the capacity of the Iowa DOT hybrid NAT for testing unbound material’s MR through a detailed laboratory testing programme and regression analyses using non-linear stress-dependent models

Material characterisation for discrete element modelling calibration

The accurate determination of the microparameters needed in a Discrete Element Method (DEM) simulation is essential to obtain reliable results. In this work the DEM model parameters sensitivity in three different laboratory tests (single particle drop test, uniaxial particle compression and rotating drum) are investigated with respect to parameter value changes. The DEM parameters are varied by ± 25% from standard values. Materials used are 3.0 mm soda lime glass spheres and 3.0 mm polyamide spheres. Drop test simulations were sensitive only to change in coefficient of restitution parameter. The single particle compression test indicates that mainly the elasticity parameters influence the numerical response, Young’s modulus and Poisson’s ratio respectively. The sensitivity analysis indicates that the dynamic angle of repose in simulations depends on static as well as rolling friction coefficients

Passive thermoelectric power monitoring for material characterisation

Monitoring deterioration of material properties is important for assessing the structural integrity of engineering components, as it may indicate susceptibility to damage. This article focusses on the example of thermoelectric power measurements, which are known to be indicative of thermal and irradiation embrittlement and may therefore act as a proxy metric for material integrity. A passive thermoelectric power–monitoring technique is proposed which is suitable for permanent installation on engineering components. In passive measurements, the active perturbation (in this case, the heating required to create a temperature gradient) is replaced by incidental perturbation from the environment. The reduction in the ‘signal’ amplitude associated with relying on incidental perturbations may be compensated by increasing the number of individual measurements, facilitated by the greatly reduced power demand of the passive modality. Experimental studies using a stainless steel tube as a test component demonstrate thermoelectric power accuracy of <0.03 μV/°C is achievable with temperature gradients of the order of 2°C; in many cases of practical importance, this is sufficient to track the anticipated changes in thermoelectric power associated with thermal degradation

Thermal influence of welding process on strength overmatching of thin dissimilar sheets joints

The investigation addresses the overall performance of black and white joints (BWJ) of low carbon steel and stainless steel thin sheets achieved by laser hybrid welding. First, thermal field modelling is carried out by considering Goldak’s double ellipsoidal heat source model, together with a contribution of the authors related to the shape coefficients. In parallel, the technological development of BWJ laser hybrid welding is also addressed. Material characterisation by means of macro and microstructural examination and hardness tests is performed. The overall tensile performance of BWJ is discussed together with the weld metal strength overmatching. The tensile tests results indicate that in case of transversally loaded joints, the positive difference in yield between the weld metal and the base materials protects the weld metal from being plastically deformed; the flat transverse tensile specimens loading up to failure reveals large strains in low carbon steel, far away from the wel