Mohd Roshdi Hassan

Aerogels in Aerospace: An Overview

Aerogels are highly porous structures prepared via a sol-gel process and supercritical drying technology. Among the classes of aerogels, silica aerogel exhibits the most remarkable physical properties, possessing lower density, thermal conductivity, refractive index, and dielectric constant than any solids. Its acoustical property is such that it can absorb the sound waves reducing speed to 100 m/s compared to 332 m/s for air. However, when it comes to commercialization, the result is not as expected. It seems that mass production, particularly in the aerospace industry, has dawdled behind. This paper highlights the evolution of aerogels in general and discusses the functions and significances of silica aerogel in previous astronautical applications. Future outer-space applications have been proposed as per the current research trend. Finally, the implementation of conventional silica aerogel in aeronautics is argued with an alternative known as Maerogel.

In-plane Tensile Behavior of Shape Memory Alloy Honeycombs with Positive and Negative Poisson’s Ratio

This work illustrates the manufacturing and tensile testing of a novel concept of honeycomb structures with hexagonal and auxetic (negative Poissons ratio) topology, made of shape memory alloy core material. The honeycombs are manufactured using Nitinol ribbons having 6.40 mm of width and 0.2 mm of thickness. The ribbons were inserted in a special dye using cyanoacrilate to bond the longitudinal strips of the unit cells. Tensile tests at room temperature (full martensite) were performed on the honeycombs. Finite element models of the honeycomb assemblies under tensile loading have been developed using nonlinear beam elements from a commercial code. Good agreement is observed between numerical nonlinear simulations and the experimental results.

Review of the Machining Difficulties of Nickel-Titanium Based Shape Memory Alloys

The purpose of this study is to identify machining difficulties of nickel-titanium based shape memory alloys. Nickel-titanium (Nitinol) is one the widely used shape memory material which is applied in many products in the aerospace, medical, and biomedical fields. NiTi alloy cannot be machined easily because of high tool wear, high cutting force, huge hardness and surface defects are made many problems into their machining. Investigation in micron precision shows plenty surface defects in machining process, something like debris of microchips, feed marks, tearing surface, deformed grains, material cracking and chip layer formation which consists the main problem in the machining of shape memory alloys. Moreover, these defects can be reduced or eliminated by changing the cutting parameters such as: feed rate, cutting speed and cutting depth so that, machining of nickel-titanium alloys would be improved.

Review of Self-Healing Effect on Shape Memory Alloy (SMA) Structures

Self-healing has usually an emphasis on special materials that is metallic materials. When there is a minor damage, almost all biological organisms, even complex ones, have the ability to repair themselves. Recently, a novel field of materials science is constituted by self-healing in organic materials or material systems and it is rapidly expanding. These materials have a particular ability to heal themselves. The initial crack is healed to the point that upon reloading, a new crack is formed next to the original, rather than the original crack reopening. Only simple heating can reverse transformation and cause reinforcement for these cracks. The shape memory alloy wires are activated by heating the system and therefore the healing begins. Due to the heat, the wires relapse to their original shape at the shape change in martensite to austenite transition temperature. The concentration of most of the studies so far has been on polymers and ceramics and the reason is that it includes self-healing in non-metallic materials. Also, they are more convenient than including it in metallic materials. In this review paper the design principles of self-healing materials and their improvement methods are investigated.

A Review of the Flammability Factors of Kenaf and Allied Fibre Reinforced Polymer Composites

Natural fibre is a well-known reinforcement fibre in polymer-matrix Composites (PMC) lately. Natural fibre has fast growing and abundance properties which make it available at very low cost. For kenaf fibre there is long lists of research projects which have been done regarding its behaviour, and properties and modification made to it. In this paper, fire flammability is the main concern for natural fibre reinforced polymer (NFRP) composites especially kenaf fibre. To estimate its flammability, a wide range of factors can be considered such as fibre content, type of matrices, pH conditions, treatment, and fire retardant (FR) filler’s type. The most important criteria are the ignition time, rate of propagation, and fire behavior. thermogravimetric analysis (TGA), different scanning calorimetric (DSC), and dynamic mechanical analysis (DMA) are the three most famous methods used to investigate the fire behaviour of composites.

Modeling and testing of shape memory alloy chiral honeycomb structures

Shape memory alloy honeycombs are constitute a novel set of cellular structures developed by the authors using initially centersymmetric honeycomb configurations (hexagonal ones), and pseudo-plastic Nitinol ribbons as core. Chiral honeycomb structures feature a noncentresymmetric unit cell configuration, with rotational symmetry only and in-plane Poissons ratio equal to -1. Nonlinear unit cell FE models of these chiral honeycombs have been developed using the formulation proposed by Auricchio et al. related to pseudo-elastic and superelastic SMA materials. The numerical results are compared with experimental ones from tensile tests of chiral honeycomb samples subjected to uniaxial tensile loading at full martensite phase, and analytical results from the model proposed by Prall and Lakes on hexachiral configurations. A working prototype of a deployable antenna made out hexachiiral cells with 1-way SMA ribbon is also described.

Using Design of Experiments Methods for Assessing Peak Contact Pressure to Material Properties of Soft Tissue in Human Knee

Contact pressure in the knee joint is a key element in the mechanisms of knee pain and osteoarthritis. Assessing the contact pressure in tibiofemoral joint is a challenging mechanical problem due to uncertainty in material properties. In this study, a sensitivity analysis of tibiofemoral peak contact pressure to the material properties of the soft tissue was carried out through fractional factorial and Box-Behnken designs. The cartilage was modeled as linear elastic material, and in addition to its elastic modulus, interaction effects of soft tissue material properties were added compared to previous research. The results indicated that elastic modulus of the cartilage is the most effective factor. Interaction effects of axial/radial modulus with elastic modulus of cartilage, circumferential and axial/radial moduli of meniscus were other influential factors. Furthermore this study showed how design of experiment methods can help designers to reduce the number of finite element analyses and to better interpret the results.

Experimental Determination of Fatigue Life of Automotive Jounce Bumper

It is evident that most rubber components in the automotive industry are subjected to repetitive loading. Vigorous research is needed towards improving the safety and reliability of the components. The study is conducted on an automotive rubber jounce bumper with a rubber hardness of 60 IRHD. The test is conducted in displacement controlled environment under compressive load. The existing models by Kim, Harbour, Woo and Li are adopted to predict the fatigue life. The experimental results show strong similarities with the predicted models.

Thermochemical Properties of Glass Wool/Maerogel Composites

Aerogel blankets are composites of silica aerogel particles dispersed in a reinforcing fiber matrix that turns the brittle aerogel into durable and flexible insulating materials. In this study, silica aerogel was loaded on glass wool with different concentrations (0–18.6%) and morphological and thermal characteristics of the aerogel blankets were studied. Rate of modified blanket decomposition was slower at temperatures between 250°C and 650°C due to the retardant effect of the silica aerogel. The average diameter of the fiber for either original glass wool or modified glass wool materials was approximately 20 μm and samples had porous, interconnected particles with dendritic-like structure.

Shape Memory Alloy Applications in Bone Fixation: State of the Art

Shape Memory Alloy (SMA) can transform its shape back to its original shape when subjected to a thermomechanical process. Applications of SMA in the bone fixation have been successful due the material’s ability to exhibit Shape Memory Effect (SME) as well as biocompatibility. A good design of bone fixation device made of SMA is capable of exerting a constant compressive force to the bone fracture while remains inert to the environment inside the host’s body. This study presents the application of SMA in bone fixation devices. These include SMA suturing devices, OSStaple, SMA patellar concentrator and SMA embracing fixator.