Showing papers by "Weimin Huang published in 2009"

Shape-Memory Polymers—A Class of Novel Smart Materials

Abstract: Shape-memory polymers (SMPs) offer a number of potential technical advantages that surpass other shape-memory materials such as shape-memory metallic alloys and shape-memory ceramics. The advantages include high recoverable strain (up to 400%), low density, ease of processing and the ability to tailor the recovery temperature, programmable and controllable recovery behavior, and more importantly, low cost. This article presents the state-of-the-art regarding SMPs. First, the architecture, type, and main properties of the traditional and recently developed SMPs are introduced. Second, structural and multifunctional SMP composites are summarized and discussed. These composites greatly enhance the performance of the SMPs and widen their potential applications. Finally, current applications of SMP materials in aerospace engineering, textiles, automobiles, and medicine are presented.

Thin Film Shape Memory Alloys: Fundamentals and Device Applications

Abstract: This book, the first dedicated to this exciting and rapidly growing field, enables readers to understand and prepare high-quality, high-performance TiNi shape memory alloys (SMAs) It covers the properties, preparation and characterization of TiNi SMAs, with particular focus on the latest technologies and applications in MEMS and biological devices Basic techniques and theory are covered to introduce new-comers to the subject, whilst various sub-topics, such as film deposition, characterization, post treatment, and applying thin films to practical situations, appeal to more informed readers Each chapter is written by expert authors, providing an overview of each topic and summarizing all the latest developments, making this an ideal reference for practitioners and researchers alike

Analysis and comparison of sleeping posture classification methods using pressure sensitive bed system

Abstract: Pressure ulcers are common problems for bedridden patients. Caregivers need to reposition the sleeping posture of a patient every two hours in order to reduce the risk of getting ulcers. This study presents the use of Kurtosis and skewness estimation, principal component analysis (PCA) and support vector machines (SVMs) for sleeping posture classification using cost-effective pressure sensitive mattress that can help caregivers to make correct sleeping posture changes for the prevention of pressure ulcers.

Nature of the multistage transformation in shape memory alloys upon heating

Abstract: The processes developing in shape memory alloys due to heating with application of load and without the latter are investigated. The accompanying multistage reverse martensitic transformation is studied by the method of differential scanning calorimetry. The causes of the multistage transformation are analyzed.

Reversible surface morphology in shape-memory alloy thin films

Abstract: Reversible surface morphology can be used for significantly changing many surface properties such as roughness, friction, reflection, surface tension, etc. However, it is not easy to realize atop metals at micron scale around ambient temperature. In this paper, we demonstrate that TiNi and TiNi based (e.g., TiNiCu) shape-memorythin films, which are sputter-deposited atop a silicon wafer, may have different types of thermally-induced reversible surface morphologies. Apart from the well-known surface relief phenomenon, irregular surface trenches may appear in the fully crystallized thin films, but disappear upon heating. On the other hand, in partially crystallized thin films, the crystalline structures (islands) appear in chrysanthemum-shape at high temperature; while at room temperature, the surface morphology within the islands changes to standard martensite striations. Both phenomena are fully repeatable upon thermal cycling. The mechanisms behind these phenomena are investigated.

2-layer Erroneous-Plan Recognition for dementia patients in smart homes

Abstract: People with dementia lose their ability to learn, solve problems, and communicate. And they are all around us. To potentially replace some of their diminished memory and problem-solving abilities, Erroneous-Plan Recognition (EPR) aims to detect defects or faults in the execution of correct plans by the dementia patient, and send timely audio and visual prompts to the dementia patient and caregiver in order to correct these faults. The scope of this work is for the patient who lives alone in a smart home. One challenge is that the definition of plan can be very subjective. It is necessary to regard a plan as an Activity of Daily Living (ADL), choose the ADLs to monitor, and deploy available sensors to acquire data. With the sensor data, there can be activity recognition, followed by plan recognition. Another challenge is the highly random and erroneous behaviour of dementia patients. Multiple, sequential, and independent layers of error detection can be arranged in a prioritised manner to detect specific errors first, and provide an error probability if no specific errors are detected. On the whole, most of the EPR results are very good as they are at least 0.9, indicating that the data is linearly separable. The 2-layer EPR system, which uses the blacklist and whitelist as Layer 1 and naive Bayes classifier as Layer 2, is significantly more accurate than each individual layer. In fact, 5 out of 6 actors have an accuracy above 0.9. With the encouraging results, there will be more technical and domain challenges which we can address in the near future.

Formation of combined surface features of protrusion array and wrinkles atop shape-memory polymer

Abstract: We demonstrate a simple and cost-effective approach to realize two combined surface features of different scales together, namely submillimeter-sized protrusion array and microwrinkles, atop a polystyrene shape-memory polymer. Two different types of protrusions, namely flat-top protrusion and crown-shaped protrusion, were studied. The array of protrusions was produced by the Indentation-Polishing-Heating (IPH) process. Compactly packed steel balls were used for making array of indents. A thin gold layer was sputter deposited atop the polymer surface right after polishing. After heating for shape recovery, array of protrusions with wrinkles on the top due to the buckling of gold layer was produced.

Formation of Protrusive Micro/Nano Patterns atop Shape Memory Polymers

Abstract: The surface morphology of materials is of fundamental importance to many applications (e.g., surface wetting, friction, surface roughness, reflection, drag, adhesion, etc). Various approaches for micro/nano patterning atop polymer surfaces have been proposed in recent years. However, a cost effective technique is still highly in demand. In this paper, we demonstrate a few novel but rather simple and generic approaches for surface micro/nano patterning using shape memory polymers (SMPs). Reversible micro vertical chains, crown shaped protrusion arrays and strip/labyrinth wrinkles atop SMPs are presented.

Thin film shape memory alloys and microactuators

Abstract: For Micro-electro-mechanical System (MEMS) applications, TiNi-based thin film Shape Memory Alloys (SMAs) possess many desirable properties, such as high power density, large transformation stress and strain upon heating and cooling, superelasticity and biocompatibility. In this paper, recent development in TiNi-based thin film SMA and microactuator

Wet to Shrink: an Approach to Realize Negative Expansion upon Wetting

Abstract: Composites can be designed to have special properties, and even such properties that are difficult to find in nature. We propose a simple approach to realize negative expansion upon wetting, i.e., contraction upon wetting, using swelling materials. The key parameters in one-dimensional case are investigated, and the possible configurations for two and three-dimensional cases are presented. The feasibility is demonstrated through a simple test.

Wrinkling atop shape memory polymer with patterned surface

Abstract: We have previously demonstrated that various types of patterns at different scales can be easily realized atop shape memory polymers (SMPs) through a procedure in three steps, namely, indentation, polishing and heating (IPH). On the other hand, by coating a thin metallic layer (e.g., a few nanometers thick of gold) atop SMPs with or without prestraining, different types of wrinkles could be generated. In this paper, we investigate the wrinkling patterns formed on the top of SMPs with a patterned surface, i.e., wrinkling atop a surface with a protrusion pattern. As the wrinkles are resulted simultaneously by two phenomena upon heating, namely the shape recovery of the SMP substrate and buckling of the elastic metallic layer, the wrinkle pattern varies from one location to another depending on the exact local strain. Utilizing this technique, we are able to simultaneously produce a surface with complicate surface patterns at both micro and millimeter levels. Such surfaces could significantly enhance many surface properties, e.g., bonding, adhesion and friction etc.

Lamb-wave-based damage detection using wave signal demodulation and artificial neural networks

Abstract: The interaction between Lamb wave and damage will modify the response wave signal from which information related to damage can be extracted for automated damage detection. However, the interpretation of the response wave signal is not easy due to the complex nature of the wave-damage interaction. This paper discusses a damage detection algorithm based on wave signal demodulation and artificial neural networks (ANNs). The response wave signal is considered as a low-frequency signal modulated by a high-frequency carrier signal. After baseline subtraction, frequency domain convolution and filtering, the original signal is demodulated and transformed into a new simplified signal related to the energy change due to damage. Subsequently feature extraction is carried out by finding the local maxima in the new signal and the obtained peak values and locations are used as inputs into the ANNs for damage characterization. The validity of this damage detection algorithm is then verified using a finite element (FE) model of a composite laminate with notch defects. The response wave signals of different notch depths and locations are acquired from the simulations and used as the training and testing samples. Finally the assessment of the network's accuracy and generalization ability is performed and the result is satisfactory.

Indentation on very smooth silicon wafers

Abstract: At present, indentation is considered as the most convenient approach for characterising materials for MEMS and even NEMS devices. Here, we demonstrate that a very slight change in the average surface roughness (Ra) of a commercial silicon wafer, that is, from 1.6 to 4.4 nm, can dramatically alter the indentation result. Another surface condition, namely, wetting, is also influential. Since it is not easy to quantitatively describe the effects of the interface between the indenter and tested material, the results of indentation test, as an approach for revealing the properties of a material, should be treated with great cautions.

Abrupt Softening Phenomenon in a Shape Memory CuAlNi Single Crystal under Uniaxial Compression

Abstract: Abrupt softening phenomenon was observed in a shape memory CuAlNi single crystal upon uniaxial compression. Sudden martensite variant(s) reorientation was found to be the reason behind this anomalous behavior. The significance of this finding is twofold. On one hand, it clearly demonstrates that the stress induced transformation can follow a sequence of the phase transformation (martensitic transformation, austenite to martensite) and then reorientation (from one martensite variant to another). On the other hand, the anomalous softening provides a good evidence for explaining the propagation of the phase transformation front.

Polystyrene based shape memory nanocomposites

Abstract: Shape memory nanocomposites were fabricated using cross-link polystyrene as a matrix and different nano-fillers (including alumina, silica and clay) were used as the enhancing agencies. Their thermo-mechanical properties and shape memory effect (SME) were characterized using micro-indentation, tensile tests and differential scanning calorimetry. Experimental results clearly revealed the reinforcement effect from the nanofillers, good thermal properties and SME.