with Mg? And can alloying be used to produce such insoluble compounds.Imperative Defensive Research: The corrosion mechanism indicates that stress corrosion cracking (SCC) is a concern. Moreover, there is the expectation that environment assisted cracking (EAC) (including SCC and hydrogen embrittlement (HE)) failures will increase with increased use of Mg alloys in load bearing applications. The low incidence of service SCC failures can be attributable to low actual stresses in service in the past. However, the incidence of EAC is expected to increase because the service conditions for Mg alloys are changing, particularly in the automobile industry where magnesium components are being increasingly used in structural load-bearing applications. Furthermore, increased loading on these magnesium components is a natural progression as designers increase the loads and decrease the section sizes of components as part of the environment imperative to decrease weight. Moreover, the magnesium components in the load bearing applications are increasing in complexity, and this increasing complexity increases the probability of high loads in some parts of such components. It is imperative that research is undertaken to provide understanding of this issue before there are some service incidents. It is important to understand (1) environmental influences and (2) alloys influence.The study of the localised corrosion of the current alloys is needed for a deeper understanding of their corrosion behavior. It is known that localised corrosion is the most common form of corrosion for magnesium alloys, but so far there have been no mechanistic studies of this form of corrosion for magnesium alloys. In addition, it necessary to understand the corrosion performance of existing (and new) alloys so that it is possible to make engineering decisions about their service performance.
The benefits of combining different homogeneous materials to give heterogeneous materials have been recognized since our early history; straw-reinforced brick and goat hairreinforced pottery are examples. [1] Such combinations are known as multi-materials [2] or hybrid materials. [3] A useful working definition [4] is "a combination of two or more materials in a pre-determined configuration and scale, optimally serving a specific engineering purpose". Established examples are particular and fiber-reinforced composites, [1,5] like CFRP and GFRP, and sandwich structures. Barbero classifies multi-materials -composites as he terms them -into three classes: reinforced composites, laminated composites and hybrid composites. [6] Ashby includes lattice materials and segment materials in addition to reinforced composites and sandwich structures. [7] Four classes of multi-materials, following Ashby, [7] are presented in Figure 1. This article describes a tool to support designers in comparing the performances of multi-materials with those of other materials and to guide their selection for a given application. One particular type, sandwich panels, is chosen as a focus to implement and illustrate the methodology.Approaches to multi-material selection: Designers should ideally explore the widest possible range of conceptual solutions before selecting one. Thus, the material search space should be as broad as possible at the conceptual design stage, as shown in Figure 2. As the design proceeds this space is narrowed, culminating in a single choice.Multi-material selection is more complicated than that of monolithic materials for two reasons: first, because the configuration in which the constituents are to be combined must be chosen, and, second, because, in optimizing the combination, the number of free variables is greater -it now includes the relative volumes of the two constituents, their configuration and their scale. What is needed is a way of exploring and optimizing these. Designers can then bring multi-materials into consideration in either of two broad approaches, as mentioned by Phillips [8] and Quinn. [9] Catalogue approach: Particulate and fibrous compositesthe best known hybrids -can be included in a materials database in the same way as monolithic materials, allowing direct comparison and selection by established material-selection methodologies. [7] An example is the Cambridge Engineering Selector (CES) database, [10] which includes some 200 composites and foams. Work on developing a knowledge-based system to assist composites selection has also been undertaken. [11] This allows selection from among existing, commercially available composites, but it does not allow for optimization; to do that requires ways of exploring all feasible combinations of material, configuration, and, where relevant, scale.The proposed approach: The alternative is to think of multimaterials as the combination of several constituents. This approach might well lead to a better solution since the multimaterials can be tailored to meet t...
Cone-beam computed tomography (CBCT) has become increasingly popular in dental and maxillofacial imaging due to its accurate 3D information, minimal radiation dose, and low machine cost. In this paper, we have proposed the newly developed CBCT scanner, called DentiiScan. Our gantry system consisting of a cone-beam X-ray source and an amorphous silicon flat panel detector is rotated around a patient's head. With the large area detector, only a single rotation is needed to reconstruct the field-of-view area from chin to eyes and our reconstructed algorithm based on GPU calculation is about 30 times faster than the CPU-based algorithm. The radiation dose was measured and compared to other dental and medical CT machines. The absorbed radiation dose from our proposed CBCT machine is significantly low. In addition, geometric accuracy was analyzed when the test object was scanned at the normal position as well as the inclined position. The results from three observers repeated for five times confirm that the machine can produce reconstructed images with high accuracy.
Due to accurate 3D information, minimal radiation dose, and low machine cost, cone-beam computed tomography (CBCT) has become increasingly popular in dental and maxillofacial imaging. In this paper, we propose the first development of the CBCT scanner in Thailand, called DentiiScan. The gantry system uses a cone-beam X-ray source and a large amorphous silicon flat panel detector to rotate around a patient's head and capture raw data. Our reconstructed algorithm based on GPU calculation can produce 3D image data in approximately 5 seconds. Image quality of reconstructed images was evaluated through a standard phantom as well as visual analysis on real clinical data. The results show that our system is suitable for diagnosis and treatment planning in dental and maxillofacial applications.
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