Papers by Keyword: Material Evaluation

Abstract: Porous Al is a lightweight material with excellent heat insulation and sound absorption properties and is expected to be used in a wide range of applications. A method based on mechanochemical reactions has been developed as an environmentally friendly approach to porous Al production. Pure Al powder reacts with pure water to form a coating layer of Al (OH)₃ on the surface of the powder particles. Adjacent particles then bind together by adhesion of their coating layers. Since a large number of voids remain between the individual particles, the compact is classified as porous Al. In the present study, a mixture of pure Al powder and pure water was subjected to uniaxial compressive stresses ranging from 0 to 100 MPa to form porous Al. The mechanical properties of the resulting compact were evaluated in terms of the amount of H₂ produced, the density, the Al (OH)₃ texture, the amount of Al (OH)₃ formed, and the results of subsequent compression tests. The density of the porous Al was found to increase with increasing compressive stress during formation. The largest amounts of H₂ (800 ml) were produced under a compressive stress of 10 MPa. As the compressive stress was increased, the total amount of generated Al (OH)₃ increased, was approximately constant from 30 to 50 MPa, and then decreased. The initial maximum stress, the plateau stress, and the absorbed energy increased with increasing compressive stress and were 100 MPa, 17.5 MPa, and 10.1 MJ/m³, respectively, for a compressive stress of 100 MPa.

Abstract: Base on current status of rural residential roofs in northeast China, in order to improve and ensure the qualities, safety and functions of flat roofs in this region, this paper first put forward the “rural secure flat roof”, then according to the weather characteristic and the needs of residents, proceeded the construction design of rural secure flat roof. Finally established the comprehensive evaluation system and used VRS model to evaluate several common roofing insulation materials. Results show that hydrophobic expanded perlite, rock wool and glass wool can be the ideal roofing insulation materials. The research on construction design and material evaluation is significant on promoting the functions and safety of rural residence.

Abstract: Ti has high strength, good corrosion resistance, is lightweight and shows good biocompatibility. It has thus been used extensively for mechanical and medical structural components. On the other hand, the disadvantages of Ti include a high melting point, ease of oxidization at high temperatures, low specific heat and low thermal conductivity. There are three specific problems associated with Ti metallurgy. The first is that powder metallurgical processing requires high temperatures and a high vacuum, the second is that samples produced by existing powder metallurgy techniques have a low density, and the third is the occurrence of burning because of a local temperature rise during the cutting process. Therefore, in the present work, a new high-speed, room-temperature molding process involving compression rotation shearing was developed. This method can be used for solidification of metal powders by enforced plastic flow and breaking of oxide films. Therefore, no external heat is required and the molding time is short. The proposed method represents an easy approach to consolidating high melting point metallic materials.

Abstract: The presence of damage or cracks modifies the elastic properties of a sample, introducing nonlinear components in the elastic response to an ultrasonic excitation. Among other effects, we discuss here conditioning and memory, i.e. the transition of the sample to a new (non equilibrium) elastic state when perturbed by a strain, even at a relatively low amplitude. A quantification of these phenomena can be the basis for a novel Nondestructive Method to evaluate the integrity of a structural or mechanical component.

Abstract: In this paper the relationship between CAI and compressive design allowables of composite structures were discussed and it was pointed out that traditional CAI values could not reflect the behavior of composite materials to withstand impact adequately and no relationship between CAI values and compressive design allowables existed. Based on the integrity requirements of composite structures, it was pointed out that the evaluation system of composite materials to withstand impact should include both damage resistance and damage tolerance. Large numbers of test data verified that the knee point phenomenon of composite laminates to withstand impact existed. Based on failure mechanisms, it was proposed that the behavior evaluation system of composite systems to withstand impact was based on the properties at the knee point, that is, the maximum capability to keep integrity of the front plies (the maximum contact force) characterizing damage resistance and the threshold of dent depth(or impact energy)~compressive strength(or failure strain) curves characterizing damage tolerance.