The structural relaxation of a cluster containing 55 atoms at elevated temperatures is simulated by molecular dynamics. The interatomic interactions are given by using the embedded atom method （EAM） potential. By de...The structural relaxation of a cluster containing 55 atoms at elevated temperatures is simulated by molecular dynamics. The interatomic interactions are given by using the embedded atom method （EAM） potential. By decomposing the peaks of the radial distribution functions （RDFs） according to the pair analysis technique, the local structural patterns are identified for this cluster. During increasing temperature, structural changes of different shells determined by atom density profiles result in an abrupt increase in internal energy. The simulations show how local structural changes can strongly cause internal energy to change accordingly.展开更多
Natural materials such as bone, tooth and nacre achieve attractive properties through the ＂staggered structure＂, which consists of stiff, parallel inclusions of large aspect ratio bonded together by a more ductile a...Natural materials such as bone, tooth and nacre achieve attractive properties through the ＂staggered structure＂, which consists of stiff, parallel inclusions of large aspect ratio bonded together by a more ductile and tougher matrix. This seemingly simple structure displays sophisticated micromechanics which lead to unique combinations of stiffness, strength and toughness. In this article we modeled the staggered structure using finite elements and small Representative Volume Elements （RVEs） in order to explore microstructure-property relationships. Larger aspect ratio of inclusions results in greater stiffiless and strength, and also significant amounts of energy dissipation provided the inclusions do not fracture in a brittle fashion. Interestingly the ends of the inclusions （the junctions） behave as crack-like features, generating theoretically infinite stresses in the adjacent inclusions. A fracture mechanics criterion was therefore used to predict the failure of the inclusions, which led to new insights into how the interfaces act as a ＂＇soft wrap＂ for the inclusions, completely shielding them from excessive stresses. The effect of statistics on the mechanics of the staggered structure was also assessed using larger scale RVEs. Variations in the microstructure did not change the modulus of the material, but slightly decreased the strength and significantly decreased the failure strain. This is explained by strain localization, which can in turn be delayed by incorporating waviness to the inclusions. In addition, we show that the columnar and random arrangements, displaying different deformation mechanisms, lead to similar overall prop- erties. The guidelines presented in this study can be used to optimize the design of staggered synthetic composites to achieve mechanical performances comparable to natural materials.展开更多
基金Project supported by the National Natural Science Foundation of China （Grant No 50572013） and the National Basic Research Program of China （Grant No 2006CB605103）. Corresponding author.
文摘The structural relaxation of a cluster containing 55 atoms at elevated temperatures is simulated by molecular dynamics. The interatomic interactions are given by using the embedded atom method （EAM） potential. By decomposing the peaks of the radial distribution functions （RDFs） according to the pair analysis technique, the local structural patterns are identified for this cluster. During increasing temperature, structural changes of different shells determined by atom density profiles result in an abrupt increase in internal energy. The simulations show how local structural changes can strongly cause internal energy to change accordingly.
文摘Natural materials such as bone, tooth and nacre achieve attractive properties through the ＂staggered structure＂, which consists of stiff, parallel inclusions of large aspect ratio bonded together by a more ductile and tougher matrix. This seemingly simple structure displays sophisticated micromechanics which lead to unique combinations of stiffness, strength and toughness. In this article we modeled the staggered structure using finite elements and small Representative Volume Elements （RVEs） in order to explore microstructure-property relationships. Larger aspect ratio of inclusions results in greater stiffiless and strength, and also significant amounts of energy dissipation provided the inclusions do not fracture in a brittle fashion. Interestingly the ends of the inclusions （the junctions） behave as crack-like features, generating theoretically infinite stresses in the adjacent inclusions. A fracture mechanics criterion was therefore used to predict the failure of the inclusions, which led to new insights into how the interfaces act as a ＂＇soft wrap＂ for the inclusions, completely shielding them from excessive stresses. The effect of statistics on the mechanics of the staggered structure was also assessed using larger scale RVEs. Variations in the microstructure did not change the modulus of the material, but slightly decreased the strength and significantly decreased the failure strain. This is explained by strain localization, which can in turn be delayed by incorporating waviness to the inclusions. In addition, we show that the columnar and random arrangements, displaying different deformation mechanisms, lead to similar overall prop- erties. The guidelines presented in this study can be used to optimize the design of staggered synthetic composites to achieve mechanical performances comparable to natural materials.
