Engineering Design Of Materials Research Articles

Inherent Anharmonicity of Harmonic Solids.

Atomic vibrations, in the form of phonons, are foundational in describing the thermal behavior of materials. The possible frequencies of phonons in materials are governed by the complex bonding between atoms, which is physically represented by a spring-mass model that can account for interactions (spring forces) between the atoms (masses). The lowest-order, harmonic, approximation only considers linear forces between atoms and is thought incapable of explaining phenomena like thermal expansion and thermal conductivity, which are attributed to nonlinear, anharmonic, interactions. Here, we show that the kinetic energy of atoms in a solid produces a pressure much like the kinetic energy of atoms in a gas does. This vibrational or phonon pressure naturally increases with temperature, as it does in a gas and therefore results in a thermal expansion. Because thermal expansion thermodynamically defines a Grüneisen parameter , which is a typical metric of anharmonicity, we show that even a harmonic solid will necessarily have some anharmonicity. A consequence of this phonon pressure model is a harmonic estimation of the Grüneisen parameter as , where is the ratio of the transverse and longitudinal speeds of sound. We demonstrate the immediate utility of this model by developing a high-throughput harmonic estimate of lattice thermal conductivity that is comparable to other state-of-the-art estimations. By linking harmonic and anharmonic properties explicitly, this study provokes new ideas about the fundamental nature of anharmonicity, while also providing a basis for new material engineering design metrics.

A perspective on intelligent design of engineered materials and structures by interface mechanics

Engineering design of materials and structures has evolved radically from earliest employment of single phase materials with a focus on optimization of geometric shapes to recent multiphase materials with tactful integration and assembly in both geometric shapes and material domains. In these recent design concepts and strategies, the interfaces are crucial and leveraged to achieve properties and functionalities surpassing those of individual material/phase components and/or their simple superpositions. This perspective focuses on the underpinned interface mechanics view in which insights are essential to understand fundamentals of integration, tailoring and assembly of multiphase materials with diverse geometric layouts. The view also provides insights to enable creations of intelligent new design concepts and approaches of materials and structures capable of being readily manufactured with current technologies. Selected examples of engineered materials and structures enabled by either solid-solid or solid-liquid interactions are provided to highlight the driving role of interface mechanics in designs and to outlook the associated future opportunities and challenges.

The Tip Field of Mode III Crack in Damage Material

The research of crack-tip field in damage materials is a very complex problem. The core question is how to give the damage constitutive equation and determine the crack tip singularity order of magnitude of the physical quantities. Taking into account the damage process is a process which the energy (strain) accumulates, and the initial damage threshold value existence, on the Lemaitre’s research foundation, the brittle material damage constitutive equation that has the initial damage quantity and the power order relationship with strain is given. Under the assumption that stress (strain) is finite, the construction of III mode crack tip damage fields is studied and the solution of crack-tip stress (strain) asymptotic field is given. Finally, the relationship of the initial crack tip damage zone and full damage zone Scale and material parameters are discusses. These works provide theoretical basis for the material engineering design and the appraisal structure reliability.