Faculty of Engineering


Research Highlights

Understanding and Controlling Defects in Materials

Materials are used to support structures and join components at various scales, from massive infrastructures to tiny devices. However, damage to or destruction of those structures can lead to injury or death if not properly prevented. Even if structural damage does not endanger human life, it can have economic impacts to a greater or lesser extent. We all know that materials eventually break when subjected to large forces or repeated deformation, but what happens in a material during this process, and how do we determine the conditions under which said material breaks? The key to more accurate predictions of material behavior and the development of better materials is to understand what is happening inside of them. 

Zooming in on a material that appears to be homogeneous reveals a hierarchy of structures and discrete properties. Metallic materials usually have a crystalline structure. When you hear the word "crystal," you may imagine that their atoms are lined up in an orderly fashion, but in reality, crystals contain a myriad of structures called lattice defects, which are disordered arrangements of atoms. When a material is put under stress, these defects move and interact with each other, multiplying or disappearing to form a heterogeneous and complex structure. These defects can damage or destroy a material, but they can also impart exceptional strength and toughness by moderately constraining each other's motion. 

In the Material Mechanics Laboratory, our research theme is "understanding, controlling, and exploiting defects". We mainly use atomistic simulations, but also use more microscopic electron-level calculations (first-principles calculations) and more macroscopic simulation methods, and sometimes combine them to study metal deformation from a microscopic viewpoint. Currently, we are working on (i) hydrogen embrittlement and (ii) deformation behavior of magnesium alloys. Here, we will briefly introduce the former.  

Hydrogen embrittlement is a phenomenon in which the strength of a metal is greatly degraded when hydrogen enters the metal during the manufacturing process or in the operating environment. This phenomenon is called Hydrogen Embrittlement (HE). The development of fuel cell vehicles and other devices is underway due to environmental concerns, and the number of fracture accidents caused by HE will surely increase as a result. The main goal of our research is to clarify the causes of HE, which will be useful for material development and design. The strength loss due to hydrogen is attributed to the fact that hydrogen acts on lattice defects and negatively changes their behavior. Therefore, we predict the distribution of hydrogen around various lattice defects based on atomistic simulations and analyze in detail the effects of hydrogen on the motion and interaction behavior of lattice defects to unravel the effects of hydrogen one by one from a microscopic viewpoint.