The extent to which materials can withstand mechanical loads is crucial to the safety of components – e.g. in aeroplanes. Researchers have now discovered a previously unknown mechanism of damage in metals, which is particularly relevant to materials’ formability and safety with an eye to recycling processes.
When manufacturing components, it is important to understand the loads to which the materials are going to be subjected. Any material’s behaviour will be affected by mechanical loads such as tension, compression, bending or shear. Under shear load, parts of the material shift against one another, giving rise to internal stresses known as shear stresses. Hitherto, researchers had assumed that shear load caused no significant rise in damage in materials; consequently, there was previously no explanatory basis for material failure under such loads. Now, scientists from the Institute for Photon Research and Synchrotron Radiation (IPS) and the Laboratory for Applications of Synchrotron Radiation (LAS) at the Karlsruhe Institute of Technology (KIT), in collaboration with colleagues from the French university Mines Paris – PSL, have discovered a previously unknown mechanism of damage in metals under shear load: under shear load, contaminants in the form of rigid particles can cause the volume of pores to increase up to sixfold as the pores deform.
“Material impurities in the form of rigid particles can lead to significant damage propagation under shear load as well,” says Dr Mathias Hurst from the IPS at KIT. The researchers demonstrated this mechanism of damage using an aluminium alloy as an example. Aluminium alloy is particularly suitable for lightweight construction in the transport sector – especially in aircraft manufacturing. Accordingly, the study is, on the one hand, highly relevant to material formability, including in the mobility and transport sectors. On the other hand, it is of great importance for recycling processes, as recycled metals often contain higher levels of particulate impurities.
Study employs synchrotron radiation computed laminography and 3D simulations
To demonstrate the progression of damage under shear load, the researchers combined imaging and simulation: they used synchrotron radiation computed laminography (SR-CL), a method developed at KIT that is similar to computer tomography. The method enables high-resolution 3D visualisation of the interior of flat, wide objects and allows specific areas within centimetre-sized samples to be examined at micrometre-level resolution. In addition, the team used advanced 3D simulations, which they had developed in collaboration with scientists from France, to replicate the observed damage in the model.
Rigid particles obstruct material flow and promote the growth of voids
The researchers investigated an aluminium alloy (AA2198-T851) by first subjecting the material to a tensile load and then to a shear load. The tensile load caused voids to form in the material, and the team watched as these voids continued to grow under shear load. This went hand-in-hand with a sixfold increase in the volume of the pores formed on the intermetallic particles. “Intermetallic particles are therefore a key driver of damage growth in metals under shear load,” says Hurst. “Rigid particles obstruct the material and promote the growth of voids.” The findings of the study provide new insights into damage mechanisms under shear load and help to improve our understanding of component failure under loads relevant to practical applications. This could allow the design of components that are both more durable and lighter in the future – which represents an important contribution to safety and sustainability, particularly in the transport sector.
Source: KIT
