Scientists at the University of Leeds in the UK have developed a new method for directly measuring the strength of composite concretes and predicting fractures using a simple epoxy-based light-refracting coating.
Understanding why and where materials fracture is associated with their ability to resist what is referred to as shear stress. There are some optical methods available to sense shear stress distribution on transparent (light-transmitting) materials. But many of the industrial materials, such as composite concretes, are opaque. “There is not an easy way to directly measure shear stress on such materials to estimate their resistance to fracture under service loads; in other words, its fracture toughness,” says Dr Joseph Antony from the Leeds School of Chemical and Process Engineering, who led the research. Using a simple epoxy-based light-refracting coating, the expert in photonics for stress measurements and mechanics of materials has now achieved just that in collaboration with colleagues from the University of Qatar. “The property of the coating material that helps to do this job is called ‘birefringence’,” he explains. Being birefringent means the complex light-refracting coating has the ability to split light waves in different directions at different speeds depending on the amount of stress in those directions — and reflecting back to a photonic camera.
From sensing stress in the human cornea to concrete
In 2015, Antony succeeded in sensing shear stress concentrations on the human cornea. The research was published in Scientific Reports at the time. He explains that the human cornea is naturally birefringent, and it was therefore possible to sense the stresses in vivo using ordinary white light. “In simple terms, this functionality of the cornea is transferred back on concrete structures efficiently in the current research using an equivalent light-refracting coating material to sense candle-flame-like shear stress distribution patterns.”
Advantages of the new photonic method
Antony says while other ways for measuring stresses and strain on materials are used in the engineering industries, “the current research demonstrates the ‘direct’ measurement of shear stresses and its link to predict ‘fracture toughness’ of complex materials efficiently.”
Understanding stress and damages in concrete
According to its creator, the methodology is generic in nature. Thus, in the future, it could find application not only in the traditional construction sector but also in a wide range of industries, such as automobile, space, food processing, nuclear energy containers and storage vessels to assess their risk of damages in service.
Impact on development of tomorrow’s concrete materials and how we build in the future
“The depleting natural resources in the world warrant us to think of new ways of manufacturing durable and sustainable composite materials with high strength and durability,” says the professor. Researchers in the UK, he notes, are looking for new ways to develop composite concretes using particles recycled from existing throwaway plastic wastes as a partial replacement for natural river sand, for example. “To address these needs, the present research provides a new pathway of measuring fracture toughness on opaque materials using the light-refracting coating,” says Antony.
Down the line, Antony envisions one can wear special glasses “and see colorful stress distribution patterns on the painted walls of the homes and buildings in our streets.”
Written by Sandra Henderson, Research Editor, Novus Light Technologies Today