New method could lead to lighter and safer vehicles

A new doctoral thesis at Luleå University of Technology presents a method that could contribute to lighter, more fuel-efficient, and at the same time safer vehicles. By predicting how manufacturing processes affect the fatigue life of metals under repeated loads, development time can be shortened and the need for expensive testing reduced, benefiting both industry and the climate.

"If you cannot quantify how, for example, cut edges affect the fatigue properties of steel sheets, you risk using unnecessarily large safety margins, which leads to heavier vehicles. Without that knowledge, you might also select a steel that looks better on paper but performs worse in practice, which in the worst case could cause damage to critical components," says David Gustafsson, Doctor in Solid Mechanics at Luleå University of Technology.

Smarter way to predict material lifetime

Reducing the weight of chassis components is a constant challenge for the automotive industry. Lighter vehicles mean lower fuel consumption and reduced emissions, but thinner materials also result in greater mechanical stress. The new research shows how engineers can predict how forming, cutting, and post-processing affect a metal’s strength without having to perform numerous costly and time-consuming tests.

"Often, the simplest models are the most useful because they are easy to understand and reason about. Our goal was to create a clear framework for quantifying how manufacturing processes influence the fatigue properties of steel sheets, using data that is already available," says David Gustafsson.

David Gustafsson, doctoral student in solid mechanics at Luleå University of Technology.

Predictability reduces the need for testing

The thesis presents a framework for quantitatively and qualitatively assessing how sheet metal forming affects material lifetime under cyclic loading. The results show that a simplified method for simulating processes such as shear cutting is sufficient to calculate residual stresses and thereby predict how test specimens will behave in practice. The method can be applied to various load types and combined with surface finish measurements and basic material data.

"The method is intended to help engineers compare materials and plan testing more efficiently at an early stage," says David Gustafsson.

The research also shows that the method can be used to assess the effects of other manufacturing steps, such as bending and shot peening. This allows manufacturers to consider the entire production chain already in the design phase and develop lighter and at the same time safer chassis designs.

"Every small improvement that speeds up the development of lighter components is important. Regulations put enormous pressure on manufacturers to save grams wherever possible, and we see great interest from industry – both among vehicle and steel manufacturers," says David Gustafsson.

• Solid mechanics