September 2008 - Issue #3
The sandwich factor for safer cars
Story by Belinda Humphries
View articles in related topics: Automotive Industry, Sustainability & The Environment, Design, Film, Multimedia
The dawn of unprecedented high petrol costs, plus the ongoing need to make cars safer, is adding extra relevance and urgency to research into light, but strong, automotive materials.
Two aluminium-based developments - aluminium 'foam' and aluminium honeycomb structural components - are showing promise in testing being undertaken at Swinburne University of Technology. The timely research into these materials could be laying the groundwork for a new, lightweight generation of vehicles that would increase motorists' safety and reduce the hip-pocket pain from the petrol pump.
"It will uplift Australia's design of environmentally friendly, lighter and safer cars."
Dr Tracy Dong Ruan
Swinburne researchers have been testing the strength and safety of aluminium foam and aluminium honeycomb structural components, and Swinburne mechanical engineering lecturer Tracy Dong Ruan says the work could place Australia at the forefront of innovative automotive materials.
Dr Ruan says the research will provide a thorough understanding of the crashworthiness and energy absorption of materials and constructs such as aluminium honeycombs and foams and their products - metallic foam sandwich panels and foam-filled tubes.
"It will potentially open the way for their application in safer automobiles, and it will uplift Australia's design of environmentally friendly, lighter and safer cars," she says.
Dr Ruan says the novel forms under investigation at Swinburne will better protect passengers in a crash than regular car bodies because aluminium foams and honeycombs can undergo large plastic deformation at a nearly constant and relatively low force. "Therefore, in a car crash, aluminium foams and honeycombs and their products would crush to absorb impact energy, protecting passengers from injury or the car structure from being damaged."
By way of explanation she says the reason electrical goods are packaged inside the familiar white foam casings is because this type of cellular structure has a great capacity to absorb impact and shock.
In a similar manner, the metallic foam core inside the sandwich panels being studied would compress to absorb the energy of an impact, decreasing the impact force of a collision on a vehicle's passengers. The Swinburne research has already proven the materials' ability to absorb considerable energy in this situation. "Typically, the energy absorbed by aluminium sandwich panels is double the energy absorbed by solid metals of equivalent mass," Dr Ruan says.
The Cooperative Research Centre for Advanced Automotive Technology (Auto CRC) is supporting Swinburne's work. Its research program manager Dr Gary White says metallic foams are well suited to parts of the car that sustain impacts but also protect the occupants. "Bumper mounts, door openings and intrusion bars are examples of components that may improve in crash performance if metal foams are part of their design," he says.
Aluminium foams and honeycombs are also lightweight, non-flammable and recyclable. "From the environmental perspective, the use of metal foams and metal composites simplifies the recycling process," Dr White says.
The Swinburne team's ongoing research builds on work it began in 2000. Dr Ruan says it was important to understand the characteristics of core materials before turning attention to forms more often used in real-life applications - such as sandwich panels with a foam or honeycomb core between metallic skins and foam-filled metal tubes.
The Swinburne researchers aim to build a complete picture of the mechanical response of these relatively new materials when subjected to various stresses - data Dr Ruan says is crucial in encouraging their use in vehicle manufacture.
Professor Guoxing Lu, an international expert on novel materials and structures, leads the team. It includes Dr Ruan, four PhD students - two of whom are sponsored by the Auto CRC - a postdoctoral fellow and a visiting academic.
As well as gathering extensive experimental data using Swinburne's impact test facilities, the team's work includes a theoretical component (developing equations that explain the behaviour) and finite element analysis (using computer software to help model the findings).
Although the researchers are still building data on the sandwich panels and foam-filled tubes, they are already able to show how various samples absorb energy - allowing manufacturers to judge the best form, or construction, for different applications.
Dr White says this is important given that the range of materials available, such as novel metallic foams, is continually growing "flooding the vehicle designer with options. So, the more relevant available test information is, the more confident the designer will be when selecting materials."
Dr Ruan says vehicle designers worldwide are starting to appreciate the potential benefits of such materials, with a number now working with metallic foam producers and researchers. BMW and Austrian firm LKR have designed an engine-mounting bracket incorporating a metallic foam core, while French automotive supplier Valeo is working on a crash box with metallic foams manufacturer Cymat.
Dr Ruan believes the shock of recent fuel-price rises is likely to provide extra impetus to developing energy-efficient vehicles, increasing interest in the materials at the centre of the Swinburne study.
She is confident vehicle manufacturers will go down this road, given that the aerospace and aircraft industries have already used these types of sandwich panels: "All it will take is more data from the type of tests we are running."
