Casting a glance at the types and make of automobiles present on Singapore streets, I realized that cars in the city state is increasingly larger and with bigger engine capacity. Compared to the situation ten years ago, cars in Singapore have indeed gone a step up in weight and size. But, what accounts for the difference in car size given the same engine capacity?
Knowing that engine capacity provides the critical impetus for propelling a car forward and is correlated with car weight, what drives the increase in car size at a small increment in engine capacity, for example, from 1600 cc to 2000 cc? Could it be composite material aiding the increase in car size and volume?
Possibility exists that composite materials such as those between carbon fiber and steel could help increase the volume available to occupants given a particular engine capacity or power. However, are composite materials as strong as steel? The answers depend on the type and angle of impact, and naturally, most important of all, the power of an impact. In general, a carbon fiber and steel alloy constructed through having a grid like meshwork of carbon fiber in steel has sufficient strength to withstand both lateral and perpendicular forces. However, the same cannot be said for another popular alloy: aluminium and steel.
Aluminium is lightweight but lacks strength. Given its low mass per unit volume, it is an attractive material for use in cars as material of construction and, most importantly, modern metallurgy does have the technological tools for shaping aluminium into a resilient alloy with stainless steel 316. However, low impact strength of aluminium meant that the resulting steel/aluminium alloy lacks the necessary impact strength against even a low impact force collision. Hence, use of aluminium as an alloy to steel or even as a material of construction in cars must be severely restricted or even banned, given the poor impact strength of aluminium for an application requiring high strength.
Contemporary developments in car manufacturing has witnessed a significant increase in car volume and size without a direct correlation with weight increase. This suggests that composite materials have gained a substantial foothold as materials of construction in cars, thereby, allowing car volume to increase without a corresponding gain in car’s weight that would have drove the adoption of larger capacity engines with more power. While carbon fiber may be the fashionable material for car construction now, for example, in axle and suspension of some high end vehicles such as sports utility vehicles, its high cost have hampered its widespread adoption. On the other hand, the well understood metallurgy of aluminium together with its relative low cost compared to carbon fiber, makes it a possible choice as alloy material for 316 stainless steel or as an independent material of construction for cars. However, the inherent low strength of aluminium makes it ill-conceived as an alloy material for steel in applications important to impact strength such as in automobiles. More importantly, the low resilience of the non-rusting metal, aluminium, would significantly increase the risk profile of cars whose material of construction is aluminium/steel alloy. Hence, use of aluminium in automobile applications should be severely curtailed by tight regulations around the world.
Category: physics, mechanical engineering, materials, materials engineering,
Acknowledgement: Ng Wenfa thank Seah Kwi Shan for co-authoring this blog post.