Composite materials offer a distinct advantage over metals in stiffness, strength, and weight.
When designing a part for stiffness and mass, it should be noted that all metals have an upper bound on the stiffness of a part for a given mass (regardless of metal material selection). Stiffness is a base material property which is unaffected by alloying elements and material processing. The nominal stiffness per unit density (Stiffness/Density) remains a constant for all industry used metals, therefore there is a threshold on how light parts can be made regardless of metal choice.
|Property||Aluminum||Steel||Titanium||Infused Unidirectional CF
(65 wt%. Fiber)
|Tensile Stiffness (GPa)||68||200||116||98|
|Nominal Stiffness Per Unit Density||0.025||0.025||0.025||0.064|
Part strength is typically a tradeoff between strength, cost, and manufacturability. Most exotic alloys for aluminum and steel can cost twice as much as a standard alloy and drive up manufacturing cost and time.
|Property||3003 H16 Aluminum||AISI 1005 Cold Drawn Steel||Grade 5 Titanium||Infused Unidirectional CF
(65 wt%. Fiber)
|Ultimate Tensile Strength (MPa)||179||330||620||988|
|Nominal Strength Per Unit Density||0.066||0.041||0.137||0.65|
Traditional sheet metal parts are processed on press brakes and stamping machines resulting in limited design freedom. Designs are limited to being prismatic and not aesthetically pleasing. In addition, localized yielding on bend edges in sheet metal parts can be starting points for cracks and could lead to unexpected part failure. Designers are also limited to using a single thickness throughout a part because of manufacturing reasons. This often leads to heavier parts. To bring down weight and remove material in regions of low stresses, additional manufacturing costs are endured and the amount of wasted material is increased.
Composite parts offer designers more freedom as molds can easily be produced to allow curved surfaces with no significant increase in cost. In addition, designers have control over the number of plies in particular regions allowing for pad-up in regions of concentrated stress and a reduced number of plies in areas of low stresses. This produces no significant increase in the costs required to manufacture the part and reduces the material consumption.