Composite Stroller Frame Member Case Study
The Client's stroller program objective was straight forward; reduce structural weight by replacing thin walled round 6061-T6 aluminum tubular frame members with FRP composite adaptations but do so without sacrifice bending stiffness, strength, or durability. Design constraints included maintaining the existing frame member bent shape, attachment points, and cross section width. The cost sensitive consumer product application also required economical design and manufacturing choices throughout the program.
Stroller Frame Member Location
Carbon fiber reinforced polymer composite (CFRP) materials provided the best chance of delivering the desired weight savings however subtle design changes, such as morphing from a round cross section shape to an elongated oval in bending critical spans, were necessary to meet the weight savings objectives. The elongated oval's higher section modulus allowed CSS to maintain the required bending stiffness with a thinner wall.
The material saved in the elongated oval spans was redistributed to fastener hole and notched end locations for additional out-of-plane and bearing strength.
Aluminum Stroller Frame Member Geometry
CSS utilized low Fiber Areal Weight (FAW) prepregs to achieve the required bending and torsional stiffness and strength; 75 g/mē FAW unidirectional standard modulus carbon/epoxy hotmelt prepreg.
Bladder Inflation Molding (BIM) was selected as the manufacturing method for the stroller's curved tubular frame members. CSS worked directly with an overseas vendor to develop low cost BIM clamshell tooling and eventually BIM composite prototypes. The same overseas vendor made a suitable low FAW carbon fiber prepreg in-house which eliminated the need to source prepreg and incur supplier mark-ups.
Carbon Fiber Composite Frame Member
Carbon fiber composite prototypes were bladder molded, cut to length, and machined to specification overseas then evaluated in the Client's test laboratory. The carbon fiber composite frame members had an average weight savings of 48%, were 53% stronger in bending strength, and twice as durable based on assembly life cycle fatigue testing.