Fatigue-life of two manual wheelchair cross-brace designs.

Objective: To compare the durability of two designs of cross-braces for folding manual wheelchairs and to determine the nature of wheelchair cross-brace failures.

Design: Fatigue testing of two folding wheelchair cross-brace designs (one with a rectangular cross-section and the other with a circular cross-section). A total of 20 cross-brace pairs were tested.

Results: The cross-braces with a circular cross-section endured a mean +/- SD of 100,159 +/- 45,814 cycles before experiencing a fatigue failure, whereas the cross-braces with a rectangular cross-section endured an average of 261,254 +/- 160,741 cycles. A t test showed significant differences (p = .01) in fatigue-life between cross-braces with a circular cross-section versus cross-braces with a rectangular cross-section. All 20 cross-braces experienced similar fatigue failures that would develop at the bolt hole where the two cross-braces connect to form a hinge.

Conclusion: The results suggest that the rectangular cross-brace design has a longer fatigue-life than the circular cross-brace design. People should regularly inspect the cross-brace for cracks. The area around the bolt forming the hinge should be inspected carefully. If a crack is observed, the cross-brace should be replaced immediately.