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Specializing in: product liability, failure analysis, patent disputes and intellectual property. We have 25 years experience with glass, ceramics, plastics, wood and metals; 100 depositions & many court appearances.

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2 triangles   Plastic Failure Analysis:
Plastic Andirondack Lawn Chair Failure

Introduction

A failure analysis was performed on a polypropylene Adirondack lawn chair that had collapsed. The subject chair failed during expected normal use when a 190 pound man sat in it.

Procedure

The failed plastic lawn chair was evaluated visually. In addition, the fracture surfaces were examined with a low power microscope.

Root Cause Failure Analysis: Result Summary

Please refer to the photographs below for the failure analysis results.

Andirondack chair
Left Side of Chair
Andirondack chair
Right Side of Chair
Figure #1: Two views of the failed plastic lawn chair. The failed leg is seen in the photograph on the right.
Andirondack chair failed rear leg
Figure #2: Close up of the failed leg on the right side of the chair. The chair was re-assembled to demonstrate the location of the failure. The chair’s right leg “splayed” out (i.e. bent outwards) and broke off in a brittle manner.
Andirondack chair under failed leg
Andirondack chair under failed leg
Figure #3: Photograph of the underside of the chair showing the failed leg. Please note that there are three failure origins. The photograph on the right shows that the traveling crack “skirts” the re-enforcing gussets. Two of the origins (A & B) are associated with cylindrical artifacts attached to the underside of the seat and the side wall of the leg (mini gussets?). It is believed that the failure was sequential beginning at origin ‘A’.
Andirondack chair failure origin
A
Andirondack chair failure origin
B
Figure #4: Close ups of plastic failure origins A & B. These are the half of the plastic fracture surface remaining on the chair.
Andirondack chair failure origin
Figure #5: Close up photograph of failure origin ‘B’. This photograph shows the brittle nature of the fracture surface. In addition, it demonstrates clearly that this part of the failure is emanating from the origin. In addition, the crack is driven by bending forces from the inside out.
Andirondack chair inside wall
Figure #6: Photomicrograph of the right side of the plastic fracture surface shown in Figure #5 (i.e. near origin B). This shows a crack arrest line; its shape demonstrates that the leg failed due to outward bending. This is a brittle fracture (Mag. 20X)
Andirondack chair inside wall final failure
Figure #7: Close up photograph of failure origin ‘C’. This part of the fracture initiated at a very small gusset. It is believed that this is the final break as the leg finally collapses. The final part of the failure is very straight.