Characterization and failure analysis of a polymeric clamp hanger component

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Contents

Abstract

This paper characterizes the failure of a polymeric clamp hanger component using finite element analysis coupled with experimental methods such as scanning electron microscopy, x-ray computed tomography, and mechanical testing. Using Fourier transform infrared spectroscopy, the material was identified as a polypropylene. Internal porosity that arose from the manufacturing procedure was determined using three dimensional x-ray computed tomography. From static mechanical experiments, the forces applied on the component were determined and used in a finite element simulation, which clearly showed the process of fracture arising from the pre-existing processing pores. The fracture surfaces were observed under a scanning electron microscope confirming the finite element simulation results illustrating that low-cycle fatigue fracture occurred in which the fatigue cracks nucleated from the manufacturing porosity.

Figures

clamp hanger fractured polymer grip
(a) (b)
Picture of product and fractured component: (a) clamp hanger and (b) fractured polymer grip.
Illustration of grip closure. In Position 1, the clasp is completely opened and unloaded. In Position 2, the clasp is being closed and is contacting the steel bars. In Position 3, the clasp is fully closed and locked into the operating position. The static loads imparted from the rods on the “clasp” during operation.
(a) (b)
(a) Illustration of grip closure. In Position 1, the clasp is completely opened and unloaded. In Position 2, the clasp is being closed and is contacting the steel bars. In Position 3, the clasp is fully closed and locked into the operating position. (b) The static loads imparted from the rods on the “clasp” during operation.
side view cross-section view scanning electron micrograph of fractured surface of the boxed area in (b)
(a) (b) (c)
Images of the fractured surfaces of a failed grip during operation: (a) side view; (b) cross-section view; and (c) scanning electron micrograph of fractured surface of the boxed area in (b).
magnification of the central pore overall fracture surface discolored edge
(a) (b) (c)
ESEM image of fractured surface: (a) magnification of the central pore; (b) overall fracture surface; and (c) and discolored edge.
overall 3-D rendering a central cross-section image showing porosity line the left side a cross-section image showing porosity line the right side
(a) (b) (c)
Micro X-ray computed tomography scans on the clasp: (a) overall 3-D rendering; (b) a central cross-section image showing porosity line the left side; and (c) a cross-section image showing porosity line the right side.

The FTIR spectrum of the specimen used in this study with the characteristic transmittance bands matching those of isotactic polypropylene (iso-PP)

The FTIR spectrum of the specimen used in this study with the characteristic transmittance bands matching those of isotactic polypropylene (iso-PP)

elastic simulation of a single rod subjected to 100 N showing the displacement illustration of the compliance directions of the rods
(a) (b)
Finite element compliance study of the steel rods: (a) elastic simulation of a single rod subjected to 100 N showing the displacement and (b) illustration of the compliance directions of the rods.

Estimated normal load at various rod positions during closure.

Estimated normal load at various rod positions during closure.

Compressive stress–strain response of the polypropylene clasp.

Compressive stress–strain response of the polypropylene clasp.

without pores, whole model with pores, cross-section of model to show pores
(a) (b)
Solid models for finite element analysis: (a) without pores, whole model and (b) with pores, cross-section of model to show pores.

Cross-section of the coarse mesh containing pores.

Cross-section of the coarse mesh containing pores. The stress is applied at Area #1 while Area #3 is fixed in the x- and y-directions. The Area #2 denotes the artificially created pores to mimic the micro CT findings.


without pores with pores
(a) (b)
High fidelity meshes in the curved region of the model for both non-pore and pore cases: (a) without pores and (b) with pores.


stress triaxiality without pores stress triaxiality with pores von Mises stress without pores von Mises stress with pores
(a) (b) (c) (d)
Clipped models showing: (a) stress triaxiality without pores; (b) stress triaxiality with pores; (c) von Mises stress without pores; and (d) von Mises stress with pores.
without pores with pores
(a) (b)
An isosurface of triaxiality for meshes (a) without pores and (b) with pores. The isosurface is shown in green and represents a triaxiality value of 0.6

Publication

[D.K. Francis, J. Deang, R.S. Florea, D.R. Gaston, N. Lee, S. Nouranian, C.J. Permann, J. Rudd, D. Seely, W.R. Whittington, M.F. Horstemeyer, Characterization and failure analysis of a polymeric clamp hanger component, Engineering Failure Analysis, Volume 26, December 2012, Pages 230-239.]

Licensing

The figures of this page was reproduced with permission from Elsevier/Rights Link Order No. 501116679.

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