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Research Papers

# Total Hip Wear Assessment: A Comparison Between Computational and In Vitro Wear Assessment Techniques Using ISO 14242 Loading and Kinematics

[+] Author and Article Information
George Matsoukas

Department of Mechanical and Materials Engineering, Queen’s University, McLaughlin Hall 305, 130 Stuart Street, Kingston, ON, K7L 3N6, Canadageorge@traxtal.com

Ryan Willing

Department of Mechanical and Materials Engineering, Queen’s University, McLaughlin Hall 305, 130 Stuart Street, Kingston, ON, K7L 3N6, Canadawilling@me.queensu.ca

Il Yong Kim1

Department of Mechanical and Materials Engineering, Queen’s University, McLaughlin Hall 305, 130 Stuart Street, Kingston, ON, K7L 3N6, Canadaiykim@me.queensu.ca

1

Corresponding author.

J Biomech Eng 131(4), 041011 (Feb 12, 2009) (11 pages) doi:10.1115/1.3049477 History: Received August 27, 2007; Revised September 30, 2008; Published February 12, 2009

## Abstract

In the present study a direct comparison was made between in vitro total hip wear testing and a computational analysis considering the effects of time and a nonlinear stress-strain relationship for ultrahigh molecular weight polyethylene (UHMWPE) at $37°C$. The computational simulation was made correct through calibration to experimental volumetric wear results, and the predicted damage layout on the acetabular liner surface was compared with results estimated from laser scanning of the actual worn specimens. The wear rates for the testing specimens were found to be $17.14±1.23 mg/106 cycles$ and $19.39±0.79 mg/106 cycles$, and the cumulative volumetric wear values after $3×106 cycles$ were $63.70 mm3$ and $64.02 mm3$ for specimens 1 and 2, respectively. The value of the calibrated wear coefficient was found to be $5.32(10−10) mm3/N mm$ for both specimens. The major difference between the computational and experimental wear results was the existence of two damage vectors in the experimental case. The actual location of damage was virtually the same in both cases, and the maximum damage depth of the computational model agreed well with the experiment. The existence of multiple wear vectors may indicate the need for computational approaches to account for multidirectional sliding or strain hardening of UHMWPE. Despite the limitation in terms of describing the overall damage layout, the present computational model shows that simulation can mimic some of the behavior of in vitro wear.

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Copyright © 2009 by American Society of Mechanical Engineers
Topics: Wear , Cycles , Simulation
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## Figures

Figure 1

The AMTI Force 5 servohydraulic machine with attached hip testing components

Figure 2

Lower hip specimen holder with femoral head (left) and the titanium acetabular shell and UHMWPE acetabular liners (right)

Figure 3

Finite element model of the experimental apparatus constructed with Altair HYPERMESH preprocessing software (left) and views of the components showing the various elements used in the construction of the model (right)

Figure 4

The ISO 14242-1 waveforms used in both the computational simulation and the experiment (top). Loading was applied in the experimental simulation using the MPC method in ANSYS (bottom). One pilot node governed the acetabulum while the other controlled the lower hip specimen holder.

Figure 5

Modulus-stress relationship taken from Cripton (23) showing a line fit up to the yield stress of 17 MPa (top) and the nonlinear stress-strain material model for UHMWPE at 37°C adapted from the modulus-stress relationship and used in the finite element analysis (bottom)

Figure 6

Cumulative wear in milligrams (top) and cumulative volumetric wear (bottom) of the two 32 mm diameter UHMWPE liners tested against cobalt-chrome femoral heads as well as the soak control liner

Figure 7

von Mises stress results at selected loadsteps throughout the gait cycle. Loadsteps are numbered accordingly. The top of the figure corresponds to the front of the AMTI Force 5.

Figure 8

Contact pressure results at selected loadsteps throughout the gait cycle. Loadsteps are numbered accordingly. The top of the figure corresponds to the front of the AMTI Force 5.

Figure 9

Comparison between the computational and experimental cumulative volumetric wear data of the calibrated result for the first experiment (left) with a head-liner clearance of 0.460 mm and a calibrated wear factor of 5.322(10−10) mm3/N mm, and the second experiment (right) with a head-liner clearance of 0.285 mm and a calibrated wear factor of 5.320(10−10) mm3/N mm

Figure 10

Wear, creep, and total damage depth distributions at every 500,000 simulated gait cycles with a head-liner clearance of 0.46 mm and a calibrated wear factor of 5.322(10−10) mm3/N mm (test 1)

Figure 11

Wear, creep, and total damage depth distributions at every 500,000 simulated gait cycles with a head-liner clearance of 0.285 mm and a calibrated wear factor of 5.320(10−10) mm3/N mm (test 2)

Figure 12

Wear, creep, and total damage depth progression for the computational simulation of experiment 1 (left) with a head-liner clearance of 0.46 mm and a calibrated wear factor of 5.322(10−10) mm3/N mm, and experiment 2 (right) with a head-liner clearance of 0.285 mm and a calibrated wear factor of 5.320(10−10) mm3/N mm

Figure 13

In vitro damage depth distribution on the liner surface after 3×106 gait cycles produced using laser scanning of the SEM gold-coated liners in experiment 1. The top of the figure denotes the front of the Force 5.

Figure 14

Comparison of the damage depth profile of experiment 1 to the damage depth profile of the computational simulation with a wear factor calibrated to experiment 1

Figure 15

A comparison of the cumulative maximum damage depth progression of experiment 2 estimated using laser scanning and the computational simulation tuned to the second experiment, and the logarithmic line fit to the experimental damage depth data and the computational damage depth data

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