Download HW 2 Problems 1-6.pdf

Katie Sherrick
MANE-6960: Friction & Wear of Materials
Homework #2 - 9/22/2009
1. Find a scholarly recent publication describing the effect of a manufacturing processes on the
nature and features of a metal surface and write a 100 word essay summarizing it.
F. Javier Gil, Josep A. Planell, Alejandro Padros, Conrado Aparicio, The effect
of shot blasting and heat treatment on the fatigue behavior of titanium for
dental implant applications, Dental Materials, Volume 23, Issue 4, April 2007,
Pages 486-491, ISSN 0109-5641, DOI: 10.1016/j.dental.2006.03.003.
This article discussed the effect of shot blasting and heat treatment on the fatigue properties of titanium
alloys that are commonly used in dental implants. Since dental implants are intended for use for several
decades and constantly experience cyclic loads related to biting and chewing, improving the fatigue
properties of such alloys is desirable. Shot blasting the implant induces residual stresses in the surface
layer of the implant due to local deformation. Implants machined from both equiaxed (alpha) and acicular
commercial purity titanium were shot blasted with alumina and heat treated, then tested for fatigue
properties while submerged in a medium of artificial saliva. It was found that the samples that were shot
blasted had significantly longer fatigue life than the as-machined samples, particularly when an equiaxed
grain structure was present as opposed to acicular. The maximum yield strengths were relatively similar for
the as-machined and blasted/heat treated samples, while ductility was sharply reduced for the blasted
samples (due to the plastic deformation of the surface due to shot blasting). Overall, the process of shotblasting the titanium alloy surface appears to extend fatigue life while also improving osseointegration when
implanted in bone.
2. Find a scholarly recent publication describing the effect of a surrounding atmosphere on
the nature and features of a freshly exposed metal surface and write a 100 word essay
summarizing it.
B. Lonyuk, I. Apachitei, J. Duszczyk, The effect of oxide coatings on fatigue
properties of 7475-T6 aluminium alloy, Surface and Coatings Technology, Volume 201,
Issue 21, EUROMAT 2005, 'EUROMAT 2005' congress on Advanced Materials and
Processed, 25 August 2007, Pages 8688-8694, ISSN 0257-8972, DOI:
10.1016/j.surfcoat.2006.02.002.
This article is about the the effect of oxide coatings on fatigue properties of 7475-T6 aluminum alloy, for use
in the aerospace and automotive industries. Two coating types were evaluated: hard anodized and PEO
(plasma electrolytic oxide) coatings were formed at thicknesses of 60 μm and 65 μm respectively, and
samples were tested in a uniaxial fatigue test machine. The anodic coating had a 75% reduction in fatigue
strength of the aluminum, while the PEO process resulted in a comparatively low 58% reduction for a
comparably-thick coating layer. The anodic coating was found to be uniform despite the presence of
intermetallic particles in the oxide layer. Deep cracks were observed in the oxide layer, believed to form
due to differences in thermal expansion between the substrate metal and the oxide layer. These cracks
reduce fatigue properties due to the brittle nature of the oxide layer. The PEO layer was composed of
three sub-layers; a porous outer layer, a dense inner layer, and a thin transitional layer between the two.
This structure induces internal residual stresses between the coating layers, which improves fatigue
properties relative to the anodic coating.
3. Identify a modern profilometer and write a brief 100 word essay describing its features.
The Mitutoyo Surftest SJ-400 Portable Surface Roughness Tester is a compact, high accuracy portable
profilometer. It features a measuring range of 0-50 mm with five different sampling lengths (0.08, 0.25, 0.8,
2.5, 8 mm). The detector has a resolution of 0.000125 μm over a 800 μm measuring range.
It features exchangeable nose pieces to allow for either skidless or skidded measurements. This
profilometer also has a height and tilt adjustment with an optional leveling table. The SJ-400 can also
measure the roughness of cylindrical or spherical objects by electronically filtering the data from the
detector to remove the influence of the object radius. The SJ-400 can either use the built-in thermal printer
and LCD screen to show measurements, or it may be attached to a computer running the Mitutoyo Surfpak
software. It can measure and evaluate Ra, Rq, Rz, Rz(JIS), Ry, Ry (DIN), Rc, Rpi, Rp, Rpmax Rvi, Rv,
Rvmax, Rti, Rt, R3zi, R3z, R3y, S, Pc (Ppi), Sm, HSC, mr, δc, plateau ratio, mrd, Rk, Rpk, Rvk, Mr1, Mr2,
Δa, Δq, λa, λq, Sk, Ku, Lo, Lr, A1, and A2.
4. A certain surface is found to have an approximately Gaussian roughness distribution with
mean μ = 4 μm and standard deviation = 1 μm. Asperity height data has been determined
with a resolution of 1 μm along the direction tangential to the surface. Use the inverse transform
method to create 1000 simulated asperity height data points to compute all relevant
statistical functions for the simulated surface and comment on your results.
I used Minitab's random data generation function to create a 1000-point data set with a normal (Gaussian)
distribution with mean of 4.0 and standard deviation of 1.0. The cumulative distribution function and
probability density functions of the generated data set were plotted, showing a normal distribution. The
average of the randomly generated data set was 4.007 um and the standard deviation was 1.021 um.
See the “HW2 Problem 4” PDF for plots and the data set.
5. The roughness of a certain surface is approximately described by a Weibull distribution with
cumulative distribution function given by
z 4
F  z =1−exp −  
4
Obtain and plot the various statistical functions useful in the description of the surface.
I used Mathcad to plot the CDF and PDF of this distribution, as well as calculate the mean, median, mode,
variance, standard deviation, and skewness for this Weibull distribution.
See the “HW2 Problem 5” PDF for the Mathcad output.
6. The following table summarizes experimental data on the asperity heights of a shot peened
aluminum surface in terms of the cumulative distribution function
z(μm)
1
2
3
4
5
6
7
8
F(z)(-)
0.01
0.05
0.22
0.5
0.8
0.95
0.99
1
Use the data to obtain the various statistical functions useful in the description of the
surface.
Plotting F(z) versus z, it is apparent that the cumulative distribution function is that of a normal (Gaussian)
distributon. The mean is 4.0 um (50% probability on CDF centered at 4.0 um).
Cumulative Distribution Function
1.2
1
F(z)
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
6
7
8
9
z
To determine the standard deviation, Minitab was used to generate three CDFs for a normal distribution
with a mean of 4.0 and standard deviations of 0.5, 1.0, and 1.5. Based on the shape of these generated
CDF plots, the standard deviation is between 1 and 1.5. Minitab was again used to generate a CDF for a
normal distribution with mean 4.0 and standard deviation of 1.2 and was found to fit almost exactly to the
data table summarizing the asperity heights of the shot peened surface.
Therefore, the mean of this data set is 4.0 um, with a standard deviation of 1.2 um. Since the asperity
height data is described by a normal distribution, the skewness and excess kurtosis are both zero.