This is not the document you are looking for? Use the search form below to find more!

Report home > Technology

THE EFFECT OF SAMPLE PREPARATION ON THE FLEXURAL STRENGTH OF REINFORCED NYLON 66

2.50 (2 votes)
Document Description
Cutting flexural test specimens from molded plaques is commonly used in material testing. The mechanical properties of these cut specimens may be affected by the cutting process as it could introduce extrinsic flaws and thermal residual stress on the cut surfaces. The objective of this experimental research is to determine how band saw cutting affects the flexural strength of 33% short glass fiber reinforced nylon 66. The specimens for the flexural test were obtained by cutting molded plaques using different blade types, blade speeds, feed rates, and levels of polishing. The results were compared with those from uncut specimens. Surface morphology of specimens’ cut edges was observed by using Scanning Electron Microscopy. The results indicate that lowest strength of cut specimens is achieved at the lowest blade speed and highest work piece feed rate.
File Details
  • Added: October, 28th 2009
  • Reads: 1752
  • Downloads: 107
  • File size: 460.93kb
  • Pages: 9
  • Tags: sample preparation, flexural strength, nylon 66
  • content preview
Submitter
  • Username: shinta
  • Name: shinta
  • Documents: 4332
Embed Code:

Add New Comment




Related Documents

Effect of Sample Preparation Methods and Extraction Time on Yield and Antioxidant Activity from Kradonbok (Careya sphaerica Roxb.) Leaves

by: shinta, 7 pages

Kradonbok (Careya sphaerica Roxb.), one of Thai indigenous vegetables, was selected for studying the effect of sample preparation method and extraction time on antioxidant activity. The ...

EFFECT OF BLANCHING TIME ON SELECTIVE MINERAL ELEMENTS EXTRACTION FROM THE SPINACH SUBSTITUTE COMMONLY USED IN BRAZIL

by: shinta, 6 pages

The true spinach does not grow well in warm climates and for that reason is not commercialized in Brazil. Instead, a spinach substitute , originally from New Zealand, is widely used ...

The Effect of Information Quality on Liquidity Risk

by: shinta, 59 pages

The relation between information quality and cost of capital is of significant academic interest and many explanations (e.g., estimation risk, market risk, liquidity) have been posited ...

Effect of Cell Tower radiation- Just a hype

by: ypatnayak, 35 pages

Like any myth constantly reiterated sounds like truth, myths on the effect of cell tower radiation have been hammered on the common man's mind so often that it is considered as the fact of life. ...

The effect of leverage increases on real earnings management

by: shinta, 18 pages

Main subject of this paper is to understand whether there could be an incentive for managers to manipulate cash flow from operating activities (CFO) through the use of real earnings ...

Effect of diet on the fatty acid pattern of milk from dairy cows

by: shinta, 8 pages

Twelve dairy cows 130 days in milk were sorted by milk production and body weight and assigned to three feeding regimens in a 3 × 3 Latin-square design, in order to study the effects of diet on ...

License to Sell: The Effect of Business Registration Reform on Entrepreneurial Activity in Mexico

by: shinta, 45 pages

The number of procedures for registering a business varies from 2 in Canada to 21 in the Dominican Republic. Many have argued, on the basis of cross country evidence, that complex ...

The Effect of Leverage on Financial Markets

by: shinta, 8 pages

When people get excited about their prospects on the stock market, they borrow money from the bank to invest. This leverage effectively couples the bank to the stock market. Thus, interest

‘The One’ by Baani Sector 66, Gurgaon 9711206301 commercial shop available.

by: fortune realtech, 1 pages

This will be the first market place available on Golf Course Extension Road, Good Connectivity from Sohna road, Metro Connectivity will Gurgaon, Delhi & NCR.

The Effect of Excessive Crying on the Development of Emotion ...

by: wick, 20 pages

The goal of this study was to examine the effect of excessive crying in early infancy on the development of emotion self-regulation. Cry diaries were used to categorize excessive criers and typical ...

Content Preview
THE EFFECT OF SAMPLE PREPARATION ON THE FLEXURAL STRENGTH OF
REINFORCED NYLON 66
P.J. Bates, Royal Military College of Canada,
C.Y. Wang, Centre for Automotive Materials and Manufacturing,
Abstract
One study on the surface integrity of continuously
carbon fiber reinforced epoxy composites was found [6].
Cutting flexural test specimens from molded
An experimental study of orthogonal cutting with
plaques is commonly used in material testing. The
polycrystalline diamonds tools was conducted on the edge
mechanical properties of these cut specimens may be
trimming of unidirectional and multi-directional
affected by the cutting process as it could introduce
graphite/epoxy composites. This study focused on the fiber
extrinsic flaws and thermal residual stress on the cut
orientation effect on the surface integrity. It concluded that
surfaces. The objective of this experimental research is to
machining can affect bulk strength as well as failure
determine how band saw cutting affects the flexural
initiation and propagation.
strength of 33% short glass fiber reinforced nylon 66. The
specimens for the flexural test were obtained by cutting
The objective of this study was to assess the effect
molded plaques using different blade types, blade speeds,
of band saw cutting and surface preparation parameters on
feed rates, and levels of polishing. The results were
the ultimate flexural properties of short glass fiber
compared with those from uncut specimens. Surface
reinforced nylon 66. The band saw was chosen for this
morphology of specimens’ cut edges was observed by
work as it is a relatively rapid method for preparing small
using Scanning Electron Microscopy. The results indicate
mechanical test specimens from injection molded
that lowest strength of cut specimens is achieved at the
components.
lowest blade speed and highest work piece feed rate.
Specimen Preparation
Introduction
Material
The mechanical testing of polymeric materials in
sheet form often involves sample preparation such as
The material used in this study was an injection
cutting, sanding and grinding. The cutting of the samples
molding nylon 66 reinforced with 33% short glass fiber [7]
may introduce extrinsic flaws on the machined surfaces.
provided by Dupont Canada. Rectangular plaques and
These defects may cause stress concentrations, which may
flexural bars were used in this study. The plaques had
influence the mechanical test results. In addition, it is well
dimensions 100.5 mm x 102.5 mm x 3.2 mm and the
known that polymers are thermally sensitive. Hence the
flexural bars had dimensions 12.8 mm x 135 mm x 3.2
cutting may not only induce defects at the cut surfaces, but
mm. Both parts were injection molded using the same
the thermal energy resulting from cutting may affect
material and similar molding conditions on an Engel 55 ton
polymer crystallinity or molecular weight. Most of studies
injection molding machine. The plaque was edge gated
on this issue have focused on brittle materials such as
along the 100.5 mm x 3.2 mm face using a 2 mm thick film
ceramics or thermoset composites. The work described in
gate. The flexural bar was edge gated along the 3.2 mm x
this paper is believed to be one of the first on the effect of
12.8 mm face using a 3.2 mm thick edge-gate. The molded
cutting on the mechanical properties of thermoplastic
plaques were subsequently cut into 13 mm x 102.5 mm x
polymers reinforced with short glass fibers.
3.2 mm flexural specimens. The cutting procedure used on
the plaques is described in the next section.
Much of the previous work on the machining of
advanced materials has focused on ceramics [1-5]. Despite
It is important to note that these flexural specimens
their many advantages, the strength of brittle ceramics can
were cut parallel to the flow direction. For this reason, the
be significantly reduced by machining. These machining
preferential fiber orientation in both the thin cut flexural
constraints have therefore limited the use of structural
specimens and in the thin molded flexural bars are along
ceramics in many applications. The flexural strength of
the longest dimension of the part [8]. Although the
brittle materials is generally influenced by the surface
preferential fiber orientations are in the same direction for
finish, specimen size and shape as well as the testing
the cut specimens and molded bars, the degree of
environment.
orientation is not expected to be identical. Mold edge
1

effects in the narrower flexural bar would be expected to
Three-point bending test
cause slightly more fiber orientation in the flow direction.
In order to assess whether a relationship existed
between the flexural strength of Nylon 66 and various
Cutting and surface preparation
cutting and treating parameters, three-point bending tests
were conducted on all specimens. The first flexural test
Each molded plaque was cut into seven flexural
followed ASTM D790. The molded bar and cut specimens
specimens. The two outside specimens each containing an
rested flat on two supports 60 mm (L) apart and were
outside, uncut edge were discarded. Two band saws were
loaded at 2 mm/min by means of a loading nose midway
employed for cutting the plaques. A Heska Model ESU
between the supports. The flexural stress (?
H63 band saw that allowed precise control the work piece
max) is
calculated using equation 1 where F is the applied load and
feed rate and blade speed was the primary cutting
b and h are the width and thickness respectively.
instrument. A laboratory King Industrial KC-1433FX band
3FL
saw was also used for comparison purposes. This model
?
=
(1)
max
2
allowed for limited range of blade speed and only manual
2bh
control of work piece feed rate.
In order to focus the tensile and compressive
stresses on cut surfaces, a modified flexural test was
For a given material, the parameters of blade type,
developed. In this test method, the molded bar or cut
blade speed and work piece feed rate influence cutting
specimen was oriented such that the smaller 3.2 mm edge
quality [9]. For band saws, the blade generally has four
contacted the test fixture. In order to prevent the molded
major parameters: teeth per unit length (pitch), tooth form,
bar or cut specimen from slipping during testing, two
set pattern and width [9]. The blades used in this research
copper guides were employed on each support as shown in
are shown schematically in Figure 1.
Figure 2.
For the study involving the Heska band saw, the


For both the standard and modified test, a
effect of the pitch (120 and 240 teeth/m), blade speed
minimum of six specimens was tested for each
(1200 m/min and 200 m/min) and work piece feed rate (7.9
cutting/surface preparation condition.
m/min and 0.09 m/min) were studied using skip tooth
blades with a straight set. The width of the blade was 12.5
mm. These cut flexural specimens were tested without any
Microscopy of edge surfaces
further surface preparation.
The edge surfaces resulting from different
The laboratory band saw was used to examine the
cutting/surface preparations were examined using scanning
effect of blade tooth shape. A 10 mm wide, 160 teeth/m
electron microscopy (SEM). An SEM magnification of 25
saw blade that had a hook tooth and raker set (Figure 1)
was chosen to view the surface roughness.
was used on this machine. The blade speed and work piece
feed rate were set to approximate as close as possible the
high blade speed and low feed rates of the larger Heska
Results and discussion
machine: 660 m/min and 0.1 m/min respectively. The
effect of post-cutting surface preparation was examined
The results from the cutting study performed
using samples cut on the lab machine. One set of cut
using the Heska saw are shown in Table 1. The results of
flexural specimen was polished using 240, 320, 400 and
the modified technique are observed to be consistently
600 grit sandpaper in order to remove any surface
lower than those from the standard test method. This is
asperities prior to mechanical testing.
most likely due to higher shear stresses occurring in the
modified technique caused by the higher thickness/span
The mechanical results from cut samples were
ratio.
compared with those of directly molded bars. Although the
glass fiber orientation of the molded bars was similar to
Interestingly, over a wide range of teeth per unit
that of the cut specimen, it was expected that the glass
length (highest/lowest=2), blade speeds (highest/lowest=6)
fibers in the these samples would be more oriented due to
and work piece feed rates (highest/lowest=90), the results
molding edge effects absent in the cut specimens. In order
are all within 10% of each other suggesting that the cutting
to isolate this potential orientation effect from cutting
technique used did not greatly affect the flexural strength of
effects, the edges of some of the molded bars were also cut
33% glass reinforced nylon 66. Although nylon 66 might
using the lab scale saw and the cutting conditions described
be expected to be more sensitive to these notches given its
previously.
high glass transition temperature, the relatively slow test
speed may have allowed the polymer to yield locally. High
speed impact testing is currently planned.
Evaluation Procedure
2

A closer inspection of the results suggests that the
combination of low blade speeds and high work piece feeds
leads to lower strengths. This is shown in Figures 3 and 4
for the 120 teeth/m blade.
3

Figure 5 shows micrographs of parts cut with low
smoother edge surface shown in Figure 8, one must recall
and high work piece feed rates for the 120 teeth/m blade at
that the glass fibers in the molded bar are more highly
a blade speed of 200 m/min. The higher feed rate appears
oriented in the test direction due to edge effects during
to leave fewer but more pronounced ridges. The distance
filling. In order to assess the effect of cutting given this
between ridges is proportional to the volume of material
glass fiber orientation difference, 0.5 mm of each 3.2 mm
cut per tooth. If this large distance between ridges is
edge of the molded bar were cut off with the laboratory
related to the lower mechanical properties, it should
scale band saw using the conditions described above. This
therefore be possible to collapse the data for all cutting
would introduce surface roughness comparable to that on
conditions onto a master curve.
the cut specimens described previously. The results
(Figure 9) show that cutting had a small but statistically
If T is the number of teeth per meter, and v the blade
insignificant effect on the strength of these bars. This
speed in m/min, then the time (t) between teeth on the same
again confirms that, under the correct conditions, band saw
side of the blade passing a given position on one work
cutting has little effect on the average flexural properties of
piece is:
33% glass reinforced nylon 66. It should be noted
2
t =
(2)
however, that the standard deviations were generally higher
T v
for the cut specimens.
The 2 appears in the equation because only every
second tooth contacts a given work piece on the straight set
blade. If F is the work piece feed in m/min, then the
Conclusions
distance (d) that the work piece travels during that time is:
2 F
The flexural strength of glass reinforced nylon 66
d =
(3)
T v
samples cut on a band saw can be maximized by cutting
under conditions of high blade speed and a low work piece
d represents the spacing between cut marks on the
feed rate. Under these optimized cutting conditions,
cut specimen. Figure 6 shows a plot of flexural strength
polishing the cut surface does not significantly improve the
versus d for all feed rates, cutting speeds and teeth per
flexural strength.
meter used in this research. It shows that as d is increased
the strength drops off. The results would therefore suggest
Molded bars were observed to have higher
that, ideally, it is desirable to use low work piece feed rates
flexural strengths than cut specimens of the same
along with high blade speeds and large number of teeth per
dimensions. This is believed to be due to differences in
meter to minimize the material removed per tooth.
glass fiber orientation. Cutting the edges off the molded
bars, thereby inducing possible notches, did not
The smaller laboratory band saw was used to
significantly affect the molded bar’s average flexural
examine the effect of using a hook tooth, raker set blade.
strength although the property variability did increase.
The value of d used with this saw was small (0.002 mm) in
order to maximize properties. The results with the hook
Given that polishing cut specimens and cutting the
tooth, raker set blade are shown on Figure 6 to be
edges off molded bars did not significantly affect the
statistically equal to the results obtained under similar
average flexural strength of these parts, it can be concluded
cutting conditions with the skip tooth, straight set blade.
that cutting, under the correct conditions, does not
significantly affect the average flexural strength of 33%
The cut edges of parts made with smaller
glass fiber reinforced nylon 66. More work is underway to
laboratory saw were also polished using 240, 320, 400 and
assess the effect of cutting on impact properties.
600 grit sandpaper to remove any asperities. The results
compared with the unsanded specimens are given in Figure
7. It shows that, for these materials and cutting conditions,
sanding had no significant effect on flexural strength.
Acknowledgements
The flexural strength of the molded bar using the
The authors would like to thank the Centre for
standard test method was found to be 287 MPa with a
Automotive Materials and Manufacturing for funding this
standard deviation of 2 MPa. The test result using the
work. The assistance of Steve Lockridge, and John
modified method was observed to be 280 MPa with a
Perreault in cutting the samples and assisting in the
standard deviation of 3 MPa. Again the modified method
preparation of the modified test fixture is greatly
yielded slightly lower results due to shear stresses caused
appreciated.
by higher thickness to span ratios.
The flexural strength results from the molded bar
were, on average, 10% higher than those obtained on cut
specimens. Although this may be partly due to the
4

6. References:
Table 1 – Strength using standard and modified test methods as a
1 K. Li, T.W. Liao, et al, Wear of diamond wheels in
function of cutting parameters. The values in round brackets
creep-feed grinding of ceramic materials, II. effects on
represent measurement standard deviations.
process response and strength, Wear, V.211, No.1,
1997, 104-112.
Strength [MPa]
2 W.J. Tomlinson, R.C. Newton, Effect of grinding,
Teeth
Blade
Feed
Standard
Modified
lapping and various surface treatments on the strength
[teeth/m]
speed
rate
test
test
of silicon nitride, Ceramics international, V.16, No.15,
[m/min]
[m/min]
method
method
1990, 253-257.
120
200
0.09
265 (7)
251 (3)
3 B.P. Bandyopadhyay, H. Ohmori, The effect of ELID
grinding on the flexural strength of silicon nitride,
120
200
7.9
244 (7)
229 (3)
International journal of machine tools and
120
1200
0.09
265 (9)
242 (7)
manufacturing, V.39, 1999, 839-853.
120
1200
7.9
257 (6)
245 (7)
4 J.H. Zhang, T.C. Lee, X. Ai and W.S. Lau,
Investigation of the surface integrity of laser-cut
240
200
0.09
258 (7)
250 (8)
ceramic, Journal of materials Processing technology,
V.57, 1996, 304-310.
240
200
7.9
259 (11)
232 (8)
5 T.W. Liao, K.Li and K. Breder, Flexural strength of
240
1200
0.09
268 (10)
249 (6)
ceramics ground under widely different conditions,
240
1200
7.9
260 (6)
239 (8)
Journal of materials Processing technology, V.70,
1997, 198-206.
6 M. Ramulu, Machining and surface integrity of fibre-
Straight
Raker
reinforced plastic composites, Academy proceedings in
Skip
set
set
Hook
Engineering Sciences, V.22, No.3, 1997, 449-472.
tooth
tooth
7 DuPont Engineering Polymers, Zytel® 70G33HRL
NC010 Product Information data sheet.
8 N.G. McCrum, C.P. Buckley, C.B. Bucknall,
"Principles of Polymer Engineering”, Oxford
University Press, NewYork, 1988.
9 S.F. Krar, J.W. Oswald, J.E. St.Armand, Technology of
Machine Tools, Second Edition, McGraw-Hill
Ryerson, New York, 1976.
Figure 1 – Schematic representation of the different band saw
set patterns and tooth forms used in this research.
Figure 2 – Side and front view of the modified flexural testing
fixture used to test molded bars and cut specimens on their small
3.2 mm face.
5

265
270
265
257
250
Strength
244
(MPa)
230
210
0.09
1200
Feed rate
(m/min)
7.9
200
Blade speed (m/min)
Figure 3 - Flexural strength as a function of blade speed and work piece feed rate
using the Heska saw with 120 teeth/m. Standard flexural test method used
270
251
242
250
245
Strength
(MPa)
230
229
210
0.09
1200
Feed rate (m/min)
7.9
200
Blade speed (m/min)
Figure 4 - Flexural strength as a function of blade speed and work piece feed rate
using the Heska saw with 120 teeth/m. Modified flexural test method used
6

Figure 5 - SEM micrographs of specimens cut at low (left) and high (right) work piece feed
rates at a blade speed of 200 m/min using a 120 teeth/m blade.
Heska Saw - standard flexural test
Heska Saw - modified flexural test
270
Laboratory Saw - standard flexural test
Laboratory Saw - modified flexural test
)
250
Strength (MPa 230
210
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Distance (d) between cuts (mm)
Figure 6 - Flexural strength as a function of the distance between cuts for standard and
modified test fixtures on the Heska and laboratory band saws. The lines are drawn to
show trends for the standard and modifed flexural test method.
7

No sanding
270
With sanding
250
268
266
Strength (MPa)
258
254
230
210
standard flexural test
modified flexural test
Figure 7 - Flexural strength of specimens cut using the laboratory band saw. One
specimen had no further surface preparation and the second was sanded.
Figure 8 - SEM micrograph of
the edge of a molded flexural
bar.
8

No edge cutting
290
With edge cutting
270
250
287
282
280
Strength (MPa)
277
230
210
standard flexural test
modified flexural test
Figure 9 - Flexural strength of molded bars as molded and with 0.5 mm shaved off of
each edge using the laboratory band saw using both standard and modified flexural
test methods..
9

Document Outline
  • THE EFFECT OF SAMPLE PREPARATION ON THE FLEXURAL STRENGTH OF REINFORCED NYLON 66
    • Abstract
        • Material
  • 6. References:

Download
THE EFFECT OF SAMPLE PREPARATION ON THE FLEXURAL STRENGTH OF REINFORCED NYLON 66

 

 

Your download will begin in a moment.
If it doesn't, click here to try again.

Share THE EFFECT OF SAMPLE PREPARATION ON THE FLEXURAL STRENGTH OF REINFORCED NYLON 66 to:

Insert your wordpress URL:

example:

http://myblog.wordpress.com/
or
http://myblog.com/

Share THE EFFECT OF SAMPLE PREPARATION ON THE FLEXURAL STRENGTH OF REINFORCED NYLON 66 as:

From:

To:

Share THE EFFECT OF SAMPLE PREPARATION ON THE FLEXURAL STRENGTH OF REINFORCED NYLON 66.

Enter two words as shown below. If you cannot read the words, click the refresh icon.

loading

Share THE EFFECT OF SAMPLE PREPARATION ON THE FLEXURAL STRENGTH OF REINFORCED NYLON 66 as:

Copy html code above and paste to your web page.

loading