NBSIR A 1 1 1 4 237S5B 78-1493

&

Cutting Experiments with

Plastic Edges

Stanley K. Wakamiya

Product Safety Technology Division

Center for Consumer Product Technology

June 1978

Report To:

100

. U56

78-1493

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20016

NBSIR 78-1493

*

a

CUTTING EXPERIMENTS WITH

PLASTIC EDGES

$Mor<a1 Bureao of Standard APR 17 1979

Q^lOO

Stanley K. Wakamiya

Product Safety Technology Division

Center for Consumer Product Technology

June 1978

Report To: Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20016

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

I

.

INTRODUCTION

In March 1977, MBS initiated a research program to provide

technical support to the Consumer Product Safety Commission in developing a procedure to identify potentially hazardous plastic edges on toys and

children's articles. A previous NBS program had been concerned with

potentially hazardous steel edges.

Most of the effort in this program thus far has been directed

towards obtaining quantitative experimental data on which a test procedure

and safety criteria could be based. Since any test procedure and safety

criteria that may be established for plastic edges should be equitable with

those for metal edges, all experiments included tests using reference steel

edges* so that the performance of plastic edges could be related to the

performance of reference steel edges under the same test conditions. The

following specific tasks were accomplished:

1 . Characterization of typical plastic edges found on toys

according to material, geometry, and hardness.

2. Preliminary cutting experiments on pig skin using replicas of

the plastic edges characterized in task 1

.

3. Cutting experiments to investigate the effect of velocity on cutting performance of plastic edges.

4. Experiments to assess the cutting ability of various types of

plastic edges.

5. Ranking of the plastic edges tested in task 4.

II. CHARACTERIZATION OF PLASTIC EDGES

In order to identify the types of edges which may be hazardous and are likely to appear on toys, NBS assembled a sample of twelve plastic

edges from thirty different toys, the edges of which were subjectively

judged to be sharp. Two of these edges were taken from toys similar to

those which were reported by CPSC to have caused laceration injuries. The

remaining ten edges were selected to represent the thirty edges in terms of

hardness of the plastic materials and the subjective sharpness of the

edges. The edges were then characterized according to edge tip geometry,

chemical composition and hardness.

A. Edge Geometry

The geometry of the edge tips were determined from photographs

taken through a light sectioning microscope and a conventional optical

microscope. Typical photomicrographs of the plastic edge tips are shown in

*The metal reference edges were sheared steel edges, judged "marginally

safe" when tested according to the proposed Sharp Edge Test Method for

metal and glass published in the Federal Register Vol. 43; No. 58; March

24, 1978.
- 2 -

figure 1. The tip radii of the edges observed through the light-sectioning

microscope at 200X magnification ranged from 0.013 mm (0.0005 inch) to

0.102 mm (0.004 inch). The included angles of the edges were observed to

range between 0 and 88 degrees. The side profiles of the edges were observed using an interference microscope. Side profiles of nine of the

edges were observed to be devoid of any discernible peaks and valleys at

33X and at 78X magnifications. Three edges samples had minute serrations

on the order of .02 mm to .09 mm (.001 to .004 in). The geometry of each

of the 12 edges is listed in figure 2.

B. Edge Materials

The material composition of the plastic edges were identified

through infrared spectroscopy. The twelve edges were found to be four each

of styrene-butadiene, polypropylene and polyethylene.

There were two reasons for identifying the materials of the edges.

The first reason was to insure that the materials of the edges selected for

this investigation be representative of the plastic materials most

commonly used in toys. The second reason was that knowledge of the edge

materials would enable identification of some of the physical properties of

such materials which may be related to the cutting mechanism.

C. Physical Properties

The tensile elastic modulus and hardness are two physical

properties of materials which probably affect the cutting performance of

edges. Both properties are measures of a material's resistance to

deformation. The higher the tensile elastic modulus and hardness, the more

resistant a material is to deformation. An edge made of a material which

is more resistant to deformation would have less tendency to buckle, or flatten or become less sharp due to deformation when brought into contact

with another object. Thus, if two edges have identical edge tip geometries

the edge with higher tensile elastic modulus and hardness measurements

should be more likely to lacerate skin.

The Shore D hardness measurements* , made according to ASTM D-1484

for some of the edges, are shown in figure 3. The range of tensile elastic

moduli, obtained from the Modern Plastics Encyclopedia V, for the edge

materials are shown in figure 4. These hardness values and tensile elastic

moduli indicate that, in general, styrene-butadiene (a high impact

polystyrene) is the most resistant to deformation, and polyethylene is the

least resistant to deformation.

*The ASTM test method requires flat test specimens. Some edges were taken

from toys with no relatively flat surfaces. In such instances no hardness

measures were taken.
- 3

-

III. PRELIMINARY CUTTING EXPERIMENTS

A. Test Edges

The test edges used in these experiments were epoxy replicas of the toy

edges described in section II. Plastic edges on toys, being relatively

soft and flexible, dull rapidly during cutting tests. Thus, the geometry

of the edges can change drastically after only a few attempted cuts. In

order to run repeated tests and to obtain consistent results, replicas of

the original edges were needed. After investigating several techniques for

producing replicas, a casting method, using an RTV mold and an epoxy

plastic casting material was found to produce satisfactory results. Figure

5 shows photomicrographs of typical original and replica edges.

B. Skin Specimens

All tests described in this report were conducted using excised,

defatted samples of pig skin for determining the skin cutting ability of

edges. Pig skin was selected for these tests based on results of earlier

experiments performed by Deck 2/ at the University of Virginia. Deck's

test results show that excised, defatted pig skin reacts to laceration by

edges in a similar way as does excised, defatted human skin: for a particular edge at some given force, similar injuries occur on human skin

and pig skin.

The pig skin samples were procured from a local slaughterhouse. All

samples were excised from the shoulder areas of freshly killed yearling

pigs and were kept moist and refrigerated until shortly before the cutting

experiments were conducted. The test specimens were defatted carefully to

remove the subdermal fat, leaving the dermal and epidermal layers of the

skin. The samples were trimmed into 2.5 cm X 5 cm (1 in X 2 in) test

specimens, with an average thickness of approximately 2.5 mm (0.1 inch).

The test samples were taken out of refrigeration and allowed to reach room

temperature before testing.

C. Experimental Procedure and Apparatus

The set-up used in this cutting experiment is illustrated schematically

in figure 6. The skin specimen was mounted on a specimen holder, a hardwood dowel 1.6 cm (5/8 in) in diameter by 3.2 cm (1 1/4 in) long, with

the outermost layer of skin (epidermis) facing out. The specimen was held

in place by means of steel prongs inserted in the dowel. The test edge was clamped firmly in a small clamp as shown in figure 6. The skin sample,

mounted on the specimen holder at one end of a lever arm, was manually

translated* along the edge of the test edge at approximately 5 cm/s

*The translational cutting mode was used to minimize the effects of

localized deformation of plastic edges during testing. By translating the

skin sample, rather than rotating the sample at the fixed portion of the

edge, the skin specimen was continuously brought into contact with

undeformed portions of the test edge during a cutting attempt.
- 4 -

(2 in/s). The normal force was applied between the skin sample and the

test edge by means of a constant force spring which exerted a moment about

the pivot point of the lever arm. The normal force was adjusted by varying

the length of the lever arm between the skin sample and the pivot point.

Several precautions were taken to minimize the inertial loading effects

and end effects. First, before the start of a test run, the skin was initially brought into contact with the loading surface, rather than the

test edge. Then, the skin specimen was translated smoothly along the

loading surface and passed over the length of the edge to the unloading

surface. Secondly, to minimize end effects, the test edge was critically

positioned and clamped so that the ends of the cutting surface of the test

edge were flush with the loading and unloading surfaces as shown in figure

6. Thus, initial contact and final separation between the pig skin and the

test edge occurred at essentially constant force and velocity.

Skin cutting tests were conducted using the epoxy replicas of the

original toy edges mentioned in section II at normal forces of 4.4 N (1 lb)

8.9 N (2 lb) and 13 N (3 lb).* At least three and a maximum of five cutting

attempts were made on one skin specimen using one replica edge at 4.4 N (1

lb) normal force. This was repeated with two other replicas of the same edge at 8.9 N (2 lb) and 13 N (3 lb). This procedure was followed for

replicas of all twelve edges mentioned in section II. Since skin samples

were found to vary in resistance to laceration, each skin specimen was "calibrated” by making a test cut with a reference edge and recording the

results. Results of test cuts produced by plastic edges were compared to

the test cuts on the same skin specimen made by the reference edge.

D. Results and Discussion

The results of the cutting tests using the replica edges indicated that

these edges were significantly less sharp than the reference steel edges.

For purposes of this investigation, the depth of cut was assumed to be an adequate measure of the injury sustained by the skin. The reference steel

edges caused abrasions of the epidermis (the outermost layer of skin) at

4.4 N (1 lb) force. At 8.9 N (2 lb) the reference edge produced cuts of 20

to 40 percent of the total thickness of the pig skin. The depth of cuts

produced at 13 N (3 lb) ranged between 30 and 50 percent. In contrast,

none of the replica edges produced even an abrasion of the epidermis at the

highest test force, 1 3 N (3 lb).

If the original toy edges had been used in these tests, similar results

would probably have been obtained. As shown in figure 3, the hardest toy

edge measured 82 on the Shore D hardness test; most toy edges were

considerably softer. The replica edges had an average Shore D

*The upper test force limit was set at 13 N, since this was the force at

which the reference steel edge consistently cut pig skin to a depth of 30

to 40% of the skin specimen thickness.
- 5

-

hardness of 80, which is comparable to the reading for the hardest toy

edges in the original samples. Comparisons of the photomicrographs of the

replicas and the corresponding original edges showed that the edge tip

radii were about 20 percent smaller on the replicas. Thus, since the

replica edges were at least as hard as the original edges, and since the

replicas were slightly sharper than the original, it appears reasonable to

deduce that the replicas caused at least the same amount of cutting as the

original edges would have caused.

IV. INVESTIGATION OF VELOCITY EFFECTS

The effect of velocity on cutting of human skin was reported to be

minimal or non-existent by Sorrells and Berger 3/ for metal edges.

However, since the cutting mechanism for plastic edges may differ from that

for steel edges, an investigation of velocity effects on cutting of skin by

plastic edges was judged necessary.

A. Test Procedure and Apparatus

Using the same experimental procedure and apparatus used in

experiments discussed in the preceding section (III.C), tests were

conducted on pig skin using plastic edges at edge velocities ranging from 5

cm/s (2 in/s) to 127 cm/s (50 in/s). Although the relative velocity

between the edge and the skin sample was manually controlled, a photocell

sensor connected to a digital time interval meter was used to measure the

elapsed time over a premeasured distance on the edge during each test run. The average velocity of the edge relative to the skin was calculated from

the elapsed time and the premeasured distance.

Two types of plastic edges were tested; scribed and broken acrylic

edges, and functional serrated plastic knife edges. Several samples of

both types of edges were used in the tests to minimize the dulling effects.

B. Measurement of Cut

In order to quantitatively assess the cutting ability of edges at

different velocities, it was necessary to use an instrument for measuring

the depth of a test cut. The instrument selected is essentially a depth

gage with a dial indicator identical to the one used by Sorrells and Berger

3/ to measure the depth of cut in their human skin cutting experiments. As

shown in figure 7, the depth gage consists of a special probe tip

mechanically linked to a read-out dial. The wedge shaped tip is

approximately 1.3 cm (1/2 in) long with an edge tip radius of 0.2 mm (8 mil

inch) and an edge tip angle of 15 degrees. A piece of 1.3 cm (1/2 in)

aluminum rod provided a reference surface on which to place the skin

specimen after a test run to measure the depth of cut as shown in figure 7

.

The curved reference surface was chosen to facilitate measurement at the

deepest part of the cut.
- 6 -

The depth of cut was measured immediately after each test cut. Two

measurements were taken for each test cut. The thickness of the skin

specimen immediately adjacent to the test cut was measured by placing the

skin specimen between the probe tip of the depth gage and the skin

specimen. This measurement was recorded as T . Then, the probe tip of the

depth gage was inserted into the test cut. Tne position of the specimen

was carefully adjusted to obtain the lowest reading on the dial to insure

that the measurement was being made at the deepest part of the cut. This

reading was recorded as Tp. The percent depth of cut, D, was calculated

from these two measurements by:

C. Results and Discussion

The results of the tests are shown graphically in figures 8 and 9.

In both of these graphs the percent depth of cut is plotted as a function

of the velocity. Although the data in these figures show a slight trend

toward decreased depth of cut at higher velocities, this trend is

practically negligible considering the large scatter in the data.

Furthermore, note that velocity was varied over a very wide range. For

acrylic edges, for example, the average depth of cut decreased from 28% to

16% when the velocity was varied from 5 cm/s (2 in/s) to 127 cm/s (50

in/s). Thus a 25-fold increase in velocity is associated with a decrease

in depth of cut by a factor of only 1.8. For the serrated plastic knife

edges, the average depth of cut decreased from 36 to 28 percent when the

velocity was increased from 25 cm/s* to 127 cm/s. Thus, the average

percent depth of cut dropped by a factor of 1.3, when the velocity was increased by a factor of 5.

It is quite possible that the slight trend towards decreasing depth

of cut at increasing velocities is due to other factors. For example, it

might well stem from the differences in the length of time the edge was in

contact with the skin specimen. Since all test edges were of the same length (4 cm), the time of contact between the skin and the edge decreased

when the velocity was increased. Conceivable an edge in contact with the

skin for a shorter period of time might not cut as deep.

A series of tests were conducted to compare the effect of force on cutting of skin with the velocity effect. As shown in figures 10 and 11, an increase in normal cutting force results in a proportional increase in

depth of cut, i.e.; doubling the cutting force also approximately doubles

the percent depth of cut.

*The serrated edges could not be tested at velocities lower than 25 cm/s.

The edge snagged the skin at lower velocities and made the data unreliable.
7

Since no appreciable velocity effect was noted in this investigation,

it appears that velocity may be ignored as a significant factor. The

normal cutting force has a much greater effect on the cutting performance

of plastic edges.

V. CUTTING EXPERIMENTS FOR RANKING PLASTIC EDGES

Skin cutting experiments were conducted to rank various plastic edges

from sharp to dull according to cutting performance. As previously

described, the depth of cut is assumed to be an adequate measure of the

degree of injury sustained by the skin, and hence the measure of the degree

of sharpness of that edge.

If a set of edges could be ranked from sharp to dull and could be

related in cutting performance to the reference steel edges, then this set

of edges could serve as a basis for devising an inspection procedure and

safety criteria for plastic edges.

A. Test Procedure and Apparatus

A photograph of the apparatus used in this investigation is shown in

figure 12. The basic cutting action was similar to that shown in figure 6

in section III.C. The skin sample was translated along the length of the

test edge which was clamped in the edge holder. The same precautions were

taken as described in III.C to minimize inertial loading effects and end

effects.

As shown in figure 12, the test edge was secured in the edge holder,

and clamped in a vise, which was attached rigidly to the stationary frame

of a metal turning lathe. The picture also shows the pig skin specimen

mounted around the hardwood specimen holder at one end of a pivoted lever

arm. The skin was held in place by steel prongs protruding from the

specimen holder in a radial direction away from the test edge. A tension

spring attached to the other end of the lever arm provided a means for

adjusting the normal force. The lever arm and spring assembly was mounted

on a plate, which was rigidly attached to the lathe carriage. Using the

lead screw mechanism of the lathe, the skin sample was moved along the

length of the test edge at a constant speed of 5 cm/s (2 in/s).

B. Test Edges

Twelve different types of edges were used in this investigation.

Figure 13 describes the test edges and lists the material, method of

fabrication, and hardness for each edge. In general the materials for the

edges were selected for their brittleness. Brittle materials break

relatively easily when dropped on hard surfaces and tend to form fragments

with sharp edges. Thus, toys made of brittle materials may present a safety hazard.
- 8 -

It is recognized that edges, like AS, ASB and PB, made of very brittle

plastics, such as general purpose acrylic and certain types of polyester

are seldom used in toys. Similarly, plastic edges molded in certain

configurations intended for cutting, such as edge B are unlikely to be

found on toys. However, these edges were selected to represent worst case conditions: to include some of the sharpest edges which could conceivably

occur on manufactured toys or on fragments of broken toys.

General purpose polystyrene was included as an edge material since it

is sometimes used in toys. Two toys in a sample of thirty were found to be

made of this plastic, although no subjectively sharp edges were found on these toys.

Edge EC was used as a test edge since it resembles many of the actual

toy edges in geometry and has hardness approximately equivalent to that of

the harder toy edges.

Styrene-butadiene, although relatively ductile, was included as an edge

material since it is one of the most widely used plastics for toys today.

The two types of sheared steel edges were included as test edges to

allow comparison between unfinished sheared metal edges which might be

found on toys, and edges which might occur on plastic materials. Note that

edge ER is the reference steel edge.

Most of the edges were fabricated by either shearing the material on a power shear or by scribing and breaking the material. These methods of

fabricating edges were used because they produced edges with fairly

consistent cutting characteristics. Furthermore, these methods produced

edges similar to those found on fragments of broken plastics.

Photomicrographs of the test edges are contained in the Appendix.

C. Measurement of Cut

The depth of cut was measured using the procedure described in IV. B.

When testing the duller edges, it was found that the skin sample was sometimes crushed, forming a groove, rather than a cut. In such cases the

depth of the groove was measured, but it was noted that no penetration of

the epidermis occurred.

D. Results and Discussion

This investigation was carried out in two phases. In Phase I a series

of cutting tests were conducted at a particular force to compare the

cutting ability of edges at that force. In Phase II each type of edge was tested at various forces to investigate the effect of changes in normal

force on the cutting performance of edges. Since no appreciable velocity

effect on cutting of skin had been observed earlier, as described in

section IV. D, all tests were conducted at 5 cm/s (2 in/s).
- 9 -

Several precautions were taken to minimize the variability in the data

and to minimize bias of the results due to differences in cutting

characteristics of the pig skin specimens. First, the skin specimens used

in tests at one particular force level were prepared from a pig skin sample

measuring 10 cm (4 in) by 20 cm (8 in) taken from the shoulder area of one

pig. Secondly, all test cuts were made on the skin in the same direction,

perpendicular to the backbone of the pig.

The results of the Phase I experiments are shown in figures 14 and 15.

The percent depth of cut is plotted as a function of the edge type at 13 N

and 22 N in these figures. In these figures the test edges are arranged in

order of decreasing average percent depth of cut from left to right. Each

data point represents a test cut produced by one test edge on a skin

specimen. Filled in circles represent cases where cutting attempts

produced grooves in the skin, but not true cuts.

As shown in figures 14 and 15, edge DS (the steel edge sheared on a dull shear) produced much deeper cuts than any other edge at both 13 N and

22N normal force. Five plastic edges, B, AS, PS, ASB and SS produced

results similar to the reference steel edge, ER. All of these edges always

penetrated the epidermis and cut partially into the dermal layer of the

skin. Two of the plastic edges, SSB and EB, sometimes penetrated the

epidermis; on other occasions, these edges left only a groove on the skin

without cutting. Three plastic edges, EC, HSB and HSS never penetrated the

epidermal layer of skin.

Thus, the results of the Phase I test suggest that the plastic edges

tested can be grouped into three categories. Group I consists of edges

ASB, B, AS, SS and PS which always produced cuts of approximately the same percentage depth of cut as the reference steel edge. These edges were considered about equal in cutting performance with the reference steel

edges. Group II includes edges EB and SSB which sometimes cut skin. These

edges were considered slightly less sharp than the reference steel edges.

Group III consists of edges HSB, EC and HSS, which never produced cuts and,

therefore, were judged much less sharp than the reference steel edges. The

percent depths of cuts for the various edges at 13 N cannot be directly

compared to the results at 22 N since different pig skin samples were used

for these two tests. However, the relative ranking of the edges can be

compared

.

The Phase II tests were conducted to study the effect that changes in

normal force has on the cutting of skin by plastic edges. Figures 16 and

17 summarize the results of these tests. One sample of each type of the

twelve types of edges were tested at normal forces of 6.7 N (1.5 lb), 13 N (3 lb), 22 N (5 lb) and 31 N (7 lb). All of these tests were conducted on skin specimens prepared from the shoulder area of one pig. To insure that

all the skin specimens for the test had similar cutting characteristics,

each skin specimen was cut at 13 N force using the reference steel edge,

ER. Only those specimens on which the depth of cut deviated no more than 5

percentage points from the mean percent depth of cut were selected as test

specimens.
12 -

4. Ten plastic edges, most of which are harder than those normally

found on plastic toys, were grouped into three categories according

to their cutting ability relative to the reference steel edges.

The three categories are: Group I, consisting of edges which are very similar in cutting ability to the reference steel edges; Group

II, containing edges which appear to be slightly less sharp than

the reference edges; and Group III, consisting of those which are significantly less sharp than the reference edges. No plastic edge was found to be appreciably sharper than the reference steel edges.

(See section V.E.

)

5. Although it would be extremely difficult to develop a test method

which would distinguish among edges within any one of the Groups

defined in item 4, it appears possible to develop a procedure and a test device which would discriminate among the three groups of

edges.
Section View of

Edge 2-2, 200X

Profile of Edge 2-2

33X Magnification

Section View of

Edge 7-1 , 100X

Profile of Edge 7-1

33X

Figure 1. Typical Plastic Edge Tips

Taken From Actual Toys

Figure 2. Geometry and Material of Plastic Toy Edges

Edge No. Material Section Profile

I Side Profile

Radius, mm

(in)

Angle

deg.

Avg. Roughness

Height, mm(in)

El— 1 Styrene-Butadiene .025 - .050)

(.001 - .002)

27

i .02 (.001)

EIV-1 Styr en e-Bu tad i en e .050

(.002)

0 Smooth

E2-1 Polypropylene .025 - .050

(.001 - .002)

0 Smooth

E2-2 Polypropylene .050 - .100

(.002 - .004)

26 Smooth

NB32-1 Polypropylene .015 - .045

(.0005 - .002)

56 Smooth

MBS 3-1 Polyethylene * 60 .09 (.004)

NBS4-1 Polyethylene .050

(.002)

67 Smooth

NBS5-1 Styrene-Butadiene .025 - .050

(.001 - .002)

59 Smooth

NBS7-1 Polyethylene .025

(.001)

74 .05 (.002)

NBS9-1 Polypropylene .075

(.003)

62 Smooth

NBS10-1 Polyethylene .030 - .070

(.001 - .003)

27 Smooth

MBS 12-1 Styrene-Butadiene .025

(.001)

L

88 Smooth

*Not observable due to irregular shape of the edge tip.
Figure 3. Hardness Measurements of Some Plastic Toy Edges

Edge Material Hardness, Shore D*

NBS-12 Styrene-Butadiene 79

NBS-5 Styrene-Butadiene 81

NBS-III Styrene-Butadiene 62

E-2-1 Polypropylene 65

NBS-3 Polyethylene 46

NBS-7 Polyethylene 61

N3S-4 Polyethylene 62

Hardness measurements were taken according to ASTM

D1484 on 1" X 2

M X 1/16" specimens. The results

are averages of five readings for each edge. The

standard deviations ranged from 0.5 to 2.1.
Plastics

Commonly

Used

in

Toys.

Section View, 100X Profile of Edge, 33X

Actual Toy Edge

Section View, 100X Profile of Edge 33X

Replica of the Actual Toy Edge

Figure 5. Photomi crographs of Actual

and Replica Toy Edges

Skin

specimen

Figure 7 Cut Measurement Method

gss

@

PM8M

6/3 O

US

® *3*

§**

««< '3

js

®s

s»S3S3 *s

WS PM o

_C4-> ^

Cl

<U CTn Q • CC

00 4-> > ro

>- oo

4-> CU

•r- cr U "C O LiCU u

<U > CU CT L U

-o

U i- LU d O O O<4- _Q 4-> r

O -t- I— 3 C\J Cl C_)

00

CU

i_Z3 cr

m en PM

luaojad 'ms *o qidaQ
Uidajad 'ins *0 qidaQ

Fiqure

9.

Plot

of

Fdqe

Velocity

vs.

Oenth

of

Cut

for

Serrated

Plastic

Knife

Fdqes

at

8.9 N

(?

lh)

Force.
_j

6**^ LO

m «="

o

©

Finure

10.

Plot

of

Depth

of

Cut

vs.

Cutting

Force

for

Acrylic

Edges.
T T

_ CM «- PSJ St St ^ e c e s s c 333333

E

= u, .. r1 ^ N n n n 1 1 1 1 1 BQ 00 Qfi CO QQ 00 • 4 m o <3

un PO cm luasjad ino jo qjdag

Figure

11.

Plot

of

Denth

of

Cut

vs.

Cutting

Force

for

Serrated

Plastic

Knife

Edges
Figure

12.

Test

Apparatus

Figure 13. Description of the Test Edges

Edge Material Method of Fabrication

ER 0.5 mm thick galvanized steel Sheared on a power shear with a sharp cutting edge.

DS 0.5 mm thick galvanized steel Sheared on a power shear with

dull cutting edges.

PS 3 mm thick sheet cast

polyester

Sheared on a power shear with

dull cutting edges.

AS 3 mm thick general purpose

acrylic sheet

Sheared on a power shear with

dull cutting edges.

SS 3 mm thick general purpose

styrene sheet

Sheared on a power shear with

dull cutting edges.

HSS 3 mm thick styrene-butadiene

sheet

Sheared on a power shear with

dull cutting edges.

ASB 3 mm thick general purpose

acrylic sheet

Scribed and broken in a sheet

metal bender.

5SB 3 mm thick general purpose

styrene sheet

Scribed and broken in a sheet

metal bender.

HSB 3 mm thick styrene-butadiene

sheet

Scribed and broken in a sheet

metal bender.

EB 3 mm thick cast epoxy resin

sheet

Scribed and broken in a sheet

metal bender.

EC Epoxy resin *

B 2 mm thick molded

polystyrene

Injection molded. (A purchased \ serrated functional edge)

*Uncured epoxy resin was poured into a rectangular container. After the

epoxy hardened , meniscus formed by the resin at the sides of the container

was used as the test edge.
Non-cut Mean

depth

of

cut

or

groove

m so to ®i£i <58- co esi

I

COCO

O • «

i! O < O

• cm

o 8 o

ODJD

Q0

Q| OO

O OJOO «8

ocqp

00040 o

QQCO

COCO

CO

CO

CO 09

COCO<

CO

a.

CO<

CO

OS GO to LD o C*1 CNJ

luoojad ‘pa jo gidao

Graph

of

DeDth

of

Cut

vs.

Edne

Tyne
O

O o

S3 OO I-* o o 4© 4C3 PO ev

C/3

C/3 zoUJm

e/3

00

C/3 C/3

osUJ

£0

a.

c/3

C/3

C/3

oa

OC

UJ

QQ

00

«£

00

£0

CDQ.>

cvC7 "O

LlJ3 CD

<-J

u

M— o O Ll_ «

Q. _C .—.

S>» 4-> Q_

-C

G3 a> S3 c: ln T3 UJ <4-o

C\j -H c\j

rG e:

aj3

CT
Force

Force

Force

Force

60

40

20

0

60

40

20

0

Fiqure 16. Graphs of Depth of Cut vs. Force

Figure 18. Hardness Measurements of Plastic Test Edges

Material Edge Type Hardness, Shore D*

Epoxy resin EB 80

EC

! Styrene- HSS 80 ! butadiene HSB

j Polyester Resin PS 84

j General Purpose SSB 85

Polystyrene SS, B

General Purpose AS 90

Acrylic ASB

•Hardness measurements were made per ASTM D1 484

.

Results are shown as the average of five measurements made on 1" X 2" X 1/8” specimens. Standard

deviations ranged from 0.5 to 1.7.
oCO G1X1 O oCM o an IB t*n

if)

if)

u

m

gg

QQm

m

60

60

m

<

60

O.

60

SOm

<

60

a

QJCl>

cs a;

t_> u

<4- o

O LlCS

03

s_

pasjsd Ins |o

Edge

type
Figure 20. Ranking of Edges

Ranking of Edges in Order

Decreasing Sharpness

of

D Overall

Rank // At 13N (3 lb) 22N (5 lb) 31 N (7 lb) ~T Ranking

1 B ASB ASB ASB ASB

2 ER ER ER PS ER

Group I 3 AS B B ER B

4 PS AS PS B PS

5 ASB SS AS SS AS

6 SS PS SS AS SS

7 EB EB SSB EB EB

Group II

8 SSB SSB EB SSB SSB

9 EC HSB HSB EC EC

Group III 10 HSB EC EC HSB HSB

11 HSS HSS HSS HSS HSS
REFERENCES

1. Modern Plastics Encyclopedia, Vol. 49, No. 10A, McGraw-Hill, New

York (1972).

2. Deck, J.D., "Skin Histology After Cuts, Punctures and Related

Injuries," unpublished data, University of Virginia School of

Medicine (1976).

3. Sorrells, J.R. and Berger, R.E., "Some Cutting Experiments on Human

Skin and Synthetic Materials," National Bureau of Standards Report

NBSIR73-262 (1973).



Edge ER (Reference Steel Edge ER Profile, 78X

Edge) Section View, 200X

Photomicrographs of Steel Test Edges
I
Edge PS Profile, 78X Edge AS Profile, 7 8

X

Photomi crographs of Plastic Test Edges
t
Edge SS Profile, 78X Edge EB Profile, 78X

Edge SSB Profile, 78X Edge EC Profile, 78X

Photomi crographs of Plastic Test Edges

Photomicrographs of Plastic Test Edges

as- 1 14A (REV 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLIC A ITON OR R I- PORT NO. NBSIR78-1493

2. Gov’t Accession

No.

3. Recipient's Accession No.

TITLE AND SUBTITLE

CUTTING EXPERIMENTS WITH PLASTIC EDGES

5. Publication Date June 1978

6. Performing Organization Godt 763

t^anVey’ K. Wakamiya

8. Performing Organ. Report Nc

PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit Nc 7632502

11. Contract/Grant No.

Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, MD 20016

13. Type of Report & Period Covered

14. Sponsoring Agency ('ode

SUPPLEMENTARY NOILS

. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

An investigation was conducted to determine the skin lacerating ability of

plastic edges. The purpose of this study was to obtain quantitative experimental

data on which to base a test procedure and a safety criteria for identifying

potentially hazardous plastic edges found on toys and children's articles.

A variety of plastic edges including plastic replicas of edges taken from

toys were used to cut excised, defatted pig skin. Cutting experiments were

performed at various forces and velocities and the depth of the resulting cuts were measured.

Test results indicate that over the range 5 cm/s to 127 cm/s the relative

velocity between the test edge and the skin sample apparently does not significantly

affect the cutting of skin whereas the normal force exerted by the edge on the skin

has a definite effect on the cutting performance of plastic edges.

The experimental data obtained in this study shows that there are some types

P^sstic materials, which when broken, form edges with lacerating abilities

similar to that of the reference sheared steel edges, which were judged "marginally

safe" when tested with the Consumer Product Safety Commission (CPSC) Metal Sharp

Edge Test. However, the results of this study indicate that most plastic edges

found on toys are less likely to cause laceration injuries than these reference

steel edges.

KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons ) Cut; edge; force; injury; pig skin; plastic; velocity

AVAILABILITY [X^ Unlimited

[2 j For Official Distribution. Do Not Release to NTIS

[ J Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C . 20402, S D Cat. No. C 1 3

[_. ] Order From National Technical Information Service fNTIS)

Springfield, Virginia 221*>1

’ 19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

40

22. Price

$4.50

USCOMM-DC 29042-P74