1. Abstract— In this lab, students learned how to use the Instron
Universal Testing Machine to test adhesive materials. The two
adhesives that were tested include: cyanoacrylate (abbreviate as
CA) and epoxy. Using the data obtained in lab, students were
responsible forfinding the maximum shearstress/maximum shear
strength of each adhesive and constructing a 95% confidence
interval for the maximum shear stress of each specimen. Once
complete, students compared the shear strength results obtained
in lab with those of CA and epoxy adhesives from a credible
reference.
Index Terms—Confidence interval, cyanoacrylate, epoxy, shear
stress
I. INTRODUCTION
HIS lab was fairly quick and simple. Two double lap shear
specimens (one for CA and one for epoxy) were tested to
failure using the Instron Universal testing machine. The test
results as well as images of the failed adhesives were posted on
canvas for the students to analyze. Images of the failed test
specimens were analyzed using ImageJ software so that the
areas of the adhered surfaces could be calculated by using the
number pixels within the contact area. The area average was
calculated for each section and recorded. From this, the shear
stress and shear strength of each adhesive can be calculated.
Fig. 1. Double lap configuration
Fig. 2. Diagram of shear stress experienced by an adhesive in single lap
II. PROCEDURE
Specimen Testing
The first step in this lab was to test the double lap
specimens. The specimens were pre-prepared for testing prior
to coming to lab so no preparation was necessary.The test
were performed using the Instron Universal testing machine.
The failed specimens were shown to the class and
observations were made on how the specimen failed. The
Instron data and images of the failed specimens were uploaded
to canvas for students to analyze.
Area estimations using ImageJ
Images of the failed surfaces for both specimens were
imported into Image J in order to estimate the area of the
contact surfaces.This was done by manually drawing around
the contact area and seeing the resulting pixel area. A ruler
was included in each image in order to accurately find the
calibration constant (k) where k:
𝑘 =
𝑝𝑑
𝑑
(1)
Where 𝑑 is the measured length along the ruler and 𝑝𝑑 is the
number of pixels along the measured length. Once the
calibration constant is found, the contact area can be
calculated in 𝑐𝑚2
using the following formula.
𝐴 = 𝑘2
(𝑝𝑎 ∗ 𝑝𝑏 ) (2)
Where 𝑝𝑎 is the number pixels along length a and 𝑝𝑏 is the
number of pixels measured along length b. The average area
found by students in the section was then calculated and
uploaded to canvas.
III. RESULTS
TABLE I
STATISTICAL DATA OF BOTH SPECIMENS
Average
maximum shear
stress (MPa)
Standard
deviation of
maximum shear
stress (MPa)
Number of
samples
Using The Instron Universal Testing Machine to
Test Adhesives
Ballingham, Ryland
Section 3236 3/16/2016
T

2. <Section####_Lab#> Double Click to Edit 2
2
Cyanoacrylate 3.18 1.47 12
Epoxy 5.60 2.92 12
TABLE II
95% CONFIDENCE INTERVAL OF MAX SHEAR STRESS
Cyanoacrylate
(MPa)
High-strength epoxy
(MPa)
Aluminum/Aluminum 3.18±0.83 5.60±1.65
IV. DISCUSSION
The above results were calculated using excel and the
equations used can be found in the appendix. It appears that
epoxy has a higher shear strength than cyanoacrylate. Some
factors contributing to the shear strength of the specimen
include: preparation of contact area, the adhesive used and
configuration of the adhesive joint. The cleaner the contact area
is prior to bonding, the larger the shear strength will be. This
makes sense as a bonding surface with a lot of contaminates
will have a smaller contact area between the adhesive and the
metal due to these contaminants causing the shear stress to
increase. The type of adhesive is going to affect the shear
strength of the specimen, because adhesives have a wide range
of material properties including shearstrength. Forthis lab data,
epoxy has the higher shear strength. Finally, the configuration
of the adhesive joint is going to affect the shear strength of the
specimen. For example, a specimen in a double lap
configuration is going to have a larger shear strength than one
in a single lap configuration. This is because the contact area is
doubled for this configuration, causing the shear stress to
decrease.
The range of shear strength values for Cyanoacrylate is 6.9-
13.8 MPa [2]. The average shearstrength ofcyanoacrylate from
the data is 3.18 MPa. The range of shear strength values for
epoxy is 10.3-27.6 MPa [2]. The average shear strength from
the data is 5.60 MPa. The most likely reasons for the lab data
showing a much smaller shear strength for both specimens is
that the testing conditions/specimen preparation in a student lab
are most likely not as good as in a professional testing setting.
In a professional testing setting, specimens are likely prepared
much more effectively and thoroughly to clear any
contaminates from them. Also, more care is likely taken when
applying the adhesives to the specimen in a professional testing
setting,causing the applied load to be more uniformly over the
bonding area thus increasing the shearstrength ofthe specimen.
V. CONCLUSION
Adhesive joints are becoming more abundant in engineering
applications. Adhesive joints offer a ton of advantages to
traditional fastening methods. Adhesives remove stress
concentrations, reduce weight/design complexity, improve
dissipation of vibrational energy and can allow dissimilar
materials to be joined that otherwise couldn’t be using other
methods [2]. In this lab, epoxy appears to have a higher shear
strength than Cyanoacrylate.
APPENDIX
Uncertainty equations used
𝑈𝐴 = ((
2𝑑𝑝 𝑎 𝑝 𝑏
𝑝 𝑑
2
)
2
( 𝑢 𝑑)2
+ (
𝑑2
𝑝 𝑏
𝑝 𝑑
2
)
2
( 𝑢 𝑝𝑎 )
2
+ (
𝑑2
𝑝 𝑎
𝑝 𝑑
2
)
2
( 𝑢 𝑝𝑏)
2
− (
2𝑑𝑝 𝑎 𝑝 𝑏
𝑝 𝑑
3
)
2
( 𝑢 𝑝𝑑 )
2
)
1/2
𝑈𝑃 = √(
𝜕𝑃
𝜕𝑚
)
2
( 𝑈 𝑚
)2 + (
𝜕𝑃
𝜕𝑎
)
2
( 𝑈𝑎
)2 (4)
𝑈𝜏 = √(
𝜕𝜏
𝜕𝑃
)
2
( 𝑈𝑃
)2 + (
𝜕𝜏
𝜕𝐴
)
2
( 𝑈𝐴
)2 (5)
Statistic equations used for calculations in excel
𝜎𝑓 = √
1
𝑁
∑( 𝑥 𝑖 − 𝑥̅)2
𝑁
𝑖 =1
(6)
𝑥̅ =
∑ 𝑥𝑖
𝑁
(7)
𝑥 𝑖 = 𝜇 𝑓 ± 1.96
𝜎𝑓
√ 𝑁 (8)
TABLE III
LAB DATA FOR CYANOACRYLATE
Area
(𝑐𝑚2
)
Max load
(kN)
Maximum shear stress
(MPa)
7.40 2.90 3.92

3. <Section####_Lab#> Double Click to Edit 3
3
6.14 2.26 3.68
5.53 1.80 3.26
5.88 1.18 2.00
7.24 1.06 1.47
7.43 2.17 2.92
13.42 1.96 1.46
12.79 3.29 2.58
12.22 1.82 1.49
6.27 2.97 4.73
4.22 2.00 4.74
6.37 3.77 5.91
TABLE IV
LAB DATA FOR EPOXY
Area
(𝑐𝑚2
)
Max load
(kN)
Maximum shear stress
(MPa)
5.80 4.66 8.04
4.26 2.37 5.55
5.77 2.93 5.07
4.76 4.98 10.46
10.90 8.91 8.18
6.08 5.51 9.09
9.40 1.16 1.23
10.59 2.47 2.33
9.25 2.30 2.49
5.54 2.88 5.20
6.58 2.17 3.29
5.68 3.55 6.26
TABLE V
UNCERTAINTY VALUES
Parameter Calculated Uncertainty
𝑈(𝐴)2
±102 𝑝𝑖𝑥𝑒𝑙𝑠2
𝑈 𝜎 ±0.5 %
𝑈 𝑃 ±0.25 kN
𝑈 𝜏 ±0.20 MPa
REFERENCES
[1] Ridgeway, S. “Lab 4 ImageJ Uncertainty,” EML 3301C Mechanics of
Materials Lab – Spring 2016
[2] Shigley, Joseph Edward., andCharles R. Mischke. Mechanical
Engineering Design.NewYork: McGraw-Hill, 1989. Print