MECH 3200
Lab 1 Report: Mechanical Properties of Plastic
Prepared for: Emmanual Sey (em445321@dal.ca)
Written By:
Bashar Morelly (B00879270)
Shivam Patel (B00)
Apurva Bhuva(B00914481)
Mahir Labib Biswas (B00922796)
Abstract
The primary objective of this laboratory experiment was to measure and compare the
mechanical properties of two thermoplastic polymers; Polyvinyl Chloride (PVC) and
Polypropylene (PP) with a 6061 Aluminum Alloy serving as a metallic reference. The
investigation focused on evaluating each material’s tensile strength, elastic modulus,
ductility, and hardness, to understand how composition and structure influence
mechanical performance. Tensile testing was conducted using a universal testing machine
to obtain stress–strain curves, from which the elastic modulus, yield strength, and
elongation at fracture were determined. Additionally, Shore D hardness testing was used
to assess surface resistance for the plastic specimens. The results showed that PVC had a
relatively high stiffness (E ≈ 1.80 GPa) and hardness (Shore D 80), indicating suitability for
rigid applications such as piping or fittings. Polypropylene, in contrast, exhibited lower
stiffness (E ≈ 0.36 GPa) but superior ductility (elongation ≈ 94.9%), making it ideal for
flexible components such as living hinges. 6061 Aluminum Alloy demonstrated the
highest stiffness (E ≈ 29.05 GPa) and strength (σ_y ≈ 56.9 MPa) but lower ductility (9.44%),
validating its use in lightweight structural components. Analysis of the yield strength-toweight ratios highlighted the engineering significance of optimizing both strength and
weight in material selection. Overall, the experiment effectively demonstrated the
contrasting behaviors of metals and polymers under tensile and hardness testing,
emphasizing the importance of matching material properties to functional requirements in
design.
Table of Contents
Abstract ...................................................................................................................... 2
Table of Contents ......................................................................................................... 3
List of Tables................................................................................................................ 4
1. Introduction ............................................................................................................. 5
2. Experimental Procedure ............................................................................................ 6
3. Results and Discussion ............................................................................................. 7
3.1. PVC ................................................................................................................... 7
3.2. Polypropylene .................................................................................................... 9
3.3. 6061 Aluminum Alloy ........................................................................................ 10
4. Discussions ........................................................................................................... 12
Conclusion ................................................................................................................ 14
References ................................................................................................................ 15
List of Figures
Figure 1: PVC Stress-Strain Plot ..................................................................................... 8
Figure 2: Polypropylene Stress-Strain Plot ...................................................................... 9
Figure 3: 6061 Aluminum Alloy .................................................................................... 11
List of Tables
Table 1: Initial Measurements for PVC ............................................................................ 7
Table 2: Calculated Mechanical Properties for PVC ......................................................... 8
Table 3: Initial Measurements for Polypropylene ............................................................. 9
Table 4: Calculated Mechanical Properties for Polypropylene ........................................ 10
Table 5: Initial Measurements for 6061 Aluminum Alloy ................................................. 10
Table 6: Calculated Mechanical Properties for 6061 Aluminum Alloy .............................. 11
1. Introduction
The primary objective of the lab is to measure and compare hardness and tensile
characteristics of various materials. The materials tested in the lab include Polyvinyl
Chloride (PVC) and Polypropylene (PP); both of which are thermoplastic polymers as well
as 6061 Aluminum Alloy, which serves as a metallic reference for comparison. This
investigation aims to evaluate how each material behaves under tensile loading and
localized surface indentation, providing a comprehensive understanding of their
mechanical characteristics and potential engineering applications.
Tensile testing is a fundamental technique in materials engineering used to evaluate a
material’s behavior under stretching loads. During the test, a specimen is elongated until
fracture, and the resulting relationship between stress and strain is plotted to form a curve.
This stress–strain curve reveals key mechanical properties such as elastic modulus, yield
strength, ductility, and fracture stress, as well as the overall deformation behavior of the
material.
The typical response of our samples under tension can be divided into several distinct
stages:
•
Elastic Region: The initial linear portion of the curve where deformation is
reversible. When the load is removed, the sample returns to its original dimensions.
•
Yield Point: Marks the end of elastic behavior; beyond this point, deformation
becomes permanent.
•
Strain Softening: A reduction in stress following yielding, often due to localized
neck formation.
•
Cold Drawing: Continued stretching causes polymer chains within the necked
region to reorient and align in the loading direction.
•
Strain Hardening: As molecular alignment increases, further deformation requires
greater stress.
•
Fracture: The final stage, where the material ultimately fails and separates into two
pieces.
In addition to tensile testing, hardness testing was performed to measure each material’s
resistance to surface indentation. For softer materials such as plastics, hardness is
commonly determined using the Shore Durometer method. The test involves pressing an
indenter into the specimen’s surface under a specified load and measuring the resulting
depth of penetration. The Shore D scale, used in this experiment, is suitable for hard
plastics and provides a quick, standardized measure of surface resistance.
Through these tests, this lab seeks to compare the mechanical performance of plastics
and metals, emphasizing how their structural composition affects their strength, stiffness,
and suitability for practical applications in engineering design.
2. Experimental Procedure
The experiment was carried out according to a standardized procedure to obtain the
necessary measurements for analysis. Before performing the tensile tests, the following
preliminary measurements were taken for each sample:
• Hardness: The Shore D hardness of the plastic specimens was measured by
pressing the durometer needle firmly onto the shoulder (wider, non-gauge section)
of each sample and recording the reading.
• Weight: Each specimen’s mass was measured using a digital scale.
• Initial Dimensions: Calipers were used to measure the initial diameter and gauge
length of each sample’s central section.
Each specimen was then individually mounted on the tensile testing machine. Under the
supervision of the TA, the test was initiated and continued until the specimen fractured.
Following failure, the final gauge length was recorded. Finally, the complete load–
elongation data from each test was uploaded to Brightspace by the TA for further analysis.
3. Results and Discussion
With the applied force and overall extension of each sample, along with the initial
measurements taken for length and diameter, the calculations for stress and strain can be
performed. Stress can be found by taking the force applied and dividing it into the original
cross-sectional area of the sample. The strain of the samples can be calculated by taking
the change in length and dividing it by the original gauge length. After conducting these
measurements and performing the necessary conversions, the resulting stress-strain data
could be plotted to generate characteristic curves for each of the samples. From these
curves, the key mechanical properties outlined in the lab procedure can be evaluated.
These principles include the elastic modulus from the initial linear slope, the yield
strength, stress at the fracture, and the percent elongation. These values along with the
hardness measurements obtained in the SHORE D test will allow for a comparison of the
mechanical properties of PVC, Polypropylene, and 6061 Aluminum alloy, and for an
assessment of their strength to weight ratios.
3.1. PVC
Initial Measurements
Property
Original Gauge Length
Original Guage Diameter
Original Cross-Sectional Area
Hardness (Shore D)
Weight
Table 1: Initial Measurements for PVC
Symbol
Lo
Do
Ao
HD
𝑚
Value
91.5
9.76
74.81514409
80
46.45
Units
𝑚𝑚
𝑚𝑚
𝑚𝑚2
No unit
𝑔
Stress-Strain Plot
Figure 1: PVC Stress-Strain Plot
Calculated Mechanical Properties
Property
Elastic Modulus
Yield Strength
Stress at Fracture
% Elongation
Yield Strength-to-Weight Ratio
Symbol
E
𝜎
Ao
%𝜖
𝜎
𝑚
Value
Units
1.80
1.34
36.09
34.78
0.02877
GPa
MPa
MPa
No unit
MPa/g
Table 2: Calculated Mechanical Properties for PVC
Discussion
The graph and recorded values for your PVC sample indicate a high elastic modulus (~1.80
GPa) and a high Shore D hardness (80). These results imply that the material is relatively
stiff and surface-hard compared to many polymers. In practical terms, this stiffness
means the material will resist bending or deformation under load, and the hardness
suggests good wear resistance and durability.
Features on the plot:
The PVC curve starts with a short elastic region that ends at about 46 MPa, where yielding
occurs. Immediately after the yield point, the stress drops slightly to around 41 MPa,
showing strain softening as polymer chains begin to slip and a neck forms in the material.
The curve then shows a nearly constant stress region between 38 and 41 MPa, which
represents cold drawing as the neck travels along the gauge length and the chains align in
the loading direction. The curve finally falls to about 35 MPa when the material fractures at
roughly 35 % strain.
3.2. Polypropylene
Initial Measurements
Property
Original Gauge Length
Original Guage Diameter
Original Cross-Sectional Area
Hardness (Shore D)
Weight
Symbol
Lo
Do
Ao
HD
𝑚
Table 3: Initial Measurements for Polypropylene
Stress-Strain Plot
Figure 2: Polypropylene Stress-Strain Plot
Value
92.1
9.71
74.05055898
64
30.91
Units
𝑚𝑚
𝑚𝑚
𝑚𝑚2
No unit
𝑔
Calculated Mechanical Properties
Property
Elastic Modulus
Yield Strength
Stress at Fracture
% Elongation
Yield Strength-to-Weight Ratio
Symbol
E
𝜎
Ao
%𝜖
𝜎
𝑔
Value
Units
0.36
5.40
NO FRACTURE
94.90
0.17476
GPa
MPa
MPa
No unit
MPa/g
Table 4: Calculated Mechanical Properties for Polypropylene
Discussion
The graph and recorded values for polypropylene indicate that it possesses a relatively low
elastic modulus, coupled with a very high elongation. This illustrates its ability to stretch
significantly before reaching its breaking point. This characteristic can be attributed to its
semi-crystalline morphology, which consists of both crystalline and amorphous regions
within the polymer.
Features on the plot :
The polypropylene curve has an initial slope, reflecting its low stiffness. It yields at around
24 MPa and a strain of about 0.15. After this point, the stress decreases slightly, showing
strain softening as the necking forms. The curve then remains nearly constant between 16
and 22 MPa for a large range of strain, indicating a long cold-drawing region where the
chains orient and crystallize.
3.3. 6061 Aluminum Alloy
Initial Measurements
Property
Original Gauge Length
Original Guage Diameter
Original Cross-Sectional Area
Hardness (Shore D)
Weight
Symbol
Lo
Do
Ao
HD
𝑚
Table 5: Initial Measurements for 6061 Aluminum Alloy
Value
94.85
9.81
75.58365619
96
90.96
Units
𝑚𝑚
𝑚𝑚
𝑚𝑚2
No unit
𝑔
Stress-Strain Plot
Figure 3: 6061 Aluminum Alloy
Calculated Mechanical Properties
Property
Elastic Modulus
Yield Strength
Stress at Fracture
% Elongation
Yield Strength-to-Weight Ratio
Symbol
E
𝜎
Ao
%𝜖
𝜎
𝑚
Value
Units
29.05
56.89
195.82
9.44
GPa
MPa
MPa
No unit
0.62548
MPa/g
Table 6: Calculated Mechanical Properties for 6061 Aluminum Alloy
Discussion
The aluminum alloy sits way above the plastics in stiffness (modulus) and strength (yield),
but in our test, it shows much lower elongation compared to the polymers. This is because
aluminum and other metals are composed of a crystal lattice where atoms are arranged in
a regular, repeating pattern.
Plot features
The 6061-aluminum alloy curve begins with a straight elastic region where stress and
strain increase proportionally. This portion ends near 215 MPa, marking the yield point
where permanent deformation begins. After yielding, the stress continues to rise until it
reaches plastic deformation as the metal strain hardens due to the interaction of
dislocations. The curve then reaches its maximum stress around 250 MPa before necking
starts, which reduces the cross-sectional area and eventually leads to fracture.
4. Discussions
Comment on which material closely resembles the typical curve for plastic materials
as shown in the introduction of this lab
•
The stress-strain graphs of PVC and polypropylene exhibited notably different
deformation behaviours. PVC demonstrated a distinct and sharp yield point,
followed by an extended, flat region of cold drawing where the stress remained
nearly constant. This characteristic indicates that PVC deforms in a more defined
and step-wise manner once it begins to yield. In contrast, polypropylene exhibited a
smoother and more rounded curve, without a clearly defined yield point, indicating
a more gradual deformation process. When compared to the typical plastic curve
presented in the lab manual, PVC aligns more closely, as it distinctly illustrates the
elastic region, yield point, strain softening, and cold drawing.
Based on the mechanical properties of the plastics tested, give a potential
application for each plastic, and explain your answer.
•
Our PVC specimen exhibits a high elastic modulus (approximately 1.80 GPa) and a
Shore D hardness of 80, making it suitable for structural applications that require
both stiffness and durability. A prime application for this material is in rigid
plumbing or drainage pipes, where it must withstand bending under load, maintain
dimensional stability, and resist abrasion or impact during installation.
Unplasticized PVC (PVC-U) is known for its mechanical stability and hardness,
confirming its ideal use in the building industry, particularly in piping applications.
In summary, the combination of high modulus and hardness positions our PVC
sample as a material for long-service structural components, including waste and
water pipes in civil infrastructure.
•
Our polypropylene (PP) sample demonstrates a low elastic modulus of
approximately 0.36 GPa, alongside an impressive elongation of around 94.90%. This
combination makes it particularly suitable for applications that demand high
flexibility and ductility. A prime example of such use is in flip-top bottle caps or
container hinges, where the plastic must bend and flex repeatedly while
maintaining its structural integrity. The low stiffness of the material facilitates easy
deformation, while its exceptional elongation capacity allows it to withstand
numerous cycles of bending, functioning as a “living hinge” without breaking.
Consequently, Polypropylene is a popular choice for living hinge designs due to its
outstanding fatigue resistance and ability to flex repeatedly.
Calculate the yield strength to weight ratio of the different materials and comment on
why the strength to weight ratio is important when selecting a material for a specific
component
The yield-strength-to-weight ratio is vital for us as engineers and designers in industries like
automotive and aerospace because it shows how much load a material can bear before
deforming, relative to its weight. We don’t just seek strong materials; we look for those that
provide a perfect balance of strength and lightness. Materials with high yield strength but
higher weight can lead to heavier structures, which in turn increase fuel consumption and
require more support. Conversely, a high yield-strength-to-weight ratio enables us to
produce lighter components that still resist deformation under service loads. This focus on
optimizing strength without adding unnecessary weight is crucial, as every gram counts in
engineering for safety and efficiency designs.
Conclusion
Through our tensile testing of aluminum, PVC, and polypropylene, we discovered how the
structural and molecular differences between these materials affect their mechanical
behavior. The 6061 aluminum alloy showed the highest yield strength and elastic modulus,
which means it has the best stiffness and ability to carry loads, even though it’s not as
ductile as the polymers. When we looked at the yield strength-to-weight ratio, we found
that aluminum, despite being denser, actually provides the greatest strength for its weight,
making it really important for light-weight applications like in cars and airplanes. Overall,
we learned how to pull out and understand mechanical properties from stress–strain data,
link large-scale behavior to molecular structure, and assess how different materials meet
design needs based on factors like stiffness, strength, hardness, and ductility.
References
•
•
•
https://analyzing-testing.netzsch.com/en-US/polymers-netzsch-com/commoditythermoplastics/pvc-u-polyvinyl-chloride-unplasticized
https://www.palmetto-industries.com/polypropyleneproperties/?srsltid=AfmBOoqBjjaEibu4AOgxm4g7MaPQz6oyMGM4_UQ8by6DY5M
mJ9M8LxZn&utm
https://www.specialchem.com/plastics/guide/polypropylene-pp-plastic
https://www.sciencedirect.com/topics/engineering/semicrystalline-polymer
•
•
https://www.sciencedirect.com/science/article/pii/S258884201830124X
https://stampingsimulation.com/strength-to-weight-ratio-of-metals/
•