ME 220 – Mechanicals of Materials Laboratory
Test Title: Charpy Test
Name: Mannat Gill
Section: 1
TA: Elijah Blankenship
1. Summary:
Purpose:
The purpose of this experiment was to evaluate the impact toughness of different engineering
materials and to investigate the effect of temperature on their fracture behavior. Specifically, the
Charpy impact test was used to examine how materials transition between ductile and brittle
behavior under high stress and varying thermal conditions, highlighting the importance of
toughness in material selection.
Experimental Methods:
In the Charpy impact test, aluminum alloy 6061, A36 steel, and 4140 alloy steel were tested
using a standard Charpy impact machine. Each material was fully soaked in controlled liquid
baths ranging from cryogenic temperatures (liquid nitrogen) to elevated temperatures (boiling
water). Each material was soaked for approximately 10 minutes and tested within five seconds of
removal from the bath to ensure accurate temperature conditions. The pendulum impact hammer
fractured each notched specimen, and the absorbed fracture energy was recorded directly from
the machine scale for each temperature condition
Results:
The absorbed impact energy varied significantly with temperature and material type. Impact
energy decreased with temperature for both steels, while 6061 aluminum showed little
temperature sensitivity. Among all materials tested, 4140 alloy steel exhibited the highest overall
impact resistance, absorbing the greatest fracture energy at most temperatures. At room
temperature (~70°F), 4140 steel absorbed 155 ft·lb, compared to 124 ft·lb for A36 steel and 23
ft·lb for 6061 aluminum. At elevated temperatures, 4140 steel continued to outperform the other
materials, absorbing 124.5 ft·lb at ~209°F.
As temperature decreased, both steels experienced a sharp reduction in absorbed energy,
indicating a ductile-to-brittle transition. A36 steel showed the most severe drop, falling to 2–4
ft·lb at cryogenic temperatures. 4140 steel, while also losing toughness, retained higher impact
energy than A36 at several low-temperature conditions (up to 53 ft·lb near –110°F). In contrast,
6061 aluminum maintained relatively constant but low impact energy (19–28 ft·lb) across all
temperatures, indicating stability but lower overall impact strength.
Conclusion:
The Charpy impact test demonstrated that material toughness is strongly dependent on
temperature, particularly for body-centered cubic steels that exhibit a ductile-to-brittle transition.
The results emphasize the critical role of impact testing in evaluating material performance under
dynamic loading and adverse environmental conditions. Understanding temperature-dependent
toughness is essential for preventing brittle fracture and ensuring safety.
2. Results:
a. Test Data Table
A – 36 Steel
Temperature
(F)
209.3
142.9
69.8
30.8
-15.6
-71.7
-107.3
-305.3
Fracture
Energy
(ft-lb)
103
114
124
121
73
17
4
2
6061 Aluminum
Temperature
(F)
208.9
144.4
70.7
32.7
-7.7
-78
-108.8
-305.2
Fracture
Energy
(ft-lb)
19
22
23
24
21
28
23
24
b. Calculations: Temperature vs Fracture Energy Plot
4140 Steel
Temperature
(F)
208.8
143.2
70.1
31.5
-5.1
-71.5
-109.7
-305.2
Fracture
Energy
(ft-lb)
124.5
117
155
34
12
7.5
53
17
3. Discussion:
a. As test temperature decreased, clear differences were observed in fracture behavior,
impact properties, and low-temperature suitability among the materials tested. A36 and
4140 steels showed a strong reduction in absorbed impact energy with decreasing
temperature, consistent with a transition from ductile to brittle fracture. At higher
temperatures, these steels would exhibit more smooth fracture surfaces and higher energy
absorption, while at low and cryogenic temperatures their very low absorbed energies
indicate predominantly brittle, crystalline fracture surfaces. In contrast, 6061 aluminum
maintained relatively constant impact energy across all temperatures, suggesting ductile
fracture behavior with minimal change in fracture surface appearance. Consequently,
aluminum is the most suitable material for low-temperature applications due to its
resistance to brittle fracture, whereas the steels become increasingly unreliable for
impact-loaded applications at low temperatures.
b. Strength and toughness are distinct mechanical properties that describe different aspects
of material behavior. Strength refers to a material’s ability to withstand applied stress
without yielding or failing, while toughness describes the ability of a material to absorb
energy and undergo plastic deformation before fracture. A material can possess high
strength yet low toughness if it fractures with little or no plastic deformation. Brittle
materials often fall into this category. Although they may sustain high stresses, they
absorb very little energy prior to failure and fracture suddenly. This makes brittle
materials less practical for many engineering applications, since they provide little
warning before failure and are highly sensitive to defects and notches. As a result,
materials with adequate toughness are generally preferred in structural and impact-loaded
applications to ensure safer and more reliable performance.
c.
1. Initial Potential Energy (PEinitial): We know that the potential energy is the product of
the objects weight and its height above the point of impact:
𝑃𝐸 = 𝑊 × ℎ
Using the values given, we get the following:
PE𝑖𝑛𝑖𝑡𝑎𝑙 = 43.26lbs × 5.085ft = 219.98 ftlb
2. Striking velocity (v): Assuming no energy loss due to friction or air resistance, the
potential energy at the release point is converted to kinetic energy.
PEinital = KEimpact
𝑊 × ℎ=
1
𝑚𝑣 2
2
We also know that weight is equal to mass multiplied by gravity. Plugging that
simplification in we get:
𝑚𝑔ℎ =
1
𝑚𝑣 2
2
𝑣 = √2𝑔ℎ
𝑣 = √2 × 32.2 × 5.085
𝑣 = 18.09 𝑓𝑡/𝑠
Final Results:
Initial Potential energy = 219.98 ft-lb
Striking velocity = 18.09 ft/s
d. During impact, the side of the specimen containing the V-notch experiences tensile stress.
Because the material is ductile, it does not fracture immediately but instead undergoes
significant plastic deformation. As the tensile load increases, the material stretches and
begins to thin locally, producing a necking effect near the notch. This inward pulling
results in the visible contraction seen near the top of the fracture surface, showing the
material’s tendency to elongate and reduce its cross-section as it is pulled apart.
In contrast, the side opposite the notch is subjected primarily to compressive stress as the
specimen bends around the point of impact. Under compression, a ductile metal cannot
reduce its volume, so the material is forced to flow laterally. This causes the compressed
region to bulge outward, producing a flared or expanded base. The combined effects of
tensile necking on the notched side and lateral expansion on the compression side are
what create the characteristic fracture profile seen in ductile materials.
4. Conclusion:
The Charpy impact tests demonstrated that material toughness is highly dependent on
both temperature and material type. The 4140 alloy steel exhibited the highest overall
impact resistance, while A36 steel showed a pronounced ductile-to-brittle transition at
low temperatures, losing nearly all toughness, and 6061 aluminum maintained low but
relatively consistent impact energy across the tested range. These results highlight that
body-centered cubic steels are susceptible to brittle fracture in cold conditions, whereas
aluminum remains ductile and more reliable under low-temperature impact.
Understanding these temperature-dependent behaviors is very important for selecting
materials in engineering, where safety under dynamic loading and extreme environments
is critical.