Lap Report 2 Impact Testing

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Jan 9, 2024

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1 Impact Testing Lab Report Material Science MIE 270 Kai Henderson Group E2 Lab TA: Amin Jamshidi MIE270 Lab 2: Impact Testing of Engineering Materials Abstract: In lab 2, students tested 4 different materials with varying manufacturing processes and internal temperatures to determine how such characteristics effected the materials inherent toughness. These materials included Steel, Brass, Aluminum and Nylon. This determination was achieved by conducting the Izod and Charpy impact test on polymer and metallic based specimens respectively, in the which a pendulum would be adjusted to angle of 150 degrees to the vertical and allowed free collide with specimen, fracturing it. By analyzing each specimen’s mode fracture, fracture surface morphology, and total energy absorbed before fracture, student could gain greater insight into the specimen’s toughness. Each material had 2 specimens with different characteristic properties, and each were always tested consecutively to the other, as best highlight their differences in mechanical behaviour under loading. After all the specimens had been tested a comparative analysis was conducted between specimens of similar material as to determine the effect and to what degree their inherit toughness had been altered. After analysis it was seen that low carbon steel, annealed brass and nylon at high temperature exhibited the greatest toughness, while high carbon steel, cold rolled brass and room temperature nylon exhibited the least toughness.

2 1.0 Introduction In the field of material science and engineering determining a material’s reliability, performance and safety under dynamic loading is crucial for material selection. Often engineers rely on understanding the mechanical behaviour of material to determine such factors, with common testing parameter being that of toughness. Toughness is defined as a material’s ability to absorb energy before undergoing fracture [1] and is determined by analyzing the fracture area’s surface morphology, the deformation upon impact and the measurable energy absorbed. This analysis may be achieved through the impact testing of materials using American Society for Testing and Materials (ASTM) standardized Charpy and Izod methods [2,3]. The Charpy and Izod impact test are meant to determined he relative toughness of metallic and polymer materials respectively. Both methods differ in the specimen and test configuration, Leading to V-notch and horizontal specimen alignment in the Charpy test verses U-notch and vertically cantilevered specimen alignment in the Izod test. These differences are primarily justified due to the difference in the required energy to fracture a metallic and polymer materials. As the guiding principle behind both tests is not to purely fracture a specimen, but instead analyze how the specimen behaves to the crack propagation caused by the impact, often resulting in fracture [2,3]. In lab 2 the objective of the experiment was to determine how the manufacturing process or internal temperature of material influences its characteristic of toughness. The goals of the experiment was to test each specimen using the appropriate Charpy and Izod standards and record the toughness indicators previously mentioned. Through this analysis, conclusion may be drawn as to the factors that may improve or adversely a effect material’s performance given certain conditions. This data may be used to inform material selection within a design context, as to improve the reliability and safety of user products. 2.0 Procedure Students were required to test 4 different materials with 3 of those materials having 2 specimens with varying internal temperatures or manufacturing processes. Each material’s specimens were tested consecutively as most accurately conduct a comparative analysis of the specimens. In total 5 metallic sample were tested using the Charpy method, followed by the 2-polymer specimens using the Izod method, with all specimens configured to their respective ATSM standards. All specimen’s measured approximately 10cm in the length and were of cylindrical shape. 2.2 Equipment • The Instron CEAST 9050 impact pendulum • Charpy Pendulum Impact mount • Izod Pendulum Impact mount

3 2.3 Methods The Instron CEAST 9050 testing apparatus was calibrated as to account for resistive forces within the system, swinging 12 times freely to do so. The Charpy specimen mount was then secured to the machine. The V-notched metallic specimen was then placed on the Charpy mount with their notch facing opposite to the point of impact but aligned along the impact axis. The pendulum was then adjusted to an angle of 150 degree to the vertical and locked in place using the adjusting knob. The glass covering of the machine was then secured as to prevent debris from scattering upon impact. The pendulum was then released and allowed to freely collide with the specimen, with the machine registering the total energy absorbed by the specimen on it’s digital monitor. The specimen was then collected from the machine as to study it’s surface morphology after the impact. This process was repeated for all 5 metallic specimens. The Izod test followed the same methodology as previous stated, but instead used a vertical cantilever mount, in which specimen were secured vertically. The U-notch of the specimen was also facing the towards the area of impact but was not aligned with the point of impact. 3.0 Results Material Specimen Energy Absorbed % Energy Absorbed ft lb High Strength Steel 11.30% 4.1661 Mild Strength Steel 99.88% 36.8182 Cold Rolled Brass 15.75 5.8052 Annealed Brass 47.14% 17.3766 Aluminum 9.90% 3.6503 Nylon 25C 6.49% 0.5236 Nylon 90C 99.6% 8.0806 (Table.1. The total energy absorbed by a specimen during the Charpy and Izod impact test, as measured in percent and ft.lb by the Instron CEAST 9050) Material Observation Mode of Fracture High Strength Steel (Carbon Content 0.6%)[6] Specimen fracture surface was semi perpendicular to axis of impact force. Fracture surface was relatively smooth aside from minute piece of material protruding from surface in concentrated pockets. (Brittle Fracture)

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4 Mild Strength Steel (Carbon Content 0.025- 0.03%) [5] Specimen did not fracture fully and deformed along the axis of impact. Fracture surface was irregular with jagged pieces of the material protruding from fractur surface. These protrusions seem deform along a common axis and seems to have fractured outward. (Ductile Fracture) Cold Rolled Brass Relatively flat fracture surface, with little to no deformation along the outer perimeter of the specimen. Fracture surface appeared somewhat grainy. No discernable fracture direction. (Brittle Fracture) Annealed Brass Material along the fracture surface aligned along a common axis. Slight plastic deformation along the perimeter of the fracture surface. (Ductile Fracture) Aluminum Specimen exhibited ‘cupping’ deformation within fracture area. Fracture surface was grainy with concentrated pockets of material within the surface. No discernable fracture direction .(Ductile Fracture) Nylon 25C Fracture surface as was uneven and jagged, with small misalignments along surface. Specimen did not exhibit a deformation with fracture area. (Brittle Fracture)

5 Nylon 90C Specimen did not fracture fully only deforming along the axis of impact. (Ductile Fracture) (Table.2. Qualitative description of a specimen’s surface morphology after fracture indicating it’s mode fracture, accompanied by the corresponding picture of the specimen after impact) (Table.3. Temperature vs Energy Absorbed line graph of Nylon material, with the glass transition temperature lying a at approximately 47 degrees Celsius) 4.0 Discussion The annealing process of brass and low carbon content of steel appeared to increase their inherent toughness, based on their ductile fracture. The high internal temperature of nylon appeared to increase its toughness as it was able to plastically deform compared to the brittle fracture of room temperature nylon. 4.1 What are the key features of and the differences between Izod and CVN? The Izod and CVN testing methods differ in their testing and specimen configuration. This is done as to best quantify the material performance under dynamic loading, in order to assess its inherent characteristic of toughness. In an Izod test a specimen is vertically cantilevered with it’s notch facing towards direction of impact [3], while the Charpy specimen is supported horizontally with notch facing opposite to that of direction of impact [2]. Furthermore, the pendulum in Izod test collides with top portion of the specimen, while the pendulum in Charpy test strikes a specimen along the V-notched axis [2,3]. Both theses differences are motivated by the difference in required fracture energy between polymer and metallic based samples. With 0 1 2 3 4 5 6 7 8 9 25 90 Energy Absorbed (ft lb) Tempature (Celcius) Tempature Vs Energy Absorbed of Nylon

6 differences meant to reduce any variability in the way a specimen fractures, in effect increasing the accuracy of the experiment. 4.2 Discuss the shape of notches and their significances in the impact test. The V-notch of the Charpy test is characterized as 45-degree V-shaped indentation of 2mm depth in the sample specimen [4]. The U-notch of the Izod test is characterized as small U-shaped indentation in the testing specimen of depth 5mm and base width 1mm [4]. Both notches are meant to propagate formation of cracks within a specimen while under dynamic loading, by acting as point stress concentration. This is done as to encourage fracture within material as to ascertain the amount energy absorbed upon impact, calculated from the difference in potential energy between the starting and ending position of the pendulum [1] . 4.3 What is the practical use of the impact tests? Why are the tests considered more qualitative than quantitative even with numbers involved? While the Charpy and Izod impact tests do have quantitative measurements associated to them, defined as the energy absorbed by specimen, these tests are more of a qualitative nature. This is because the dynamic loading conducted in both tests are meant to the emulate the complex loading conditions of a real-life impact. Often the impact scenario are function time, angle and force, and cannot be fully replicated in lab setting. While the quantitative data provided about the experiment can act as functional base line to determining material toughness, qualitative data associated gives greater insight into how a material specimen might fail under real-life dynamic conditions. As ultimately knowing the amount energy a small specimen of high strength steel can absorb compared to how high strength steel deforms and factures, will have greater application in a real impact scenario. 4.4 Briefly explain the phenomena of Ductile to Brittle Transition. Ductile to Brittle transition phenomenon describes the range of ductility a material may exhibit dependent of its internal temperature and inherit mechanical behaviour. At higher temperatures a material may exhibit ductile behaviour and deform plastically when subjected to dynamic loading, which may increase its relative toughness. At lower temperature a material may exhibit more brittle behavior and be less ductile, decreasing its relative toughness. The transition point between both behaviors, as material changes temperature, dependent on the material crystal structure [7]. These changes are best exhibited in difference in mechanical performance of the Nylon specimens at high and low temperature, during the experiment [Table.2]. Extrapolating the quantitative data of the Nylon experiment [Table.1] into graphical representation, a linear relation may be discerned between the energy absorbed and temperature of Nylon, showing its ductility at higher temperature and brittleness at lower temperatures. This change in its internal structure due to the increase in temperature, effecting it’s mechanical performance, demonstrates the Ductile to Brittle Transition phenomenon [Table.3]. 4.5 What are the failure mechanisms in the materials? Relate your answer to the morphology of the sketched fractured surfaces.

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7 The context of impact testing the main mechanisms of failure is range of consisting of brittle to ductile fracture. Ductile fracture may be characterized as the extensive plastic deformation of material until fracture, while brittle fracture is characterized as sudden fracture with plastic deformation [1]. Analyzing the differences in the fracture surface morphology of high and mild strength steel, the high strength had smooth break, while mild strength steel had distinct and irregular protrusion along its surface [Table.2]. This demonstrates how the high strength steel absorbed less energy than its mild steel counterpart, as this energy was dissipated less with in the internal structure of the specimen, causing no plastic deformation. Through this analysis of surface morphology, a clear correlation can be ascertaining as to material’s mode of failure. 4.6 Error Possible sources of error within the experiment include, not fully calibrating the machine properly as to account for resistive forces, giving a greater yield in the impact energy data. Another source of error includes notch indentation not being standardized across all specimens, making fracture easier or harder upon impact, giving false impact energy data . 5.0 Conclusion In conclusion the annealing of alloyed brass metals and low carbon content of ferritic metals, was seen to improve their characteristic toughness, compared their counterparts [Table.1]. The increase of internal temperature in the polymer-based material Nylon was also seen to increase its characteristic toughness compared to its room temperature [Table.3]. This was demonstrated to by their surface morphology, high absorption of impact energy and plastic deformation which indicated ductile fracture. These finding may be used to inform material selection within a design context as to improve a products safety and reliability, within given parameters. 6.0 References 1. [1] W. D. Callister and D. G. Rethwisch, Fundamentals of Materials Science and Engineering: An Integrated Approach . Hoboken, NJ: Wiley, 2012. 2. [2]ASTM E23 - Standard Test Methods for Notched Bar Impact Testing of Metallic Materials 3. [3]ASTM D256 - Standard Test Methods for Determining the Izod Pendulum 4. [4] “Charpy Impact Test: ASTM E23,” Wmtr.com , 2019. https://www.wmtr.com/en.charpy.html 5. [5]AG, F.A. et al. (2014) ASTM A36 mild/low carbon steel , AZoM.com . Available at: https://www.azom.com/article.aspx?ArticleID=6117 (Accessed: 26 September 2023). 6. [6 ] Admin, “Low vs me dium vs high- carbon steel: Blog posts,” OneMonroe, https://monroeengineering.com/blog/low-vs-medium-vs-high-carbon- steel/#:~:text=Low%2Dcarbon%20steel%20consists%20of%20less%20than%200.30%2 5%20carbon.,it%20becomes%20stronger%20and%20harder. (accessed Sep. 26, 2023). 7. [7] Yena Engineering, “Ductile -Brittle Transition Temperature and Impact Energy Tests,” Yena Engineering . https://yenaengineering.nl/ductile-brittle-transition- temperature-and-impact-energy-tests/