This experiment examined the impact of polypropylene at various conditions through the Charpy test. Three different forms of specimens including unnotched ones, blunt-notched and sharp-notched were examined to measure the impact energy. Results confirmed that low temps resulted in the loss of impact energy. These results have important implications for real human designed applications regarding the toughness of polymers at different heat.
The review of impact test has become an important aspect of toughness. Some improvement has been designed to understanding the mechanical characteristics of various polymers, especially toughness. Toughness, ability of a material to soak up energy and deform plastically before fracturing [1], is a concept most people have been accepted. It can be determined by the areas under a stress-strain curve.
Impact test, which explains the response of materials to a sudden high-speed drive, can be split into two different methods. One test method uses an instrument in which a pendulum of known energy attacks a sample of defined size and shape. The other one test way uses an instrument where weights or others are permitted to fall freely through known levels on to specimens. [2]
The first method mentioned above can be segregated from two types, which entail in cantilever (Izod) ensure that you recognized beam (Charpy) test. The illustrations of two assessments are shown in Fig. 1. The specific difference between your two methods is the actual fact that a specimen tested in the Izod is set in the horizontal route rather than vertical direction analyzed in the Charpy.
Fig. 1 Izod and Charpy Impact Test
(b) Charpy
(a) Izod
Temperature has an obvious impact in the action of polymers, such as tensile strength, shear stress, toughness, etc, because temps affects the micro-structure of polymers. On the list of changes, the inherent toughness is obviously dependent on temps, structural orientation, stress concentration effects and rate of loading [3]. However, there were few published studies directly addressing the problem of the result on polypropylene at various temperatures. This test was to make clear of the partnership between the impact power of polypropylene and heat range referenced in Charpy test.
Experimental
Equipment
The equipment photo is shown in Fig. 2 and the variables of computer are determined in Desk 1.
Fig. 2 Charpy impact test system
Location: S. 2. 10
Table 1. Parametres of Charpy Impact Test Equipment
Hammer Velocity
Hammer Weight
Hammer standard
2. 9m/s
1. 189kg
ISO
2. Specimens
A quantity of different rectangular-section standard polypropylene (PP) Charpy test examples including sharp notched, blunt notched and unnotched ones were analyzed at different temperature conditions. The different specimens are shown in Stand 2. which also entails in the sizes (width and width) of the trials specimens. , , and in Desk 2 are the four different proportions separately.
Table 2 Variables of the specimens
Room temperature
Experimental Steps:
The specimens are split into two parts, and one of the parts was placed into the freezer before being tested.
All of the info of the unnotched specimen at room temps were input in to the via keypad, and the test was held onto the correct position of the gear.
A pendulum grew up to a particular level and then released when the gear was started. Then the specimen was separated by the high-velocity pendulum.
The impact energy was recorded in the Charpy impact test equipment.
Steps 2 to 4 were repeated for every of the unnotched specimens to achieve a series of data.
Steps 2 to 5 were repeated for all of the blunt-notched samples and then the sharp-notched examples.
Steps 2 to 6 were repeated for the unnotched, the blunt-notched and the sharp-notched at -20.
Results and Discussion
1. Tabulate the average person worth and average value of impact energy consumed by the specimens for each test temperature.
The individual data and average principles of impact energy assimilated by the specimens for both two temperature are outlined in the two tables below. Table 3 illustrates the info at room heat, and Stand 4 exhibits the data at -20.
2. Discuss the effect of temp on impact energy for razor-sharp notched, blunt notched and unnotched examples.
Since the impact durability would depend on the absorbed, a structure that is a lot much easier to move will react easier to the impact [4]. Therefore, the impact durability increase with the increase of temperatures and rubbery condition has higher impact strength than glassy state. The higher the temperatures is, a lot more significantly the molecular chains will move. Because of this, the impact energy is significantly lower at -20 than that at room heat range. It may also be found in Table 4.
3. Analyze experimental error
(a) Once the parameters of specimens were measured, the apparatus mistake of vernier calipers could not be avoided. At the same time, the positioning of specimens was changeable, which was an operation error existed.
(b) The sharp-notched samples were cut artificially, thus the factitious errors cannot be disregarded.
(c) For the reduced heat range test, the iced specimens were transferred from a refrigerator to atmosphere, which can lead to the increasing of temperature. Because of this, the impact energy acquired a slight increase.
(d) The errors of Charpy impact test equipment could not be disregarded. Movement in the clamp and energy imparted to broken fragments might be the factors of the rest of the energy of the pendulum and then the impact energy increased. [5]
4. Explain the cause of the whitening observed in a few of the fractured samples.
All sorts of the examples are shown in the Fig. 3.
Fig. 3 The examined samples
Through the observing of most different sorts of specimens, whitening is the most evident in the unnotched samples. Many reasons shown lead to this happening. Stress-whitening crazing usually can be viewed for thermoplastics at levels of stress that below those required for large size yielding. [6]When there's a sudden insert to the test, fracture crazes will be developed. More often than not, it occurs in amorphous, brittle polymers and generally consist of an wide open network of polymer fibrils between 10 and 40nm in diameter, interspersed by void around 10-20nm. [6]
Conclusions
After the test completed, many advantages of toughness and impact test have been listed below.
There is a huge variety of solutions to assess impact energy of polymers and the most common used test is the Charpy test.
With the loss of temp, the impact energy of same shaped specimens has a substantial decline.
The whitening of polymers is easier to be observed in the unnotched examples than that in sharp-notched and blunt-notched.
