Essential Work of Fracture - Essay Example

The Literature Review The aim of this assessment is to understand the development of the Essential Work of Fracture concept. This section will be devoted to an investigation of past researches conducted within the field of study. To begin with, in studying the characteristics of polymers in fractures many tests are usually performed. Most of these tests are carried out experimentally, such as the Charpy impact test, Gardner impact and tensile test. Swallowe did a tremendous effort on explaining each of these test techniques.

Upon testing the polymers, it was discovered that two important factors greatly influenced the results. These two factors are the geometry of the specimen and the test configuration. However, the result does not demonstrate the behavior of the polymers. This uncertainty gave birth to other theoretical concepts, which helped to provide clarification on the behavior of polymers . Understanding the behavior of polymers under the mechanism of fractures guided the evolution of theoretical concepts within the field.

The study that is responsible for this is known as Fracture Mechanics. Here, the resistance of a material to the applied load is known as the “toughness” of the polymer. The fracture toughness of a material is a property that determines the amount of energy a material can withstand before it undergoes its final rupture. However, this could be impeded by external factors such as environmental, design or geometry factors. As a result, more accurate tools were found to obtain correctness on the determination of the polymer’s fracture toughness.

The next section explores a commonly used technique for specimen testing configuration. A proper investigation on specimen configuration will be the initial milestone on this review in order to understand how the geometry of polymers interacts in the testing field. Classification of Specimen Configuration As mentioned in the previous section, we shall first investigate on the configuration of tested specimens. Determining the fracture behavior of polymers is an important aspect of this research.

And specimen configuration plays a significant influence on the determination of polymer toughness . Many specimen configurations became standard for testing the toughness of polymers with their mathematical equations. However, only a few were regularly used for testing. In this section, commonly used specimen configuration will be reviewed and discussed. Single edge notch bend (SENB) or three-point bend (3-P) This is one of the most commonly used geometry on determining fracture toughness. Even though SENB consumes more material compared to other configurations, it is an easier configuration to manage, for it assures low cost in less time.

Another advantage of the SENB configuration is the inadequate amount on the supplied material for testing. Tested configurations could be fixed by welding extensions to the ends of the tested sample . As in testing mechanisms, the tested specimen is supported on each end with a fixed supporter. The specimen is then loaded with force on the middle of the specimen where the notch is located. This mechanism is s very useful tool in testing small elongations on polymers . Figure. Single-edge notched specimen Single edge notch tension (SENT) This is another type of configuration used in measuring the fracture toughness of polymers.

The single-edge notched in tensile was developed after the SENB was used. It is said that SENT shows more accurate results comparable to SENB. SENT is always associated with a small crack opening tip and is a very useful tool in finding plane strain fracture toughness. The scheme of determining fracture toughness using SENT was initially founded in the pipeline fields . Figure. Single-edge notched in tensile Tensile loaded specimens Compact test specimen (CT) Compact specimen is a standardized configuration.

This configuration requires less material to build but does require more time to work on than SENB. Moreover, this configuration is more expensive to build compared to SENB. The compact specimen is used to obtain the values of fracture toughness for a material. The mechanism works by exposing the compact specimen to a tensile cyclic load in testing. This applied force causes a crack to propagate on the notched area. This procedure shows the real reaction and how the material interferes with applied loads. Figure. Compact test specimen Double Cantilever beam (DCB) The double cantilever beam configuration began testing the fracture toughness of specimens during the 1960’s.

Also the mathematical approach of the contouring shape was defined in the late 1960’s. In this configuration, the DCB specimen configuration produces a fracture toughness value that’s directly proportional to the applied load and independent to the crack size. One of the benefits of using the DCB configuration is that a list of fracture toughness values could be attained from using just one specimen. As a result, DCB is a very useful tool and is advantageous on testing the quality control of fracture toughness when combined with other variables.

An example herein is temperature or strain rate. In contrast, the DCB variety of dimensions and its complexity of manufacturing, limit the uses of this configuration in rapid fracture toughness testing . Figure. Double cantilever beam specimen Surface flawed (SF) Surface flawed configuration has been used since 1960. This type of geometry is used extensively on determining the structure fracture life of a material. The surface flawed specimen evaluates how a crack propagates on the surface of a material.

The fracture of a material is evaluated by exposing the specimen under cyclic loading over a period of time. The data collected shows how the material resists the flaw and the applied load until it reaches its final rupture. As a result, this type of configuration has been a useful tool in understanding the failure of a structure. Engineers uses surface flawed specimen in many applications. Aerospace, ship hull and pressure vessel structures are some of the applications. Where the analytical analysis of the structure is considered, ensuring the structure does not need to go through brittle fractures before it meets the lifetime requirement . Figure. Surface Flawed Specimen References