Class: BE210
Group: 101_A3
Members:

Siddharth Bhattacharyya
Ali Dhanaliwala
Jingjing Li
Nicholas Steinmetz

Powerpoint Presentation
Full Text

As a material is loaded, it absorbs energy. At a certain point, the material can no longer absorb any more energy and the material fractures, releasing the energy that was stored in the material. This energy required to induce fracture is known as the fracture energy of the material. The fracture energy depends on many factors including both geometric and material properties. Often a primary material is reinforced with a secondary material in order to increase the fracture energy of the primary material and make it more suitable for an application. Secondary materials can either be integrated directly into the primary material during synthesis or are added afterwards as coatings. Examples include iron intercalated with impurities to make alloys and bones surrounded by plaster to form a cast. Understanding how to improve the strength of a material through the addition of a secondary material is important for creating better composite materials.

Fracture energy is determined using a pendulum impactor device. Using conservation of energy analysis it is possible to determine the energy required to fracture the bone by comparing the initial and final angle of the pendulum arm as it swings through and breaks the material. The formula to calculate the fracture energy of the wooden specimen is:
    Ewood = Etotal – Efriction - Esystem
Where Efriction is energy lost to the friction in the swinging pendulum arm and Esystem is energy lost to moving and bending the rubber reinforcing material.

Wooden surrogates are used instead of bone specimens because of their characteristic uniformity. Previous experiments involving both wooden surrogates and bones to determine fracture energy found that the variation of the bones was 0.239 J whereas the wooden surrogates had a variation of only 0.07 J (Table 1 and 2 respectively). The low variation in the wooden surrogates is most likely due to the uniform manufacturing procedure making it a better candidate for testing the effect of reinforcing materials on fracture energy. The rubber reinforcement may increase the fracture energy by either increasing the amount of energy the system, wooden dowels reinforced with rubber tubing, can absorb or by redistributing the energy of impact in such a way that prevents material fracture.