Iqra abdul rashid Polymer Engineering department Polymer Science

Iqra abdul rashid Polymer Engineering department

Polymer Science & Engineering TM-2052 Lecture # 02

Impact test • Measure the energy expanded up to failure under conditions of rapid loading • Hammer like weight, dart test and falling ball strikes the specimen • Used to determine whether the specimen has sufficient energy absorbing properties for particular applications • Impact strength decreases with decreasing temperature and with increasing rate of deformation

Impact test • Amorphous polymers with large bulky substituent groups and nonlinear backbones are brittle • Unoriented crystalline structure also contributes to brittleness in polymers whose Tg is above the testing temperature

Impact test • Types of impact test • Izod test • Charpy test

Izod test • Izod impact testing is an ASTM standard method of determining the impact resistance of materials. • An arm held at a specific height (constant potential energy) is released. The arm hits the sample. The specimen either breaks or the weight rests on the specimen. • From the energy absorbed by the sample, its impact energy is determined. • A notched sample is generally used to determine impact energy and notch sensitivity.

Izod test • The Izod impact test differs from the Charpy impact test • Test material was placed in vertical position • Hammer strike at the upper tip of the specimen • Both V-noth and U-noth are used • Izod test use Farming hammer as striker • ASTM D 256 is mostly used for plastics

Izod test

Izod test

Charpy test • Test material placed in horizontal position • Hammer strike at point of notch but in opposite direction • Only V-noth is used • Charpy test use Ball Pin hammer as striker • ASTM D 23 and ISO 148 -1 used

Charpy test

Fatigue test • Used to determine the number of cycles (N) of applied strain at a given level of stress that a sample can sustain before complete failure • Fatigue life ØNumber of cycles to failure is called the fatigue life • Endurance limit ØMaximum value of applied stress for which failure will not occur irregardless of how many cycles the stress is applied

Fatigue test • Fatigue life decreases with increasing frequency of oscillation and as temperature is decreased • Fatigue test is important in evaluating engineering and composite materials considered for load bearing applications