• Apostol, Marian
• Kuokkala, Veli-Tapani
• Lepistö, Toivo
• Rämö, Jari

Abstract

Amongst the wide variety of consumer electronics, mobile phones are probably the most susceptible to impacts. Furthermore, in the phone structure the display glass is usually the most vulnerable to damage for example in the case of dropping the phone on a hard surface. For these reasons, the phone manufacturers have a great interest to obtain reliable experimental data on the behavior of the display glasses during various types of impact that the phone may encounter during use. Another important reason for the experimental studies of such events is that while much of the design work of the mechanical structures of the phones are today conducted via computer modeling and simulation, the modeling work needs reliable material data and, in particular, the simulation results still need to be validated by experimental testing. In this study, the impact response of selected display glass materials were experimentally studied using various types of testing methods. The tests can be divided into two different classes: controlled dropping of entire mobile phones from different heights on various hard surfaces, and pendulum impact testing of plain glasses with various degrees of pre-damage. In both cases, the tests were followed by a high-speed camera from different directions to obtain information about the sequence and locations of events during the impacts. With the pendulum tests, the impact energies and their dependence on the glass type and pre-damage could also be determined. Dropping of phones on a thick glass plate allowed video recording of the impact event also from the oncoming direction. The tests on a clean glass plate, however, did not damage the phone glass even at the highest drop height of 1.5 meters. Therefore, the glass plate was sprinkled with small sized crushed granite particles or by particles sieved from lake sand. The results of these experiments showed that the minimum particle size that may break the glass is 63 – 125 µm, with the failing probability increasing with increasing particle size. It was also found that 0.5 m height is roughly a threshold for the dropping distance, below which no glass failure occurs. The impact tests were conducted for specimens pre-damaged using several different techniques, including indentations made with a Vickers hardness tester and scratching with a diamond tip, hardmetal cone, and grinding (‘sand’) paper. The measure of the glass durability was the absorbed energy in the test leading to the breakage of the glass sample.

Topics

• impedance spectroscopy
• surface
• experiment
• simulation
• grinding
• glass
• glass
• hardness
• impact test
• durability
• impact response