Date: June 2020
Type: BSc
Student(s): Leopold Manuel Godthjælp Petersen
Asbjørn Lauge Skou Poulsen
Supervisor(s): Jens H. Nielsen
Martin J. Meyland
Others:
Report:
The tensile strength of glass is well known to be dependent on the greatest flaw on the glass surface. Due to the conditions in which glass might have been produced and/or handled, flaws on the glass surface, invisible to the naked eye, could be present and affect the mechanical strength of glass subjects. Small variations in flaw sizes have a significant effect on the specimens tensile strength. As a result of this, a batch of glass specimens produced under identical conditions can vary largely in tensile strength.
Experimental work has been done throughout this thesis to reduce the variation in tensile strength, by inducing flaws greater than pre-existing ones. Utilizing a Vickers hardness tester, indentations were performed with different loading forces (2.5, 5.0 and 10.0 kgf), thereby inducing various sized flaws, and afterwards tested in a coaxial double ring test setup. Based on obtained critical forces, corresponding stresses were simulated using the Finite Element Method in Abaqus. Results showed a remarkable reduction in strength and a significant decrease in the variation of critical tensile stress, compared to the reference series. When fitted to a normal distribution, the outcome spectrum for ±2 standard deviations was reduced from 257.44 MPa to 23.53 MPa for loading forces at 2.5 kgf, 5.00 MPa for loading forces at 5.0 kgf and 3.22 MPa for loading forces at 10.0 kgf, thus drastically narrowing the margin of stress where fracture occurs.
It can be concluded from the experiments, that Vickers indented specimens have a more reliable tensile strength compared to specimens treated as received.