The Science & Technology
Cambridge - Monday 4th to
Wednesday 6th September 2017
article posted 19 July 2017
Atsushi Hashimoto is a Professor in the Department of Mechanical Engineering, College of Engineering, Nihon University in Japan. He received M. Eng. in 1979 and Dr. Eng. in 1984 from
Nihon University respectively. His research fields are Strength of materials and Non-traditional processing utilizing the fracture of brittle materials.
Fracture and Cutting of Glass Plates under Local Compression
Kensuke Fujimura, Ryota Aoshima & Atsushi Hashimoto*
This report presents the experimental results and the explanation for both the fracture and the cutting of glass plates under local compression in the processing of lens glass.
Figure 1 shows the experimental method. In the diagram, T is a piece of glass plate (length l, width b and thickness t).
A is a plate (thickness h) on a flat surface. The relation of Young’s
modulus between the glass plate T (Young’s modulus E) and the plate A (Young’s modulus E0
) must be E>E0
in this experiment. The pressing piece B looks like a rectangular bar as shown in figure 1.
It is used to apply local compression to the center of the glass plate T. In this state, the compressive load P is applied to the pressing piece B. When glass plate T is loaded in such a way
that it makes positive contact with the pressing piece B, glass plate T will bend in a V-shape at the cross-section of the center of the glass plate. This bending occurs not only because of the
compressive load P applied to the pressing piece B, but also because the relation of Young’s modulus of E>E0
is preserved. Thus, the bending moment of glass plate T occurs naturally in proportion
to the applied compressive load P. When the compressive load P reaches the certain value PF, the glass plate fractures toward the pressing piece B.
The glass plates T used in the experiments were soda-lime glass plates with various lengths l=15mm~80mm (b=30mm and h=8mm). Plate A was an acrylic plate with the thickness h=50mm. As Young’s
modulus of the glass and the acrylic was E=70.9GPa and E0
=3.41GPa respectively, the relationship between E and E0
satisfies the present experiment. The pressing piece B was a square steel bar
with the length of 3mm.
Figure 2 shows fractured glass plates with l=15mm. The difference between (a) and (b) is one of the stress concentration factor. At the center position on the bottom surface of the glass plate
shown in (b), the scribe line was made with a common glass cutter, but the glass plate shown in (a) didn’t have the scribe line. Therefore as the fracture load PF
in the case of (b) was smaller
than that of (a), the glass plate shown in (b) was split at the bisectional position along the scribe line, while the glass plate shown in (a) had many branches of cracks. The cutting of glass
plates can be specified by making a scribe line.
Figure 3 shows a sample of a lens glass cut by making a scribe line. The lens glass could be cut instantaneously at the bisectional position along the desired scribe line and we could get two
cubes of the lens glass. Ordinarily, the cubes made from lens glass are produced by a cutting machine using a diamond saw. However this cutting method is accompanied by many disadvantages
that are not only the consumption of the diamond saw, but also the generation of waste and noise, and moreover the consumption of a lot of energy and time to finish the cutting.
On the other hand, in the cutting shown in figure 1, the lens glass could be cut without the above disadvantages at the cross-section along the scribe line.
In order to analyze the experimental results on the relationship between the fracture load PF and the length l, we attempted “Problems of Beams on Elastic Foundation”. That analysis was
confirmed by the experimental results.
Hidenka Kobo Inc., Terakohei, Nasu-machi, Zip.329-3222, Japan
Graduate School of Eng., Nihon Univ., Koriyama, Zip.963-8642, Japan
College of Eng., Nihon Univ., Tamura-machi, Koriyama, Zip.963-8642, Japan