The first phase is focusing on the material characterization of different types of glass (all made of the same raw material: soda-lime-silica) at varying loading rates primarily in a range equivalent to explosion and impact loads, as this is almost unreported in the literature. The following types of glass will be investigated:
- Float glass (FG)
- Heat strengthened glass (HSG)
- Fully tempered glass (FTG)
To achieve the desired loading rates, a new experimental test setup will be designed and established. The fracture mechanism will be studied using high-speed cameras together with digital image correlation (DIC). The experiments with different types of glass will give the opportunity to determine how the strength and the fracture mechanism depends on the state of the residual stress in the glass. All tests will be carried out on small specimens that are centered on a support ring and dynamically loaded with a smaller load ring (ring-on-ring test) until failure. The following parameters will be investigated in the tests:
- Strain rate (about 10 different)
- Residual stress state (about 5 different)
The experimental results are used in the second phase to develop a material model for describing and understanding the fracture mechanics of the different types of glass that will provide a basis for predicting the global structural response.
Update from 06-04-2020:
Novel experimental setup
A new milestone in the industrial PhD project is reached! Thanks to the Ramboll Foundation (Rambøll Fonden) and our laboratories at DTU Civil Engineering, we have finally achieved full funding of 460.000 DKK for an in-house developed novel experimental setup, which initially is intended for the dynamic material characterization of conventionally used glass. The setup will soon be manufactured by AVOS A/S and is expected to be ready for the first tests around late summer 2020.
Here, short about the experimental setup. In the world of the dynamic material characterization the split Hopkinson pressure bar (SHPB) technique, also known as Kolsky bar, is a widely used and well-known method. A typical SHPB setup is in general simply build up by three main parts: 1) a loading device (mostly seen as an air gun), 2) bar components made up by an incident bar and a transmission bar, and 3) a data acquisition system. The same principals are also applied to the novel developed setup, where the novelty lies within the bar components. The main objective of the design was to combine an experimental setup for dynamic equibiaxial flexural testing in a ring-on-ring configuration with the possibility of using high-speed cameras for recording the fracture process during loading of the specimen. To satisfy this, a full view on the specimen surface is required, which is not feasible in a regular SHPB setup as the specimen surfaces are hidden between the bars. A possible solution to this is to transform the transmission bar into a tube having the incident bar going through. The load ring is then mounted to the incident bar, and the support ring to the transmission tube having a hole going through that exposes the tensile surface of the circular specimen. This transformation not only allows a free view on the specimen but also reduces the total length of the setup considerably compared to a regular SHPB design.
A walkthrough video presenting the novel developed experimental setup is provided below. Enjoy watching!
Related publications:
Meyland, M. J., Eriksen, R. N. W., & Nielsen, J. H. (2019). A novel full-view split Hopkinson pressure bar technique for flexural testing. Paper presented at 13th International Conference on Shock & Impact Loads on Structures, Guangzhou, China.