Micromechanical Laboratory

The micromechanical laboratory has been established to investigate failure mechanisms in advanced materials and structures at different scales. Gaining such knowledge in a systematic manner allows you to gain insights or prove the existence of a variety of different modes of failure, validate the models and design new materials or structures.

Equipment

At macroscale, a universal tensile machine (Zwick/Roell with 5kN load cell) is used. This classical equipment allows you to study force and displacement response of materials and structures under load, and to analyse their derivatives. Different experimental set-ups are available for tension, compression, bending or fracture experiments. The machine can also be used for low to medium cycle fatigue or for relaxation and creep experiments.

For ‘soft’ materials (the load cell capacity is 150N) and dynamic mechanical analysis (DMA), a Bose® machine with a friction-free moving magnet is used. In addition to providing exceptional DMA performance, the Bose test instrument is designed to accommodate creep and stress-relaxation testing, monotonic tensile and compression testing as well as high-cycle fatigue and durability testing.

At macro-meso scale, a large field of view digital image correlation system Aramis (GOM, Germany) is used. Equipped with two 4 Mpix cameras, the system allows a full 3D displacement field to be measured as shown in Fig. 1. Fields of views used for this system vary from 20x20 and up to 200x200 mm.

Fig. 1. Displacement maps of a bimaterial bonded ring (PMMA bonded to stainless steel) under compressive loading. Ring diameter is 30 mm. (Figure: Michal Budzik)


For meso–micro scales, a small field of view digital image correlation system Vic3D (Correlated Solutions, USA) is used. The system is equipped with two 5Mpix cameras with very low noise to signal ratios. They have a capability of shooting up to approx. 500 frames per second with full resolution. The observed fields of view go down to 500x500 μm with subpixel accuracy allowing, in principle, nm scale displacements to be measured. The equipment is used for in-situ observations of failure and fracture, e.g. as shown in Fig. 2 where displacement and strain fields in the vicinity of a propagating crack were investigated.

Fig. 2. von Mises strain intensity in the vicinity of a propagating crack. The specimen was made of two carbon fibre plates bonded with structural adhesive. The panorama view, 6x1 mm, consists of five frames taken at different stages of propagation. (Figure: Michal Budzik)


For in-situ microscopic observations, two digital microscopes (Dino-Lite, Netherlands) with magnifaction of 200x and 500x are available. Due to their small size, around 10 cm in length, and ease of operating, they are used for experimental arrangements where the details of failure mechanism are of interest. Data from the camera could be used later for image correlation calculations using Vic3D software.

The laboratory is also equipped with a state-of-the-art 3D scanner/macro/microscope using the principle of fringe projection light (Keyence, Japan). 3D features of centi-, milli- and micrometre structures and materials can be detected and analysed to gain useful information for example about local roughness, waviness, sizes and shapes of inclusions or similar. All that with up to 50 nanometre precision in out-of-plane height and direction.

To allow a smooth transition from the universal tensile machine to microscopic observations, the laboratory is equipped with a micro-tensile machine. The machine is capable of performing any standard experiments, tensile, compression, bending, etc., also under fatigue loading, on small specimens of micro/centimetre dimensions with 5kN capacity of the load cell. Due to the small size of the machine, it can be easily placed under a 3D microscope, any standard optical microscope or inside the scanning electron microscope (Zeiss Evo, Germany) available at the ground floor of the Navitas building.