This paper reviews major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two‐stage light‐gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta. In addition, explosive setups, membrane‐driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high‐temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise (1) projectile–target interaction, (2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, (3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, (4) in situ target damage, (5) ejecta dynamics, and (6) geophysical survey of experimental craters.

The ingress of water into mortar and concrete is an ongoing problem which can reduce the lifetime of cementitious structures. Commonly used approaches that aim at preventing water ingress mainly employ an additional surface treatment after the casting process. Thus, they are time-consuming and make use of synthetic, nonsustainable additives. In contrast, it was shown recently that a biological material, i.e., a bacterial biofilm generated by B. subtilis 3610 bacteria, can be used as a bulk additive which leads to hybrid mortar with increased wetting resistance. Here, we demonstrate that a similar enhancement of the water resistance of mortar can be achieved by using different bacterial additives, i.e., wet biofilm, freeze-dried biofilm powder, and bacterial suspensions, each of which can be produced by one of three selected variants of B. subtilis bacteria. We characterize the mechanical properties of the different hybrid mortar variants regarding their setting behavior, tensile and compressive strength, and density. Our results imply that bacterial additives could be an eco-friendly and sustainable alternative to existing synthetic mortar additives.

This research examines the effect of fiber alignment on the performance of an exceptionally tough 3D-printable short carbon fiber reinforced cementitious composite material, the flexural strength of which can exceed 100 N/mm2. The material shows pseudoductility caused by strain-hardening and microcracking. An extrusion-based manufacturing process allows accurate control over the spatial alignment of the fibers’ orientation, since extrusion through a tight nozzle leads to nearly unidirectional alignment of the fibers with respect to the directional movement of the nozzle. Specimens were investigated using mechanical tests (flexural and tensile load), augmented by non-destructive methods such as X-ray 3D computed tomography and acoustic emission analysis to gain insight into the microstructure. Additionally, digital image correlation is used to visualize the microcracking process. X-ray CT confirms that about 70% of fibers show less than 10° deviation from the extrusion direction. Systematic variations of the fiber alignment with respect to the direction of tensile load show that carbon fibers enhance the flexural strength of the test specimens as long as their alignment angle does not deviate by more than 20° from the direction of the acting tensile stress. Acoustic emission analysis is capable of evaluating the spatiotemporal degradation behavior during loading and shows consistent results with the microstructural damage observed in CT scans. The strong connection of fiber alignment and flexural strength ties into a change from ductile to brittle failure caused by degradation on a microstructural level, as seen by complementary results acquired from the aforementioned methods of investigation.

The basis for creating a digital twin is a suitable model with a close connection to reality in the form of measurement data. In this paper it is explained how model and measurement data of the support structure of a wind turbine can be obtained. The procedure is implemented on a real wind turbine with a concrete/steel hybrid tower. The monitoring includes the acquisition of vibrations, strains and temperature as well as the determination of the dynamic Young's modulus of the concrete structure by sound velocity measurements. For modeling, a finite element model with shell elements was chosen, which takes into account stiffening effects from static loads. A comparison between model and reality is the most important premise for the use of a digital twin: Therefore, a multi-stage model validation based on modal parameters and local material stresses is performed. The Digital Twin offers different usage scenarios; here one is carried out: the fatigue calculation and remaining useful life (RUL) estimation. For this purpose, material stresses at highly stressed positions are determined using measurement data and model. The results are currently still unrealistically high lifetimes for the concrete part. The results are based on relatively short (1 h, 24 h) stress time series. This could be one reason for the high values. It could also be an indication that fatigue is a non-critical load case for the concrete part.

Excavation of deep underground openings causes redistribution of primary stresses and induces initiation and propagation of micro cracks. Changes in rock properties ahead of an advancing tunnel face may influence stability and penetration rates in TBM tunneling. This study is part of a PhD project where the focus is on stress-induced micro cracking and its influence on rock strength reduction. We demonstrate results from acoustic emission (AE) measurements on two homogeneous diorite samples tested under uniaxial compression. The aim was to gain information about the influence of experimental setup and settings on AE events in brittle rock. From the stress strain curve and the number of acoustic signals, main deformation stages could be determined. A three-dimensional localization of acoustic events showed a typical conjugate shear system. Future work will include tests on different rock types after inducing controlled damage by uniaxial loading. Lateral strain measurements combined with AE analysis will be applied in order to quantify rock damage and its influence on rock strength.