Research programs

Mechanics of materials

• Fracture mechanics, computational mechanics, software development, theory of finite deformations.
• Mesomechanics, thermomechanical behavior of shape memory materials.
• Mechanics of polymer composites.

Application of high-performance materials is a trend worldwide. Nowadays these materials are used in astronautics, aeronautics, industry and medicine, and the number of applications and the fields of application continue to increase. Among the most important representatives of this group of materials are materials with shape memory. The phenomenon of shape memory can be detected in many materials, but only those materials can be practically used, where the extent of shape memory is expressive.
There are two groups of such materials: (i) binary and ternary metallic alloys, and (ii) shape memory polymers. The advantage of metallic alloys lies in the high recovery stresses they are able to exhibit (up to 300MPa), while the advantage of polymers in their high recoverable deformation (up to 400%).

Mathematical modelling of the complicated thermomechanical properties of these materials is a difficult problem. The difficulty lies in the substantial dependence of these properties on temperature and in the strong hysteresis they exhibit. Up to now mathematical modelling has usually been based on broad thermodynamic considerations followed by phenomenological assumptions. Our specific approach - aimed at metallic shape memory materials - is based on a description of heterogeneity on the atomic scale that is characteristic for metallic materials exhibiting significant shape memory.

The other important representatives of the group are polymeric composites. Studies of the rheonomic behaviour of polymer composites form the main part of research activity in the field. Attention is paid to experimental methods to define their mechanical characteristics, constitutive equations, ageing, dependence of structural and mechanical properties, and assessment of their rheonomic behaviour.

Dynamics and stochastic mechanics of systems in interaction with the environment

• Dynamics of systems.
• Reliability of structures.
• Dynamic effects of wind, seismic activity and traffic.

Basic research in the field of stochastic mechanics, focusing on the dynamics of systems of rigid and deformable bodies, stability of motion, aeroelasticity, natural and technical seismicity, reliability of structures and dynamics of structures with high-speed movable load. An inherent part of this research concerns sustainable developments in the branch of signal analysis, developments in the field of stochastic finite element method, stochastic differential equation solutions, numerical and experimental methods.

Mechanics of plate and shell structures under the action of repeated loading

Research on damage to plate and shell structures under the action of combined operational loading and an aggressive corrosion environment.
Modelling of the initiation and growth of cracks in the welds of thin-walled cylindrical shells and in thin-walled plate elements with the aim to ensure (i) their integrity under extreme conditions of exploitation, (ii) methods for increasing barriers against the degradation of bodies, and (iii) means of diagnostic of damage.

Analysis and modelling of particular and cemented materials and environments

Selection of a material model plays a key role in the numerical simulation of boundary value problems in geotechnical engineering (e.g.
bearing capacity of foundations or deformations in the vicinity of deep excavations). Therefore, development and testing of constitutive models is a major research task of the Laboratory of Soil Mechanics ITAM.

Due to the complexity of the phenomena observable for various types of soils it is not possible to define a unique approach leading to a perfect model. It is always necessary to take into account specific features and ways of loading of particular geomaterials. The research at ITAM concentrates on structural phenomena and formulations in the framework of hypoplasticity. The hypoplastic approach represents a relatively new model which does not distinguish between elastic and plastic deformations. Incorporation of critical states (e.g. Kolymbas et al., 1995) enables a consistent way of describing of noncohesive soils of different densities, and simplifies the calibration of material parameters (Herle and Gudehus, 1999). The cyclic behaviour can be described by introducing a further state variable, so-called intergranular strain (Niemunis and Herle, 1997). At present, the research is focused on enhancing the model for cohesive and cemented soils. Another research direction covers implementation of the model into FEM and evaluation of its influence in simulations of boundary value problems.

The geotechnical part of the research activity involves fundamental research and developing theories of lateral pressure of multi-phase granular materials together with designs theories, especially Limit State Design. In spite of the focus on the theoretical research, the results are directly useable for implementation in codes and standards.

The concept of a new, more general "General Lateral Pressure Theory" has been elaborated and is being verified and further developed by physical and numerical experiments. Due to the originality of the conception, the new original experimental equipment, instruments and computing programmes have had to be developed. The development of very advanced concepts of computing programmes is supported. At present, the stand is being modernised, the monitoring of the pressure and movements of the arbitrarily moved wall are being digitised and adapted for computer drawings. The new stand set-up will enable arbitrarily slow and continuous movement of the retaining wall, which will be drawn, monitored and recorded by the computer, as will the contact pressures.
The two components (normal and shear vertical) of the contact pressures are monitored separately, using the Czech invention of a two-component sensor (Šmíd-Novosad). The development of a three-component pressure sensor (normal, shear vertical and moment) is near to completion.

Work on design theories concentrates on Limit State Theory connected with the upcoming implementation of European Building Codes, especially EUROCODE 7-1 "Geotechnical design". A number of analyses carried out by us and by other scientists and engineers have shown that EC 7-1 is less suitable and less effective than contemporary Czech standards.
Acceptance of EC7-1 without the changes and appendices in the National Annex would be a retrograde step. Present-day Limit State Theory does not take into account the special character of geotechnics and granular materials. Thus, the basis of Limit State Theory, i.e. definitions of the characteristic and design values, is being verified. The development of appropriate alternative design approaches has already begun.

Interdisciplinary problems of architectural heritage materials.

Research at ITAM focuses on physical properties of historic materials, particularly on properties of lime mortars (Válek J. 2000), fibre reinforced mortars and their modern substitutes (Drdácky M. et al.
2003), in-situ testing of renders, mortars and historic masonry. It also involves work on problems of compatibility of new renders with historic renders and masonry.

Biomechanics of the human musculo-skeletal system

Biomechanics is a significant interdisciplinary science that studies the mechanical principles and functions of living organisms during their movement. In spite of the successful use of total endoprosthesis of joints, there are still a number of problems connected with the artificially created co-existence and interaction between the bone tissue and the technical material of the endoprosthesis. Currently we are working on extending the selection of joint replacements that will ensure optimum function for each patient after therapy. This effort requires biomechanical research on the implant during everyday activity.

Mathematical models in biomechanics are constructed on the basis of data obtained from Computed Tomography (CT), Magnetic Image Resonance (MRI) or Ultrasound Scanning (US). Algorithms from computer graphics are applied for automatic tissue segmentation, surface reconstruction of different organs and mesh optimisation for use in the Finite Element Method (FEM). The resulting models are used in stress analysis of new types of implants of the human skeletal system (total hip replacement, finger joint replacements, etc.) and their influence over the stress state of the respective tissues.

Another area of research is the development experimental methods for assessment of the mechanical properties of human tissues, in particular of long bones, muscles and ligaments. Algorithms are developed for assessing surface deformations of small samples using an image registration method with the help of a fast CCD camera able to capture up to 25 images per second. The experimental results are applied for numerical modelling of spongy bone (material models for FEM - viscoelastic properties).

Experimental methods in material and structural mechanics

In order to understand the mechanical properties of materials, bodies and structures there is a need for theoretical models of the mechanics of solid bodies. The required data is acquired by methods of experimental mechanics. In addition to generic measurement (based on the use of traditional measurement elements like tensometers, strain gauges, etc.) various methods utilizing 2D fields of data acquired by application of various physical principles (e.g. optical pixel detectors, X-ray pixel detectors, thermography, scanning electron microscope) are widely used. These methods have manifested significant development in recent years thanks to the introduction of digital means of data recording and computer assisted data processing.

Evaluation of the properties of civil (mainly historical) structures is an additional field of research. A technique for remote data transfer using the GSM network is under development for long-term observation of the mechanical properties of structures.

Elements of large civil structures are assessed by a method based on detecting of changes in the dynamic characteristics of the studied element. The development of extremely precise gauges and the availability of computational power encourages the idea of utilizing changes in dynamic characteristics for estimating the size and location of damage in a structure. Theoretical tools for this task have been prepared for both continuum and discrete systems. This task requires an experimental approach to identify the fundamental system and to locate imperfections in the system.

Diagnostics and sustainability of historical structures, materials and sites

• Sustainability of historic materials, structures and sites
• Historic timber structures including analysis of traditional technologies
• Forensic analysis in civil engineering

For safeguarding architectural and built heritage a broader interdisciplinary research of historic materials, structures and sites has been developed in recent years. It includes development of relevant methods for diagnostics, monitoring and failure analysis of mainly timber and masonry structures as well as methods of their surveying, investigation, documentation, consolidation and conservation. The Institute takes part in formulation of strategies of scientific research in this field, on building up the necessary research infrastructure, support of application and dissemination of results by means of creating methodologies for management and safeguarding historic objects and cities. There has been also developed forensic analysis which is important for the Institute activity as an Expert Institute of the highest rank listed at the Ministry of Justice of the Czech Republic and elaborating expert opinions for courts in especially difficult cases requiring scientific approach.