Rostislav Chudoba

Effect of Twist, Fineness, Loading Rate and Length on Tensile Behavior of Multifilament Yarns (A Multivariate Study)

The purpose of the present study was a multivariate experimental analysis of continuous multifilament glass yarns. The experimental design involved four main factors affecting the yarn tensile behavior, namely twist, fineness, loading rate and specimen length. In the evaluation, both the main effects and their interactions were considered. In the initial test design, each factor had been covered by at least two levels. The performed analysis of variance on the constructed response surface allowed us to exclude some factors and interactions and to narrow the test design space in the second step. The interaction effect of twist and fineness could be well documented. In particular, the nonlinear effect of twist with a pronounced maximum allowed us to discuss the role of local interactions due to pressure sensitive frictional bond that gets amplified at a particular level of twist.

Using Python for scientific computing: Efficient and flexible evaluation of the statistical characteristics of functions with multivariate random inputs ✩

Abstract This paper examines the feasibility of high-level Python based utilities for numerically intensive applications via an example of a multidimensional integration for the evaluation of the statistical characteristics of a random variable. We discuss the approaches to the implementation of mathematically formulated incremental expressions using high-level scripting code and low-level compiled code. Due to the dynamic typing of the Python language, components of the algorithm can be easily coded in a generic way as algorithmic templates. Using the Enthought Development Suite they can be effectively assembled into a flexible computational framework that can be configured to execute the code for arbitrary combinations of integration schemes and versions of instantiated code. The paper describes the development cycle using a simple running example involving averaging of a random two-parametric function that includes discontinuity. This example is also used to compare the performance of the available algorithmic and executional features. The implemented package including further examples and the results of performance studies have been made available via the free repository [1] and CPCP library. Program summary Program title: spirrid Catalogue identifier: AENL_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AENL_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Special licence provided by the author No. of lines in distributed program, including test data, etc.: 10722 No. of bytes in distributed program, including test data, etc.: 157099 Distribution format: tar.gz Programming language: Python and C. Computer: PC. Operating system: LINUX, UNIX, Windows. Classification: 4.13, 6.2. External routines: NumPy ( http://numpy.scipy.org/ ), SciPy ( http://www.scipy.com ) Nature of problem: Evaluation of the statistical moments of a function of random variables. Solution method: Direct multidimensional integration. Running time: Depending on the number of random variables the time needed for the numerical estimation of the mean value of a function with a sufficiently low level of numerical error varies. For orientation, the time needed for two included examples: examples/fiber_tt_2p/fiber_tt_2p.py with 2 random variables: few milliseconds examples/fiber_po_8p/fiber_po_8p.py with 8 random variables: few seconds

ORICRETE : Modeling support for design and manufacturing of folded concrete structures

Abstract The paper presents a flexible and efficient modeling approach to the simulation of the folding process of general crease patterns. The development of the model has been motivated by the need to provide support for targeted design and efficient manufacturing of shell structures inspired by the origami technique. This type of structures is becoming increasingly popular in many engineering disciplines and has been referred to as origamics. In the present work the folding technique is used to produce spatial structures from continuously reinforced thin-walled cementitious composite plates without the need to construct curved spatial formworks. In order to support the targetted design and manufacturing of folded concrete (oricrete) structures numerical model has been formulated as an optimization framework with several types of optimality conditions and equality constraints. The model is used both for form-finding of the spatial structure and for the realization of the manufacturing process.

A novel tensile test device for effective testing of high-modulus multi-filament yarns:

The paper introduces a novel clamp adapter with the goal to improve the quality of the tensile test setup for high-modulus multi-filament yarns. Common tensile test machines damage the yarns initially or prematurely due to non-uniform load introduction which causes stress concentrations. As a result, the theoretical yarn strength (perfectly clamped filaments at a unique length and no initial damage) is underestimated. With the new clamp adapter, higher strengths close to the theoretical values can be measured since the adapter largely eliminates the problems with non-uniform load introduction. A test series comparing yarns strengths tested with the clamp adapter and with commonly used test methods has been performed and the results are discussed in this paper. Furthermore, they are compared with theoretical values using the Daniels’ fibre-bundle model.

Adaptive probabilistic modeling of localization, failure and size effect of quasi-brittle materials

Objective simulation of response of nonlinear structures must reflect the spatial variability of local material properties. The main target of the paper is to present ideas behind a computational tool oriented toward adaptive nonlinear simulation driven by spatially (and randomly) varying model properties which is currently under development by authors. In particular, we focus on detailed tracing of the evolution of damage or other nonlinear phenomena during loading of structure with varying properties by nonlinear finite element method with mesh refinement/coarsening in highly/low stressed or damaged regions. We have developed the major ingredients of the algorithm and we present the current stage of progress on the computational platform in this paper. The computations is illustrated on a simple one-dimensional example involving a bar made of plastic material with hardening under uniaxial tension.

Numerical and experimental evaluation of damage parameters for textile reinforced concrete under cyclic loading

The textile reinforced concrete (TRC) has emerged in the last decade as a new composite material combining the textile reinforcement with cementitious matrix. Its appealing feature is the possibility to produce filigree high-performance structural elements that are not prone to corrosion as it is the case for steel reinforced concrete. In comparison with other composite materials, textile reinforced concrete exhibits a high degree of heterogeneity and imperfection that requires special treatment in the development of numerical models.

Numerical and Experimental Characterization of Anchorage Length for Textile Reinforced Concrete

In this paper we propose an experimental and numerical framework for systematic characterization of anchorage behavior of textile fabrics used as reinforcement in Textile Reinforced Concrete (TRC). The experimental test setup utilized to examine the anchorage length and bond behavior can easily be adapted to the varying material characteristics of different textile fabrics. Depending on the fiber material and the type of impregnation resin, variable increments of anchorage length up to the full anchorage length necessary for roving rupture can be tested. The hydraulic clamping of the specimens allows for a rapid yet robust test procedure. Whereas steel reinforcement bars are usually tested in a single bar pullout test, the proposed method tests multiple rovings in parallel with a symmetric, double sided pullout from the concrete matrix. Thus, the test implicitly accounts for the statistical variation of bond characteristics of textile fabrics. The specimens are either cast directly or cut from actual prefabricated structural components such as thin facade panels. This allows for a realistic evaluation of the anchorage behavior of TRC components like plates and shells.

Identification of the effective bundle length in a multifilament yarn from the size effect response

The article proposes a method for characterizing the in situ interaction between filaments in a multifilament yarn. The stress transfer between neighboring filaments causes the reactivation of a broken filament at some distance from the break. The utilized statistical bundle models predict a change in the slope of the mean size effect curve once the specimen length becomes longer than the stress transfer length. This fact can be exploited in order to determine the stress transfer length indirectly using the yarn tensile test with appropriately chosen test lengths. The identification procedure is demonstrated using two test series of tensile tests with AR-glass and carbon yarns.

Cross-sectional failure criterion combined with strain-hardening damage model for simulation of thin-walled textile-reinforced concrete shells

Abstract. Application of textile reinforced concrete (TRC) can significantly facilitate the manufacturing of thin-walled shell structures. Thanks to the high tensile strength and longtime durability of textile reinforcement, construction of much thinner cross sections compared to ordinary reinforced concrete has become possible. Furthermore the form-flexibility of textile reinforcement allows for much more freedom in design of shells with more complex geometries. However, these advantages make the prediction of the structural behavior under imposed loads much more difficult. Due to the complex stress redistribution in the plane of shell and also the anisotropic behavior of the composite material, different modes of failure can be observed in TRC shell structures. In this paper we focus on the failure criterion of thin-walled TRC shell elements. In particular, we propose a criterion reflecting the interaction of normal force and bending moment in a shell cross section. The failure criterion has been implemented in combination with an anisotropic damaged-based material model in order to provide realistic prediction of the structural load-carrying behavior. The accuracy of the model in prediction of different failure modes has been validated using three different types of tests setups.

Formalisation and implementation of collaborative material research process

This paper describes concepts used in formalising the research processes in order to integrate them into a technical information system (TIS) supporting the collaborative material research. The present modelling approach is based on three requirements: (1) persistent recording of the process, (2) need for a local notification mechanism and (3) straight forward transformation of formalised processes into process classes within the TIS. We shortly review the techniques available for process modelling and discuss their applicability for the present domain of application. The utilisation of the modelling techniques is shown on the system application for research on textile reinforced concrete (TRC). Two real-world examples and applications from the TRC research are presented: (1) scheduling and coordination of tests on new material components spanning several users and experimental set-ups and (2) generic specification of automated calibration procedure to identify material parameters. The paper also discusses the applicability of the formulated concepts and of the developed system in interdisciplinary projects on other composite materials. The users perspective and interaction with the system has been described in more detail in the companion paper.