Materials

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20 pages, 23601 KiB

Open AccessArticle

Dynamic Single-Fiber Pull-Out of Polypropylene Fibers Produced with Different Mechanical and Surface Properties for Concrete Reinforcement

by Enrico Wölfel, Harald Brünig, Iurie Curosu, Viktor Mechtcherine and Christina Scheffler

Materials 2021, 14(4), 722; https://doi.org/10.3390/ma14040722 - 04 Feb 2021

Cited by 21 | Viewed by 2604

Abstract

In strain-hardening cement-based composites (SHCC), polypropylene (PP) fibers are often used to provide ductility through micro crack-bridging, in particular when subjected to high loading rates. For the purposeful material design of SHCC, fundamental research is required to understand the failure mechanisms depending on [...] Read more.

In strain-hardening cement-based composites (SHCC), polypropylene (PP) fibers are often used to provide ductility through micro crack-bridging, in particular when subjected to high loading rates. For the purposeful material design of SHCC, fundamental research is required to understand the failure mechanisms depending on the mechanical properties of the fibers and the fiber–matrix interaction. Hence, PP fibers with diameters between 10 and 30 µm, differing tensile strength levels and Young’s moduli, but also circular and trilobal cross-sections were produced using melt-spinning equipment. The structural changes induced by the drawing parameters during the spinning process and surface modification by sizing were assessed in single-fiber tensile experiments and differential scanning calorimetry (DSC) of the fiber material. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurements were applied to determine the topographical and wetting properties of the fiber surface. The fiber–matrix interaction under quasi-static and dynamic loading was studied in single-fiber pull-out experiments (SFPO). The main findings of microscale characterization showed that increased fiber tensile strength in combination with enhanced mechanical interlocking caused by high surface roughness led to improved energy absorption under dynamic loading. Further enhancement could be observed in the change from a circular to a trilobal fiber cross-section. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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23 pages, 11252 KiB

Open AccessFeature PaperArticle

Low-Velocity Impact Experiments and Modeling of TRC Skin-Aerated Concrete Core Sandwich Composites

by Chidchanok Pleesudjai, Anling Li, Vikram Dey and Barzin Mobasher

Materials 2021, 14(2), 390; https://doi.org/10.3390/ma14020390 - 14 Jan 2021

Cited by 5 | Viewed by 2268

Abstract

Mechanical response of textile-reinforced aerated concrete sandwich panels was investigated using instrumented three-point bending tests under quasi-static and low-velocity impact loads. Two types of core material were compared in the sandwich composite consisting of plain autoclaved aerated concrete (AAC) and fiber-reinforced aerated concrete [...] Read more.

Mechanical response of textile-reinforced aerated concrete sandwich panels was investigated using instrumented three-point bending tests under quasi-static and low-velocity impact loads. Two types of core material were compared in the sandwich composite consisting of plain autoclaved aerated concrete (AAC) and fiber-reinforced aerated concrete (FRAC), and the stress skins were alkali-resistant glass (ARG) and textile reinforced concrete (TRC). The textile-reinforced layer promoted distributed cracking mechanisms and resulted in significant improvement in the flexural strength and ductility. Digital Image Correlation (DIC) was used to study the distributed cracking mechanism and obtain impact force-crack width response at different drop heights. A constitutive material model was also developed based on a multi-linear tension/compression strain hardening model for the stress-skin and an elastic, perfectly plastic compression model for the core. A detailed parametric study was used to address the effect of model parameters on the flexural response. The model was further applied to simulate the experimental flexural data from the static and impact tests on the plain aerated concrete and sandwich composite beams. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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20 pages, 7026 KiB

Open AccessArticle

Tensile Behavior of High-Strength, Strain-Hardening Cement-Based Composites (HS-SHCC) Reinforced with Continuous Textile Made of Ultra-High-Molecular-Weight Polyethylene

by Ting Gong, Iurie Curosu, Frank Liebold, Duy M. P. Vo, Konrad Zierold, Hans-Gerd Maas, Chokri Cherif and Viktor Mechtcherine

Materials 2020, 13(24), 5628; https://doi.org/10.3390/ma13245628 - 10 Dec 2020

Cited by 11 | Viewed by 2257

Abstract

The paper at hand presents an investigation of the tensile behavior of high-strength, strain-hardening cement-based composites (HS-SHCC), reinforced with a single layer of continuous, two-dimensional textile made of ultra-high molecular weight polyethylene (UHMWPE). Uniaxial tension tests were performed on the bare UHMWPE textiles, [...] Read more.

The paper at hand presents an investigation of the tensile behavior of high-strength, strain-hardening cement-based composites (HS-SHCC), reinforced with a single layer of continuous, two-dimensional textile made of ultra-high molecular weight polyethylene (UHMWPE). Uniaxial tension tests were performed on the bare UHMWPE textiles, on plain HS-SHCC, and on the hybrid fiber-reinforced composites. The bond properties between the textile yarns and the surrounding composite were investigated in single-yarn pullout experiments. In order to assess the influence of bond strength between the yarn and HS-SHCC on the tensile behavior of the composites with hybrid fiber reinforcement, the textile samples were analyzed both with, and without, an additional coating of epoxy resin and sand. Compared to the composites reinforced with carbon yarns in previous studies by the authors, the high elongation capacity of the UHMWPE textile established the higher strain capacity of the hybrid fiber-reinforced composites, and showed superior energy absorption capacity up to failure. The UHMWPE textile limited the average crack width in comparison with that of plain HS-SHCC, but led to slightly larger crack widths when compared to equivalent composites reinforced with carbon textile, the reason for which was traced back to the lower Young’s modulus and the higher elongation capacity of the polymer textile. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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20 pages, 10882 KiB

Open AccessFeature PaperArticle

Impact Analysis of Thermally Pre-Damaged Reinforced Concrete Frames

by Joško Ožbolt, Luka Lacković and Daniela Ruta

Materials 2020, 13(23), 5349; https://doi.org/10.3390/ma13235349 - 25 Nov 2020

Cited by 4 | Viewed by 2152

Abstract

In the present study, the influence of thermally induced damage of reinforced concrete (RC) frames on their static and dynamic response is experimentally and numerically investigated. In the experimental test, the RC frame is first pre-damaged through fire exposure and then loaded from [...] Read more.

In the present study, the influence of thermally induced damage of reinforced concrete (RC) frames on their static and dynamic response is experimentally and numerically investigated. In the experimental test, the RC frame is first pre-damaged through fire exposure and then loaded from the side with the impact of a steel pendulum. To verify the recently developed coupled thermo-mechanical model for concrete, transient 3D FE simulation is carried out. The rate and temperature-dependent microplane model is used as a constitutive law for concrete. It is first shown that the simulation is able to realistically replicate the experimental test. Subsequently, the numerical parametric study is performed where the dynamic and static response of RC frame is simulated for both hot and cold states. It is shown that the pre-damage of RC frame through fire exposure significantly reduces the resistance and changes the response. Finally, it is demonstrated that for the impact load the rate sensitive constitutive law of concrete significantly contributes to the response of RC frame. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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35 pages, 5879 KiB

Open AccessArticle

Modelling of High Velocity Impact on Concrete Structures Using a Rate-Dependent Plastic-Damage Microplane Approach at Finite Strains

by Bobby Rio Indriyantho, Imadeddin Zreid, Robert Fleischhauer and Michael Kaliske

Materials 2020, 13(22), 5165; https://doi.org/10.3390/ma13225165 - 16 Nov 2020

Cited by 3 | Viewed by 2065

Abstract

Concrete is known as a quasi-brittle material and the microplane model has been proven to be a powerful method to describe its constitutive features. For some dynamic cases, however, numerous microplane models used successfully at small strains are not sufficient to predict the [...] Read more.

Concrete is known as a quasi-brittle material and the microplane model has been proven to be a powerful method to describe its constitutive features. For some dynamic cases, however, numerous microplane models used successfully at small strains are not sufficient to predict the nonlinear behaviour of damaged concrete due to large deformations. In this contribution at hand, a combined plasticity-damage microplane model extended to the finite strain framework is formulated and regularised using implicit gradient enhancement to achieve mesh insensitivity and to obtain more stable finite element solutions. A modified smooth three surface Drucker–Prager yield function with caps is introduced within the compression-tension split. Moreover, a viscoplastic consistency formulation is implemented to deliver rate dependency at dynamic cases. In case of penetration into concrete materials, the proposed model is equipped with an element erosion procedure to yield a better approximation of crack patterns. Numerical examples on impact cases are performed to challenge the capability of the newly proposed model to existing experimental data. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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19 pages, 1436 KiB

Open AccessArticle

Computational Micro-Macro Analysis of Impact on Strain-Hardening Cementitious Composites (SHCC) Including Microscopic Inertia

by Erik Tamsen, Iurie Curosu, Viktor Mechtcherine and Daniel Balzani

Materials 2020, 13(21), 4934; https://doi.org/10.3390/ma13214934 - 03 Nov 2020

Cited by 4 | Viewed by 1464

Abstract

This paper presents a numerical two-scale framework for the simulation of fiber reinforced concrete under impact loading. The numerical homogenization framework considers the full balance of linear momentum at the microscale. This allows for the study of microscopic inertia effects affecting the macroscale. [...] Read more.

This paper presents a numerical two-scale framework for the simulation of fiber reinforced concrete under impact loading. The numerical homogenization framework considers the full balance of linear momentum at the microscale. This allows for the study of microscopic inertia effects affecting the macroscale. After describing the ideas of the dynamic framework and the material models applied at the microscale, the experimental behavior of the fiber and the fiber–matrix bond under varying loading rates are discussed. To capture the most important features, a simplified matrix cracking and a strain rate sensitive fiber pullout model are utilized at the microscale. A split Hopkinson tension bar test is used as an example to present the capabilities of the framework to analyze different sources of dynamic behavior measured at the macroscale. The induced loading wave is studied and the influence of structural inertia on the measured signals within the simulation are verified. Further parameter studies allow the analysis of the macroscopic response resulting from the rate dependent fiber pullout as well as the direct study of the microscale inertia. Even though the material models and the microscale discretization used within this study are simplified, the value of the numerical two-scale framework to study material behavior under impact loading is demonstrated. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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13 pages, 5363 KiB

Open AccessArticle

Reinforced Concrete Plates under Impact Load—Damage Quantification

by Marcus Hering, Franz Bracklow, Silke Scheerer and Manfred Curbach

Materials 2020, 13(20), 4554; https://doi.org/10.3390/ma13204554 - 14 Oct 2020

Cited by 8 | Viewed by 2211

Abstract

A large number of impact experiments have been carried out at the Technische Universität Dresden in recent years in several research projects. The focus was on reinforced concrete plates on the one hand and on subsequently strengthened reinforced concrete plates on the other [...] Read more.

A large number of impact experiments have been carried out at the Technische Universität Dresden in recent years in several research projects. The focus was on reinforced concrete plates on the one hand and on subsequently strengthened reinforced concrete plates on the other hand. Based on these investigations, two fundamental tasks arose: (1) finding an objective description of the damage of components made of steel reinforced concrete that had previously been subjected to an impact load and (2) quantification of the effect of a subsequently applied strengthening layer. In this paper we will focus on both. At first, the experimental conditions and program as well as the used drop tower facility at the Otto Mohr Laboratory of the Technische Universität Dresden are briefly explained. In the summary presentation of the main test results, the focus is on the observed component damage. Based on the observations, an approach for a damage description is presented. To define global damage, the stiffness of the investigated structural components before and after the impact event is used. At the end of the paper, the potential of the method, but also gaps in knowledge and research needs are discussed. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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19 pages, 24563 KiB

Open AccessArticle

An Experimental Investigation of the Behavior of Strain-Hardening Cement-Based Composites (SHCC) under Impact Compression and Shear Loading

by Ali A. Heravi, Oliver Mosig, Ahmed Tawfik, Manfred Curbach and Viktor Mechtcherine

Materials 2020, 13(20), 4514; https://doi.org/10.3390/ma13204514 - 12 Oct 2020

Cited by 10 | Viewed by 1893

Abstract

The ductile behavior of strain-hardening cement-based composites (SHCC) under direct tensile load makes them promising solutions in applications where high energy dissipation is needed, such as in earthquakes, impacts by projectiles, or blasts. However, the superior tensile ductility of SHCC due to multiple [...] Read more.

The ductile behavior of strain-hardening cement-based composites (SHCC) under direct tensile load makes them promising solutions in applications where high energy dissipation is needed, such as in earthquakes, impacts by projectiles, or blasts. However, the superior tensile ductility of SHCC due to multiple cracking does not necessarily point to compressive and shear ductility. As an effort to characterize the behavior of SHCC under impact compressive and shear loading relevant to the aforementioned high-speed loading scenarios, the paper at hand studies the performance of a particular SHCC and its constituent, cement-based matrices using the split-Hopkinson bar method. For compression experiments, cylindrical specimens with a length-to-diameter ratio (l/d) of 1.6 were used. The selected length of the sample led to similar failure modes under quasi-static and impact loading conditions, necessary to a reliable comparison of the observed compressive strengths. The impact experiments were performed in a split-Hopkinson pressure bar (SHPB) at a strain rate that reached 110 s⁻¹ at the moment of failure. For shear experiments, a special adapter was developed for a split-Hopkinson tension bar (SHTB). The adapter enabled impact shear experiments to be performed on planar specimens using the tensile wave generated in the SHTB. Results showed dynamic increase factors (DIF) of 2.3 and 2.0 for compressive and shear strength of SHCC, respectively. As compared to the non-reinforced constituent matrix, the absolute value of the compressive strength was lower for the SHCC. Contrarily, under shear loading, the SHCC demonstrated higher shear strength than the non-reinforced matrix. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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15 pages, 8251 KiB

Open AccessArticle

Crack Propagation Velocity Determination by High-speed Camera Image Sequence Processing

by Frank Liebold, Ali A. Heravi, Oliver Mosig, Manfred Curbach, Viktor Mechtcherine and Hans-Gerd Maas

Materials 2020, 13(19), 4415; https://doi.org/10.3390/ma13194415 - 03 Oct 2020

Cited by 11 | Viewed by 2346

Abstract

The determination of crack propagation velocities can provide valuable information for a better understanding of damage processes of concrete. The spatio-temporal analysis of crack patterns developing at a speed of several hundred meters per second is a rather challenging task. In the paper, [...] Read more.

The determination of crack propagation velocities can provide valuable information for a better understanding of damage processes of concrete. The spatio-temporal analysis of crack patterns developing at a speed of several hundred meters per second is a rather challenging task. In the paper, a photogrammetric procedure for the determination of crack propagation velocities in concrete specimens using high-speed camera image sequences is presented. A cascaded image sequence processing which starts with the computation of displacement vector fields for a dense pattern of points on the specimen’s surface between consecutive time steps of the image sequence chain has been developed. These surface points are triangulated into a mesh, and as representations of cracks, discontinuities in the displacement vector fields are found by a deformation analysis applied to all triangles of the mesh. Connected components of the deformed triangles are computed using region-growing techniques. Then, the crack tips are determined using the principal component analysis. The tips are tracked in the image sequence and the velocities between the time stamps of the images are derived. A major advantage of this method as compared to the established techniques is in the fact that it allows spatio-temporally resolved, full-field measurements rather than point-wise measurements. Furthermore, information on the crack width can be obtained simultaneously. To validate the experimentation, the authors processed image sequences of tests on four compact-tension specimens performed on a split-Hopkinson tension bar. The images were taken by a high-speed camera at a frame rate of 160,000 images per second. By applying the developed image sequence processing procedure to these datasets, crack propagation velocities of about 800 m/s were determined with a precision in the order of 50 m/s. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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18 pages, 3930 KiB

Open AccessArticle

Influence of Crack Width in Alternating Tension–Compression Regimes on Crack-Bridging Behaviour and Degradation of PVA Microfibres Embedded in Cement-Based Matrix

by Majid Ranjbarian, Xiaomeng Ma and Viktor Mechtcherine

Materials 2020, 13(18), 4189; https://doi.org/10.3390/ma13184189 - 21 Sep 2020

Cited by 6 | Viewed by 2151

Abstract

The use of high-performance polymeric microfibres in enhancing the ductility of cementitious composites is widespread. A vivid example is the application of strain-hardening cement-based composites (SHCCs) in the construction industry. However, there are a few challenges which need to be addressed with respect [...] Read more.

The use of high-performance polymeric microfibres in enhancing the ductility of cementitious composites is widespread. A vivid example is the application of strain-hardening cement-based composites (SHCCs) in the construction industry. However, there are a few challenges which need to be addressed with respect to material design. For instance, the ductility of SHCC diminishes under alternating tension–compression loading, where the fibres lose their crack-bridging capacity due to specific damage mechanisms. The damage development and its influence on crack-bridging capacity have been studied in previous works by the authors. The paper at hand focuses on the influence of crack width on the crack-bridging capacity of polymeric microfibres in conjunction with the number of cycles in an alternating tension–compression regime with different cyclic compressive force levels. It shows that bridging capacity can be markedly influenced by crack width: an increase in crack width leads to more severe damage to the fibres and thus to lower crack-bridging capacity. Then, after analysing the specimens by means of electron microscopy, a hypothesis is presented to address the effect of crack width on damage development. Finally, a simple approach is proposed for estimating the influence of different parameters on fibre degradation. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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29 pages, 72281 KiB

Open AccessArticle

Numerical Mesoscale Analysis of Textile Reinforced Concrete

by Alexander Fuchs, Iurie Curosu and Michael Kaliske

Materials 2020, 13(18), 3944; https://doi.org/10.3390/ma13183944 - 06 Sep 2020

Cited by 5 | Viewed by 2449

Abstract

This contribution presents a framework for Numerical Material Testing (NMT) of textile reinforced concrete based on the mesomechanical analysis of a Representative Volume Element (RVE). Hence, the focus of this work is on the construction of a proper RVE representing the dominant mechanical [...] Read more.

This contribution presents a framework for Numerical Material Testing (NMT) of textile reinforced concrete based on the mesomechanical analysis of a Representative Volume Element (RVE). Hence, the focus of this work is on the construction of a proper RVE representing the dominant mechanical characteristics of Textile Reinforced Concrete (TRC). For this purpose, the RVE geometry is derived from the periodic mesostructure. Furthermore, sufficient constitutive models for the individual composite constituents as well as their interfacial interactions are considered, accounting for the particular mechanical properties. The textile yarns are modeled as elastic transversal isotropic unidirectional layers. For the concrete matrix, an advanced gradient enhanced microplane model is utilized considering the complex plasticity and damage behavior at multiaxial loading conditions. The mechanical interactions of the constituents are modeled by an interface formulation considering debonding and friction as well as contact. These individual constitutive models are calibrated by corresponding experimental results. Finally, the damage mechanisms as well as the load bearing behavior of the constructed TRC-RVE are analyzed within an NMT procedure based on a first-order homogenization approach. Moreover, the effective constitutive characteristics of the composite at macroscale are derived. The numerical results are discussed and compared to experimental results. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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16 pages, 5051 KiB

Open AccessArticle

Extrusion-Based Additive Manufacturing with Carbon Reinforced Concrete: Concept and Feasibility Study

by Viktor Mechtcherine, Albert Michel, Marco Liebscher and Tobias Schmeier

Materials 2020, 13(11), 2568; https://doi.org/10.3390/ma13112568 - 04 Jun 2020

Cited by 55 | Viewed by 4265

Abstract

Additive manufacturing with cement-based materials needs sound approaches for the direct, seamless integration of reinforcement into structural and non-structural elements during their fabrication. Mineral-impregnated Carbon-Fibre (MCF) composites represent a new type of non-corrosive reinforcement that offers great potential in this regard. MCF not [...] Read more.

Additive manufacturing with cement-based materials needs sound approaches for the direct, seamless integration of reinforcement into structural and non-structural elements during their fabrication. Mineral-impregnated Carbon-Fibre (MCF) composites represent a new type of non-corrosive reinforcement that offers great potential in this regard. MCF not only exhibits high performance with respect to its mechanical characteristics and durability, but it also can be processed and shaped easily in the fresh state and, what is more, automated. This article describes different concepts for the continuous, fully automated integration of MCF reinforcement into 3D concrete printing based on layered extrusion. Moreover, for one of the approaches presented and discussed, namely 3D concrete printing with MCF supply from a continuous, stationary impregnation line and deposition of MCF between concrete filaments, a feasibility study was performed using a gantry 3D printer. Small-scale walls were printed and eventually used for the production of specimens for mechanical testing. Three-point bend tests performed on two different beam geometries showed a significant enhancement of both flexural strength and, more especially, deformability of the specimens reinforced with MCF in comparison to the specimens made of plain concrete. Full article

(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)

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