Evaluation of loading methods for determination of material and elastic constants of cement fiber board

Content from this work may be used under the terms of theCreativeCommonsAttribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd Young Scientist 2021 IOP Conf. Series: Materials Science and Engineering 1209 (2021) 012050 IOP Publishing doi:10.1088/1757-899X/1209/1/012050 1 Evaluation of loading methods for determination of material and elastic constants of cement fiber board O Nespesny1, J Pencik1, J Vystrcil1 and D Beckovsky1 1 Faculty of Civil Engineering, Institute of Building Structures, Brno University of Technology, Veveří 331/95, 602 00 Brno, Czech Republic E-mail: [email protected] Abstract. Cement fiber boards (CFB) are special group that are used in a wide range of structural civil engineering. For the correct design of a cement fibre board structure, it is important to define their material and elastic constants, which are usually determined by destructive tests. The paper deals with a definition of a suitable method of loading for the determination of basic materials and elastic constants of cement fiber boards reinforced with organic fibers loaded in the midplane. The publication compares and evaluates load tests by three-point and four-point bend. 1. Introduction Composite boards based on cement and organic fibers (referred to as cement fiber boards) are today an environmental, universal and durable building material. It serves as a substitute for natural wood and wood products, such as plywood or oriented strand boards (OSB). The properties of cement fiber boards as a building material use a variety of uses in a wide range of building structures. Those that include cladding of ventilated facades (Figure 1) for the reconstruction of new buildings, internal and external ceilings, cladding of internal and external structures, cable bridges or fire protection structures. Figure 1. Ventilated facade, application of cement fiber boards 0 Currently, the Hatschek method is one of the most widely used processes for the production of cement fiber boards 0. This production process consists in laying individual thin layers (called monolayers) on top of each other until the required thickness is reached, this layer is then pressed. In Young Scientist 2021 IOP Conf. Series: Materials Science and Engineering 1209 (2021) 012050 IOP Publishing doi:10.1088/1757-899X/1209/1/012050 2 this way of production, the reinforcing fibers are divided in a board-plane, they are oriented in the direction of production. In the case of normal use, cement fiber boards are loaded and tested (Figure 2) primarily in the y-z (y-z) direction, and y-x (x-y). In the case of innovative use, for example in the form of stairs (Figure 3), the slabs are stressed primarily in the x-z (z-x) direction, the methodology for experimental testing in this direction is not defined. Figure 2. Scheme of loading directions with regard to the direction of production of cement fiber boards produced by the Hatschek method Figure 3. Stairs, the main supporting element of the stair staircase, marking of the primary directions of loading 2. Calculation methods Determination of material and elastic constants for flat cement fiber boards (direction y-z and y-x) is governed by ČSN EN 12467 + A2 0. Here it is recommended to choose test specimens with dimensions of 250 × 250 mm, regardless of the thickness of the board. It is recommended to perform the load by three-point bending (index 3) with a constant path increment. Subsequently, the values of modulus of elasticity (MOE) and tensile strength in bending (MOR) are determined according to equations (1) and (2). 𝑀𝑂𝐸3= (𝐹2−𝐹1) ∙ 𝑙s 3 4 ∙ 𝑏 ∙ 𝑒3(𝑓2−𝑓1) (1) 𝑀𝑂𝑅3= 3 ∙ 𝐹∙ 𝑙𝑠 2 ∙ 𝑏 ∙ 𝑒2 (2) where MOE is modulus of elasticity in [N/mm2]; F1 and F2 are forces in two points located in the linear part of the loading displacement diagram graph expressing dependence between vertical displacement and applied load in [N]; ls is a distance between supports, in [mm]; b and e is the width and thickness of specimens, in [mm]; f1 and f2 are vertical displacements corresponding with the selected load, in [mm], F is failure force, in [N]. Ranachowski and Schabowicz describes in 0 as a suitable method of loading (for direction y-z and y-x) by four-point bending (index 4), where the values of modulus of elasticity (MOE) and tensile strength in bending (MOR) are determined by relations (3) and (4). 𝑀𝑂𝐸4=23 ∙ (𝐹2−𝐹1) ∙ 𝑙s 3 108 ∙ (𝑤2−𝑤1) ∙ 𝑏 ∙ ℎ3 (3) 𝑀𝑂𝑅4=𝐹max ∙ 𝑙s 𝑏 ∙ ℎ2 (4) y x z directionofproduction z x Young Scientist 2021 IOP Conf. Series: Materials Science and Engineering 1209 (2021) 012050 IOP Publishing doi:10.1088/1757-899X/1209/1/012050 3 where Fmax is failure force in [N]; h is height, respectively thickness, in [mm]; F1 is force, in [N], corresponding to 10 % of failure force (Fmax); F2 is force, in [N], corresponding to 40 % of failure force (Fmax); w1 is vertical displacement of testing specimens corresponding to F1, in [mm]; w2 is vertical displacement of testing specimens corresponding to F2, in [mm]. Equations (1) to (4) are based on European standards and are in principle applicable to flat plates, ie. for the basic directions y-z and y-x (Figure 2). In the case of defining material and elastic constants in the z-x direction, the procedures from ČSN EN 408 0 can be applied analogously, similarly to Pěnčík in 0 for wooden beam specimens. The position of the loading forces and the size of the test specimens are described in Figure 5. The modulus of elasticity (MOE4) in this case can be determined according to equation (5) 𝑀𝑂𝐸4=𝑙3∙ (𝐹2−𝐹1) 𝑏ℎ3 ∙ (𝑤2−𝑤1)[(3𝑎 4𝑙)−(𝑎 𝑙)3] (5) where a is the distance between the load and the nearest bend test support in [mm] and l the bending span in [mm]. Figure 4. Description of tests under three-point bend loading. Figure 5. Description of tests under four-point bend loading. To create a complex material model, ie. in the directions y-x, y-z, x-z (x-y, z-y, z-z) it is appropriate in all cases to choose the size of test specimens defined according to ČSN EN 408 0 (Figure 4) and (Figure 5) on the basis of the search. To determine the modulus of elasticity (MOE3) and tensile strength in bending (MOR3) under three-point bending loading, it is appropriate to apply equations (1) and (2) on the basis of research. To determine the modulus of elasticity (MOE4) and tensile strength in bending (MOR4) under loading by four-point bending, it is appropriate to apply equation (4) and (5) on the basis of research. 3. Comparison of three-point and four-point bend test The essential difference between the three-point and four-point bend test in the course of internal forces. During the three-point bend test, one point is exposed to the maximum shear force (V) and at the same time to the maximum bending moment (M), the course of internal forces is shown in (figure 6). In the case of four-point bend load, the bending moment is evenly distributed between the forces and thus allows a more accurate determination of the modulus of elasticity during the bending test (Figure 7). Young Scientist 2021 IOP Conf. Series: Materials Science and Engineering 1209 (2021) 012050 IOP Publishing doi:10.1088/1757-899X/1209/1/012050 4 Figure 6. Diagram of the course of shear forces (V) and bending moment (M) under loading by three-point bending. Figure 7. Diagram of the course of shear forces (V) and bending moment (M) under loading by four-point bending. The four-point bend test is suitable for brittle materials with low shear stress. The magnitude of the flexural tensile strength depends on the toughness and severity of the defects of the test specimens. In the case of cement fiber boards produced by the Hatschek method, delamination and cracking very often occur due to the natural maturation of the material. Exposure of one point to maximum stress (Figure 8) will reduce the measured flexural strength because there is an increased likelihood that cracks will reach a critical length at the applied load. Four-point bend test (Figure 9) is suitable for determining the strength of joints, the location of the joint area is repeatable. Figure 8. The real test arrangement in threepoint bend load. Figure 9. The real test arrangement in fourpoint bend load. 4. References [1] CEMVIN s.r.o., product catalog, available from: https://www.cemvin.cz/upload/katalog.pdf [2] Ardanuy M, Claramunt J and Toledo Filho R D 2015 Cellulosic fiber reinforced cement-based composites: A review of recent research Construction and Building Materials 79 pp 115-128 [3] Delvasto S, Toro E F, Perdomo F and de Gutiérrez R M 2010 An appropriate vacuum technology for manufacture of corrugated fique fiber reinforced cementitious sheets Construction and Building Materials 24 pp 187-192 [4] Anon. 2020 ČSN EN 12467+A2: Fibre-cement flat sheets - Product specification and test methods (Office for Technical Standardization, Metrology and State) [5] Ranachowski Z and Schabowicz K 2018 The Fabrication, Testing and Application of Fibre Cement Boards (Lady Stephenson Library, Newcastle upon Tyne, NE6 2PA, UK: Cambridge Scholars Publishing) [6] Anon. 2004 ČSN EN 408: Timber structures - Structural timber and glued laminated timber - Determination of some physical and mechanical properties (Office for Technical Standardization, Metrology and State) Young Scientist 2021 IOP Conf. Series: Materials Science and Engineering 1209 (2021) 012050 IOP Publishing doi:10.1088/1757-899X/1209/1/012050 5 [7] Pěnčík J 2015 Tests of Wooden Specimens from Scots Pine (Pinus sylvestris) with the Help of Anisotropic Plasticity Material Model Drvna industrija 66 pp 27-33 Acknowledgments The paper was produced with support for specific university research at Brno University of Technology, FAST-J-21-7449 (2021) and the Technological Agency of the Czech Republic within programme EPSILON, TH04020263 (2019-2021).