Role Of Fiber Reinforcement Research Articles

Phase evolution and mechanical performance of an ettringite-based binder during hydrothermal aging

Little is known about the performance of ettringite-based binders in hydrothermal conditions. This investigation aims to gain insights into the phase evolution and corresponding mechanical performance of an ettringite-based binder considering crystallization pressure caused by late-reaction products. Additionally, the role of fiber reinforcement on the strength retention of the binder was investigated. When aged at an elevated temperature under water-saturated conditions, hard-burned MgO hydrated to form brucite. The precipitation and growth of the brucite crystals led to a crystallization pressure of approximately 200 MPa calculated using thermodynamic modelling. Damage was observed after 4 months of aging with cracks in the microstructure and eventually a failure at the macro scale. Ettringite remained stable at 60 °C due to the water-saturated conditions. Polypropylene fiber delayed crack propagation and thus reduced the damage caused by crystallization pressure. The fiber improved the flexural performance of composite attaining deflection-hardening behavior regardless of aging conditions.

The Essential Work of Fracture parameters for 3D printed polymer sheets

Additive manufacturing is becoming increasingly popular in academia and industry. Accordingly, there has been a growing interest in characterizing 3D printed samples to determine their structural integrity behaviour. We employ the Essential Work of Fracture (EWF) to investigate the mechanical response of polymer sheets obtained through additive manufacturing. Our goal is twofold; first, we aim at gaining insight into the role of fibre reinforcement on the fracture resistance of additively manufactured polymer sheets. Deeply double-edge notched tensile (DDEN-T) tests are conducted on four different polymers: Onyx, a crystalline, nylon-reinforced polymer, and three standard polymers used in additive manufacturing – PLA, PP and ABS. Results show that fibre-reinforcement translates into a notable increase in fracture resistance, with the fracture energy of Onyx being an order of magnitude higher than that reported for non-reinforced polymers. On the other hand, we propose the use of a miniature test specimen, the deeply double-edge notched small punch specimens (DDEN-SP), to characterize the mechanical response using a limited amount of material. The results obtained exhibit good alignment with the DDEN-T data, suggesting the suitability of the DDEN-SP test for measuring fracture properties of additively manufactured polymers in a cost-effective manner.

Benefits of Low Modulus of Elasticity and of Fibre Reinforcement of Cement Based Mortars as Thin Bonded Overlay Materials

The paper, associating experiment and simulation approaches, deals with the debonding propagation between a thin bonded cement-based overlay and a substrate simulating a repair of old concrete structure. The material used for the overlay is a fibre reinforced and rubberised mortar. In the experimental investigations, three point static bending tests were carried out on composite specimens. The effects of shrinkage of the overlay, restrained by the substrate, and the role of fibre reinforcement are thus involved. Direct tensile tests on notched specimens were firstly conducted to obtain the tensile strength and the residual normal stress-crack opening relationship. The debonding opening-residual normal tensile stress relationship was investigated by static tensile tests. The propagation of the debonding interface was monitored using a video-microscope with an enlargement of 175x. On the basis of the parameters identified and quantified, the above mentioned static tests were modelled by the finite element method using CAST3M code developed in France by CEA (Commission for Atomic Energy). The model predictions showed good agreement with the experimental results. The shrinkage effect on the durability of the composite specimens was clarified. The results also proved the important role of fibre-reinforcement in restraining the crack opening by transferring stresses through the crack.

Microstructural mechanical study of a transverse osteon under compressive loading: The role of fiber reinforcement and explanation of some geometrical and mechanical microscopic properties

This Finite Element study aims at understanding the transverse osteon as a composite microstructure, and at differentiating the actions of each of its main components and their interactions. Three components of the osteon have been distinguished: the lamellae mineral–collagen matrix, the lamellae mineral–collagen reinforcement fibers and the Haversian canal content made of intracortical fluid and soft tissues. Numerical compression experiments have been performed, varying the microstructure properties. Our results show that fiber reinforcement of transverse osteons is only efficient at resisting dynamic compressive loadings, but that the improvement of the static compressive properties is very poor. Furthermore, the modeled stress distribution within the matrix and reinforcement fibers may explain why transverse osteons are often limited to a small number of lamellae (<8) and why internal lamellae could be stiffer than external ones.

Tool Preparation in Autoclave Manufacturing of Thermoset Matrix Composites and its Relevance to Adhesion

The choice of a manufacturing process is of primary importance to control composite materials properties and optimize their performance. Moreover, various parameters of a given implementation may also modify these properties in a significant way. Hence, this paper aims to underline the role of tool preparations in an autoclave process of composite manufacturing and their different links with adhesion performance. To this purpose, the influence of surface characteristics is discussed in terms of wettability, roughness, and by microscopy and chemical analysis. A link between the surface properties and adhesion performance has been assessed via single lap shear tests. Results clearly demonstrate the major influence of surface contamination and roughness but also the role of fibre reinforcement on adhesion properties.

Permeability of Stressed Concrete and Role of Fiber Reinforcement

The primary purpose of this paper is to study how externally applied stress influences the water permeability of concrete, while also evaluating the effects of fibers. To achieve this, the authors measure the water permeability of both plain and fiber reinforced concrete, with and without an applied compressive stress. A novel test is used to measure permeability under stress, involving one cylinder tested with stress while the other is tested without stress. Identical flow conditions are applied to both cylinders. Flow equilibrium is achieved early in the test via the use of a special design of the permeability cell that eliminates leakage. The stressed specimens are examined under two levels of applied stress -- 0.3f and subscript u and 0.5f and subscript u, where f and subscript u is the ultimate strength of concrete in compression. Collated cellulose fiber at volume fractions of 0.1, 0.3, and 0.5% is also used. Results show that fiber reinforcement reduces the permeability of concrete while in the unstressed state. However, for stressed concrete, results initially show that with an increase of the applied stress, there is an observed reduction in the permeability of both plain and fiber reinforced concrete. However, this observed reduction occurs only at a certain threshold value of stress. Beyond this stress threshold, plain concrete experiences a rapid increase in permeability. For fiber-reinforced concrete, there is also an observed increase in permeability beyond the threshold value of stress. However, the authors note that permeability still remains below that of the unstressed level.

Using acoustic emission to quantify damage in restrained fiber-reinforced cement mortars

This paper describes the use of acoustic emission (AE) for monitoring early-age cracking in restrained fiber-reinforced mortars. A steel-testing frame was used to prevent the length reduction associated with drying. AE sensors placed on both unrestrained and restrained specimens detected a high degree of activity that may be attributed to surface microcracking caused by moisture gradients that cause the surface to shrink more rapidly than the core. It was found that as the concrete neared the age of visible cracking, the acoustic waves generated in the restrained specimens had a greater amplitude and duration. For this reason, acoustic energy was utilized for these investigations. An increase in acoustic energy was detected before cracks were observed in the restrained specimens. It is believed that the role of fiber reinforcement is twofold. First, fibers arrest cracks thereby preventing unstable crack propagation, and second, they restrain the crack from opening preventing the cracking from becoming visible until a later age.

Fracture resistance of polyblends and polyblend matrix composites Part III Role of rubber type and location in nylon 6,6/SAN composites

The role of rubber particle type, location and morphology on toughening in blends of nylon 6,6 with styrene acrylonitrile (SAN), with and without fibre reinforcements was examined in this study. The rubber used was ethylene propylene diene monomer (EPDM) rubber and the results were compared to a previous study that used butadiene rubber. The compositions of the blends ranged from pure nylon 6,6 to pure SAN. EPDM rubber was chemically compatibilized with one of the matrix phases rather than grafted, as in the ABS. In order to study the effect of rubber location on fracture behaviour, the approach was to compatibilize EPDM with either the minor phase or the major phase component of the blend. Attention was focused on fracture initiation toughness and fracture propagation toughness, measured through the parameters J IC and J SS, respectively. J SS refers to the steady-state, or plateau value of the material R-curve and was therefore a measure of total toughness which included the additional component derived from crack extension. The results indicated that EPDM rubber was not as effective a toughening agent as was butadiene in the Acrylonitrile Butadiene Styrene (ABS) system, primarily due to the morphology of EPDM and its interface character with the nylon 6,6 or SAN matrix. It was demonstrated that the embrittlement effects of a second rigid polymer phase can be mitigated by selectively adding rubber to that phase in the alloy or blend. With regard to the role of fibre reinforcement, a strong fibre matrix interface was found to be essential for toughening. Further, the extent of rubber toughening was larger when fibres were present than when fibres were absent, provided the fibre matrix interface was strong. Fibres also, like rubber, enhanced local matrix plasticity as well as reduced the embrittlement effects associated with a second polymer phase.

Thin Bonded Overlays About the Role of Fiber Reinforcement on the Limitation of Their Debonding

Abstract This paper concerns metal fiber-reinforced repairs and toppings of slabs or concrete pavements. The durability of thin bonded overlays (less than 100-mm thick) depends upon the durability of their bond to the base slab onto which they have been applied. This paper focuses on the improved bond durability of fiber-reinforced overlays. Because fiber reinforcements at usual dosages have no significant effect on either the changes of length of the overlays or on the shear strength of their bond to the base, another cause of this better durability was sought. The research demonstrates, by finite elements computation and experimental verification, that the debonding of overlays is caused, in large, by the coupled effects of vertical cracking through the overlay and traffic loads. It is by restraining cracking that fibers enhance the bonding durability of overlays.