Volumetric Fiber Content Research Articles

Impact Strength for 3D-Printed PA6 Polymer Composites under Temperature Changes

This paper shows how temperature influences impact energy for continuous fiber additively manufactured (AM) polymer matrix composites. AM composites were fabricated with a nylon-based matrix and four continuous reinforcements: fiberglass, high-temperature fiberglass (HSHT), Kevlar, and carbon. The tested temperatures ranged from −40 to 90 °C. The chosen printed configuration for the lattice structure and fiber volume was the configuration that was found to perform the best in the literature, with a volumetric fiber content of 24.2%. Impact tests showed that the best response was fiberglass, HSHT, Kevlar, and carbon, in that order. The impact resistance was lowered at temperatures below ambient temperatures and above 50 °C. Additionally, each material’s impact energy was adjusted to third-degree polynomials to model results, with correlation factors above 92%. Finally, the failure analysis showed the damage mechanisms of matrix cracking, delamination in the printing direction, fiber tearing, and fiber pulling as failure mechanisms.

Flexural response of UHPC beams post-tensioned with internal unbonded tendons: Experimental study

This paper presents the results of an experimental study that deals with the characterization of the complete flexural response of post-tensioned (PT) ultra-high-performance concrete (UHPC) beams with internal unbonded tendons. A total of 6 PT UHPC beams were monotonically loaded to failure. The variables investigated include volumetric fiber content, non-prestressed reinforcement ratio, and loading configuration. Flexural response is characterized in terms of crack pattern formation, propagation, and localization as well as failure mode identification. The influence of the investigated variables on change in: strand strain, UHPC compressive and tensile strains, strand stress, moment capacity, curvature ductility and member level ductility is presented including explanations of observed phenomena. The measured flexural response and capacity are compared with the predicted response using two mechanics-based methods and a numerical method. Prestress losses are quantified and used to obtain the predicted response. UHPC material characterization is conducted to obtain the necessary inputs for the prediction models. The measured to predicted ratio of flexural capacity and the corresponding COV for the considered prediction methods vary from 0.95 to 1.02, and from 6% to 11% suggesting good predictive capabilities. The use of nonprestressed flexural reinforcement in PT UHPC flexural members is recommended from the perspective of crack distribution, delay in the precipitation of flexural failure through crack localization and subsequent hinging, and member level ductility.

Homogeneous flow performance of steel-fiber reinforced self-consolidating concrete for repair application: A biphasic approach

In this study, fiber-reinforced self-consolidating concrete (FR-SCC) was considered as a diphasic suspension of fiber and coarse aggregate (F-A ≥ 5 mm) skeleton in mortar suspension with solid particles finer than 5 mm. The coupled effect of the volumetric content of fibers, coarse aggregate particle-size distribution, and rheological properties of the mortar on the passing ability and dynamic stability of various FR-SCC mixtures was investigated. Nine high-strength and 10 conventional-strength FR-SCC mixtures for repair application were proportioned with water-to-binder ratios (W/B) of 0.35 and 0.42, respectively, and macro steel fibers of 0.1%–0.5% volumetric contents. The dosages of high-range water-reducer (HRWR) admixture were optimized to achieve a targeted slump flow of 680 ± 20 mm. The yield stress and plastic viscosity of the mortar mixtures varied between 4.6-17.7 Pa and 2.8–8.2 Pa s, respectively. Flow performance of the investigated mixtures were evaluated in terms of flowability (slump-flow test), passing ability (J-Ring and L-Box set-ups), and dynamic stability (T-Box test). According to the established correlations, the main influencing parameters on homogeneous performance of FR-SCC include W/B, paste volume, volumetric content-to-packing density of F-A (φ/φmax), HRWR dosage, fiber content, mortar rheology, and volume of excess mortar. The robustness analyses results revealed that homogeneous flow performance of FR-SCC is more sensitive due to variations of the φ/φmax and paste volume rather than mortar rheology, W/B, and HRWR dosage. The characteristics of the mixture constituents for FR-SCC mixtures with different strength levels were finally recommended to ensure acceptable homogeneous performance under restricted flow conditions of repair application.

CONSTRUCTION OF A MODEL OF NONLINEAR DEFORMATION OF SPATIALLY-REINFORCED FIBER MATERIALS WITH DISORDERED FIBERS

A model of nonlinear deformation of fibrous materials of multidirectional reinforcement with misoriented fibers and a physically nonlinear matrix is proposed. A spatially reinforced fibrous material is regarded as a multicomponent material with a random arrangement of fibers. It is based on stochastic differential equations of the physically nonlinear theory of elasticity. The solution to the problem of the stress-strain state and the effective properties of the composite material is constructed by the method of conditional moments of L.P. Khoroshun. An algorithm for determining the effective deformative properties of a spatially reinforced material with a physically nonlinear matrix has been developed. The solution of nonlinear equations taking into account its physical nonlinearity is constructed by an iterative method. The law of connection between macrostresses and macrostrains in a spatially reinforced material and the dependence of average strains and stresses in its matrix on macrostrains have been established. Material deformation curves are plotted for various values of the fiber volumetric content. The dependence of the effective deformative properties of the spatially reinforced material on the volumetric content of fibers has been studied. The influence of the nonlinearity of the matrix on the deformation of a spatially reinforced composite material is investigated. It has been established that the nonlinearity of the matrix has a significant effect on the effective deformative properties and the stress-strain state of spatially reinforced materials.

Novel 3D printing method to reinforce implant-supported denture fiberglass as material for implant prosthesis: A pilot study.

ObjectivesDespite a large amount of materials and methods to make an implant‐supported denture, nowadays there is no gold standard. Every solution has pros and cons that guide the clinician and the technician to choose the best solution for a single case. The aim of this study was to evaluate the mechanical characteristics of the fiber‐reinforced composite superstructure made by using a novel three‐dimensional (3D) printing technology able to create a reinforcing structure patient‐specific, more reliable, structurally optimized, and faster than conventional methods.Materials and MethodsTo evaluate mechanical performances of 3D‐printed fiberglass, mechanical characterization of 3D‐printed material was performed. Before proceeding with the realization of the final prosthesis, five specimens were created on which the tensile test and volumetric fiber content measurement were performed. Then denture reinforcement 3D printing process began. Initially, the robot prints layers of fiber. Finally, the obtained 3D‐printed reinforcement structure was finalized in the lab.ResultsThe prosthesis obtained through this process was lighter than a traditional prosthesis, there was a greater chemical adhesion between resin and 3D‐printed reinforcement structure and a better result was obtained from an esthetic point of view.ConclusionsThe outcomes we obtained endorse its performance both mechanical and esthetic. The entire process is automatic and does not require human operation thanks to specific software programming.

MODEL OF DEFORMATION OF FIBROUS MATERIALS OF MULTIDIRECTIONAL REINFORCEMENT WITH NONORIENTED FIBERS

A model of deformation of multidirectional reinforcement fibrous materials with differently oriented fibers is proposed. The solution to the problem is built in two stages. At the first stage, the known properties of fibers and binder are used to determine the effective thermoelastic properties and stress-strain state of the subsystem with fibers oriented in a certain way relative to the main coordinate system. It is based on stochastic differential equations of the physically nonlinear theory of elasticity using the method of conditional moments. At the second stage, using a given distribution function based on the Voigt scheme, a model of deformation of the entire system is constructed from the calculated properties of the subsystems. Strain curves are obtained for simple loading, and the deformation of materials at uniform orientation of fibers is investigated. It was found that a fibrous composite material with differently oriented fibers in a macrovolume is isotropic, and its effective thermoelastic constants substantially depend on the volumetric content of fibers.

Evaluation Through SEM Image Processing of the Volumetric Fiber Content in Continuos Fiber-Reinforced Additive Manufacturing Composites

This work shows the estimation of the volumetric fiber content (Vf) using image processing techniques. The Vf is needed to establish mechanical properties of composites using the rule of mixtures or other more advanced prediction models for the mechanical properties. The proposed method is tested with images acquired for carbon, Kevlar, and fiberglass fiber bundles used in the fiber deposition modeling (FDM) in the additive manufacturing process. The fiber bundles are provided by Markforged ® and are used in the Markforged Two ® printer. Then, different gray threshold and segregation algorithms are convolved with the digitized images to to isolate matrix from fibers such that a separate fiber and matrix area counting can be done and an appropriate Vf can be established. Results obtained with image analysis are close to values reported using technical standards, hence validating the proposed method.

Experimental Tests and Reliability Analysis of the Cracking Impact Resistance of UHPFRC

Ultra-high performance (UHP) concrete is a special type of fibrous cementitious composite that is characterized by high strength and superior ductility, toughness, and durability. This research aimed to investigate the resistance of ultra-high performance fiber-reinforced concrete (UHPFRC) against repeated impacts. An adjusted repeated drop mass impact test was adopted to evaluate the impact performance of 72 UHPFRC disc specimens. The specimens were divided into six mixtures each of 12 discs. The only difference between the mixtures was the types of fibers used, while all other mixture components were the same. Three types of fibers were used: 6 mm micro-steel, 15 mm micro-steel, and polypropylene. All mixtures included 2.5% volumetric content of fibers, however with different combinations of the three fiber types. The test results showed that the mixtures with the 15 mm micro-steel fiber absorbed a higher number of impact blows until cracking compared to other mixtures. The mixture with pure 2.5% of 15 mm micro-steel fiber exhibited the highest impact resistance, with percentage increases over the other mixtures ranging from 25 to 140%. In addition, the Weibull distribution was used to investigate the cracking impact resistance of UHP at different levels of reliability.

Water Impact-Abrasion Erosion of Hybrid Fiber-Reinforced High Performance Concrete

Aiming to evaluate the resistance of High Performance Concrete (HPC) against the abrasion erosion due to the continual impact of water and water borne materials, six HPC mixtures reinforced with different fibers and fiber combinations were prepared and tested experimentally in this study. All mixtures share the same contents of all materials, while the types and combinations of fibers used were different among the mixtures. All mixtures included a total of 2.5% volumetric content of fibers. The mixture S6 included pure 6 mm micro-steel fiber (S6), S15 mixture included pure 15 mm micro-steel fiber (S15), while the S6-S15 mixture included 1.25% of each of S6 and S15. S6-PP and S15-PP included 2.0% of S6 or S15, respectively, in combination with 0.5% of polypropylene fiber (PP), while the sixth mixture included 1.0% S6, 1.0% S15 and 0.5% PP. The impact abrasion test was conducted on 200×200 mm plat targets with 50 mm thickness that were fixed perpendicular to a water jet with a high speed of 20 m/s. The results revealed that all HPC mixtures exhibited much higher abrasion resistance than normal concrete. The results also showed that the S15 mixture was the one with highest abrasion resistance with an abrasion loss of only approximately 20 grams after 12 hours testing.

Abrasion of Reactive Powder Concrete under Direct Water Impact

An experimental program was directed in this study to evaluate the abrasion resistance of reactive powder concrete (RPC) under direct normal impact of water jet. Abrasion and compressive strength specimens were cast from six RPC mixtures using different single and hybrid distributions of 6 mm-length and 15 mm-length micros-steel fibers and 18 mm-length polypropylene fiber. Fixed mix proportions were used for the six RPC mixtures and with fixed total volumetric fiber content of 2.5%. In addition to the RPC mixtures, a normal concrete mixture was prepared for comparison purposes. All specimens were cured in the same conditions and tested at an age of 28 days. The test results showed that abrasion weight losses increase with time at rates that are independent of fiber type and fiber distribution. The results also showed that all RPC mixtures exhibited significantly lower abrasion losses than normal concrete. The lowest percentage abrasion weight losses were recorded for the mixture with pure 15 mm micro-steel, where after 12 testing hours, it was 0.41% of the total weight before testing. On the other hand, the mixture with pure 6 mm micro-steel fiber exhibited the highest percentage abrasion weight loss (0.98%) among the six RPC mixtures. Another conclusion is that the inclusion of polypropylene fiber to compose hybrid fiber distribution with micro-steel fiber led mostly to lower abrasion losses.

Shear performance of reinforced concrete beams incorporating stiff slender elements

The present work investigates the shear performance of concrete beams reinforced longitudinally with steel rebars incorporating randomly distributed stiff elements known as “needles”. Compared to commonly used fibers, needles function differently in concrete members that carry increasing internal stresses. To measure the effect of needles on the mechanical performance of concrete, 32 longitudinally reinforced concrete (RC) beams and 96 non-reinforced concrete prisms were tested. Among numerous possibilities, the dimensions of the needles used in the present study were selected based on a number of practical considerations. The results showed that the needles increased the peak and residual shear capacity of the reinforced beams significantly. However, the improvements were not greater than those achieved by using the same volumetric content of fibers made of the same material as that the needles were produced from. Based on the measured results and the observation of cracking patterns, guidance for optimizing the geometry of needles and test specimens are provided for future research.

Mechanical damage evolution in UHPFRC: Experimental and numerical investigation

Ultra-high performance fiber reinforced concrete (UHPFRC) is a class of cement-based composite with outstanding strength, durability, and ductility. The strain hardening behavior in tension and flexure and the high toughness in compression make the composite a proper material to carry severe cyclic loads, as in earthquakes. However, there are limited data that characterizes the cyclic response of this material. In this context, the present research focused on providing such laboratory results for UHPFRC with different fiber contents. Besides, analytical models for damage evolution and stress-strain relationship are proposed and applied in numerical simulations. Cyclic loading tests were carried out in tension (dog-bone), compression (cylinders) and bending (prisms). Cracking stress, peak stress, strain at peak stress, toughness and residual strength after cyclic loading were significantly improved with the increase in volumetric fiber content. Besides, the unloading/reloading cycles enabled to determine damage evolution in tension and compression. Stiffness degradation occurred rapidly in UHPFRC under tensile loading while occurred gradually in compression. Also, fiber content influenced toughness and degradation evolution significantly over the loading cycles. Proposed equations were utilized in the Plastic-Damage model of Abaqus that predicted accurately damage growth and cyclic envelopes during all the phases of the tension, compression, and bending tests.

Prediction of specific electrical resistivity of polymeric composites based on carbon fabrics

We have proposed an improved approach to forecasting electrical resistivity of composite materials based on carbon fabrics by using a finite element method that takes into consideration a deformation of the reinforcing material during molding. Electrical characteristics of homogenized reinforcing fibers are determined by using known dependences for unidirectional composites. Based on the developed approach, we calculated values of electrical resistivity of composite materials based on the carbon fabric of twilled weaving and the weft-knitted carbon fabric. To account for a change in the thickness of the weft-knitted carbon fabric during molding, we simulated its deformation under the action of vacuum pressure. The obtained calculated values of electrical resistivity of the examined materials are in good agreement with the results of experimental study. Divergence between the calculated and experimental results for a material based on the carbon fabric of twilled weaving is 10 %. For materials based on the weft-knitted carbon fabric, divergence is 11 % towards the weft and 32 % in the direction of the base of the fabric. Given that the volumetric fiber content in a material from the weft-knitted carbon fabric was determined based on the results of modeling its deformation at molding, as well as the results of similar studies, reliability of the simulation can be considered quite satisfactory. The proposed approach could be applied when choosing a rational scheme for weaving a fabric in order to estimate specific resistivity in the absence of information about volumetric fiber content and the actual structure of the material after its fabrication.

Splice length of prestressing strands in field-cast UHPC connections

The development length of reinforcement embedded into ultra-high performance concrete (UHPC) can be significantly shorter than the lengths normally associated with conventional concrete. Shortening the development length of prestressing strands can allow for a redesign of some structural systems, including spliced girder and continuous-for-live-load bridges. UHPC, when used in field-cast connections between prefabricated elements, can create robust connections which emulate monolithic components. This study investigated the development length of 12.7- and 15.2-mm diameter untensioned prestressing strands embedded in steel fiber and PVA fiber reinforced UHPC. The volumetric fiber content was 2 %. A novel tension test method allowed for replication of the stress state that occurs when strands are lap spliced within a connection between two linear elements. The results suggest that, for the steel fiber reinforced UHPC, the 12.7-mm diameter strands can be fully developed within 51 cm and the 15.2-mm diameter strands can be fully developed in approximately 61 cm. The 12.7-mm diameter strands can be fully developed in the PVA fiber reinforced UHPC in approximately 91 cm. Applying UHPC to create lap splice connections of prestressing strands may allow for increased structural efficiency and increased structural redundancy through the use of simple, non-congested, non-post-tensioned connection details.

Scientifically substantiated approach to choosing the parameters for forming polymer composites for shell structures

This article how the strength properties of polymer composites made by ring winding are affected by the parameters of the production process. Relations are found to connect the contact pressure generated during the formation of the composite with the volumetric content of fibers in its structure. It is shown that the tension on the reinforcing material affects the variation of filament length in the roving. The thickness of the composite is found to influence the uniformity of its structure. Scientifically substantiated recommendations are made for choosing the parameters used to make polymer composites employed in shell structures.

Modelling fatigue in quasi-brittle materials with incomplete self-similarity concepts

In this study, a generalized Barenblatt and Botvina dimensional analysis approach to fatigue crack growth is proposed in order to highlight and explain the deviations from the classical power–law equations used to characterize the fatigue behaviour of quasi-brittle materials. According to this theoretical approach, the microstructural-size (related to the volumetric content of fibers in fiber-reinforced concrete), the crack-size, and the size-scale effects on the Paris’ law and on the Wohler equation are presented within a unified mathematical framework. Relevant experimental results taken from the literature are used to confirm the theoretical trends and to determine the values of the incomplete self-similarity exponents. All this information is expected to be useful for the design of experiments, since the role of the different dimensionless numbers governing the phenomenon of fatigue is herein elucidated. Finally, a numerical model based on damage mechanics and nonlinear fracture mechanics is proposed for the prediction of uniaxial S–N curves, showing how to efficiently use the information gained from dimensional analysis and how the shape of the S–N curves is influenced by the parameters of the damage model.

Corrosion protection performance of High Performance Fiber Reinforced Cement Composites as a repair material

Abstract This paper regards the corrosion protection performance of High Performance Fiber Reinforced Cement Composites (HPFRCC) as a repair material. For the purpose of improving workability, the volumetric fiber content in HPFRCC was decreased from its usual rate of 1.5% to as low as 0.75%. The applicability of HPFRCC as a repair material for preventing steel corrosion was investigated using specimens that simulated either surface coating repair or patch repair. The results can be summarized as follows: Patch repair with HPFRCC to depths beyond the backside of the reinforcement effectively suppressed chloride penetration and prevented reinforcement corrosion, whereas surface coating with HPFRCC could not prevent corrosion of the steel in the RC substrate. As long as the fiber content is set so that only fine cracks are formed under service conditions, differences in fiber content did not affect the corrosion preventing performance of HPFRCC as a repair material.

鋼繊維補強コンクリートの一軸引張およびせん断に対する変形挙動のモデル化

The deformational behavior of steel fiber reinforced concrete is important because it affects the crack width which influences the durability of the structure. In this study the deformational behavior of steel fiber reinforced concrete subjected to uniaxial tension and shear was investigated experimentally. In the experiment the effects of the volumetric fiber content, the fiber geometry and the fiber embedment length were investigated. Highstrentgh concrete was used in the specimen. From the experimental results models for the deformational behavior of steel fiber reinforced concrete under uniaxial tension and shear were obtained.