Short Fiber-reinforced Composites Research Articles

Fatigue failure of anterior teeth without ferrule restored with individualized fiber-reinforced post-core foundations

ObjectivesThe aim was to explore the survival of extensively damaged anterior teeth without ferrule restored with different fiber-reinforced composite (FRC) post-core foundations and composite crowns. Materials and methodsSixty extracted upper central incisors were decoronated and randomly divided into four groups (n = 15). After endodontic treatment, the specimens were restored with different individualized fiber-reinforced post-core foundations as follows: control group (CTRL): multiple unidirectional FRC-post + dual-cure composite-core, PFC: multiple unidirectional FRC-post + packable short fiber-reinforced composite (SFRC), BPFC: Bioblock technique with only packable SFRC, BFFC: Bioblock technique with only flowable SFRC. After core build-up, the teeth were finalized with adhesively luted CAD/CAM composite crowns. Cyclic isometric loading (5 Hz) was applied at 100 N for 5000 cycles, and then 200 N and 300 N for 15,000 cycles each in a fluid chamber. The specimens were loaded until fracture occurred or when a total of 35,000 cycles were reached. Kaplan-Meyer survival analysis was conducted, followed by pairwise log-rank post hoc comparisons (Mantel-Cox). ResultsThe survival rates of the control (8279 cycles) and PFC (6161 cycles) were significantly higher compared to BPFC (3223 cycles) and BFFC (2271 cycles) (p < 0.05). Regarding fracture pattern, nearly all specimens fractured in a restorable manner. ConclusionsFor restoring extensively damaged anterior teeth, multiple unidirectional FRC posts are recommended. Clinical relevanceAlthough different FRC post/core systems are available for the restoration of damaged root canal treated anterior teeth, multiple unidirectional FRC posts tend to be a good option when the ferrule is missing.

Effects of Different Fiber-Reinforced Solutions on Fracture Strength and Pattern in Endodontically Treated Molars.

To evaluate the fracture strength of endodontically treated molars filled with different composite resins with vs without fiber reinforcement. A total of 60 intact mandibular molars were selected and endodontically treated. A standardized mesio-occlusal-distal cavity was prepared with cervical margins 1 mm above the cementoenamel junction and oral and buccal walls with 1.5-mm thickness. Universal adhesive was used in all specimens in etch-and-rinse mode. Specimens were divided into four groups (n = 15 each) according to restoration technique: group CSM = adhesive overlay with hybrid ceramic; group EXP = direct restoration with short fiber-reinforced composite; group ESU = direct restoration with nanohybrid composite; and group EST = direct restoration with nanohybrid composite reinforced with horizontal bidirectional glass fibers placed over the pulpal chamber floor. After 7 days of storage in water, samples were loaded until fracture using a universal testing machine. The maximum breaking loads were recorded in Newtons, and statistical analysis was then conducted with two-way ANOVA and post hoc Tukey test. Fragments were analyzed using scanning electron microscopy. Mean fracture resistance values were: CSM = 1,428.91 ± 316.90 N; EXP = 1,874.57 ± 299.47 N; ESU = 1,557.44 ± 355.65 N; and EST = 1,870.27 ± 145.11 N. The CSM and EXP groups showed the highest strength values when compared to the other groups. The variable fiber insertion did not significantly alter the fracture resistance. The origin of the fracture was always located on the occlusal surface, mainly in the major contact loading area. The use of fiber-reinforced composite showed great improvement in fracture resistance, similar to a cuspal coverage restoration. However, only short fiber-reinforced composites showed a favorable fracture pattern. Int J Prosthodont 2023;36:603-611.

Effective behavior of long and short fiber-reinforced viscoelastic composites

We study the homogenized properties of linear viscoelastic composite materials in three dimensions. The composites are assumed to be constituted by a non-aging, isotropic viscoelastic matrix reinforced by square or hexagonal arrangements of elastic transversely isotropic long and short fibers, the latter being cylindrical inclusions. The effective properties of these kind of materials are obtained by means of a semi-analytical approach combining the Asymptotic Homogenization Method (AHM) with numerical computations performed by Finite Elements (FE) simulations. We consider the elastic-viscoelastic correspondence principle and we derive the associated local and homogenized problems, and the effective coefficients in the Laplace–Carson domain. The effective coefficients are computed from the microscale local problems, which are equipped with appropriate interface loads arising from the discontinuities of the material properties between the constituents, for different fibers’ orientations in the time domain by inverting the Laplace–Carson transform. We compare our results with those given by the Locally Exact Homogenization Theory (LEHT), and with experimental measurements for long fibers. In doing this, we take into consideration Burger’s and power-law viscoelastic models. Additionally, we present our findings for short fiber reinforced composites which demonstrates the potential of our fully three dimensional approach.

Porous materials reinforced with short fibers: Unbiased full-field assessment of several homogenization strategies in elasticity

This work is concerned with the micromechanical modeling of porous short fiber-reinforced composites considered as three-phase microstructures: cavities and short fibers embedded in a matrix phase. Several homogenization strategies are evaluated in isothermal linear elasticity: two-level, two-step and direct Mori-Tanaka (MT) models. Unbiased evaluation of the methods is conducted based on full-field finite element (FE) analyses. No Eshelby-based analytical mean-field models are used. A parametric study for a porous thermoplastic polymer matrix reinforced with short glass fibers is carried out, for both fixed and distributed fiber orientations. The predictions of the various homogenization strategies are compared against reference FE results of the original three-phase composites. The reported numerical simulations are in 2D plane stress, but provide nevertheless insight into 3D situations. There are three main findings. (1) The best predictions are obtained with a two-level strategy, where in the lower level the actual porous matrix is homogenized, and in the upper level, fibers are embedded in the homogenized matrix. (2) The direct MT model can generate nonphysical predictions: effective properties outside the Voigt and Reuss estimates, and non-symmetric effective stiffness matrix. (3) For misaligned fibers, two-step homogenization methods can be used at the upper level in combination with the recommended two-level strategy. Acronyms and abbreviations: FE: finite element, BC: boundary condition, PBC: periodic BC, MF: mean-field, MT: Mori-Tanaka, ODF: orientation distribution function, OT: orientation tensor, RVE: representative volume element, SFRC: short fiber-reinforced composite, UC: unit cell, UD: unidirectional.

Fatigue behavior of endodontically treated premolars restored with different fiber-reinforced designs

ObjectivesThe aim was to investigate the fatigue survival and marginal-gap inside the root-canal of endodontically treated (ET) premolars reinforced by various fiber-reinforced post-core composites (FRCs). Moreover, composite-curing at different depths in the canal was evaluated. Methods170 intact upper-premolars were collected and randomly divided into ten groups (n = 15). One group served as control (intact-teeth). After endodontic procedure standard MO cavities were prepared and restored with different post-core fiber-reinforced materials and designs. Three-group (A1-A3) were restored with either packable and flowable short fiber-reinforced composite (SFRC) core or conventional composite-core. Two-group (B1-B2) were restored with SFRCs as short post (3 mm) and core. Four-group (C1-C4) were restored with SFRCs as post (6 mm) and core with or without unidirectional FRC posts (individually-made or conventional). After completing the restorations, teeth from Group C1-C4 (n = 5/group) were sectioned and stained. Specimens were viewed under a stereo-microscope and the percentage of microgaps within the root-canal was calculated. Fatigue-survival was measured using a cyclic-loading machine in the rest of the specimens. ResultsApplication of flowable SFRC as luting-core material with individually-made FRC post (Group C3) did not differ from intact-teeth regarding fatigue-survival (p > 0.05). The rest of the groups produced significantly lower survival (p < 0.05) compared to intact-teeth. Post/core restorations made from packable SFRC (Group C1) had a lower microgap (19.1%) at the examined interphase in the root-canal than other groups. SignificanceThe restoration of ET premolars with the use of individually-made FRC post and SFRC as luting-core material showed promising achievement regarding fatigue-resistance and survival.

A computational modeling approach based on random fields for short fiber-reinforced composites with experimental verification by nanoindentation and tensile tests

In this study a modeling approach for short fiber-reinforced composites is presented which allows one to consider information from the microstructure of the compound while modeling on the component level. The proposed technique is based on the determination of correlation functions by the moving window method. Using these correlation functions random fields are generated by the Karhunen–Loève expansion. Linear elastic numerical simulations are conducted on the mesoscale and component level based on the probabilistic characteristics of the microstructure derived from a two-dimensional micrograph. The experimental validation by nanoindentation on the mesoscale shows good conformity with the numerical simulations. For the numerical modeling on the component level the comparison of experimentally obtained Young’s modulus by tensile tests with numerical simulations indicate that the presented approach requires three-dimensional information of the probabilistic characteristics of the microstructure. Using this information not only the overall material properties are approximated sufficiently, but also the local distribution of the material properties shows the same trend as the results of conducted tensile tests.

A Scaled Boundary Approach for Inelasticity of Fibre‐Reinforced Composites

AbstractAs versatile materials with elevated mechanical properties, short fibre reinforced composites (SFRCs) are currently used in many applications. To enhance the mechanical properties, e.g. the ductility, or to reduce crack propagation, short fibres are added to a matrix material, such as polymers or concrete. In the case of concrete, for example, the composite might contain additional aggregates as well. Although the addition of fibres improves the mechanical properties in general, it is well‐known that many matrix materials exhibit creep deformations under constant long‐term loads.The contribution at hand discusses a scaled boundary approach to model the inelastic behaviour of SFRCs. To allow for an efficient and automated mesh generation, the scaled boundary finite element method (SBFEM) is used in conjunction with the quadtree/octree decomposition algorithm. Within this framework, the fibres are modelled in a discrete manner, and the mesh of the matrix is generated independently of the fibres. Applying a novel embedding method, the meshes of the matrix and the fibres are combined, which results in a compatible mesh without requiring additional constraints. Furthermore, it is straightforward to combine the discussed techniques with image‐based mesh generation, e.g. based on computed tomography scans. The current contribution presents various 2D and 3D examples illustrating the efficiency and adaptability of the proposed framework.In addition, we present a methodology to incorporate non‐linear constitutive models into the SBFEM. Separate constitutive equations are formulated for the matrix, aggregates, and fibres. Whereas the mechanical behaviour of the aggregates and the fibres can be modelled within the framework of elasticity, one must make use of non‐linear approaches to account for the rate‐dependent inelastic deformation of the matrix under multiaxial stress and deformation states. Overall, this method allows for the simulation of creep in SFRCs, while considering the complex microstructure of these materials in detail. This provides the basis for a realistic estimation of the effect of long‐term loading on SFRC components.

Comparative evaluation of fracture resistance of endodontically treated premolars with one remaining cavity wall restored using different techniques and materials: An in vitro study

Introduction: This study was aimed to evaluate and compare the effectiveness of conventional posterior composites, and short fiber-reinforced composites with and without the use of glass fiber post (GFP) and polyethylene fiber post on fracture strength of endodontically treated maxillary premolar teeth. Materials and Methods: Root canal treatment was performed on the sixty extracted maxillary premolars followed by mesio-occluso-distal cavity preparation and removal of the lingual wall. The teeth were randomized into six groups (A1, A2, A3; B1, B2, and B3). In Group A, a conventional posterior composite was used as a core material, and in Group B, short fiber-reinforced composite was used. Groups A and B were divided according to the post systems used. In Groups A1 and B1, 3 mm deep cavities were prepared in the palatal canal and restored with respective core materials. In Groups A2 and B2 GFP were placed in 10 mm post space prepared in the palatal canal and restored with respective core material. While in Groups A3 and B3 polyethylene, fiber post was placed, followed by core build-up with respective core materials. Samples were subjected to fracture resistance testing in the Universal testing machine, and the fractured samples were inspected in stereomicroscope under 20× for identifying fracture patterns. The data were analyzed using one-way ANOVA, followed by post hoc Tukey's test. The failure pattern was analyzed using the Chi-square test. Results: Higher fracture resistance values were seen with groups restored with the post as compared to groups restored without post, but the difference was not statistically significant (P > 0.05). The short fiber-reinforced composite showed higher resistance values than the conventional composite (P 0.05). The use of post resulted in a significantly higher number of favorable fracture of the teeth (P Conclusion: The use of post did not have a profound effect on the fracture resistance but had a positive effect on failure patterns in teeth with one remaining wall. In root canal treated teeth with one wall remaining, the use of either post with short fiber reinforced composite is recommended.

Physical and mechanical characteristics of short fiber-reinforced resin composite in comparison with bulk-fill composites.

The objective of this study was to evaluate the physical and mechanical properties of a short fiber-reinforced resin composite: everX-Posterior and compare it with two bulk-fill composites, namely, Filtek Bulk-fill and Beautifil-Bulk, which are intended for large posterior restorations. Investigated properties were flexural strength, flexural modulus, surface roughness, volumetric shrinkage and depth of cure. Scanning electron microscopy images of each specimen after the flexural test were used for cross-sectional comparison. Results were analyzed using ANOVA following Tukey post-hoc test. Flexural strength of everX-Posterior was comparable with two other resin composites, showing higher flexural modulus. EverX-Posterior showed the highest surface roughness after polishing and the lowest volumetric shrinkage (2.29%) among all composites used in this study. Data also showed that the everX-Posterior depth of cure was 4.24 mm, which was the highest among the three groups. Based on the results of this study, it was concluded that everX-Posterior as a short fiber-reinforced composite showed improvements and satisfactory performance in mechanical and physical properties, which make it a reliable base material candidate for large posterior restorations.

The impact of fiber properties on the material coefficients of short fiber‐reinforced composites

AbstractHomogenization techniques lead to a deterministic description of a microstructure. However, the components of the microstructure for example of short fiber‐reinforced composites (SFRC) show probabilistic characteristics. In this study, a numerical approach is presented to analyze the influence of these probabilistic characteristics of the fiber length, diameter, orientation and fiber volume fraction on the elasticity tensor. The plausibility of the presented numerical approach is proven by the symmetry of the resulting elasticity tensor as well as the overall assumption of transversely‐isotropic material behavior for SFRC indicated by the elasticity tensor structure. The simulations based on PBT GF 30 reveal, that the elasticity coefficients are significantly influenced by the stochastic distribution of the fiber orientation. Besides this, except for C11, the stochastic properties of the fiber length, the fiber diameter and the fiber volume fraction only slightly influence the mean of the elasticity coefficients.

On the multi-axial fatigue modelling of short fibre reinforced composites: Extensions to the Master SN curve approach

Injection moulded short fibre reinforced composites (SFRC) have variable fibre orientation distribution at every point and are often subjected to multi-axial fatigue loading due to their inherent anisotropic nature. The fatigue properties are known to be significantly dependant on the fibre orientation distribution. Thus, the fatigue simulation of SFRC components poses dual challenges of predicting the local SN curves and also accounting for the multi-axial loading. This paper describes two models extending the Master SN curve approach (doi:https://doi.org//10.1016/j.compositesa.2015.11.038) for multi-axial fatigue modelling of SRFC. The models proposed are adaptations of two existing well-known formulations; namely the characteristic plane approach and the critical plane approach. The proposed models are validated using published experimental data confirming a match with an error less than about 15%. Both the models are compatible with the through process modelling framework of injection moulded SFRCs and thus have significant potential for use during fatigue simulation of SFRC components.

Influence of Short Fiber- Reinforced Composites on Fracture Resistance of Single-Structure Restorations.

The aim was to determine the load-bearing capacity of anterior crowns prepared using two types of single-structure short fibre-reinforced composites (SFRCs). Furthermore, fracture toughness (FT), flexural strength (FS) and flexural modulus (FM) of tested composites were measured. Seven groups of composite crowns were designed for an upper central incisor (n=8/group). Two groups were CAD/CAM fabricated made of Cerasmart 270 and experimental single-structure SFRC blocks. Two groups were 3D-printed made of GC Temp PRINT and Pro3dure GR-17 composites. Two groups were made of conventional light-cured composites (Essentia and Gradia Plus). The last group was a single-structure SFRC made of commercial flowable SFRC (everX Flow). Crown restorations were loaded until fracture. Failure-modes were then visually examined. FT, FS and FM were determined for each tested composite (n=8). The data were analysed using analysis of variance (p=0.05) followed by Tukey's post-hoc test. ANOVA revealed that crowns made of experimental SFRC blocks had significantly higher load-bearing capacities (1650 ±230 N) (p⟨0.05) among all the groups tested. Experimental SFRC blocks exhibited the highest FT (2.9 MPa m1/2) and FS (245.8 MPa) values (p⟨0.05) among tested composites. CAD/CAM fabricated restorations made of experimental SFRC blocks demonstrated encouraging performance related to their fracture-behaviour.

Tensile failure prediction of a short fiber or particle composite

AbstractAs any failure of a short fiber reinforced composite (SFRC) is caused by a matrix failure, an accurate prediction of the latter is fundamentally important. This is achievable only when the matrix homogenized stresses are converted into true values. The conversion is made by multiplying the homogenized stresses with matrix stress concentration factors (SCFs) in the composite. Only a longitudinal SCF of the matrix in the SFRC needs to be determined, because all of the other directional SCFs are the same as those in a continuous fiber composite already available. In this paper, the longitudinal tensile SCF of the matrix is obtained in terms of the matrix stress field calculated through a finite element approach. The thus obtained SCF is valid for any fiber aspect ratio. The predicted strengths of several uniaxial short fiber composites and (0/±60)s laminate subjected to longitudinal tension agree well with the available experiments.

Root Canal Retreatment and Intracoronal Bleaching on the Maxillary First Premolar

Introduction. Inadequate root canal preparation and obturation are potential causes of endodontic failure. Failed root canal treatment with intrinsic discoloration requires root canal re-treatment and intracoronal bleaching. Due to the extensive loss of hard tissues on occlusal area, the restoration requires intracanal retention with short fiber-reinforced composite. Case report. A 17-year-old male patient came to the Clinic of Conservative Dentistry Dental Hospital Prof. Soedomo. He reported pain and discomfort on maxillary first premolar while chewing after root canal procedure had been performed few months before. He felt unconvinience with the discoloration happened on those tooth. Patient had endodontic treatment one year ago and the tooth was restored with glass ionomer cement. Objective examination showed glass ionomer restoration was still in good condition, the tooth was sensitive to percussion but not to palpation, and showed no mobility. Periapical radiograph showed incomplete obturation with radioluscent around periapical region. Retreatment followed by intracoronal bleaching was performed under rubber dam isolation. Tooth was restored with short fiber reinforced composite and composite resin. After 3 month, patient was recalled for examine the previous sign and symptomps. Periapical radiograph showed diameter of periapical lesion was smaller and tooth functioned normally. Conclusion. Root canal retreatment and intracoronal bleaching are suitable options for teeth with failed root canal treatment and intrinsic discoloration

Three-scale asymptotic homogenization of short fiber reinforced additively manufactured polymer composites

In this research, prediction of mechanical properties of short fiber-reinforced composites manufactured with the help of fused filament fabrication (FFF) process is investigated. Three-scale formulation of asymptotic homogenization is employed to upscale the properties from microscale to mesoscale and from mesoscale to macroscale. Since generating microscale representative volume element (RVE) infused with short fibers requires sophisticated modeling tools, the algorithm for the microscale RVE generation is presented and discussed. Homogenization was performed for microscale RVEs with random and aligned (fibers aligned with the beads on mesoscale) fiber orientations, and for mesoscale RVEs with unidirectional and 0/90 layup formation. Tensile tests were performed for different short carbon fiber concentrations 5, 7.5 and 10% (by volume) to validate predicted homogenized properties. Moreover, to analyze the morphology of 3D printed specimens, microstructural analysis using SEM was performed on all the printed specimens. Surface morphology helped to gain more insight into the bead structure and fiber distribution. It was concluded that Young's modulus prediction using random fiber orientation has low relative errors tested in bead direction. Overall, this study has unique contribution to mechanical property prediction for FFF-made short fiber-reinforced composite parts.

Correlation structure in the elasticity tensor for short fiber-reinforced composites

The present work provides a profound analytical treatment and numerical analysis of the material properties of SFRC on the mesoscale as well as the resulting correlation structure taking into account the probabilistic characteristics of the fiber geometry. This is done by calculating the engineering constants using the analytical framework given by Tandon and Weng as well as Halpin and Tsai. The input parameters like fiber length, diameter and orientation are chosen with respect to their probability density function. It is shown, that they are significantly influenced by the fiber length, the fiber orientation and the fiber volume fraction. The verification of the analytically obtained values is done on a numerical basis. Therefore, a two-dimensional microstructure is generated and transferred to a numerical model. The advantage of this procedure is, that there are several fibers with different geometrical properties placed in a preset area. The results of the numerical analysis meet the analytically obtained conclusions. Furthermore, the results of the numerical simulations are independent of the assumption of a plane strain and plane stress state, respectively. Finally, the correlation structure of the elasticity tensor is investigated. Not only the symmetry properties of the elasticity tensor characterize the correlation structure, but also the overall transversely-isotropic material behavior is confirmed. In contrast to the influencing parameters, the correlation functions vary for a plane strain and a plane stress state.

Sliding Wear Behaviour of Nickel-Coated Short Fibre-Reinforced Al7075 Composites

In the present study, Aluminium-7075 alloy is reinforced with nickel-coated short carbon fibres in the form of short fibre. These composites were prepared by stir casting method with 2, 4, 6 and 8 wt.% of nickel-coated carbon fibres. Wear resistance of aluminium alloy and its composites were analysed according to the ASTM standards. The experiments were conducted using pin-on-disc wear test and rig wear test method with different loads. From the wear test, it was found that aluminium composites with 8% nickel-coated carbon fibre rate of wear are minimum. Worn and fractured surfaces of cast aluminium alloy and the developed composites are analysed by SEM. The test results reveal that the wear resistance of the prepared MMCs improves with the addition of carbon fibre.

Characterization of restorative short-fiber reinforced dental composites.

The aim was to evaluate and compare certain physical properties including surface-wear of five commercial short fiber-reinforced composites (SFRCs; Alert, NovaPro-Flow, NovaPro-Fill, everX Flow and everX Posterior). The following properties were examined according to ISO: flexural strength, flexural modulus, fracture toughness, water sorption. Degree of conversion was determined by FTIR-spectrometry. A wear test was conducted with 15,000 chewing-cycles using a chewing-simulator. Polymerization shrinkage-stress was measured using tensilometer. SEM was used to evaluate the microstructure of SFRCs. everX Flow exhibited the highest fracture toughness (2.8 MPa m1/2) and the lowest wear depth (20.4 µm) values (p<0.05) among the SFRCs tested. NovaPro Fill (141.5 MPa) and everX Flow (147 MPa) presented the highest flexural strength values (p<0.05). everX Flow showed the highest shrinkage-stress value (5.3 MPa) while other SFRCs had comparable values. The use of SFRCs in dentistry can be advantageous, but special attention should be given to the selection of the materials.

Characterization of short fiber-reinforced polylactic acid composites produced with Fused Filament Fabrication (FFF)

The interdisciplinary expansion of additive manufacturing (AM) technologies resulted in an increasing demand for high-performance materials for engineering applications. In order to enhance the mechanical properties of printed products, short fiber composites are of great interest recently. In this study, the development of short fiber-reinforced composite materials is performed along with the mechanical characterization of the samples produced by fused filament fabrication (FFF) technology.

Damage and fatigue life prediction of short fiber reinforced composites submitted to variable temperature loading: Application to Sheet Molding Compound composites

The majority of fatigue life prediction models which have been proposed for the Short Fiber Reinforced Composite (SFRC) materials have been developed for constant temperature. However, in real situations, SFRC structures are subjected to variable temperature. This study focus on the response of SFRC composites subjected to different sequences (or blocks) under variable temperature conditions. Experientially, this kind of study requires a lot of investment from the point of view of cost and time. In this paper, the results coming from modelling the fatigue life and residual stiffness of short fiber reinforced composites subjected to thermomechanical loadings are reported. In fact, we propose to use a hybrid micromechanical-phenomenological model to quantify the evolution of the local damage rate during each loading block. Indeed, damage accumulation is calculated and cumulated step by step through the calculation of the evolution of a local damage ratio which describes the evolution of micro-cracks density until failure. Life prediction for specimens submitted to a variable temperature loading found to give acceptable results compared to experiments.