Effects of interfacial residual stress on mechanical behavior of SiCf/SiC composites

Layer-structured interphase, existing between reinforcing fiber and ceramics matrix, is an indispensable constituent for fiber-reinforced ceramic composites due to its determinant role in the mechanical behavior of the composites. However, the interphase may suffer high residual stress because of the mismatch of thermal expansion coefficients in the constituents, and this can exert significant influence on the mechanical behavior of the composites. Here, the residual stress in the boron nitride (BN) interphase of continuous SiC fiber-reinforced SiC composites was measured using a micro-Raman spectrometer. The effects of the residual stress on the mechanical behavior of the composites were investigated by correlating the residual stress with the mechanical properties of the composites. The results indicate that the residual stress increases from 26.5 to 82.6 MPa in tension as the fabrication temperature of the composites rises from 1500 to 1650 °C. Moreover, the increasing tensile residual stress leads to significant variation of tensile strain, tensile strength, and fiber/matrix debonding mode of the composites. The sublayer slipping of the interphase caused by the residual stress should be responsible for the transformation of the mechanical behavior. This work can offer important guidance for residual stress adjustment in fiber-reinforced ceramic composites.

Proposal for a new monolithic constructive system using mycocomposite nucleus

“Green” materials and productive processes have progressively been searched for. In the last years, it has increased the number of researches regarding mycocomposites characterization and, above all, their applicability. Biofabrication is a process that is carried out by incubating the substrate composed of organic residues with fungal mycelium. During incubation, the fungus gradually develops on the substrate, penetrating the microscopic channels of the different residues, and acting both as a reinforcing fiber and as a binding material. This Project was designed to seek the most suitable combination between substrate components and the fungus Ganoderma sp.aiming to obtain a mycocomposite which could be used as a nucleus of an alternative monolithic constructive system. In this project, composites using the fungus Ganoderna sp. and five different types of waste (white wood sawdust, cornstarch, bark and coffee grounds, and piassava fiber) were investigated. The morphology of these components, as well as mycelium and substrate interaction, was studied by scanning electron microscopy technique. The mechanical properties were determined through bending and compression tests, being correlated with the Fourier transform infrared spectroscopy analysis. The fabrication of a mycocomposite panel was proposed as an application; it could be included as the core of the prototype of a building system of walls, structured with steel and mortar. Thus, this project aimed to contribute to the ecosystem’s quality, once the raw material used was composed of organic waste that would be reinserted in a production process instead of being discarded in nature. Besides, the project suggests the production of a new biologically-based material for civil construction.

Interfacial Adhesion of a Semi-Interpenetrating Polymer Network-Based Fiber-Reinforced Composite with a High and Low-Gradient Poly(methyl methacrylate) Resin Surface

The research aimed to determine the tensile bond strength (TBS) between polymerized intact and ground fiber-reinforced composite (FRC) surfaces. FRC prepregs (a reinforcing fiber pre-impregnated with a semi-interpenetrating polymer network (semi-IPN) resin system; everStick C&B) were divided into two groups: intact FRCs (with a highly PMMA-enriched surface) and ground FRCs (with a low PMMA gradient). Each FRC group was treated with: StickRESIN and G-Multi PRIMER. These groups were further divided into four subgroups based on the application time of the treatment agents: 0.5, 1, 2, and 5 min. Next, a resin luting cement was applied to the FRC substrates on the top of the photo-polymerized treating agent. Thereafter, weight loss, surface microhardness, and TBS were evaluated. Three-factor analysis of variance (p ≤ 0.05) revealed significant differences in the TBS among the FRC groups. The highest TBS was recorded for the intact FRC surface treated with G-Multi PRIMER for 2 min (13.0 ± 1.2 MPa). The monomers and solvents of G-Multi PRIMER showed a time-dependent relationship between treatment time and TBS. They could diffuse into the FRC surface that has a higher PMMA gradient, further resulting in a high TBS between the FRC and resin luting cement.

EFFECT OF WOLLASTONITE ON THE MECHANICAL CHARACTERISTICS OF CONCRETE

Improvement of the physical and mechanical properties of cement composites should be accompanied by the disposal of industrial waste of various generation. Therefore, the paper proposes the principles of controlling the strength properties of concrete, which consist in the complex effect of wollastonite obtained from boron production waste on the processes of structure formation of the cement matrix. When this introduced in an amount of 2-8 wt. % wollastonite has a dual function as a mineral filler and a reinforcing fiber. It has been proven that in the presence of wollastonite, the concrete mix becomes lighter without reducing its physical and mechanical properties. It was revealed that the early strength for all the developed compositions with the addition of wollastonite increases due to the acceleration of hydration processes. Calcium silicate, which is wollastonite CaSiO3, has a close chemical composition with cement clinker, especially with Ca2SiO4 belite and Ca3SiO5 alite. This leads to the formation of a chemically homogeneous and, as a result, hardened microstructure. Elongated wollastonite fibers with good adhesion to the cement stone provide effective micro-reinforcement of the concrete composite. Using the results will lead to the possibility of designing high-strength concretes, including for special structures

AN INVESTIGATION ON THE SHRINKAGE CHARACTERISTICS OF HYBRID FIBER REINFORCED CONCRETE PRODUCED BY USING FIBERS OF DIFFERENT ASPECT RATIO

In the present paper, effects of shrinkage in fiber reinforced concrete are studied.Here, in the current research work, an attempt is made to study the effects onshrinkage of concrete when five different fiber materials are used for reinforcing plainconcrete. Three configurations of each reinforcing fiber material is studied. Fiberaspect ratios of 40 and 100 and a combination of the fibers of the two aspect ratios inequal proportion (hybrid) make up the three configurations for one individual fibermaterial reinforcement. Shrinkage values are indicated in terms of total length ofcrack and the total area of the crack. On-field measurement of crack dimensions atperiodic time intervals ranging from 0 minutes to 28 days after casting of concrete hasbeen undertaken to determine the accurate values of shrinkage cracks in the fifteenscenarios i.e. five reinforcing fiber materials with three configurations each usingaspect ratio of fibers 40, 100 and the hybrid (40 +100) case. It is seen that,irrespective of the material of fiber used for reinforcing concrete, hybridized concreteconsistently shows better results relative to single aspect ratio fiber reinforcement.This research also aims to provide a bench mark for future research works onshrinkage characteristics of hybridized fiber reinforced concrete

PENGARUH PRESENTASE ALKALISASI NaOH TERHADAP KEKUATAN TARIK MATERIAL KOMPOSIT SERAT DAUN NANAS POLYESTER DENGAN METODE VACUUM INFUSION

Pineapple leaf fiber is currently widely used in furniture and handicraft industries (UKM) because besides being easily available, inexpensive, does not endanger health, can reduce environmental pollution so that later on as a composite reinforcing fiber can overcome environmental problems. From the considerations above, this study aims to determine the effect of the alkalization treatment (NaOH) on the tensile strength test of pineapple leaf fibers by vacuum infusion method and to determine the type of fracture of pineapple leaf fiber composites after tensile testing. Before it is made into a composite of pineapple leaves, it is soaked for 2 hours. Manufacture of composite materials based on ASTM D683-03 standard. From the composite tensile test results obtained the highest average tensile strength in specimens treated with NaOH 6% which is 112 MPa. While the lowest at 0% NaOH treatment is 68 MPa. Composites treated with NaOH have higher agility than those not treated with NaOH. The highest agility is found in composites with the highest NaOH treatment.