The effect of water on the fracture surface energy of fiber-reinforced composite materials

The effect of absorbed water on the fracture surface energy of both glass and graphite fiber unidirectional epoxy composites has been studied. The fracture energy parallel to the fiber direction was measured by the double torsion technique. Water was absorbed at 70°C while the sample was subject to an external tensile stress both parallel and perpendicular to the fiber direction. No degradation of fracture surface energy was measured for specimens stressed and immersed in water at 70°C for up to 1000 h. The fracture surface energy for the glass composite was greater than for the graphite composite, which was attributed to fiber pull-out in the case of the glass composite.     

Pull-off strength of thermoplastic fiber-reinforced composite coatings

The paper aims at presenting the results of pull-off strength tests of fiber-reinforced polymer composite coatings laminated on steel substrates. It contains the measured data on the thickness of manufactured coatings and the substrate surface’s roughness, according to the various methods of surface’s preparation with the means of abrasive blasting. The microstructure analysis of material’s cross-sections and damage analysis of samples after failure were also performed. The highest pull-off strength’s values for composite coatings were obtained for joints with the substrate modified by abrasive blasting with corundum F60 or simply degreased. To establish the compatibility of substrates with coatings the wettability of the chosen materials was tested and work of adhesion was calculated on its base. Concerning the wettability, it was found that the most preferable joints were characterized by the similar thermodynamic work of adhesion and consisted of the coating’s matrix (SBS) and the steel substrate degreased with acetone or modified with corrundum abrasive blasting and then degreased.     

A general strength theory for orthotropic fiber-reinforced composite laminae

Thin, orthotropic fiber-reinforced composite laminae under plane stress loading conditions are considered. The essential conditions that must be satisfied in developing phenomenological strength criteria for such materials are first established. A new, parametric failure criterion is then presented. It is shown that this entirely general formulation encompasses all previously proposed failure theories (e.g., tensor polynomial criterion) for orthotropic laminae. Examples of application and the inherent advantages and drawbacks of the proposed parametric approach are discussed. In the past, the formulation of strength criteria for composite materials has closely paralleled the development of yield criteria in metal plasticity. The parametric approach advocated here for the failure of composite materials was inspired by a general formulation proposed by Budiansky (1) for the plastic yielding of sheet metals.     

Flex life and long-term strength of composite materials

The relationship is shown between the flex life and long-termtensile strength of flexible composite material. The long-term strength is interpreted in terms of a kinetic theory of failure. However, it is not posible to predict the flex life from tensile strength or even long-term strength data unless the stiffness or modulus is considered along with the thickness of the sample. With these factors it becomes possible to predict the flex life of a material and to compare various flex-testing instruments utilizing a new concept, which material and to compare various flex-testing instruments utilizing a new concept, which we call “effective force.” The usefulness of the concept of effective force is explained.     

Adhesive strength of glass composite materials in the contact region

Translated from Steklo i Keramika, No. 6, pp. 12–14, June, 1992.     

Effect of laser etching on the fracture strength of the monolithic zirconia and fiber-reinforced composite inlay-retained fixed partial dentures

Aim: The aim of this study was to evaluate the fracture strength of monolithic zirconia and fiber-reinforced composite (FRC) inlay-retained FPDs, both of which are cemented to the laser-etched cavity surfaces.

Materials and Methods: Eighty freshly extracted sound human teeth were used. A premolar and a molar tooth were embedded in an autopolymerizing acrylic resin. Forty acrylic resin models were randomly divided into two groups including monolithic zirconia and FRC inlay-retained FPDs (n = 20). Then, these groups were divided into two subgroups according to conditioning of the cavity surfaces with or without Er:YAG laser etching. Monolithic zirconia inlay-retained FPDs were produced by an inLab MC XL milling device using monolithic zirconia blocks. Tescera? Fiber Reinforcement Materials were used for the FRC inlay-retained FPDs. After 10.000 thermal cycles, fracture strength test was applied to the specimens.

Results: The monolithic zirconia inlay-retained FPDs exhibited the highest fracture strength than the FRC inlay-retained FPDs. Fracture strength was increased with laser etching for both restorative materials (p < 0.05).

Conclusion: Laser etching had positively effect on the fracture strength of the inlay-retained FDPs.     

The effect of steam treatment on bonding strength of impregnated wood materials

In wood materials, the species of wood, its humidity, and the type of the adhesive have an important role to make the wood material durable for a long period both in inner space and outer space. In this study, it is aimed to determine the resistance characteristics of adhesive using different impregnation chemicals and different types of adhesives before and after steam treatment. In this study, beech and poplar as wood materials; mixture of Protim-WR 235, Tanalith-C, and Celcure-AC 500 as impregnation materials; and poly vinyl acetate (PVAc), urea formaldehyde (UF), and desmodur vinyl trie ketonol acetate (D-VTKA), resistant to water, as adhesives materials were used. All samples were kept in a steaming equipment for 2, 6, 12, 24, 48, and 96?h, afterwards the maximum force of the samples were measured for each waiting period, and then their bonding strength was determined. According to the results of the study, beech control samples had higher strength than poplar control samples. Control samples bonded with D-VTKA is the least affected one compared to all original control samples in the steam test. D-VTKA can be offered as the proper adhesive for humid places. The results also showed that Tanalith-C is the least affecting impregnation material on the bonding strength.     

Rheology of fiber-reinforced cementitious materials

An improved understanding of the influence of fibers on the rheology of cementitious systems is needed so that fiber reinforcement can be used effectively. However, conventional rheometers are not suitable for testing stiff fiber-reinforced materials. In this study, a parallel plate rheometer that is capable of evaluating the rheology of stiff fiber-reinforced cement paste and mortar systems was designed and built. The governing equations for the rheometer were derived and experimental procedures were developed that yielded reproducible results. A comparative analysis of the custom-built parallel plate rheometer, a commercial rheometer and the values reported in the literature, indicated that the measurements obtained using the rheometer were reasonable. The rheometer was then used to evaluate the rheology of a variety of cement paste systems, including stiff steel fiber-reinforced cement pastes.     

The effect of fiber-matrix adhesion on the fatigue fracture of glass-fiber-reinforced poly(vinyl chloride)

Fatigue crack propagation (FCP) of injection-molded glass-fiber-reinforced poly(vinyl chloride) was examined as a function of fiber-matrix adhesion (coupling) and fiber content at different load levels. Considering the entire FCP history, from crack initiation to critical propagation, it is shown that fatigue lifetime and fracture toughness of coupled composites increase with fiber weight fraction. Uncoupled material exhibits the highest fracture toughness at 10 wt% fiber, yet its fatigue life is considerably shorter. Damage analysis indicates that fiber debonding, pullout, and particularly fiber fracture seem to contribute to the higher fatigue lifetime noted in coupled composites. The Crack Layer Theory is employed to describe the observed FCP behavior. The effective enthalpy of damage parameterizes the resistance of the composite to FCP in terms of the observed mechanisms.     

The influence of silane coupling agent composition on the surface characterization of fiber and on fiber-matrix interfacial shear strength

It is well known that the fiber-matrix interface in many composites has a profound influence on composite performance. The objective of this study is to understand the influence of composition and concentration of coupling agent on interface strength by coating E-glass fibers with solutions containing a mixture of hydrolyzed propyl trimethoxysilane (PTMS) and n -aminopropyl trimethoxysilane (APS). The failure behavior and strength of the fiber-matrix interface were assessed by the single-fiber fragmentation test (SFFT), while the structure of silane coupling agent was studied in terms of its thickness by ellipsometry, its morphology by atomic force microscopy, its chemical composition by diffuse reflectance infrared Fourier transform (DRIFT), and its wettability by contact angle measurement. Deposition of 4.5 ‐ 10 m 3 mol/L solution of coupling agent in water resulted in a heterogeneous surface with irregular morphology. The SFFT results suggest that the amount of adhesion between the glass fiber and epoxy is dependent not only on the type of coupling agent but also on the composition of the coupling agent mixture. As the concentration of APS in the mixture increased, the extent of interfacial bonding between the fiber and matrix increased and the mode of failure changed. For the APS coated glass epoxy system, matrix cracks were formed perpendicular to the fiber axis in addition to a sheath of debonded interface region along the fiber axis.     

The influence of the degree of stress anisotropy during consolidation on the strength of cohesive powdered materials

The strength of an assembly of cohesive particles generally depends upon the magnitude of the preceding load, i.e. the consolidation load. One may further expect different effects from an isotropic versus an anisotropic stress distribution during consolidation. Molerus has presented a theoretical model that incorporates this effect of stress anisotropy during consolidation, but its validity has not yet been proved.The present paper contains experimental data on this subject, obtained from measurements with a triaxial cell. The influence of the degree of stress anisotropy during consolidation is shown to be considerable. The model of Molerus further appears to fail in predicting this influence, the possible reasons of which are indicated in an extensive discussion.     

Environmental effect on stress relaxation in polyester-fiberglass composite

Environmental behavior of reinforced polyester was studied by stress relaxation. Relaxation failure of polyester matrix and fiberglass degradation appear dramatically at short time after exposure to acid and alkali electrolytes. The relaxation spectrum is thus influenced by environmental action. Indeed, the stress relaxation modulus is a sensitive characterization of environmental effects.     

Surface modification of boron fibres for improved strength in composite materials

When boron fibres are combined with an organic matrix, such as an epoxy resin, a high-performance composite structure is created. This study investigates the surface chemistry of plasma- and organosilane-treated boron fibres with the key aim to improving the adhesion properties between the boron fibre and the epoxy matrix. Optimisation of this interfacial region plays a critical role in influencing the mechanical behaviour of composite materials and has considerable industrial applications in the aerospace and manufacturing industries. The surface chemistry of a model boron surface and boron fibres was monitored using a combination of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Initial investigation of the as-received fibres showed the presence of silicone contamination on the fibre surface, which would affect adhesion. Removal of this contaminant through solvent cleaning and plasma oxidation provided an ideal surface for attachment of the organosilane adhesion promoter. A model for the interaction of the organosilane with a boron surface is proposed. The pull-out strength of boron fibres, with different surface treatments, embedded in the epoxy resin was measured using a custom designed adhesiometer. Compared with as-received boron fibres, a 6-fold improvement in the apparent interfacial shear strength was achieved for the organosilane treated fibres. Optical microscopy was used to determine the failure mechanisms between the fibre and epoxy resin. Typically, as the surface treatment improved adhesion, the locus of failure changed from the boron–epoxy interface to failure within the epoxy and ultimately fibre breakage.     

Bond strength of fiber posts and short fiber-reinforced composite to root canal dentin following cyclic loading*

The aim of this study was to evaluate the effect of cyclic loading on the bond strength of fiber posts and short fiber-reinforced composite (FRC) to root canal. One hundred single-rooted teeth were divided into two groups according to the material used for luting fiber posts: (1) Resin-core material (Gradia Core, GC Corp.) and (2) Short FRC (EverX Posterior, GC Corp.). Then the specimens were randomly assigned into three sub-groups according to the post material and the groups are indicated as follows: (1) Short FRC (EverX Posterior) used instead of post and core, (2) Fiber post (GC post, GC Corp.) cemented with resin-core (Gradia Core), (3) Fiber post (GC post, GC Corp.) cemented with short FRC (EverX Posterior), (4) Experimental fiber post cemented with resin-core (Gradia Core, GC Corp), (5) Experimental fiber post cemented with short FRC (EverX Posterior). Then the specimens were subdivided into a further two groups in accordance with the storage condition (cyclic loading and 24 h water storage-control group) (n = 10/per group). The micropush-out bond strength between root dentin and posts was measured. Data were analyzed using three-way ANOVA and Tukey HSD tests (α = 0.05). Micropush-out bond strength of the posts to dentin was significantly affected by the type of post material (p < 0.05). However, the load cycling and the resin-based luting agent used had no effect on bond strength values (p = 0.706 and p = 0.346, respectively).     

掺合料对磷石膏基复合胶凝材料耐水性及强度的影响综述

磷石膏中含有的可溶性磷、氟等杂质使其在建筑行业利用率较低。而且磷石膏材料耐水性较差,需要复配其他水硬性掺合料来提高其耐水性,不同地区的磷石膏因其理化性质不同,其复合胶凝材料的力学性能也存在一定的差异。针对上述问题,介绍了主要的磷石膏基复合胶凝材料类型,分析了粉煤灰、矿渣、生石灰、水泥对不同磷石膏基复合胶凝材料耐水性及强度的影响,阐明其影响规律,确定了粉煤灰、矿渣、生石灰、水泥在磷石膏基复合胶凝材料中的建议掺量区间。     

The effect of sizing on composite properties for materials used in the shuttle filament wound case

An epoxy resin and a sized carbon fiber have been used to produce a light-weight filament wound case for the Space Shuttle. The sizing facilitates fiber handling during winding but may affect the amount of resin absorbed by the fiber during impregnation and the final mechanical properties of the composite. Naval Ordnance Lab rings were wound to study the effect of the sizing content on the resin absorption by the fiber bundles, the final tensile properties of the composite, and the type of failure observed at burst. The resin content of the rings studied was between 20 to 40 percent, and the sizing content, 0 to 1.6 percent by weight. Results showed that the sizing content was a critical parameter which determined the amount of resin absorbed by the fibers. The final tensile strength was dependent on the amount of sizing present. The tensile strength decreased by as much, as 60 percent when a low resin and high sizing content were present. The type of failure at burst was a function of resin content rather than size content.