Fiber-reinforced Shells Research Articles

Convexity conditions for fiber-reinforced elastic shells

Convexity conditions of the Legendre–Hadamard and quasiconvexity type are derived in the context of a theory for fiber-reinforced shells based on Cosserat elasticity. These furnish two-dimensional shell-theoretic versions of their three-dimensional counterparts.

Influence of Sisal Fiber-Reinforced Shells for Investment Casting Using Air Fluidization Spread Technology

Influence of Sisal Fiber-Reinforced Shells for Investment Casting Using Air Fluidization Spread Technology

Investigation of load-bearing capacity of rigid-plastic reinforced ellipsoidal shells of rotation

For ellipsoidal fiber-reinforced shells of rotation, the upper (kinematic) limit of load-bearing capacity is determined. The structures are clamped along the lower support contour and have rigid polar plate. The material of the components is rigid-plastic with asymmetry in tension and compression. The matrix is orthotropic. The principal axes of matrix anisotropy coincide with meridional, circumferential and transverse directions. Two-layer shell model and refined relations of structural model with two-dimensional stress state in components are used. Extreme problem is formulated and numerically solved for spherical and two different ellipsoidal shells. Influence of reinforcement parameters on limit load is investigated.

Preparation of steel fiber-reinforced shells for investment casting using ultrasonic-assisted dispersion

In this work, steel fibers were added into a silica sol binder to prepare shells for investment casting. The green strength, high-temperature self-load deformation, heat transfer, and fiber dispersion in the shell were investigated. The effect of ultrasonic power on fiber dispersion in the shell and the silica sol was studied and discussed. The results suggest that, with a fiber addition amount of 0.15%, an ultrasonic power level of 1200 W can completely disperse the fibers in silica sol. It has been found that the reinforcement effect is the best when the fiber addition amount is 0.15%. When the ultrasonic power level was 1200 W, the strength reached the maximum value of 3.29 MPa, which was 0.74 MPa higher than that without ultrasonic agitation (2.55 MPa). Under ultrasonic agitation, the fibers were in monofilament state and well-bonded with the shell. Steel fibers have good thermal stability at high temperature and still exists in the shell; thus, they can support the shell and prevent its deformation. Under an ultrasonic power level of 1200 W and fiber addition amount of 0.15%, the high-temperature self-load deformation of the shell was 0.44%. It is concluded that, the more uniform the dispersion of the fibers, the better the heat dissipation performance of the shell.

Influence of rice husk on the properties of fiber-reinforced silicon sol shells used in investment casting process

Herein, short carbon fibers were incorporated in silica sol slurry to enhance the strength of silica sol shell for investment casting. The content of carbon fibers, with a length of 3.0 mm and diameter of 7.32 µm, was varied from 0 to 1 wt. % of the refractory powder mass. The influence of fiber content on rheological properties was systematically investigated. The results showed that the apparent viscosities of slurry with different amounts of fibers decreased with increasing shear rate. The apparent viscosity of as-prepared slurry increased with increasing fiber content and a maximum value of 149.25 × 10−3 Pa·s was attained at the fiber content of 0.4 wt. %, which corresponded to an increase of 22.6%. The high shear viscosity of the slurry initially increased with the increase in carbon fiber content, followed by a gradual decrease. Similarly, thixotropic loop area of the as-prepared slurry, with 0.4 wt. % carbon fibers, exhibited maximum value of 239.41 Pa·s −1, corresponding to an increase of 265%. Moreover, when the fiber content exceeded 0.6%, the gas permeability was significantly increased, which can be attributed to the high fiber content, the occurrence of agglomeration and clustering. To improve the permeability and reduce the residual strength of the shell, rice husk was added in the back slurry. The rice husk modified fiber-reinforced shell exhibited higher green strength and lower residual strength. When the content of rice husk was 1.0%, the residual strength decreased by 29.10%. The porosity and permeability of shell after roasting has improved.

Properties of core-half wrapped shell structure wood-polymer composites containing glass fiber-reinforced shells

Glass fiber (GF) is commonly applied as a filler in the preparation of polymer composites. Due to the presence of GF, composite mechanical performance, flame resistance, and thermal performance could be greatly improved. The influence of a GF-filled polymer shell layer was investigated relative to the morphology, mechanical, thermal, and fire flammability performance of the core-half wrapped shell structured wood high-density polyethylene (HDPE) composites prepared via co-extrusion. The use of the relatively less-stiff pure HDPE with high linear coefficients of thermal expansion (LCTEs) lowered the general thermal stability and modulus of the wood polymer composites (WPCs). Flexural and thermal expansion properties were improved for the GF-filled HDPE shells in comparison to the unmodified material, enabling a well-balanced performance of this novel core–shell material. Implementation of GF-modified HDPE or unmodified HDPE layers as a shell for WPC core remarkably improved the impact resistance of the co-extruded WPCs. In comparison with composites possessing unmodified HDPE shell, the flame resistance performance of the shell layer was slightly improved in case that the GF content was below 25 wt%. A slight decrease in composite general heat release and rate was discovered in case that the GF content was greater than 25 wt%.

Study on the Strength of Short Carbon Fiber-Reinforced Silicon Sol Shells for the Investment Casting Process

Short carbon fibers are used to improve the performance of investment casting shells by mixing short-cut carbon fibers with the silica sol slurries. The influence of fiber length and content on the flexural strength and deformation under weight of fiber-reinforced shells at elevated and normal temperatures and after firing was investigated. The fractures of the shells were observed by SEM. When the carbon fiber content increased from 0.2 to 1%, the bending strength of the shell at room temperature increased significantly compared to the specimens without fibers. The Green strength of the shell reached up to 3.180 MPa, for a carbon fiber content of 0.6% and a length of 4 mm, which was 38.5% higher than that of the specimen without fibers. When the fiber content was 1%, the flexural strength of the specimen at normal temperature was 22.45% higher than that of the unreinforced specimens, and the deformation underweight at elevated temperature was reduced about 14.32%. The strength of the composite shell was increased by 24.22% after roasting after the carbon fiber reinforcing. The SEM observation and analysis revealed that the failure of the fiber-reinforced silica sol shell has a strong influence on the tensile fracture and debonding of the carbon fibers.

Effect of Firing Temperature and Time on Hybrid Fiber-Reinforced Shell for Investment Casting

Glass fiber combined with aluminum silicate fiber was mixed into the slurry for preparing fiber-reinforced shell. The fired bending strength, the self-load deformation at elevated temperature and the permeability of hybrid fiber-reinforced shells were investigated. Combining with the fracture morphology of reinforced shell by SEM, the properties of hybrid fiber-reinforced shell were investigated. The results show that the fired bending strength of shell first increases and then decreases with variation of the firing temperature from 900 to 1000 °C and reaches the maximum of 4.12 MPa with firing temperature of 950 °C. Comparison of firing time, the maximum fired bending strength was obtained when firing time was 120 min. The self-loaded deformation at elevated temperature decreases with 0.5 wt% fiber addition. The permeability increases with fiber reinforcement. It is found by SEM that the bending load was borne by deformation and fracture of aluminum silicate fiber, and the glass fiber melt transformed into globular fiber due to the heat deformation at high temperatures which would decrease the strength.

Interaction between buckling modes of imperfect cylindrical composite shells

The problem of the postbuckling behavior and sensitivity to initial geometrical imperfections of multilayered composite cylindrical shells is solved with allowance for the interaction of different buckling modes. The solution is based on the Byskov-Hutchinson asymptotic method and nonlinear equations of a Timoshenko-type shell theory. Boroaluminum, boron fiber-reinforced plastic, and glass fiber-reinforced plastic shells with imperfections in the form of five superimposed modes of similar structure and geometry are investigated. Snapping loads with and without the interaction of buckling modes are calculated and compared. The evolution of the mode amplitudes in the prebuckling and postbuckling states and their ratio at the limit point is demonstrated. 13 refs., 3 figs., 1 tab.

Association of acoustic emission with the plastic deformation of a metal

G. S. Pisarenko, A. A. Shemegan, and O. E. Boginich, "Analysis of energy dissipation in transverse oscillations of metallic specimens with damping coatings," Probl. Prochn., No. 12, 55-59 (1971). S. V. Nikolaevskii, G. M. Gunyaev, A. F. Rumyantsev, et al., "Experimental examination of energy dissipation in rods of materials reinforced with polymer composites," Probl. Prochn., No. 4, 100-104 (1980). O. G. Tsyplakov, Fundamentals of the Formation of Glass Fiber-Reinforced Plastic Shells [in Russian], Mashinostrenie, Mcscow (1968). V. V. Matveev and A. P. Yakovlev, "A method of determining energy dissipation in oscillations," Inventor's Certificate No. 377672, Byull. Izobret., No. 18 (1973). M. K. Sidorenko, Vibrometry of Gas Turbine Engines [in Russian], ~shinostroenie, Moscow (1973).

Plastic Analysis of Fiber-Reinforced Shells of Revolution

The yield surface for a shell of revolution which is loaded axisymmetrically and made of an anisotropic plastic material which obeys the maximum shear stress theory of Lance and Robinson is developed in this paper. The material is a model of a ductile matrix reinforced unidirectionally with ductile fibers. The principal axes of the material are assumed to be aligned with the principal axes of stress in the shell. Using the developed yield surface, the complete solution for the problem of plastic analysis of a shallow conical shell with circumferential reinforcement loaded by an axismmetric lateral force applied to a rigid central boss is obtained.

Vibration of fiber-reinforced spherical shells

The extensional vibrations of different fiber-reinforced spherical shells in vacuo were studied. The shells' materials are made of filament wound fiberglass in epoxy. The equivalent elastic orthotropic compliance constants are evaluated and as a result the natural frequencies and corresponding mode shapes are obtained by a closed form solution as well as by an infinite series approximation.

Elastic properties of fiber-reinforced shells.

The applicability of classical laminated thin-shell theory to the calculation of elastic coefficients of fiber-reinforced shells is demonstrated. It is assumed that currently available techniques can be used to calculate the elastic coefficients of a unidirectional layer in terms of fiber and matrix elastic constants and volume percent of fiber content. The unidirectional system is then treated as being homogeneous and anisotropic. Considering a multidirectional composite as being constructed of unidirectional layers having specified directions of fiber orientation allows laminated thin-shell theory to be applied to the determination of gross elastic properties of the material. The results of this approach often differ drastically from results obtained by treating reinforced shells as simply being homogeneous and anisotropic. This difference is emphasized through use of numerical examples and experimental data. In particular, it is shown that the modulus of elasticity in bending and the modulus of elasticity under plane deformations can be quite different. The magnitude of this difference is shown to be a function of unidirectional properties, order of stacking of the individual layers, and number of layers.