Thermal Residual Stress in a Two-Dimensional In-Plane Misoriented Short Fiber Composite

1990 ◽  
Vol 43 (5S) ◽  
pp. S294-S303 ◽  
Author(s):  
M. Taya ◽  
M. Dunn ◽  
B. Derby ◽  
J. Walker
Keyword(s):  
Residual Stress ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Fiber Composite ◽  
Short Fiber ◽  
Two Dimensional ◽  
Fiber Distribution ◽  
Fiber Volume ◽  
Distribution Type ◽  
Short Fiber Composite

Residual stress induced in a misoriented short fiber composite due to thermal expansion mismatch between the matrix and fiber is investigated. The case of two-dimensional in-plane fiber misorientation is considered. The elastic model that is developed is based on Eshelby’s equivalent inclusion method and is unique in that it accounts for interactions among fibers at different orientations. A parametric study is performed to demonstrate the effects of fiber volume fraction, fiber aspect ratio, fiber distribution cut-off angle, and fiber distribution type on thermal residual stress. Fiber volume fraction and aspect ratio are shown to have more significant effects on the magnitude of the thermal residual stresses than the fiber distribution type and cut-off angle.

Monitoring of mechanical properties of prestressed glass fiber epoxy composites over 12 months after fabrication

2021 ◽  
pp. 002199832110047
Author(s):  
Mahmoud Mohamed ◽  
Siddhartha Brahma ◽  
Haibin Ning ◽  
Selvum Pillay
Keyword(s):  
Mechanical Properties ◽  
Residual Stress ◽  
Flexural Strength ◽  
Compressive Residual Stress ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Epoxy Composites ◽  
Flexural Properties ◽  
Initial Increase ◽  
Fiber Volume

Fiber prestressing during matrix curing can significantly improve the mechanical properties of fiber-reinforced polymer composites. One primary reason behind this improvement is the generated compressive residual stress within the cured matrix, which impedes cracks initiation and propagation. However, the prestressing force might diminish progressively with time due to the creep of the compressed matrix and the relaxation of the tensioned fiber. As a result, the initial compressive residual stress and the acquired improvement in mechanical properties are prone to decline over time. Therefore, it is necessary to evaluate the mechanical properties of the prestressed composites as time proceeds. This study monitors the change in the tensile and flexural properties of unidirectional prestressed glass fiber reinforced epoxy composites over a period of 12 months after manufacturing. The composites were prepared using three different fiber volume fractions 25%, 30%, and 40%. The results of mechanical testing showed that the prestressed composites acquired an initial increase up to 29% in the tensile properties and up to 32% in the flexural properties compared to the non-prestressed counterparts. Throughout the 12 months of study, the initial increase in both tensile and flexural strength showed a progressive reduction. The loss ratio of the initial increase was observed to be inversely proportional to the fiber volume fraction. For the prestressed composites fabricated with 25%, 30%, and 40% fiber volume fraction, the initial increase in tensile and flexural strength dropped by 29%, 25%, and 17%, respectively and by 34%, 26%, and 21%, respectively at the end of the study. Approximately 50% of the total loss took place over the first month after the manufacture, while after the sixth month, the reduction in mechanical properties became insignificant. Tensile modulus started to show a very slight reduction after the fourth/sixth month, while the flexural modulus reduction was observed from the beginning. Although the prestressed composites displayed time-dependent losses, their long-term mechanical properties still outperformed the non-prestressed counterparts.

Determination of the Directional Dependent In-Plane Thermal Conductivity of K63B12 Pitch-Fiber/Epoxy Composite

2004 ◽  
Author(s):  
Jessica N. McClay ◽  
Peter Joyce ◽  
Andrew N. Smith
Keyword(s):  
Thermal Conductivity ◽  
Thermal Management ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Epoxy Composite ◽  
Fiber Composite ◽  
Fiber Volume ◽  
State Technique ◽  
Fiber Composite Materials

Measurements of the in-plane thermal conductivity and the directional dependence of Mitsubishi K63B12 pitch-fiber/Epoxy composite from Newport Composites are reported. This composite is being explored for use in the Avanced Seal Delivery System for effective thermal management. The thermal conductivity was measured using a steady state technique. The experimental results were then compared to a model of the thermal conductivity based on the direction of the fibers. These estimates are based on the properties of the constituent materials and volume of fibers in the sample. Therefore the density and the fiber volume fraction were experimentally measured. The thermal conductivity is clearly greatest in the direction of the fibers and decreases as the fibers are rotated off axis. In the case of pitch fiber composite materials, the contribution of the fibers to the thermal conductivity dominates. The experimental data clearly followed the correct trends; however, the measured values were 25% to 35% lower than predicted.

Fracture behavior of short-fiber reinforced materials

1992 ◽  
Vol 7 (11) ◽  
pp. 3120-3131 ◽  
Author(s):  
Michael Murat ◽  
Micha Anholt ◽  
H. Daniel Wagner
Keyword(s):  
Fracture Process ◽  
Fracture Behavior ◽  
Volume Fraction ◽  
Fiber Composite ◽  
Finite Size ◽  
Critical Length ◽  
Short Fiber ◽  
Fiber Volume ◽  
Linear Elastic ◽  
Fiber Reinforced Materials

A discrete model of springs with bond-bending forces is proposed to simulate the fracture process in a composite of short stiff fibers in a softer matrix. Both components are assumed to be linear elastic up to failure. We find that the critical fiber length of a single fiber composite increases roughly linearly with the ratio of the fiber elastic modulus to matrix modulus. The finite size of the lattice in the direction perpendicular to the fiber orientation considerably alters the behavior of the critical length for large values of the modulus ratio. The simulations of the fracture process reveal different fracture behavior as a function of the fiber content and length. We calculate the Young's modulus, fracture stress, and the strain at maximum stress as a function of the fiber volume fraction and aspect ratio. The results are compared with the predictions of other theoretical studies and experiments.

Can the Strength of Brittle Materials be Enhanced?

1992 ◽  
Vol 291 ◽  
Author(s):  
L. Monette ◽  
M. P. Anderson ◽  
G. S. Grest
Keyword(s):  
Computer Model ◽  
Random Distribution ◽  
Load Transfer ◽  
Volume Fraction ◽  
Fiber Composites ◽  
Short Fiber ◽  
Particulate Composites ◽  
Second Phase ◽  
Two Dimensional ◽  
Fiber Volume

ABSTRACTWe have employed a two-dimensional computer model to study the effect of volume fraction of second phase constituents on load transfer (stiffness) and strength in brittle short-fiber composites, i.e. composites containing a random distribution of aligned fibers, and brittle particulate composites. We find that the efficiency of load transfer to the second phase consituent increases with volume fraction in particulate composites, while it decreases for short-fiber composites. The strength of brittle particulate composites is found to decrease, while the strength of brittle short-fiber composites marginally increases only at fiber volume fractions equal or greater than 0.25.

Effect of Fiber Volume Fraction on High Temperature Creep of Al2O3-SiO2(sf)/AZ91D Composite

2011 ◽  
Vol 474-476 ◽  
pp. 548-552
Author(s):  
Jun Tian
Keyword(s):  
Creep Resistance ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Matrix Alloy ◽  
Short Fiber ◽  
Tensile Creep ◽  
Short Fibers ◽  
Creep Tests ◽  
Fiber Volume ◽  
The Matrix

Constant stress tensile creep tests were conducted on AZ91D–20 vol.%, 25 vol.%, and 30 vol.% Al2O3-SiO2short fiber composites and on an unreinforced AZ91D matrix alloy. The creep resistance of the reinforced materials is shown to be considerably improved compared with the matrix alloy. With the increasing volume fraction of short fibers, the creep resistance of AZ91D composites is improved, and their creep threshold stresses are also increased accordingly. Because of the increasing volume fraction of short fibers, loads of bearing and transmission of short fibers will increase, and thus the creep resistance of AZ91D composites further improves, but the precipitation of β-Mg17Al12precipitate increases in the number, it is easy to soften coarse, so that threshold stress of AZ91D composite does not increase greatly.

A New Theory for the Debonding of Discontinuous Fibers in an Elastic Matrix

1989 ◽  
Vol 170 ◽  
Author(s):  
Christopher K. Y. Leung ◽  
Victor C. Li
Keyword(s):  
Fiber Length ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Interfacial Strength ◽  
Fiber Composites ◽  
Short Fiber ◽  
Fiber Volume ◽  
Physical Reason ◽  
Pull Out

AbstractThe mechanical properties of fiber composites are strongly influenced by the debonding of fibers. When an embedded fiber is loaded from one end, debonding can occur at both the loaded end and the embedded end. Existing theories neglect the possibility of debonding from the embedded end and are thus limited in applications to cases with low fiber volume fraction, low fiber modulus, high interfacial strength/interfacial friction ratio or short fiber length. A new twoway fiber debonding theory, which can extend the validity of one-way debonding theories to all general cases, has recently been developed. In this paper, the physical reason for the occurrence of two-way debonding is discussed. The limit of validity for one-way debonding theories is considered. One-way and two-way debonding theories are then compared with respect to the prediction of composite behaviour. The determination of interfacial parameters from the fiber pull-out test will also be described.

Development of a Constitutive Theory for Short Fiber Yarns: Mechanics of Staple Yarn Without Slippage Effect

1992 ◽  
Vol 62 (12) ◽  
pp. 749-765 ◽  
Author(s):  
Ning Pan
Keyword(s):  
Fiber Length ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Stress Transfer ◽  
Transversely Isotropic ◽  
Short Fiber ◽  
Constitutive Theory ◽  
Fiber Volume ◽  
Shear Moduli ◽  
Yarn Twist

This article reports an attempt to develop a general constitutive theory governing the mechanical behavior of twisted short fiber structures, starting with a high twist case, so that the effect of fiber slippage during yarn extension can be ignored. A differential equation describing the stress transfer mechanism in a staple yarn is proposed by which both the distributions of fiber tension and lateral pressure along a fiber length during yarn extension are derived. Factors such as fiber dimensions and properties and the effect of the discontinuity of fiber length within the structure are all included in the theory. With certain assumptions, the relationship between the mean fiber-volume fraction and the twist level of the yarn is also established. A quantity called the cohesion factor is defined based on yarn twist and fiber properties as well as on the form of fiber arrangement in the yarn to reflect the effectiveness of fiber gripping by the yarn. By considering the yarn structure as transversely isotropic with a variable fiber-volume fraction depending on the level of twist, the tensile and shear moduli as well as the Poisson's ratios of the structures are theoretically determined. All these predicted results have been verified according to the constitutive restraints of the continuum mechanics, and the final results are also illustrated schematically.

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