Recent Advances in Morphology and Mechanical Properties of Rigid-Rod Molecular Composites

1989 ◽  
Vol 171 ◽  
Author(s):  
Stephen J. Krause ◽  
Wen-Fang Hwang
Keyword(s):  
Mechanical Properties ◽  
High Performance ◽  
Low Voltage ◽  
Orientation Distribution ◽  
Short Fiber ◽  
Chain Polymer ◽  
Structural Applications ◽  
Molecular Composites ◽  
Rigid Rod ◽  
Aromatic Heterocyclic

ABSTRACTRigid-rod molecular composites are a new class of high performance structural polymers which have high specific strength and modulus and also high thermal and environmental resistance. The concept of using a rigid-rod, extended chain polymer to reinforce a ductile polymer matrix at the molecular level has been demonstrated with morphological and mechanical property studies for aromatic heterocyclic systems, but new materials systems and processing techniques will be required to produce thermoplastic or thermoset molecular composites. Improved characterization and modeling will also be required. In this regard, new results on modeling of mechanical properties of molecular composites are presented and compared with experimental results. The Halpin-Tsai equations from ‘shear-lag’ theory of short fiber composites predict properties reasonably well when using the theoretical modulus of rigid-rod molecules in aromatic heterocyclic systems, but newer matrix systems will require consideration of matrix stiffness, desired rod aspect ratio, and rod orientation distribution. Application of traditional and newer morphological characterization techniques are discussed. The newer techniques include: Raman light scattering, high resolution and low voltage SEM, parallel EELS in TEM, synchrotron radiation in X-ray scattering, and ultrasound for integrity studies. The properties of molecular composites and macroscopic composites are compared and it is found that excellent potential exists for use of molecular composites in structural applications including engineering plastics, composite matrix resins, and as direct substitutes for fiber reinforced composites.

Morphology of Rigid-Rod Molecular Composites: An Overview

1988 ◽  
Vol 134 ◽  
Author(s):  
Stephen J. Krause
Keyword(s):  
Mechanical Properties ◽  
High Performance ◽  
Morphological Characterization ◽  
High Ratio ◽  
Structure Property ◽  
Chain Polymer ◽  
Specific Strength ◽  
Composite Systems ◽  
Molecular Composites ◽  
Rigid Rod

ABSTRACTRigid-rod molecular composites are a new class of high performance structural polymers which have high specific strength and modulus and also high thermal and environmental resistance. A rigid-rod, extended chain polymer component is used to reinforce a matrix of a ductile polymer with the intent of achieving a “composite” on the molecular level. After synthesis, the key to producing a molecular composite is to control morphology to disperse the reinforcing rod molecules as finely as possible in the matrix polymer. Individual rod molecules or bundles of molecular rods must have dimensions which result in a high ratio of length to width (aspect ratio) for efficient reinforcement. To achieve this, the reinforcing rod component must not phase separate at any stage of processing. Morphological characterization techniques, which can measure the orientation and dispersion (or, conversely, the degree of phase separation) of rod molecules provide the tools for correlating theoretically predicted and experimentally observed mechanical properties. Various morphological techniques which have been applied to molecular composite systems will be reviewed, including wide angle x-ray scattering and scanning and transmission electron microscopy. Structure-property correlations for molecular composite systems will be discussed with regard to models for mechanical properties. Application of new morphological techniques will also be discussed.

Morphology of High-Performance Rigid-Rod Polymer Fibers and Molecular Composites

1989 ◽  
Vol 47 ◽  
pp. 338-339
Author(s):  
W.W. Adams ◽  
S. J. Krause
Keyword(s):  
Tensile Strength ◽  
High Performance ◽  
Liquid Crystalline ◽  
Molecular Level ◽  
Synergistic Effects ◽  
Tensile Modulus ◽  
Commercial Development ◽  
The Matrix ◽  
Molecular Composites ◽  
Rigid Rod

Rigid-rod polymers such as PBO, poly(paraphenylene benzobisoxazole), Figure 1a, are now in commercial development for use as high-performance fibers and for reinforcement at the molecular level in molecular composites. Spinning of liquid crystalline polyphosphoric acid solutions of PBO, followed by washing, drying, and tension heat treatment produces fibers which have the following properties: density of 1.59 g/cm3; tensile strength of 820 kpsi; tensile modulus of 52 Mpsi; compressive strength of 50 kpsi; they are electrically insulating; they do not absorb moisture; and they are insensitive to radiation, including ultraviolet. Since the chain modulus of PBO is estimated to be 730 GPa, the high stiffness also affords the opportunity to reinforce a flexible coil polymer at the molecular level, in analogy to a chopped fiber reinforced composite. The objectives of the molecular composite concept are to eliminate the thermal expansion coefficient mismatch between the fiber and the matrix, as occurs in conventional composites, to eliminate the interface between the fiber and the matrix, and, hopefully, to obtain synergistic effects from the exceptional stiffness of the rigid-rod molecule. These expectations have been confirmed in the case of blending rigid-rod PBZT, poly(paraphenylene benzobisthiazole), Figure 1b, with stiff-chain ABPBI, poly 2,5(6) benzimidazole, Fig. 1c A film with 30% PBZT/70% ABPBI had tensile strength 190 kpsi and tensile modulus of 13 Mpsi when solution spun from a 3% methane sulfonic acid solution into a film. The modulus, as predicted by rule of mixtures, for a film with this composition and with planar isotropic orientation, should be 16 Mpsi. The experimental value is 80% of the theoretical value indicating that the concept of a molecular composite is valid.

scholarly journals Numerical Simulation of the Fracture Behaviour of High-Performance Fibre Reinforced Concrete by Using a Cohesive-Crack-Based Inverse Analysis

2021 ◽  
Author(s):  
Alejandro Enfedaque ◽  
Marcos G. Alberti ◽  
Jaime C. Gálvez ◽  
Pedro Cabanas
Keyword(s):  
Mechanical Properties ◽  
Reinforced Concrete ◽  
Inverse Analysis ◽  
High Performance ◽  
Fracture Behaviour ◽  
Constitutive Models ◽  
Cohesive Crack ◽  
Fibre Reinforced Concrete ◽  
Steel Fibres ◽  
Structural Applications

Fibre reinforced concrete (FRC) has become an alternative for structural applications due its outstanding mechanical properties. The appearance of new types of fibres and the fibre cocktails that can be configured mixing them has created FRC that clearly exceed the minimum mechanical properties required in the standards. Consequently, in order to take full advantage of the contribution of the fibres in construction projects, it is of great interest to have constitutive models that simulate the behaviour of the materials. This study aimed to simulate the fracture behaviour of five types of FRC, three with steel hooked fibres, one with a combination of two types of steel fibres and one with a combination of polyolefin fibres and two types of steel fibres, by means of an inverse analysis based on the cohesive crack approach. The results of the numerical simulations defined the softening functions of each FRC formulation and have pointed out the synergies that are created through use of fibre cocktails. The information obtained might suppose a remarkable advance for designers using high-performance FRC in structural elements.

Study on Mechanical Properties of AA6061/SiC/B4C Hybrid Nano Metal Matrix Composites

2021 ◽  
Vol 1034 ◽  
pp. 35-42
Author(s):  
Shubhajit Das ◽  
M. Chandrasekaran ◽  
Sutanu Samanta
Keyword(s):  
Mechanical Properties ◽  
High Performance ◽  
Matrix Material ◽  
Average Particle Size ◽  
Volume Ratio ◽  
Casting Process ◽  
Hybrid Nanocomposites ◽  
Average Particle ◽  
Matrix Composites ◽  
Structural Applications

The present work investigates the mechanical characterization of aluminium alloy (AA) 6061 based hybrid nanometal matrix composites (MMCs) fabricated using conventional stir casting process. Two compositions viz., AA6061+1.5 wt.% B4C+0.5 wt.% SiC (Hybrid A) and AA6061+1.5 wt.% B4C+1.5 wt.% SiC (Hybrid B) was prepared and its mechanical properties such as microhardness, tensile, compressive, flexural and impact strength were investigated to compare with unreinforced AA6061. SiC and B4C ceramic particles (purity 99.89%) of average particle size of 50 nm were used as reinforcements. Significant enhancement in microhardness of 30.2% and 31.02% for hybrid A and B are observed respectively. The ultimate tensile strength (UTS) increased by 10.72% and 16.55% for hybrid A and B respectively. Improved interaction because of the enhanced surface to volume ratio at the interface resulted in improvement of mechanical properties. Field emission scanning electron microscopy (FESEM) of the fractured surface shows brittle fracture because of the incorporation of the ceramic reinforcements in the matrix material. The developed AA6061/SiC/B­4C hybrid nanocomposites show improved mechanical properties for high-performance structural applications.

Electron microscopy of rod/coil molecular composites

1983 ◽  
Vol 41 ◽  
pp. 32-33
Author(s):  
S. J. Krause ◽  
W. W. Adams
Keyword(s):  
Critical Factor ◽  
High Strength ◽  
Chain Polymer ◽  
New Class ◽  
Reinforced Composite ◽  
Transmission Electron ◽  
The Matrix ◽  
Molecular Composites ◽  
Flexible Coil ◽  
Rigid Rod

Molecular composites are a new class of structural polymers which are lightweight, high-strength, high-modulus, and environmentally resistant. A rigid-rod, extended chain, polymer is used to reinforce a matrix of flexible, coil-like polymer with the intent of achieving a composite on the molecular level which is analagous to a macroscopic chopped-fiber reinforced composite. The critical factor in making a molecular composite is that the rod-like reinforcing molecules be well dispersed and not phase separate from the matrix polymer to insure that the aspect ratio (ratio of length to width) of the reinforcing phase has a high value. This paper reports the first transmission electron microsopy (TEM) study of phase separation in molecular composites.

Electron microscopy of a triblock copolymer molecular composite

1986 ◽  
Vol 44 ◽  
pp. 790-791
Author(s):  
T. Haddock ◽  
S. J. Krause ◽  
W. W. Adams
Keyword(s):  
Triblock Copolymer ◽  
Critical Factor ◽  
High Strength ◽  
Fiber Spinning ◽  
Chain Polymer ◽  
The Matrix ◽  
Molecular Composites ◽  
Polymer Component ◽  
Flexible Coil ◽  
Rigid Rod

Molecular composites are a new class of structural polymers which are high-strength, high-modulus, thermally stable, and environmentally resistant. A rigid-rod, extended chain polymer component is used to reinforce a matrix of flexible, coil-like polymer component with the intent of achieving a composite on the molecular level. The critical factor in processing a molecular composite is that the rod-like reinforcing component be well dispersed and not phase separate from the matrix component. We previously reported on the morphology of a molecular composite from a physical blend of rigid-rod and flexible-coil homopolymers. In this paper we are reporting on the morphology of a rigid-rod, flexible-coil, triblock copolymer processed by vacuum casting or fiber spinning from a dilute solution.

scholarly journals Elastic Properties of Thermo-Hydro-Mechanically Modified Bamboo (Guadua angustifolia Kunth) Measured in Tension

2014 ◽  
Vol 600 ◽  
pp. 111-120 ◽  
Author(s):  
Hector Fabio Archila-Santos ◽  
Martin Philip Ansell ◽  
Peter Walker
Keyword(s):  
Mechanical Properties ◽  
High Performance ◽  
Sheet Material ◽  
Construction Materials ◽  
Uniform Density ◽  
Structural Applications ◽  
Saturated Sample ◽  
Prediction Of Mechanical Properties ◽  
Water Saturated ◽  
Poissons Ratio

Guadua angustifolia Kunth (Guadua) was subjected to thermo-hydro-mechanical (THM) treatments that modified its microstructure and mechanical properties. THM treatment was applied to Guadua with the aim of tackling the difficulties in the fabrication of standardised construction materials and to gain a uniform fibre density profile that facilitates prediction of mechanical properties for structural design. Dry and water saturated Guadua samples were subjected to THM treatment. A densified homogenous flat sheet material was obtained. Mechanical properties of small clear specimens of THM modified Guadua were evaluated by testing in tension and compared to the results of the same test on a control specimen. Samples were tested in the elastic range to determine values for Modulus of Elasticity (MOE) and Poissons ratio. There was a significant increase in the tensile MOE values (parallel to the direction of the fibres) for densified samples. MOE values measured were 16.21 GPa, 22.80 GPa and 31.04 GPa for control, densified dry and densified water saturated samples respectively. Oven dry densities for these samples were 0.54 g/cm3, 0.81 g/cm3 and 0.83 g/cm3. Despite a 50 % reduction in the radial Poissons ratio for the water saturated sample, no further variation in the Poissons ratio as a result of densification was observed for control and densified dry samples. This paper presents the results of the first phase of a study focussed on the manufacturing of flat Guadua sheet (FGS) by THM treatment and the characterization of its mechanical properties. The achievement of a dimensionally stable FGS by THM modification, with a uniform density and achieved with reduced labour effort during manufacture, will be of key importance for the development of structural applications, and could have a significant impact in the bamboo industry. The final aim of the research at the University of Bath is the development of Cross Laminated Guadua (CLG) panels using THM modified and laminated FGS glued with a high performance resin.

scholarly journals Microstructural Features and Mechanical Properties after Industrial Scale ECAP of an Al 6060 Alloy

2010 ◽  
Vol 667-669 ◽  
pp. 1153-1158 ◽  
Author(s):  
Philipp Frint ◽  
Matthias Hockauf ◽  
T. Halle ◽  
G. Strehl ◽  
Thomas Lampke ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Shear Zone ◽  
High Performance ◽  
Large Scale ◽  
Low Voltage ◽  
Tensile Tests ◽  
Industrial Applications ◽  
Industrial Scale ◽  
Opening Angle ◽  
Cross Sectional

Future applications of ultrafine-grained, high performance materials produced by equal-channel angular pressing (ECAP) will most likely require processing on an industrial scale. There is a need for detailed microstructural and mechanical characterisation of large-scale, ECAP-processed billets. In the present study, we examine the microstructure and mechanical properties as a function of location and orientation within large (50 x 50 x 300 mm³) billets of an Al 6060 alloy produced by ECAP (90° channel angle) with different magnitudes of backpressure. The internal deformation is analysed using a grid-line method on split billets. Hardness is recorded in longitudinal and cross-sectional planes. In order to further characterise the local, post-ECAP mechanical properties, tensile tests in different layers are performed. Moreover, low voltage scanning transmission electron microscopy observations highlight relevant microstructural features. We find that the homogeneity and anisotropy of mechanical properties within the billets depend significantly on the geometry of the shear zone. We demonstrate that deformation gradients can be reduced considerably by increasing the backpressure: The opening-angle of the fan-shaped shear zone is reduced from ψ ≈ 20 ° to ψ ≈ 7 ° when the backpressure is increased from 0 to 150 MPa. Backpressures of 150 MPa result in excellent homogeneity, with a relative variation of tensile mechanical properties of less than 7 %. Our investigation demonstrates that ECAP is suitable for processing homogenous, high performance materials on a large scale, paving the way for advanced industrial applications.

Polycarbodiimide and polyimide/cyanate thermoset in situ molecular composites

1998 ◽  
Vol 13 (7) ◽  
pp. 1840-1847 ◽  
Author(s):  
D. R. Wiff ◽  
G. M. Lenke ◽  
P. D. Fleming
Keyword(s):  
Mechanical Properties ◽  
Molecular Weight ◽  
Phase Separation ◽  
Molecular Mechanics ◽  
High Molecular Weight ◽  
Molecular Composites ◽  
Rigid Rod ◽  
Composite Reinforcement

The synthesis of polycarbodiimide and polyimide in a cyanate resin precursor was achieved. A unique procedure for achieving a high molecular weight of the molecular composite reinforcement molecules was demonstrated. In spite of phase separation being present during the processing, the final cured composites were transparent. The enhanced mechanical properties and the presence of a single Tg, which increases with rigid rod content, were indications that a molecular composite was achieved. The agreement between measured mechanical properties and those predicted using molecular mechanics simulations CERIUS2 software was encouraging.

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