scholarly journals The Strength and Stiffness of Oriented Wood and Cellulose-Fibre Materials: A Review

2021 ◽  
pp. 100916
Author(s):  
Matthias Jakob ◽  
Arunjunai raj Mahendran ◽  
Wolfgang Gindl-Altmutter ◽  
Peter Bliem ◽  
Johannes Konnerth ◽  
...  
Keyword(s):  
Cellulose Fibre ◽  
Strength And Stiffness

A Survey of Plastics from the Viewpoint of the Mechanical Engineer

1945 ◽  
Vol 152 (1) ◽  
pp. 29-43 ◽  
Author(s):  
S. Livingston Smith
Keyword(s):  
Tensile Load ◽  
Cellulose Fibre ◽  
High Strength ◽  
Engineering Practice ◽  
Synthetic Resin ◽  
Cellulose Fibres ◽  
Reinforced Plastics ◽  
Synthetic Resins ◽  
Strength And Stiffness ◽  
Effective Use

Synthetic resin materials, or “plastics”, offer so many attractive possibilities, particularly in respect of ease of manufacture, that every engineer must be anxious to assess the suitability of these materials to his own special field. The object of the present paper is to review the prospects of the use of plastics in mechanical engineering by their application to stressed parts, and attention is therefore concentrated on the mechanical properties of these materials. The paper touches on unfilled resins and on moulding powders but the main emphasis is laid on reinforced plastics and resin-treated woods, and on their possible use as structural members, gears, and bearings. At the same time, since the value of any material in engineering practice depends not only on its strength and stiffness but also on its general serviceability, some consideration is given to other characteristics, which may affect the behaviour of plastics under service conditions. A certain degree of molecular orientation is necessary to obtain high strength and stiffness in synthetic resins and, although strong artificial fibres such as nylon have been produced, the strong element in reinforced plastics is more often the natural cellulose fibre. The synthetic resin is used in an unoriented form to stabilize the cellulose fibres so that they can carry compressive as well as tensile load and to bond the fibres together so that load may be transmitted from one fibre to another. One convenient form of fibre-filled synthetic resin is that of laminated sheet, and some research has been done on paper-filled materials in this form. It is shown that adequate bonding and stabilization of the fibres demands the avoidance of voids in the resin-bonded board, but that otherwise the strongest board is that containing the least resin. Completely to fill the voids in the paper base without the use of excess resin or very heavy pressure requires close control of the processes of impregnation and pressing; and the minimum amount of resin necessary depends upon the fibre density of the paper. Close attention to these two aspects has resulted in the development of strong boards with low resin content, which can be completely bonded at low pressures. Most synthetic resins are highly resistant to corrosive agents, but many absorb and desorb water in sympathy with changes of humidity of their surroundings. The amount of water sorbed is not serious, nor is the consequent effect on the strength very great, but the slight swelling and contraction of the materials which results from water sorption may cause trouble in certain applications. The synthetic resins at present available for the bonding of cellulose fibres enable fairly effective use to be made of the strength and stiffness of the fibre; but there is still room for considerable improvement, which should result in higher strengths in compression and shear and in greater resistance to buckling. Otherwise the further development of plastics depends principally on improvements in manufacturing processes and intelligent application of those processes to the specific problems of engineering design.

Microstructural characterization of plasma-processed Ti-Al metal matrix composites

1989 ◽  
Vol 47 ◽  
pp. 552-553
Author(s):  
M. G. Burke ◽  
M. N. Gungor ◽  
M. A. Burke
Keyword(s):  
High Temperature ◽  
Titanium Aluminide ◽  
Plasma Processing ◽  
Microstructural Characterization ◽  
High Temperature Strength ◽  
Matrix Composites ◽  
Intermetallic Matrix ◽  
Long Time ◽  
Strength And Stiffness ◽  
Intermetallic Matrix Composites

Intermetallic matrix composites are candidates for ultrahigh temperature service when light weight and high temperature strength and stiffness are required. Recent efforts to produce intermetallic matrix composites have focused on the titanium aluminide (TiAl) system with various ceramic reinforcements. In order to optimize the composition and processing of these composites it is necessary to evaluate the range of structures that can be produced in these materials and to identify the characteristics of the optimum structures. Normally, TiAl materials are difficult to process and, thus, examination of a suitable range of structures would not be feasible. However, plasma processing offers a novel method for producing composites from difficult to process component materials. By melting one or more of the component materials in a plasma and controlling deposition onto a cooled substrate, a range of structures can be produced and the method is highly suited to examining experimental composite systems. Moreover, because plasma processing involves rapid melting and very rapid cooling can be induced in the deposited composite, it is expected that processing method can avoid some of the problems, such as interfacial degradation, that are associated with the relatively long time, high temperature exposures that are induced by conventional processing methods.

Factors affecting microstructural scale in liquid crystalline polymers

1990 ◽  
Vol 48 (4) ◽  
pp. 220-221
Author(s):  
Christine M. Dannels ◽  
Christopher Viney
Keyword(s):  
Liquid Crystalline ◽  
Liquid Crystalline Polymers ◽  
Factors Affecting ◽  
Crystalline Polymers ◽  
Thermal Expansion Coefficients ◽  
Low Thermal Expansion ◽  
Lower Viscosity ◽  
Fine Microstructure ◽  
Planar Orientation ◽  
Strength And Stiffness

Processing polymers from the liquid crystalline state offers several advantages compared to processing from conventional fluids. These include: better axial strength and stiffness in fibers, better planar orientation in films, lower viscosity during processing, low solidification shrinkage of injection moldings (thermotropic processing), and low thermal expansion coefficients. However, the compressive strength of the solid is disappointing. Previous efforts to improve this property have focussed on synthesizing stiffer molecules. The effect of microstructural scale has been overlooked, even though its relevance to the mechanical and physical properties of more traditional materials is well established. By analogy with the behavior of metals and ceramics, one would expect a fine microstructure (i..e. a high density of orientational defects) to be desirable.Also, because much microstructural detail in liquid crystalline polymers occurs on a scale close to the wavelength of light, light is scattered on passing through these materials.

Observing the relaxation of molecular orientation in sheared liquid crystalline polymer solutions

1990 ◽  
Vol 48 (4) ◽  
pp. 1092-1093
Author(s):  
Wendy Putnam ◽  
Christopher Viney
Keyword(s):  
Molecular Orientation ◽  
Liquid Crystalline Polymer ◽  
Liquid Crystalline ◽  
Crystalline Polymer ◽  
Polymer Processing ◽  
Molecular Alignment ◽  
Global Alignment ◽  
Shear Direction ◽  
Axial Strength ◽  
Strength And Stiffness

Liquid crystalline polymers (solutions or melts) can be spun into fibers and films that have a higher axial strength and stiffness than conventionally processed polymers. These superior properties are due to the spontaneous molecular extension and alignment that is characteristic of liquid crystalline phases. Much of the effort in processing conventional polymers goes into extending and aligning the chains, while, in liquid crystalline polymer processing, the primary microstructural rearrangement involves converting local molecular alignment into global molecular alignment. Unfortunately, the global alignment introduced by processing relaxes quickly upon cessation of shear, and the molecular orientation develops a periodic misalignment relative to the shear direction. The axial strength and stiffness are reduced by this relaxation.Clearly there is a need to solidify the liquid crystalline state (i.e. remove heat or solvent) before significant relaxation occurs. Several researchers have observed this relaxation, mainly in solutions of hydroxypropyl cellulose (HPC) because they are lyotropic under ambient conditions.

Über die mechanische Bedeutung der Holzstrahlen | The mechanical relevance of wood rays

2003 ◽  
Vol 154 (12) ◽  
pp. 498-503 ◽  
Author(s):  
Ingo Burgert
Keyword(s):  
Beech Wood ◽  
Tensile Tests ◽  
Deciduous Tree ◽  
Biological Design ◽  
Transverse Tensile ◽  
Radial Reinforcement ◽  
Radial Strength ◽  
Transverse Tensile Strength ◽  
Strength And Stiffness ◽  
Technical Solutions

Three investigations into the mechanical relevance of wood rays were combined for this article. The main objective was to show, that, apart from physiological functions, rays also significantly influence the radial strength and stiffness of wood. In the first approach twelve deciduous tree species with various proportions of fractions of rays were examined for their transverse tensile strength and stiffness. The second approach was based on the comparison of the radial mechanical properties of wood with a very high proportion of fraction of rays and beech wood with a normal volume. In these two investigations the mechanical relevance of rays could only be deduced indirectly. By isolating big rays of beech and carrying out tensile tests on the tissue, we found direct evidence for the mechanical relevance. The results are discussed with regard to their biomechanical relevance. The importance of a radial reinforcement for the wood is underlined. Moreover, the principle of multi-functionality in nature is emphasized in keeping with a possible transfer of biological design to technical solutions.

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