Evaluation of wood characteristics of tropical post-mid rotation plantation Eucalyptus cloeziana and E. pellita: Part (d) Veneer and plywood potential.

Logs from two hardwood plantations in north Queensland were peeled to assess the veneer and plywood potential of fast-grown tropical plantation eucalypts. After visual grading and veneer recovery calculatios, selected veneers were assembled to produce plywood panels. These were tested for mechanical properties and glue bond strength to determine the suitability of young, fast-grown, tropical eucalytps for panel product applications.

Structural Veneer Based Composite Products from Hardwood Thinning - Part II: Testing of Hollow Utility Poles

Australian utility pole network is aging and reaching its end of life, with 70% of the 5 million poles currently in-service nationally installed within the 20 years following the end of World War II. The estimated investment required for the replacement or remedial maintenance of the aging 3.5 millions poles is as high as 1.75 billion dollars. Additionally, an estimated 21,700 high-durability new poles are required each year, representing further investment of 13.5 million dollars per year. Yet, agreements which progressively phase out logging of native forests around Australia have been signed, giving the industry about 25 years to make the transition from Crown native forests to plantations and private forests. As utility poles were traditionally cut from native forest hardwood species, finding solutions to source new poles currently presents a challenge. This paper presents tests on Veneer Based Composite hardwood hollow utility poles manufactured from Gympie messmate (Eucalyptus cloeziana) plantation thinning. Small diameter poles of nominal 115 mm internal diameter and 15 mm wall-thickness were manufactured in two half-poles butt jointed together, using 9 veneers per halfpole. The poles were tested in bending and shear, and experimental test results are presented. The mechanical performance of the hollow poles is discussed and compared to hardwood poles cut from mature trees and of similar size. Future research and different options for improving the current concept are proposed in order to provide a more reliable and cost effective technical solution to the current shortage of utility poles. © RILEM 2014.

Veneer based composite hollow utility poles manufactured from hardwood plantation thinned trees

Australia’s utility pole network is aging and approaching its end of life. It is estimated that 70% of the 5 million poles currently in-service nationally were installed within the 20 years following the end of World War II and require replacement or remedial maintenance. Additionally, an estimated 21,700 high-durability new poles are required each year to support the expansion of the energy network. Utility poles were traditionally cut from native forest hardwood species. However, due to agreements which progressively phase out logging of native forests around Australia, finding new sources for utility poles presents a challenge. This paper presents the development of veneer based composite hardwood hollow utility poles manufactured from mid-rotation Gympie messmate (Eucalyptus cloeziana) plantation thinned trees (also referred to as “thinning”), as an alternative to solid hardwood poles. The incentives behind the project and benefits of the proposed products are introduced in the paper. Small diameter poles, of nominal 115 mm internal diameter and 15 mm wall-thickness, were manufactured in two half-poles butt jointed together, using 9 hardwood veneers per half-pole. The poles were tested in bending and shear, and experimental test results are presented. The mechanical performance of the hollow poles is discussed and compared to hardwood poles sourced from mature trees and of similar size. Additionally, the required dimensions of the proposed hollow pole to replace actual solid poles are estimated. Results show that the proposed product represents a viable technical solution to the current shortage of utility poles. Future research and different options for improving the current concept are proposed in order to provide a more reliable and cost effective product for structural and architectural applications in general.

Veneer Recovery Analysis of Plantation Eucalypt Species Using Spindleless Lathe Technology

The Australian hardwood plantation industry is challenged to identify profitable markets for the sale of its wood fibre. The majority of the hardwood plantations already established in Australia have been managed for the production of pulpwood; however, interest exists to identify more profitable and value-added markets. As a consequence of a predominately pulpwood-focused management regime, this plantation resource contains a range of qualities and performance. Identifying alternative processing strategies and products that suit young plantation-grown hardwoods have proved challenging, with low product recoveries and/or unmarketable products as the outcome of many studies. Simple spindleless lathe technology was used to process 918 billets from six commercially important Australian hardwood species. The study has demonstrated that the production of rotary peeled veneer is an effective method for converting plantation hardwood trees. Recovery rates significantly higher than those reported for more traditional processing techniques (e.g., sawmilling) were achieved. Veneer visually graded to industry standards exhibited favourable recoveries suitable for the manufacture of structural products.

Structural Veneer Based Composite Products from Hardwood Thinning - Part I: Background and Manufacturing

In Australia, plantation forests have increased in area by around 50% in the last 10 years. While this expansion has seen a modest 8% increase for softwoods, hardwood plantations have dramatically increased by over 150%. Hardwood plantations grown for high quality sawn timber are slow to mature, with a crop rotation time potentially reaching 35 years. With this long lead-time, each year the risk from fire, pests and adverse weather events dramatically increases, while not translating into substantially higher financial returns to the grower. To justify continued expansion of Australia's current hardwood plantation estate, it is becoming necessary to develop higher value end-uses for both pulpwood and smaller 'sawlog' resources. The use of the low commercial value stems currently culled during thinning appears to be a necessary option to improve the industry profitability and win new markets. This paper provides background information on Australian forests and plantations and gives an overview of potential uses of Australian hardwood plantation thinning logs, as their mechanical properties. More specifically, this paper reports on the development of structural Veneer Based Composite (VBC) products from hardwood plantation thinning logs, taking advantage of a recent technology developed to optimise the processing of this resource. The process used to manufacture a range of hollow-form veneer laminated structural products is presented and the mechanical characteristics of these products are investigated in the companion paper. The market applications and future opportunities for the proposed products are also discussed, as potential benefits to the timber industry. © RILEM 2014.

Veneer Grade Analysis of Early to Mid-rotation Plantation Eucalyptus Species in Australia

Processing Australian hardwood plantations into rotary veneer can produce more acceptable marketable product recoveries compared to traditional processing techniques (e.g. sawmilling). Veneers resulting from processing trials from six commercially important Australian hardwood species were dominated by D-grade veneer. Defects such as encased knots, gum pockets, gum veins, surface roughness, splits, bark pockets, and decay impacted the final assigned grade. Four grading scenarios were adopted. The first included a change to the grade limitations for gum pockets and gum veins, while the second investigated the potential impact of effective pruning on grade recovery. Although both scenarios individually had a positive impact on achieving higher face grade veneer qualities, the third and fourth scenarios, which combined both, had a substantial impact, with relative veneer values increasing up to 18.2% using conservative calculations (scenario three) or up to 22.6% (scenario four) where some of the upgraded veneers were further upgraded to A-grade, which attracts superior value. The total change in veneer value was found to depend on the average billet diameter unless defects other than those relating to the scenarios (gum or knots) restricted the benefit of pruning and gum upgrading. This was the case for species prone to high levels of growth stress and related defects.

Variation in rotary veneer recovery from australian plantation Eucalyptus globulus and Eucalyptus nitens

The processing of Australian plantation-grown Eucalyptus globulus and E. nitens into rotary veneer was shown to produce acceptable recoveries. Three plantation sites for each species were sampled. Silvicultural treatments (thinning and pruning) and growing environments varied between sites. Graded veneer recoveries were dominated by D-grade veneer across all six sites. Variation between the E. nitens sites was evident, with recoveries differing between sites reflecting silvicultural treatments. However, only minimal variation in recovery was shown between the E. globulus sites. The presence of similar levels of defects across all E. globulus sites indicates that the intensive silvicultural management at one site studied was not effective in the production of clear wood, and may possibly have adversely affected grade recovery. Veneer value analysis demonstrated only minimal differences between E. globulus sites. More variation was observed in the E. nitens value analysis; however, intensive silvicultural management implemented did not necessarily result in higher veneer value.

Factors affecting log traits and green rotary-peeled veneer recovery from temperate eucalypt plantations

High levels of percentage green veneer recovery can be obtained from temperate eucalypt plantations. Recovery traits are affected by site and log position in the stem. Of the post-felling log traits studied, out-of-roundness was the best predictor of green recovery.

Thin-walled timber and FRP-timber veneer composite CEE-sections

This paper compares the structural performance between thin-walled timber and FRP-timber composite Cee-sections. While, thin-walled composite timber structures have been proven to be efficient and ultra-light structural elements, their manufacturing is difficult and labour intensive. Significant effort and time is required to prevent the cracking of the transverse timber veneers, bent in the grain direction, when forming the cross-sectional shape. FRP-timber structures overcome this disadvantage by replacing the transverse veneers with flexible, unidirectional FRP material and only keeping the timber veneers which are bent in their natural rolling direction. The Cee-sections investigated in this study were 210 mm deep × 90 mm wide × 500 mm high and manufactured from five plies. For both section types, the three internal plies were thin (1 mm thick) softwood Hoop pine (Araucaria cunninghamii) veneers, orientated along the section longitudinal axis. The two outer layers, providing bending stiffness to the walls, were Hoop pine veneers (1 mm thick) for the timber sections and glass fibre reinforced plastic (0.73 mm thick) for the FRP-timber sections orientated perpendicular to the inner layers. The manufacturing process is briefly introduced in this paper. The profiles were fitted with strain gauges and tested in compression. Linear Variable Displacement Transducers also recorded the buckling along one flange. The test results are presented and discussed in this paper in regards to their structural behaviour and performance. Results showed that the use of FRP in the sections increases both the elastic local buckling load and section capacity, the latter being increased by about 24 percent. The results indicate that thin-walled FRP-timber can ultimately be used as a sustainable alternative to cold-formed steel profiles.

Vave propagation and bandgaps in a parametrically modulated composite laminate

Wave propagation and its frequency bandgaps in a parametrically modulated composite laminate are reported in this paper. The modulated properties under considerations are due to periodic microstructure, for example honeycomb core sandwich composite, which can be parameterized and homogenized in a suitable scale. Wave equations are derived by assuming a third-order shear deformation theory. Homogenization of the wave equations is carried out in the scale of wavelength. In-plane wave and flexural-shear wave dispersions are obtained for a range of values of a stiffness modulation coefficient (alpha). A clear pattern of stop-bands is observed for alpha >= 4. To validate the band-gap phenomena, we take recourse to time domain response obtained from finite element simulation. As predicted by the proposed analytical technique, a distinct correlation between the chosen frequency band and the simulated wave arrival time and amplitude reduction is found. This promises practical applications of the proposed analytical technique to designing parametrically modulated composite laminate for wave suppression. (C) 2009 Elsevier B.V. All rights reserved.

FE analysis of piezo-laminate composites under thermal loads

A shear flexible 4-noded finite element formulation, having five mechanical degrees of freedom per node, is presented for modeling the dynamic as well as the static thermal response of laminated composites containing distributed piezoelectric layers. This element has been developed to have one electrical degree of freedom per piezoelectric layer. The mass, stiffness and thermo-electro-mechanical coupling effects on the actuator and sensor layers have been considered. Numerical studies have been conducted to investigate both the sensory and active responses on piezoelectric composite beam and plate structures. It is. concluded that both the thermal and pyroelectric effects are important and need to be considered in the precision distributed control of intelligent structures.

Strength and fatigue life evaluation of composite laminate with embedded sensors

Prognosis regarding durability of composite structures using various Structural Health Monitoring (SHM) techniques is an important and challenging topic of research. Ultrasonic SHM systems with embedded transducers have potential application here due to their instant monitoring capability, compact packaging potential toward unobtrusiveness and non-invasiveness as compared to non-contact ultrasonic and eddy current techniques which require disassembly of the structure. However, embedded sensors pose a risk to the structure by acting as a flaw thereby reducing life. The present paper focuses on the determination of strength and fatigue life of the composite laminate with embedded film sensors like CNT nanocomposite, PVDF thin films and piezoceramic films. First, the techniques of embedding these sensors in composite laminates is described followed by the determination of static strength and fatigue life at coupon level testing in Universal Testing Machine (UTM). Failure mechanisms of the composite laminate with embedded sensors are studied for static and dynamic loading cases. The coupons are monitored for loading and failure using the embedded sensors. A comparison of the performance of these three types of embedded sensors is made to study their suitability in various applications. These three types of embedded sensors cover a wide variety of applications, and prove to be viable in embedded sensor based SHM of composite structures.

Probing Photoexcited Carriers in a Few-Layer MoS2 Laminate by Time-Resolved Optical Pump-Terahertz Probe Spectroscopy

We report the dynamics of photoinduced carriers in a free-standing MoS2 laminate consisting of a few layers (1-6 layers) using time-resolved optical pump-terahertz probe spectroscopy. Upon photoexcitation with the 800 nm pump pulse, the terahertz conductivity increases due to absorption by the photoinduced charge carriers. The relaxation of the non-equilibrium carriers shows fast as well as slow decay channels, analyzed using a rate equation model incorporating defect-assisted Auger scattering of photoexcited electrons, holes, and excitons. The fast relaxation time occurs due to the capture of electrons and holes by defects via Auger processes, resulting in nonradiative recombination. The slower relaxation arises since the excitons are bound to the defects, preventing the defect-assisted Auger recombination of the electrons and the holes. Our results provide a comprehensive understanding of the non-equilibrium carrier kinetics in a system of unscreened Coulomb interactions, where defect-assisted Auger processes dominate and should be applicable to other 2D systems.

A Discussion on Modeling Shape Memory Alloy Embedded in A Composite Laminate as Axial Force and Elastic Foundation

In this paper, the possible error sources of the composite natural frequencies due to modeling the shape memory alloy (SMA) wire as an axial force or an elastic foundation and anisotropy are discussed. The great benefit of modeling the SMA wire as an axial force and an elastic foundation is that the complex constitutive relation of SMA can be avoided. But as the SMA wire and graphite-epoxy are rigidly bonded together, such constraint causes the re-distribution of the stress in the composite. This, together with anisotropy, which also reduces the structural stiffness can cause the relatively large error between the experimental data and theoretical results.