Wood Science Snippets

Taken from our Feature "Meet the WTS Board," this page will be gradually increased in topics, following publication of new issues of "Meet the WTS Board," and other items of interest.

Anobium:

(Jim Coulson)  Anobium is actually the Genus of a group of wood-eating insects: the most well-known of which in the UK is Anobium punctatum – aka the “woodworm” (more properly, the Common Furniture Beetle).  As larvae, they bore into wood and use the wood as a source of food.  Anobium attacks the sapwood of both deciduous and coniferous woods.  Although damage by Anobium is often associated with older drier timbers, attack may also originate in freshly seasoned wood.  The life cycle from egg to insect is usually three or more years, and therefore infestation may pass unnoticed until a number of generations have emerged.

On pupation the adults then break through the surface of the wood, creating very fine “saw dust like” deposits.  This is normally the first sign of evidence of Anobium.  By the way, treatment against Anobium is readily available at good DIY stores or via specialist treatment companies.

(Adult insect "Anobium."  Image courtesy of J Creffield.)

As it happens, “Anobium” has another, scientific, connection with the WTS – or rather, its predecessor, the Institute of Wood Science – in that a Past President of the IWSc, Jean Taylor, published a learned research article (click here) about the prevention of Anobium attack in Birch plywood, in 1968, when she worked as a wood scientist at the then Forest Products Research Laboratory. 

A radiograph of Jean's, dating from 1968, showing Anobium after 18 months.  (Taken from Jean's research article mentioned above.)

Lyctus: 

At the same time Jean also had published a short research article on Lyctus attack in obeche plywood."  Click here to read it. 

Wood Boring Weevil:

(Gervais Sawyer)  I became passionate about a particular wood boring weevil. My work includes inspecting wooden marine structures, which usually fail by decay fungi or marine borers such as gribble (Limnoria) or shipworm (Teredo).  On one inspection I chanced upon numerous weevils that were shaped like little hand-bells. Both the larvae and the adults were feeding on the partly decayed wood. What immediately caught my interest was that these were immersed at high tide. The respiration and osmotic challenge to these beetles is immense.

Pselactus

Back in the laboratory, I found that if you drop them into water they go into suspended animation. Take them out of water a week later, and after about 10 minutes they walk away, none the worse!

Under the scanning electron microscope you can see that dirt is kept out of the head/body socket by beautiful fan-like brushes.  Its name is Pselactus spadix (Latin for chestnut coloured hand-bell shaped).  They are easy to keep as pets!  They don't skitter around, just slowly plod along.

The full biology of Pselactus spadix was studied by Dr. Pascal Oevering.  Although only 2.5 to 3mm long, Geoff Cooper (a researcher at BRE) had the incredibly sensitive touch to dissect the animal revealing its crop and gut structure.”

Pselactus spadix adult head capsule brushes

Pselactus larva diverticuli

Wind Farms.

(Martin Ansell)  He was asked to explain why laminated wood became a material of choice for the manufacture of commercial wind turbine blades.

Today, windfarms are a common feature of the UK landscape and in 2017 15% of the UK’s electricity was derived from the wind. Back in the late 1970s and 1980s the fledgling wind turbine industry was slowly emerging, seeking credibility as a viable source of alternative energy. The British Wind Energy Association was formed in 1978 and held annual conferences where news of new developments was eagerly awaited. Early designs for turbine blades in the UK and USA were based on high density (approx. 7,500 kg.m-3) steels but the dynamic loads created by aerodynamic forces (producing lift and rotation) together with gravity self-loading led to the development of fatigue cracks in the steel and catastrophic blade failures. Many of the early Californian wind farms were built in haste to meet the deadline for the award of tax credits and the small capacity (100kW) turbines relied on medium density (approx. 2,500 kg.m-3) glass fibre-reinforced plastics for blade fabrication and these blades frequently failed by delamination and fracture of the hub end fixings. This is where Martin became involved in the fatigue evaluation of low density (approx. 500 kg.m-3) laminated wood for turbine blades. Wind turbine blades are hollow aerofoil structures and multi-layer thick D-spar walls are able to withstand buckling loads much better than thinner, stiffer materials such as carbon-reinforced plastics. Furthermore, steel studs can be directly bonded into the roots of the wooden blades to make bolted connections to the turbine hub.

Working with Jim Platts and Mark Hancock at Gifford Technology, Southampton, Martin was responsible for the fatigue testing of wood laminated from 4mm veneers, funded by a series of research grants from the EPSRC and the UK Department of Energy (later DTI). The bonded wood technology was developed originally for boat-building by Gougeon Brothers in the USA using the WEST epoxy system for bonding veneers. Back in the first half of the 20th century the aircraft designer Fokker stated that “fatigue in properly seasoned wood is unknown”. However, all engineering materials subjected to cyclic loads accumulate progressive damage ultimately leading to catastrophic failure. Martin managed a long-term fatigue testing programme of laminated wood which, as well as establishing design data for fatigue lives under cyclic and complex loads, allowed the mechanism of fatigue damage to be understood. In conjunction with BRE, very thin longitudinal sections of wood were made with a wood microtome at various stages of fatigue loading and examined in an optical microscope. Progressive fatigue failure was initiated by the formation of compression kinks in single wood cell walls. This micro-damage spread to double wood cell walls and eventually formed micro-buckles which with time became major macro-scale compression creases leading to ultimate failure of the wood laminate. As a result of the fatigue work the safe design loads permissible for a laminated wood blade subjected to complex loads with a 25 year design life could be determined.

Images of fatigue damaged cells, (a) compression kinks (5 microns wide), (b) compression crease

Images of fatigue damaged cells, (a) compression kinks (5 microns wide), (b) compression crease

Gifford Technology expertise was transferred to several companies including the Wind Energy Group (Taylor Woodrow) in a series of takeovers and finally became the property of Aerolaminates. Laminated wood-epoxy wind turbine blades were manufactured by Aerolaminates on the Isle of Wight. In 1998, following the takeover of Aerolaminates, NEG Micon built a new facility for the manufacture of hybrid laminated wood/carbon fibre-reinforced hybrid blades and in 2003 developed a commercial 110 meter diameter rotor for the Vestas Wind Systems A/S NM 110/4200 wind turbine with a rated power of 4.2 MW.

Wind Energy Group turbine with laminated wood blades

Wind Energy Group turbine with laminated wood blades