Technology Helps Turn Salvaged Trees into Moneymakers

When insect scourges run rampant through forested ecosystems they can leave behind entire stands of dead and dying trees – especially if that scourge is the spruce budworm. In the Upper Midwest, where the spruce budworm infests forests on a cyclic 30-50 year pattern, forest managers oftentimes use salvaged logs from the dead and dying trees to produce low-value wood products, such as wood pulp, or merely count the dead trees as a loss and leave them standing.

Spruce budworm mortality,
Chequamegon–Nicolet
National Forest, Summer
2014 (Steven Katovich, USDA
Forest Service, Bugwood.org).

But Forest Products Laboratory (FPL) researchers developed ways to evaluate the quality of salvaged wood and sort out the higher-quality wood for production of cross-laminated timber (CLT) – a high-value wood product that can increase forest revenues. “We’re at the point of demonstrating commercially available technologies,” said FPL engineer Robert Ross, “and the idea that we can take high-grade material out [of dead tree stands].” Continue reading

The End of an Era: Eagle Tower's Last Day

Eagle Tower, a wooden observation tower standing 75-feet tall and rising 250 feet above Lake Michigan, was built in 1932 in Wisconsin’s Peninsula State Park. A Door County icon, this well-loved landmark served visitors for generations, but an in-depth inspection conducted in the spring of 2015 indicated the structure was in poor condition and no longer safe for the public.eagletower

The inspection included core sampling to determine the general internal condition of the structural components and overall load-bearing capacity of the structure. On May 20, 2015, the tower was closed for public use. Eagle Tower was taken down on Sept. 19, 2016.

Researchers at the Forest Products Laboratory (FPL) were asked to help in the evaluation of Eagle Tower as the Lab has extensive experience in historic structure evaluation and nondestructive wood evaluation techniques. FPL researchers will be testing the dismantled wood members and determining if they can be reused in any way to pay homage to the historic tower.

Community members are currently raising funds for the tower’s reconstruction. The new tower will comply with the Americans with Disabilities Act, current construction codes, and take into consideration new construction technologies.

The Wisconsin Department of Natural Resources put together a slideshow of the deconstruction of Eagle Tower so the public could view the event.

Every Cut Counts II : Lumber Lasers Illuminate Imperfections

Earlier, we looked at nondestructive evaluation (NDE) laser scanning as applied to logs prior to sawing, but the utility of laser technology extends to dimensional lumber as well.

A typical lumber mill will use two laser scanners which capture two distinct data types — profile scanning data, and tracheid effect data.

pine

A photo demonstrating the tracheid effect across six different samples of white pine. Notice how the shape of the laser changes depending on the defect present in the sample.

A profile scanning laser is aimed at the board in shallow angle, and is primarily used to detect wane (insufficient wood at a corner or along an edge, due to surface curvature) on the board’s edges as well as splits, cracks, and holes. It also yields accurate measurements of the amount of wane, which are used to automate the edging and trimming of the lumber.

profile

Sample laser profile image of a board. The lighter shades of grey show the wane of the wood. The jagged white abnormality in the upper left hand corner could indicate a defect.

Profile scans will yield grey-level images with the normal, level surface of the board shaded in dark gray. Slightly higher areas of the board are represented as darker shades of gray, and lower areas will be shown as lighter shades of gray. This additional information about the board’s surface helps industry professionals optimize the cutting processes and eliminate waste.

Diagram of a typical laser scanner used in a lumber mill. Notice how the laser on the right is angled for tracheid effect scanning.

A tracheid effect scanning laser, on the other hand, is aimed at the board at a sharper angle. When the beam strikes the surface of the wood, the beam is propagated along the board’s elongated cells, the tracheids, creating the titular effect. The angle of glow of the laser beam shows the angle of the wood grain, and by analyzing how the laser beam’s glow changes shape, researchers and industry professionals can predict a board’s strength or even reveal defects such as knots and pitch pockets.

This type of scanning technology was first used commercially to locate defects in hardwoods and softwoods for the production of furniture and mouldings, but has since expanded. Today, there are several manufactures producing commercial laser scanning equipment capable of tracheid effect scanning.

This blogpost was adapted from FPL’s publication Nondestructive Evaluation of Wood: Second Edition.

Making Every Cut Count : NDE Helps Optimize Forest Usage

Buildings, furniture, bridges, and musical instruments — all of these wood products start with the the same fundamental building block — the log. The quality of the log can make or break the final product, and this begs the question: are all logs created equal?

The Forest Products Laboratory (FPL) and the Northern Research Station (NRS) don’t think so. In one of FPL newest publications, Nondestructive Evaluation of Wood: Second Edition, researchers document different nondestructive evaluation (NDE) methods, including x-rays and ultrasounds, to assess and report on the condition and integrity of wood. These techniques help industry professionals make informed decisions about a wooden material without destroying it or compromising its structural integrity.

Laser scanning systems consist of two primary components — a laser generator, and a camera.

One of these NDE methods used for logs is laser scanning. Although there are many variations on this technology, each laser scanning system has two main components: a laser line generator (which projects a laser line onto an object), and a camera. The camera and the laser are separated by a measured distance, and the camera is aimed toward the projected laser line at a specific angle. Using the camera angle, the distance between the camera and the laser, and triangulation, the distance of the points along the laser line projected onto an object can be determined.

When scanning logs, a series of laser lines are projected around the surface of the log along its length — and the more lines, the better. By increasing the lines and decreasing the distance between them, the resolution of the scan is increased, and operators can get a more detailed scan of the log. A laser scanning system typically has lasers spaced 6 to 24 inches apart, but the Forest Service has developed an experimental, high-resolution, scanner with lasers placed 0.0625 inches apart. At this resolution, any defects on the log’s surface become obvious.

A high-resolution scan of a hardwood log. Laser scanning technology helps industry professionals better utilize our forest resources.

“Laser scanning is normally done just before processing,” writes Edward Thomas, NRS Research Scientist and contributor to FPL’s NDE book. “To effectively convert logs into lumber, their attributes (diameter, shape, length, sweep and taper) must be accurately measured.”

If the width of the first board cut from the log is too narrow, the grade and the value of the board is decreased. If it’s too wide, then too much wood will be wasted. In addition, by knowing a hardwood log’s taper and sweep, it can be positioned so that there is minimum volume loss from the “jacket boards,” the most valuable boards cut from a hardwood log.

The use of laser scanning technology has become an accepted and economical means of determining the size, shape, and features of logs and lumber. Newer systems can determine grade, yield, and value of a log, even before sawing. The FPL, NRS, and the Forest Service will continue to work with industry partners to develop new technologies to help maximize yield, decrease waste, and maintain the health and integrity of our forests. In this pursuit, every cut counts.

If a Tree Falls in the Middle of the City…

If a tree falls in a forest and no one is around to hear it, does it make a sound?”

This question has served as an icebreaker for generations of introductory philosophy courses — highlighting the sometimes murky nature of reality and the role observation plays in determining it.

But what happens if a tree falls in the middle of a city? Whether or not it makes a sound is the least of concerns to the unfortunate city dwellers below.

Trees within an urban community provide aesthetic, social, ecological and economic benefits. Recent research even points to measurable cognitive and psychological benefits by introducing more nature to the daily regimes of urban workers. Despite these benefits, urban trees remain large physical structures in close proximity to people and property, and their failure can cause damage to individuals and infrastructure. Recognizing this, researchers at the Forest Products Laboratory (FPL) devised several methods to evaluate a tree’s condition and detect decay and defects that could jeopardize public safety.

These nondestructive evaluation techniques (NDE) allow researchers to investigate and verify the condition of a tree without causing it any damage. This way, experts avoid damaging healthy trees while they weed out the bad ones. NDE techniques vary, but can range from visual inspection regimes to cutting-edge electronic scanning technologies.

Capitol

Decay detection in red oak trees using a combination of visual inspection, acoustic testing, and resistance microdrilling.

In FPL’s home, Madison, Wisconsin, a tree stability survey was conducted on 153 trees surrounding the Capitol using NDE methods. Researchers from the laboratory first conducted visual inspections of all directly and indirectly observable defects, and then followed up with acoustic testing. Acoustic testing uses sound waves to determine the structural soundness of a material — in the case of trees, even beneath the bark.

Thanks to lab benchmarks, researchers know how sound should travel through healthy wood. If the sound waves move slower through a tree undergoing acoustic testing, there might be decay beneath the surface. In the case of the Capitol’s trees, if the sound waves had more than a 25% reduction in speed, they failed the test.

Finally, some trees received resistograph testing. The resistograph is a fine-tipped drill that detects decay by measuring the resistance where the drill bit meets the wood (or more specifically, the electrical power consumption in the motor driving the bit). Since low density, decayed wood requires less power and torque to drill through, if the resistograph drill is consuming less power, there’s a good chance that it’s chewing through a decayed part of the tree.

A 300-page report was submitted to park managers detailing the cases of internal decay and defects revealed using these combined nondestructive testing methods. Select tree removal and pruning were followed by arborists based on the report’s conclusions. Sadly, even a 100-year old red oak was given a poor bill of health and had to be removed.

Just weeks before the last two trees were removed, a violent storm with unusually high velocity winds passed through the park. Of the remaining 143 trees in the park, the only ones to fail were two that had been identified as high risk using the NDE techniques. Luckily, they caused no harm to people or buildings, but their loss did verify the effectiveness of the researcher’s work.

Whether or not they made a sound however, is still up for debate.

For more information, please see FPL’s publication Nondestructive Evaluation of Wood: Second Edition.