There is a growing demand for small round timber to be used in construction applications.  Using visual grading techniques, timbers are currently rated at approximately half of their mechanically determined design strengths.

Current State of Grading

   Trained professionals visually inspect small diameter logs and classify them by knot size, knot type, slope of grain, and defects. According to preliminary tests, visual grading classification results in a significantly reduced Modulus of Elasticity compared to non-destructive mechanical grading. The conservative nature of visual grading, results in many viable small diameter logs that are rejected for construction applications.

Future State of Grading

    A mechanical device will apply a point load to a simply supported log. The span of the supports will be related to the diameter by the ratio of 21 to 1. Using the deflection, diameter of the log, and the applied load, the Modulus of Elasticity will be calculated out. Using this method will result, according to preliminary data, in approximately a 50% increase in material properties. With this increase in material property values, the construction applications of small diameter logs will rise.

Project Objective

  The objective of this project is to design and build a test rig that is inexpensive and portable; which can grade the strength of small round timbers quickly and accurately, requiring minimal user input.


General Requirements Specific Requirements Target Performance
Durable Can survive many miles of travel Does not rattle apart on rough roads
Impact resistant Dropping a 250 lb log from 1 ft does not break anything
Inexpensive Much less than current alternatives <$10000
Adjustable Can measure wide range of timbers 3 – 9” in diameter and 6 – 16’ in length
Can apply a range of loads 0 – 1500 lbs
Portable Easily towed behind a pickup truck <1000 lbs and <30 ft
Fast Won’t bog down production <1 min
Accurately Better strength estimate than visual grading Within 5% of true value (the tester in CNR)
Safely Operators are not in danger Can stand 360 degrees around machine during operation without injury
Ease of Use Minimal user input Only span and diameter are measured by operator(s)
Automated data acquisition Parameters are entered into a computer, and MOE is displayed after log is deflected

Software Requirements
* Receive inputs from user
    - Log ID
    - Diameter
    - Span
    - Notes
* Produce outputs
    - Log ID
    - Diameter
    - Modulus of Elasticity
    - Extreme fiber
    - Timestamp
* Preload the log with 10%-20% of final force
* Run the experiment to caluclate the Modulus of Elasticity
* Calculate the Modulus of Elasticity several times while testing and fit the results to a line.
* Display the results, allow the user to either save and continue, or restart test
* Save test results to a .csv file for easy manipulation in Excell
* Allow for multiple tests to be done to the same log
* Control ultrasonic transducer, load cell, and hydraulics all programatically
* Allow for simple configuration of devices in software