Engineering Mechanics and Remote Sensing Laboratory

The Engineering Mechanics Laboratory tests and evaluates wood, wood products, and wood component specimens to determine their mechanical and material properties. Tests are performed for work units within the Forest Products Laboratory and for Experimental Station work units by special request.

Picture of the Engineering Mechanics Laboratory many years ago.

The Tests

The Engineering Mechanics Laboratory performs both load tests and non-destructive evaluation (NDE) tests. Typical load tests include specimen bending, compression, and shear. Here, loads are applied with either hydraulic or screw-driven mechanisms, loads are measured with strain-gauge load cells, and deflections are measured with linear-variable differential transformers (LVDTs). Specimens that are load-tested are generally loaded to failure.

NDE tests include transverse vibration measurements and stress wave analyses. Transverse vibration tests measure the frequency at which a long specimen will bounce when tapped, and stress wave measures the speed at which a shock wave travels through a specimen.

When a specimen is load tested, information about the testing configuration and specimen's dimensions are recorded, as well as the incremental load values and their corresponding deflection values.

Modulus of rupture (MOR) is a measure of how much force a material can take before it fails. Failure can be defined a number of ways but most often is either when the specimen suddenly breaks or when it deforms so much that it cannot perform its function. Maximum compressive strength (MCS) similarly describes failure force but applies only to compression tests. MOR and MCS are typically reported in pounds per square inch and describe how much force it takes to fail a certain cross-sectional area of material. MOR and MCS are functions of the maximum load achieved in the test, specimen dimensions, and test configuration.

Modulus of elasticity (MOE) is a measure of material stiffness, or how much force it takes to deform a material. It assumes that the material behaves approximately in a linear-elastic manner for at least part of the test. MOE has units of force per unit area and is a function of the slope of the load/deflection curve that represents the test. The engineering mechanics laboratory uses the region of the curve between 20% and 40% of the maximum load as its linear-elastic region.

TYPICAL COMPOSITION CURVE: This Figure represents the deflection values measured at incremental load values. Note that the curve is approximated by a hyperbolic tangent function. Points of interest are the maximum load achieved during the test and the regression slope of the curve between 20% and 40% of the maximum load.