Combined beam bending and contact compression need separate displacement references. Measure the beam, supports and contact regions under the sustained load to identify which deformation calls for correction. [1]
Calculation basis. Project-specific values and gates in the illustrative screens below are assumptions; cited catalogue values retain their source test conditions.
Reproduce the actual supports and loading footprint before selecting instruments. A simple three-point beam test may characterise one bending response, but it does not automatically reproduce the concentrated compression imposed by a clamping assembly.
Instrument the beam and its contacts
- Define support locations, contact areas, permitted rotation and the applied load distribution.
- Measure beam movement relative to its support chord, using an independent reference where practical.
- Measure local thickness or indentation at the loaded contacts separately.
- Record force throughout the hold, along with the specimen and environment temperatures.
- Include unloaded or fixture references that reveal drift not caused by the loaded beam.
For a symmetric illustrative beam, let the measured midspan movement be 3.0 mm and the movements at the left and right supports be 0.4 and 0.8 mm in the same positive direction. The support chord at midspan moves by their average, 0.6 mm. Chord-referenced midspan movement is therefore 2.4 mm.
These fictional readings remove that rigid support contribution, but do not isolate every compression effect. Local deformation beneath the midspan load can still enter the beam reading. Contact gauges and geometry observations are needed to separate it.
Choose the controlled quantity deliberately
Under maintained load, increasing deformation is a creep observation. Under maintained displacement, falling force is a relaxation observation. A clamping fixture whose stiffness allows both quantities to change creates a coupled response and should be described that way.
Record the initial loading rate and the interval used to define the reference deformation. Otherwise early seating or densification can be counted differently between trials. Monitor the force rather than assuming a nominal weight or initial adjustment maintains the intended beam load through every thermal condition.
Use the actual veneer arrangement, machining and oil-state preparation. The manufacturer’s bending data are conditional on material construction, and ordinary wood creep mechanisms provide no numerical factor for a densified transformerwood beam immersed in oil. Pressboard uniaxial compression data are even further from this combined geometry.
After unloading, examine recovery and residual shape in the stated time window. Inspect the contact areas and bond lines for permanent indentation, splitting or separation. A recovered midspan dimension does not prove the contacts remain undamaged.
Report bending, contact compression and force histories at their instrument locations. Use the measured mechanisms for beam design and a separately validated extrapolation method for service-life prediction.
Remove support movement and contact indentation separately
Keep material/test orientation and conditioned state identified [2]. Continue the assumed 3.0 mm midspan reading with 0.4 and 0.8 mm support movements. The interpolated support chord moves 0.6 mm, leaving 2.4 mm chord-referenced movement.
Assume independent local gauges establish 0.30 mm indentation in the midspan load contact, entering that reading in the same direction. Under an additive small-displacement model, bending movement is 3.0−0.6−0.3 = 2.10 mm. Calling the entire 3.0 mm bending would overstate it by 42.86%.
Against an assumed 2.20 mm bending-only allocation, 2.10 mm passes while the unseparated 2.4 mm would fail. Retain contact damage and support settlement as separate findings; a bending pass does not close either.
References
- Röchling Industrial, Lignostone L I/2-E3-HQ (P2R), Technical Data Sheet, version 2.0, released 20 September 2023.
- IEC, IEC 61061-2:1992, Specification for non-impregnated, densified laminated wood for electrical purposes — Part 2: Methods of test.