Standard Test Methods for Structural Panels in Flexure - PDF

ASTM D3043 Bend Fixture – Universal Grip Data Sheet (PDF)

 

ASTM D3043 covers flexural testing of structural panels: plywood, oriented strand board (OSB), and other wood-based and composite panels. It gives the panel's bending stiffness (EI), modulus of elasticity (MOE) and modulus of rupture (MOR), the values used to rate floors, roof sheathing and wall panels.

ASTM D3043 Methods A, B, C and D

• Method A – Center-point flexure: a simply supported strip loaded at mid-span (three-point bend). The most common lab method for MOE and MOR.

• Method B – Two-point flexure: load applied at two points, each 1/4 of the span in from the supports, giving a zone of constant moment between the load points.

• Method C – Pure moment: equal and opposite moments applied through free-moving loading frames on large specimens, often a full panel. Used when strength or stiffness varies across the panel.

• Method D – Quality assurance flexure: a center-point test with smaller specimens and a faster rate, widely used for mill QA of OSB.

Specimen Size and Span (Method A)

• Width: 25 mm (1 in) for panels under 6.4 mm (1/4 in) thick; 50 mm (2 in) for thicker panels

• Span: at least 48× the nominal thickness when the face grain or strands run parallel to the span; at least 24× when perpendicular

• Length: span plus 50 mm (2 in) of overhang

• Method D: 75–115 mm (3–4.5 in) wide, span 24× thickness

• Condition specimens to constant weight before testing (wood panel standards commonly use 20 °C and 65% RH); confirm exact values against your copy of D3043

Loading Rate

Method A uses a crosshead rate N = z × L² ÷ (6 × d), with a strain rate z = 0.0015 mm/mm/min (±25%). L is the span and d the panel thickness. Method D uses z = 0.0075 so the panel fails in about 1 minute (never under 10 s or over 10 min).

Calculations

Bending stiffness EI = (L³ ÷ 48) × (P/Δ)

MOE = EI ÷ I, with I = b × d³ ÷ 12

MOR = (Pmax × L ÷ 4) ÷ S, with S = b × d² ÷ 6

P/Δ is the slope of the straight part of the load–deflection curve, measured at mid-span.

Worked Example (Method A)

A 12 mm plywood strip, 50 mm wide, face grain parallel to the span. Span L = 48 × 12 = 576 mm. Rate N = 0.0015 × 576² ÷ (6 × 12) = 6.9 mm/min.

Slope P/Δ = 20 N/mm, so EI = (576³ ÷ 48) × 20 = 7.96 × 10⁷ N·mm². I = 50 × 12³ ÷ 12 = 7,200 mm⁴, so MOE = 11.1 GPa.

Maximum load 400 N: moment = 400 × 576 ÷ 4 = 57,600 N·mm. S = 50 × 12² ÷ 6 = 1,200 mm³, so MOR = 48 MPa.

Equipment

• Universal testing machine with a load cell sized to the panel; a 5 kN cell covers most Method A and D strips

• Bend test fixture with adjustable span, rounded supports and a loading nose that let the panel rotate freely

• Deflection measurement: LVDT or deflectometer at mid-span; crosshead travel includes machine compliance

• Large reaction frame and loading yokes for Method C full-panel tests

Related Standards

• ASTM D198 – static tests of lumber in structural sizes

• ASTM D1037 – wood-base fiber and particle panel materials

• ASTM D2718 – planar (rolling) shear of structural panels

• ASTM D5456 – structural composite lumber

• ASTM D790 – flexural properties of plastics

ASTM D3043 FAQ

What is the difference between Methods A, B, C and D?

A is center-point (three-point) flexure, B is two-point flexure with loads at the quarter points, C is pure moment flexure on large panels, and D is a faster center-point test for quality assurance.

What span does ASTM D3043 Method A use?

At least 48 times the panel thickness when the face grain runs parallel to the span, and at least 24 times when it runs perpendicular.

How fast is a D3043 test?

Method A uses N = z × L² ÷ (6 × d) with z = 0.0015 mm/mm/min. Method D uses z = 0.0075, so failure comes in about 1 minute.

What results does D3043 give?

Bending stiffness EI, modulus of elasticity (MOE), maximum moment and modulus of rupture (MOR), plus the failure mode.