ASTM D790 is a method of measuring the flexural properties of a plastic using a three point bending fixture and pushing down in the middle until it breaks or bends a specified distance.

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APM Testing provides A2LA accredited services for plastic flexural testing per ASTM D790 at a fair price, with prompt delivery, and a detailed test report. Our laboratory also provides laboratory services for plastic testing, metal testing, rubber testing, oil testing, paint testing, plating testing, adhesive testing, circuit board testing, and other testing.

Purpose: Measure the flexural strength and flexural modulus of a rigid plastic per ASTM D790.

Sample: Seven (7) bars, 5 x 0.5 x 0.125 inches -or- half (0.5) a square foot of sheet, 0.125 inches thick.

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Basic Description: ASTM D790 is a method of measuring the flexural properties of a plastic by setting a test bar across two supports and pushing down in the middle until it breaks or bends a specified distance. The plastic is molded or machined into a rectangular bar prior to testing. During the test, the force on the bar and how much the center is pushed down (deflection) is continuously measured. Many different test dimensions can be used but the most common is to test a 1/8 inch thick test bar laid across two supports 2 inches apart with a single loading nose in the center. Flexural strength (stress) is a measure of how much force a test bar can support before breaking and is calculated using a three point bending formula. Flexural stress at 5% strain is a measure of the force required to bend the test bar a certain amount and is used when the test bar bends too far without breaking. Flexural modulus is a measure of stiffness or rigidity and is calculated by dividing the change in stress by the change in strain at the beginning of the test. ASTM D790 flexural properties are useful for calculating how much a plastic component will flex and if it will break when subjected to bending forces. Other common mechanical properties for plastics include ASTM D256 Izod Impact Strength, ASTM D638 Tensile Properties, and ASTM D648 Heat Deflection Temperature. Flexural strength and flexural stress at 5% strain are typically reported in units of psi (pounds per square inch) or MPa (1,000,000 newtons per square meter). Flexural modulus is typically reported in units of ksi (1000 pounds per square inch) or MPa. Flexural results are reported in a table format with five replicates (individual tests) per sample.

Limitations: Samples thinner than 1/16 of an inch and very soft materials are usually not stiff enough to test per ASTM D790 because they will not support themselves when laid across two supports. Very large samples requiring support spans of more than 16 inches do not fit in our test equipment.


  • MTS Systems, Insight 50, Flexural Tester 10,000 lbf, 1000 lbf, 100 lbf, and 5 lbf load cells.

Method Publisher:


  • Flexural Strength
  • Flexural Modulus
  • Flexural Properties
  • Secant Modulus
  • Young's Modulus

Related Techniques: