Izod Impact
An Izod impact test is a standardized impact toughness test that measures the energy absorbed when a notched specimen, clamped as a cantilever, is struck by a pendulum on the notched side. Results are reported as impact strength in J/m or kJ/m², indicating resistance to fracture under sudden shock. This test is widely used for plastics and metals to screen for brittle fracture risk and notch sensitivity.
In a CNC or quality-control setting, Izod impact results guide material selection for parts exposed to shipping drops, snap fits, thin walls, hinges, or assembly abuse. The test's simulated notch acts like the stress concentrations created by machined corners, drilled holes, and routed details. Before quoting a new plastic or aluminum grade, a shop may review Izod values to anticipate chipping, cracking, or splitting during trimming, drilling, press-fit assembly, or edge finishing. Because the pendulum test is fast and repeatable, it lets shops compare resin lots or validate changes without full product drop tests. However, results are geometry-sensitive: the coupon's notch radius, depth, and surface finish must be controlled, just as tool marks and sharp corners in the finished part must be managed. It is a screening metric, not a direct predictor of real part survival; brittle materials can cause scrap, tool breakage, or field failures.
What does a high Izod value mean?
A high Izod value means the material absorbed more energy before fracture, indicating higher apparent impact toughness under the test conditions. It is a good sign for resistance to sudden shock in machined or molded parts.
How does the Izod test differ from the Charpy test?
Izod clamps a notched specimen vertically as a cantilever and strikes it near the notch, while Charpy supports a notched specimen horizontally and strikes it at midspan. The two tests are not directly interchangeable.
Why is the notch important in an Izod impact test?
The notch creates a controlled stress concentration, so the test measures crack initiation and brittle fracture sensitivity rather than general bulk strength. Machined corners, holes, and tool marks create similar stress risers in real components.