What is Impact Resistance?
The impact resistance, or toughness, of a material is its ability to absorb energy without fracturing or rupturing, even if it plastically deforms. Technically, it is the integral of energy divided by volume, aka the stress-strain curve we’ve discussed in previous blogs. It is similar to resilience, except the upper limit of integration is unrestricted. There are several ways to measure impact resistance, including the Izod Impact Test:
and the Charpy impact tests:
But the materials we commonly use at PennCoat frequently undergo the Navy’s MIL-D-3134J Military Specification for Deck Covering Materials, which addresses materials used to cover shipboard interior decks in sanitary and other wet spaces. The Navy classification scheme is as follows:
- Type 1: Deck-covering materials 1/4 inch thick with exposed chips (marble, glass, rock, etc.), in either of two classes:
- Class 1: Resin emulsion and latex mastic
- Class 2: Two part systems containing a base and a curing agent
- Type 2: Uniformly colored resin emulsion or latex mastic in thicknesses of 1/8 to 1/4 inch
Testing the Material
The material to be tested under MIL-D-3134J is prepared in an exacting fashion:
- Mix the deck-covering material according to manufacturer’s instructions.
- Trowel a 1/8- to 1/4-inch thick coat onto two 6-inch x 6-inch x 1/8-inch clean steel plates.
- Cure at room temperature for at least 96 hours but no longer than 336 hours.
- Grind Type 1 materials smooth using dry 60-grit sandpaper on a power sander.
- Finish or seal the specimens according to manufacturer’s instructions.
Each of the two specimens is tested separately by placing it on a solid horizontal surface. The tester then drops a two-pound solid steel ball onto the center of the plate from a height of eight feet. The ball is dropped twice on each plate, which is then inspected to see if the covering has fractured, cracked or otherwise failed. It’s a qualitative pass/fail test, not a quantitative one.
Loyal readers recall that we’ve been using Dur-A-Flex Poly-Crete MD, a 100-percent solids, aromatic, cementitious urethane system blended with graded silica and fine fillers, as our example for this series of articles about the physical characteristics of coatings and films. Dur-A-Flex prepares samples having a 1/8-thick coating for testing impact resistance. As you might expect, Poly-Crete MD passed the MIL-D-3134J, and, we suspect, with flying colors.