In many real-world break-ins, riots, or attacks, threats start with tools, brute force, and momentum. These are moments that define forced-entry attempts. The success or failure of security systems often depends on how materials respond to this impact.
While ASTM D256 is not a forced-entry or security standard, it's an impact resistance test that can offer insight into how certain plastics and composite materials behave under sudden impact forces. It plays a critical role in understanding how these materials stand up to the kinds of blunt force attacks common in real-world scenarios.
From retail storefronts vulnerable to blunt force attack to a healthcare clinic that needs protection from street-side violence, TSS builds and validates security systems with real-world performance in mind.
What Is ASTM D256?
ASTM D256 is the Standard Test Method for Determining the Izod Pendulum Impact Resistance of Plastics. It’s a material characterization tool that measures how much energy a plastic material can absorb when struck by a sudden, concentrated force before it breaks.
Here’s how it works:
- A precisely notched plastic specimen is clamped like a vertical cantilever and struck by a pendulum of known energy.
- The energy absorbed to break the specimen is recorded.
- Results are measured in ft-lb/in or J/m, indicating the material’s ability to resist fracture under high-stress, low-duration impact.
The notch creates a controlled stress riser to compare plastics’ toughness. Izod values do not directly predict system-level forced-entry performance; use them only as one input when selecting plastic materials.
While this simulates potential failure points, ASTM D256 is a safety-focused material test—not a simulation of forced-entry or security threats.
When Are These Izod Impact Testing Methods Applicable?
ASTM D256 is relevant when evaluating plastic components (e.g., acrylic or polycarbonate glazing, plastic liners, or polymer inserts) used in secure assemblies.
This test is often referenced when specifying materials in retail, healthcare, corporate, municipal, and government environments.
Note: ASTM D256 contains multiple Izod methods (A–E). All report absorbed energy per unit width (or area under the notch). For unnotched plastics, ASTM D4812 applies; for Charpy on plastics, see ASTM D6110; ISO 180 is the international Izod analogue.
Using ASTM D256 in Combination With Ballistic Standards
While ASTM D256 is critical for evaluating impact resistance, it’s not a substitute for ballistic testing.
When designing or specifying a ballistic system, all components—glazing, doors, framing, panels—should be tested and certified to the appropriate standards. That’s the only way to ensure real-world performance under actual threat conditions.
At Total Security Solutions, we work with clients to layer these protections strategically, combining ballistic and forced-entry-rated materials to ensure that no single point of failure compromises your system.
Contact us today to learn more.
While ASTM D256 offers valuable insight into impact resistance, it’s not a security or forced-entry standard. For a complete picture, consider it alongside UL 752 for ballistic resistance, SD-STD-01.01 for system-level ballistic and forced-entry protection, and ANSI Z97.1 or 16 CFR 1201 for safety glazing in architectural settings.
Frequently Asked Questions About ASTM D256
What does it mean to “break standard test specimens” in ASTM D256 testing?
In ASTM D256 testing, a standard test specimen refers to a precisely measured plastic sample, typically notched to create a consistent failure point. The test measures how much impact energy is required to break this specimen when struck by a pendulum. This promotes consistent, repeatable results when comparing the toughness of different plastic materials.
How does impact energy in standard test methods relate to real-world threats like forced entry?
Impact energy — measured during ASTM D256 testing — represents how much kinetic energy a material can absorb before it breaks. In a forced-entry scenario, that might mean a window being struck with a hammer or a door facing being hit with a crowbar. A higher impact energy rating means the material is better at absorbing sudden force without shattering or cracking.
What is notch sensitivity, and why does it matter in Izod pendulum impact resistance testing?
Notch sensitivity is a material’s tendency to fail at areas of concentrated stress like edges, corners, or surface flaws. Since most attacks target weak points, ASTM D256 test methods require specimens to be notched, simulating these vulnerabilities. The results help assess how materials like polycarbonate or acrylic will behave under sudden, high-stress impact in the field.
What does it mean when a material offers twice the energy absorption in ASTM D256 testing?
It means the material can withstand significantly more impact force before breaking. This is a strong indicator of material toughness. Materials with relatively low energy absorption may crack or fail quickly under stress. The more energy absorbed and the less energy lost, the better equipped materials are to resist fracture during repeated or intense impact events.
How do factors like pendulum air drag and velocity at impact affect Izod impact resistance test results?
In ASTM D256 testing, accurate measurement of pendulum velocity at impact is critical to determining how much energy is absorbed by the material when struck. Machine calibration and correction procedures specified in the standard ensure consistent energy measurement (including friction/windage corrections).
Related Resources
Our goal is to help you make informed decisions that protect your people, secure your assets, and support your mission—without sacrificing design or functionality. These resources offer guidance for your project.
Ballistic Door Solutions Guide
10 Things That Make or Break a Bullet Resistant Barrier Project
Guide to Improving Physical Security By Addressing the Human Factor
