An impact test is either a computerized brain assessment used to evaluate concussions or a mechanical engineering test that measures how much energy a material absorbs before breaking. Both are widely used, and which one you’re looking for depends on context: if you’re a parent, athlete, or coach, you’re probably thinking of the concussion test called ImPACT. If you’re in engineering, manufacturing, or a materials science course, you’re looking at the Charpy or Izod test. Here’s how each one works.
The ImPACT Concussion Test
ImPACT stands for Immediate Post-Concussion Assessment and Cognitive Testing. It’s a brief, computer-based screening tool that measures how well your brain handles specific tasks: verbal memory, visual memory, reaction time, processing speed, and impulse control. Athletes typically take it before their season starts to establish a personal baseline, then take it again after a suspected head injury. Comparing the two scores helps clinicians spot cognitive changes that might not be obvious from a conversation alone.
The test has strong detection rates. A study of high school and college athletes found the online version correctly identified 91.4% of concussed individuals. Even more striking, when athletes appeared to be hiding their symptoms (a common problem in competitive sports), the test’s accuracy jumped to 94.6% sensitivity and 97.3% specificity. That means it catches nearly all concussions and rarely flags a healthy brain as injured.
How Baseline Testing Works
Before any injury happens, you sit at a computer and complete a series of timed tasks involving word lists, shape patterns, and reaction prompts. Your scores across the five cognitive areas become your personal reference point. If you later take a hit and need evaluation, you retake the test. A clinician compares your post-injury scores against your baseline to see if memory, speed, or attention has dropped. This comparison is far more useful than a single post-injury score on its own, because everyone’s “normal” is different.
ImPACT scores are one piece of a larger evaluation. They don’t diagnose a concussion by themselves, but they give clinicians objective data to combine with symptom reports, physical exams, and balance assessments. In return-to-play decisions, improving ImPACT scores (trending back toward baseline) are one signal that the brain is recovering.
The Charpy Impact Test
In materials engineering, an impact test measures how much energy a material absorbs when it breaks under a sudden blow. The most common version is the Charpy V-notch test, used across construction, manufacturing, aerospace, and pipeline industries to ensure metals can withstand sudden forces without shattering.
The setup is straightforward. A small rectangular specimen, typically with a V-shaped notch cut into one side, is placed horizontally on a support fixture with the notch facing away from the pendulum. A heavy pendulum swings down from a known height and strikes the specimen on the opposite side of the notch, snapping it. The machine then measures how high the pendulum swings after breaking the specimen. The difference between the pendulum’s starting height and its finishing height tells you exactly how much energy the material absorbed during fracture. A material that absorbs a lot of energy is tough. One that absorbs very little is brittle.
The absorbed energy is measured in joules (or foot-pounds in older U.S. systems). The calculation is simple: the pendulum’s weight multiplied by its height gives potential energy, and the drop in potential energy from start to finish equals the energy the specimen soaked up.
Charpy vs. Izod Tests
The Izod impact test measures the same basic property but uses a different setup. In a Charpy test, the specimen lies flat and the notch faces away from the pendulum. In an Izod test, the specimen is clamped vertically, the notch faces toward the pendulum, and the pendulum strikes above the notch. The Charpy method is more common worldwide and is the standard for most structural steel specifications. The Izod test is more often used for plastics and polymers.
Why Temperature Matters in Material Testing
One of the most important things an impact test reveals is how a material behaves at different temperatures. Many metals, particularly steels with a body-centered cubic crystal structure, undergo a dramatic shift: at warm temperatures they bend and deform before breaking (ductile behavior), but at cold temperatures they snap with little warning (brittle behavior). The temperature where this shift happens is called the ductile-to-brittle transition temperature, or DBTT.
Engineers find the DBTT by running Charpy tests on identical specimens at a range of temperatures and plotting the absorbed energy. The resulting curve shows three distinct zones: an upper shelf where the material is tough and absorbs high energy, a lower shelf where it’s brittle and absorbs very little, and a transition zone between them. A common reference point places the transition at 20.4 joules (15 foot-pounds) of absorbed energy.
This matters enormously in real-world applications. A steel that becomes brittle at minus 10°C is fine for a building in a temperate climate but dangerous for an Arctic pipeline. A material with a lower DBTT can operate safely in colder environments. Impact testing at multiple temperatures is how engineers make that distinction before anything gets built.
Standards and Machine Accuracy
Charpy testing follows strict protocols to ensure results are comparable across labs worldwide. The two primary standards are ASTM E23 (used mainly in the U.S.) and ISO 148-2 (used internationally). The National Institute of Standards and Technology maintains three reference impact machines and evaluates roughly 1,300 machines per year for conformance. Machines certified through the NIST system produce results within 5% or 1.4 joules of one another, whichever is larger. That’s the tightest distribution of impact test results in the world.
Maintaining that accuracy requires periodic verification with certified reference specimens. Labs can’t simply calibrate a machine once and trust it indefinitely. The pendulum striker itself is specified down to edge radius: ASTM E23 now covers strikers with an 8 mm radius and a 2 mm radius, the latter aligning with international ISO standards adopted since 2016.
Two Tests, One Core Idea
Whether you’re measuring how a brain responds to a hit or how a steel beam absorbs a blow, impact testing is about understanding resilience under sudden force. The medical version gives athletes and clinicians a way to track cognitive function before and after injury, catching problems that might otherwise go unnoticed. The engineering version gives manufacturers and builders hard numbers on whether a material will bend or shatter when conditions get harsh. Both rely on comparing a result against a known baseline, and both exist because the consequences of guessing wrong are too serious to leave to intuition.