Impact Testing Explained: Methods, Applications, and Benefits

What is impact testing?

Impact testing is a critical evaluation process that determines a material or product’s toughness, resilience, and durability when subjected to sudden forces or shocks. This testing is essential in various industries to ensure materials and products' safety, performance, and reliability. Impact testing helps identify potential weaknesses and improve material formulations and product designs by simulating real-world conditions.

Types of impact testing

Several main impact test methods measure a material's performance under impact. The most commonly used methods include Charpy impact testing, Izod impact testing, drop weight testing, and puncture impact testing. Each method employs distinct technologies and serves unique purposes across various industries.

• Charpy impact testing

• Izod impact testing

• Drop weight impact testing

• Puncture impact testing.

Charpy impact testing

Charpy Impact Testing, also known as the “Charpy V-notch test,” is a standardized test method used to determine the impact toughness of materials, particularly metals. It assesses a material's ability to absorb energy during fracture when subjected to a sudden impact. One of the most widely used methods to measure material resilience, it was named after its inventor, French scientist Georges Charpy. This video shows how a typical Charpy impact test is performed:

How Charpy impact tests are performed

• Specimen Preparation: A small, standardized specimen, usually a rectangular bar with a V-shaped notch machined on one side. The notch creates a stress concentration that promotes fracture when impacted. The test setup includes a pendulum hammer, a notched specimen holder, and a digital or analog display to record the absorbed energy. The notched specimen is placed horizontally in the holder, and the pendulum is released from a specific height to impact the specimen at the notch.

• Test Procedure: The specimen is placed horizontally in the testing machine, with the notch facing the direction of the impact. A pendulum hammer is released from a known height, striking the specimen at a predetermined velocity.

• Energy Measurement: The energy absorbed by the specimen during fracture is measured by the decrease in the pendulum’s swing height after impact. This energy is typically reported in joules (J) or foot-pounds (ft-lb).

Charpy impact test applications

Charpy impact testing is extensively used in the construction, automotive, and aerospace industries to evaluate the toughness of metals, composites, and polymers. This test helps ensure structural steel can withstand impacts during earthquakes or other dynamic events in the construction industry.

Charpy impact test standards

• ASTM E23, ASTM D6110, ASTM A370, ASTM D256

• ISO 13479, ISO 148-1

• EN 10045-1, EN ISO 179-1 

Izod impact testing

While Charpy impact testing is widespread for metals, Izod impact testing is more often used for plastics and other softer materials. In Izod testing, the notched specimen is positioned vertically instead of horizontally. Also, the pendulum in the Izod test strikes the specimen at a single point directly above the notch, while in Charpy testing, the pendulum strikes the specimen on its surface opposite the notch. 

Izod test applications

While Charpy impact testing is used primarily for metals, the Izod method is commonly used for polymer and plastic impact testing. It helps assess the impact resistance of plastic materials used in consumer products, automotive components, and packaging materials.

Izod impact test standards

• ASTM D256, ASTM D4508, ASTM D4812

• ISO 180, ISO 148-1, ISO 9854-1

Drop weight testing

Also known as drop tower testing, this method evaluates a material's behavior under high-velocity impacts like collisions and falls. The test setup consists of a drop tower, a weight or impactor, and a specimen holder. The weight is dropped from a predetermined height onto the specimen, and sensors record the force, velocity, and energy during impact.

Drop weight test applications

Although it’s used in hundreds of industries and applications, drop weight testing is widely used in the automotive and sports equipment industries. Drop weight testing for automotive safety helps assess the crashworthiness of automotive components. In sports equipment, it verifies the impact resistance of helmets and protective gear.

Drop weight impact test standards

• ASTM E208, ASTM D7136, ASTM D3763, ASTM F1459

• ISO 6603-2, ISO 3127, ISO 13356

• EN 774, EN ISO 6603-1 

Puncture impact testing

Puncture impact testing measures material durability based on its resistance to puncture or penetration by a pointed object. This test is crucial for evaluating the toughness and durability of protective gear and packaging materials. The test apparatus includes a puncture probe, a specimen holder, and a force measurement system. The probe is driven into the specimen at a controlled speed, and the force required to puncture the material is displayed and recorded using a DAQ instrument.

Puncture impact testing applications

Puncture impact testing is commonly used in the packaging, medical, and sports equipment industries. It helps ensure that packaging materials protect contents from sharp objects and that protective gear can withstand punctures in high-risk environments.

Puncture impact test standards

• ASTM D781, ASTM D3420, ASTM D6098, ASTM D3763

• ISO 6603-2, ISO 7765-2, ISO 8295, ISO 7765

• EN 14125, EN ISO 6603-2

Gardner impact test

The test, primarily used for coatings, assesses the impact resistance of paint, varnish, or other coatings. A falling weight impacts a coated sample, and the resulting damage or cracking is examined.

Gardner impact test standards

• ASTM D2794, ASTM D4226, ASTM D5420

• ISO 6272-1, ISO 6272-2

Rockwell hardness test

This test measures a material’s hardness by measuring its ability to resist localized plastic deformation. A hard steel or carbide ball is pressed into the material under a load, and the indentation depth is measured.

Rockwell hardness test standards

• ASTM D785, ASTM E18, ASTM E140

• ISO 6508-1, ISO 6508-2

Multiaxial impact tests

Multiaxial impact testing expands on traditional impact tests by simultaneously introducing forces from multiple directions. This better mimics real-world conditions where materials are subject to complex stress states rather than simple, single-axis loading. Multiaxial testing provides deeper insight into the actual toughness, flexibility, and resilience of materials under more realistic, multidirectional loading conditions. It may expose more weaknesses or vulnerabilities in the material, providing a better understanding of how it behaves in practical use.

Multiaxial impact test applications

While well-established standards govern traditional tests (ASTM, ISO), multiaxial impact testing is more specialized and often custom-designed for specific industries. There aren't as many widely accepted standards for multiaxial testing yet, but some industries use proprietary tests and simulations to evaluate performance under multiaxial stresses, particularly in sectors like aerospace, automotive, and defense.

A specific example of multi-axial impact testing is the drop tower test used in the automotive industry to simulate a vehicle roof crush scenario during a rollover accident. This test evaluates how a vehicle's roof structure behaves under complex, multi-directional forces during a rollover event involving vertical and lateral forces acting simultaneously. This provides insight into the material's ability to protect occupants and maintain structural integrity during such crashes. This test helps determine if the vehicle meets regulatory standards for roof crush resistance.

Multiaxial roof-crush standards

• FMVSS 216 (Federal Motor Vehicle Safety Standards) (USA)

• UN/ECE Regulation 135 (Roof Strength)

• Global NCAP (New Car Assessment Programme)

Other multiaxial impact standards

• ASTM D3763, ASTM D7192

• ISO 6603, ISO 7765 

The physics of impact testing

Impact and drop testing involve principles from mechanics, particularly dynamics, to evaluate how materials or products respond to sudden forces. The basic mathematical properties and concepts relevant to these tests include:

• Force

• Kinetic Energy

• Potential Energy

• Velocity

• Momentum

• Stress

• Strain

• Impact Toughness

Let’s take a closer look at each of these:

Force

• Definition: Force is the interaction that causes an object to change its velocity or direction.

• Formula: F = ma, where F is the force, m is the object mass, and a is the acceleration.

• Application: In impact testing, the force exerted on a material during an impact is a crucial measurement. The greater the force, the more likely the material will deform or fracture.

Kinetic Energy

• Definition: The energy an object possesses due to its motion.

• Formula: Ek = 1/2 mv2, where Ek​ is the kinetic energy, m is the mass, and v is the object's velocity.

• Application: In impact testing, the energy absorbed by the material (measured by the difference in the object’s (or pendulum's) height before and after impact) is a key indicator of the material's toughness.

Potential Energy

• Definition: The energy stored in an object due to its position or height.

• Formula: Ep = mgh, where Ep​ is the potential energy, m is the mass, g is the acceleration due to gravity, and h is the height.

• Application: In drop testing, the potential energy of the weight or object is converted into kinetic energy when it is released and impacts the specimen.

Velocity

• Definition: The rate at which an object changes its position.

• Formula: v = 2gh ​ (for an object dropped from height h) 

• Application: In drop tests, the object's velocity at the moment of impact is calculated to determine the force and energy involved in the collision.

Momentum

• Definition: The quantity of motion an object has, which depends on both its mass and velocity.

• Formula: p = mv, where p is the momentum, m is the mass, and v is the velocity.

• Application: In impact testing, momentum helps analyze the collision between the pendulum (or weight) and the specimen, influencing the material's response.

Stress (σ)

• Definition: The internal force per unit area within a material arises from externally applied forces.

• Formula: σ = F/A, where σ is the stress, F is the applied force, and A is the cross-sectional area.

Strain (ϵ)

• Definition: The deformation or displacement of material in response to stress.

• Formula: ϵ = LL, where ϵ is the strain, LΔ is the change in length, and L is the original length.

• Application: Stress and strain are fundamental in assessing how a material deforms under impact, helping to determine its toughness and resilience.

Impact Toughness

• Definition: A measure of the energy absorbed by a material before fracturing.

• Formula: Toughness is often represented as the area under the stress-strain curve or calculated from the energy absorbed in impact tests (e.g., Charpy or Izod).

• Application: Impact toughness is a critical property in materials science. It indicates how well a material can withstand sudden impacts without breaking.

These properties and formulas are integral to analyzing and interpreting impact and drop testing results, providing insight into a material's ability to withstand dynamic forces and shocks.

The importance of impact testing

Impact testing ensures materials and products' safety, performance, and reliability across various industries. Here are some key reasons why impact testing is essential:

• Safety Assurance: Impact testing helps identify potential weaknesses in materials and products that could lead to catastrophic failures under sudden loads or shocks. For example, impact testing in the automotive industry ensures vehicle components can withstand collisions, reducing the risk of passenger injuries.

• Performance Optimization: Manufacturers can optimize their formulations and designs to enhance performance by understanding how materials respond to impact. For example, impact testing of composite materials in aerospace applications helps engineers develop lighter and more robust components.

• Quality Control: Regular impact testing during the production process ensures that materials and products meet specified standards and requirements. This helps maintain consistent quality and reduces the risk of defects that could compromise safety and performance.

• Research and Development: Impact testing is essential for developing new materials and products. By evaluating the impact resistance of experimental materials, researchers can identify promising candidates for further development and commercialization.

Impact testing industries and applications

Impact testing is used across various industries, each with unique requirements and standards. Here are some industry-specific applications of impact testing:

Automotive industry 🚗

Impact testing in the automotive industry is critical for evaluating the crashworthiness of vehicle components and ensuring passenger safety. Various impact tests, including Charpy, Izod, and drop weight testing, assess the impact resistance of metals, plastics, and composites used in car bodies, bumpers, and interior components. For example, drop weight testing simulates real-world crash scenarios to evaluate automotive components' energy absorption and deformation during collisions.

Aerospace industry ✈️

Impact testing in the aerospace industry ensures the safety and reliability of aircraft components subjected to high-velocity impacts, such as bird strikes and debris collisions. Charpy and drop weight testing are commonly used to assess the toughness and impact resistance of aircraft structures, engines, and landing gear materials. For instance, drop weight testing helps evaluate composite materials' damage tolerance in aircraft fuselages and wings.

Construction industry 🏗️

Dynamic load testing is essential in the construction industry to ensure the durability and safety of structural materials, such as steel and concrete. Charpy impact testing is widely used to assess the toughness of structural steel used in buildings, bridges, and infrastructure projects. The importance of impact testing in construction is undeniable. By simulating real-world impact conditions, structural impact testing helps engineers design safer and more resilient structures that can withstand natural disasters like earthquakes and hurricanes.

Consumer goods industry 📲

In the consumer goods industry, impact testing evaluates products' durability and safety, such as electronics, appliances, and packaging materials. Izod and puncture impact testing are commonly used to assess the impact resistance of plastics and polymers in consumer products. For example, puncture impact testing ensures that packaging materials can protect contents from sharp objects and rough handling during shipping and storage.

Sports equipment industry ⚽

The sports equipment industry relies on impact testing to ensure the safety and performance of protective gear, such as helmets, pads, and body armor. Drop weight and puncture impact testing evaluate the impact resistance of materials used in sports equipment. For instance, drop weight testing helps assess helmets' energy absorption and deformation during high-velocity impacts, ensuring they adequately protect athletes.

Medical industry 🏥

In the medical industry, impact testing evaluates the durability and safety of medical devices such as implants, prosthetics, and surgical instruments. Puncture impact testing is commonly used to assess the resistance of materials used in medical devices to penetration by sharp objects. For example, puncture impact testing ensures surgical gloves and protective clothing can withstand punctures from needles and other sharp instruments.

Energy industry ⛽

The energy industry uses impact testing to evaluate the durability and performance of materials used in power generation and distribution systems. Charpy and drop weight testing are commonly used to assess the toughness and impact resistance of metals and composites used in wind turbines, pipelines, and electrical transmission towers. For example, drop weight testing helps evaluate the impact resistance of composite blades used in wind turbines, ensuring they can withstand high-velocity impacts from debris and extreme weather conditions.

Impact test sensors

Impact testing relies on a range of data acquisition instruments and software to measure and analyze the response of materials under sudden forces or shocks. Load cells, accelerometers, strain gauges, high-speed cameras, displacement sensors, temperature sensors, and piezoelectric sensors provide the necessary data for a comprehensive evaluation. 

Data acquisition systems, signal processing software, finite element analysis software, data visualization tools, video analysis software, and specialized impact testing software play crucial roles in processing, analyzing, and visualizing this data. Together, these tools ensure accurate, reliable, and insightful results, contributing to safer and more durable materials and products across various industries.

• Load cells measure the force exerted during an impact. They are typically placed in the impact path to capture the force data in real time. Load cells are essential for understanding the force dynamics during impact testing.

• Accelerometers measure the acceleration of the specimen during impact. These sensors are often attached to the specimen or the impactor to capture acceleration data, which can be used to calculate the impact velocity and energy absorption.

• Strain gauges measure the strain or deformation of the specimen during impact. These sensors are attached to the specimen's surface and detect minute changes in length, providing valuable information about the material's response to impact forces.

• Force sensors measure force or weight. They convert an applied load into an electrical signal, which can then be measured and recorded.

• High-speed cameras capture high-frame-rate video of the impact event. This visual data helps analyze the material's deformation and slow-motion failure mechanisms, making high-speed cameras beneficial for studying complex impact behaviors.

• Displacement sensors measure the displacement or movement of the specimen during impact. They provide data on how much the specimen deforms under impact conditions, critical for evaluating material toughness and flexibility.

• Temperature sensors monitor the temperature of the specimen during impact testing. Some materials exhibit temperature-dependent behavior, so monitoring temperature changes can provide additional insights into the material's performance under different conditions.

• Piezoelectric pressure and force sensors convert mechanical stress into an electrical signal. They measure dynamic pressure and force changes during impact events, providing high-resolution data for analysis.

Impact testing data acquisition systems

DAQ (data acquisition) systems are heavily used during impact testing applications. DAQ systems contain signal conditioning and amplifiers, analog-to-digital converters, software, a graphical display, and data storage. 

A perfect example of such a system is the SIRIUS product line from Dewesoft. SIRIUS has various input modules compatible with the sensors mentioned in the previous section: strain gauges, accelerometers, load cells, temperature sensors, and more. SIRIUS is also capable of recording synchronized video data from high-speed cameras. The KRYPTON product line provides a wide temperature operating range, IP67 protection from the elements, and high shock and vibration ratings for harsh environmental conditions. SIRIUS and KRYPTON instruments can be used separately or connected to create integrated, synchronized systems.

Impact test benches

Impact testing requires specialized test benches or equipment designed to apply controlled impacts to materials and measure their response. Different test bench types are used depending on the specific impact testing method, such as Charpy, Izod, drop weight, and multi-axis impact tests. In addition to the primary mechanism needed to perform the test, some benches also include instrumentation configured to capture and analyze the data from the test. These are referred to collectively as instrumented test benches.

The drop test system below is an excellent example of an instrumented bench. In this video, a ruggedized KRYPTON DAQ module is subjected to a high-g force drop test.

Impact testing signal processing software

Signal processing software analyzes the raw data collected during impact testing. This software can filter noise, amplify signals, and perform mathematical operations to extract meaningful information from the sensor data. Examples include DewesoftX for data acquisition and mathematical analysis, MATLAB®, and Python™ with specialized libraries like NumPy (“numerical Python”) for array math and SciPy (“scientific Python”) for curve-fitting.

FEA (finite element analysis) software simulates impact events and predicts material behavior under impact conditions. It helps understand the material's stress distribution, deformation, and potential failure points. Common FEA software includes ANSYS® LS-DYNA® and Abaqus® FEA.

Data visualization software helps create graphical representations of impact test data. This software can generate plots, graphs, and 3D models to visualize the force, displacement, and strain data. Examples include Dewesoft®X, OriginLab®, Microsoft® Excel®, and Tableau®.

Video analysis software processes high-speed camera footage to analyze the impact event frame by frame. This software can measure displacement, velocity, and strain from the video data, providing a detailed visual understanding of the material's behavior.

Some impact testing systems use specialized, proprietary software to control the testing apparatus, collect data, and perform initial analysis.

Summary

Impact testing is vital for evaluating materials and products' toughness, resilience, and durability across various industries. Real-world impact simulation helps identify potential weaknesses, optimize material formulations, and improve product designs. The main types of impact testing, including Charpy, Izod, drop weight, and puncture impact testing, employ distinct technologies and serve unique purposes. Testing for material weaknesses ensures safety, performance, and reliability in the automotive, aerospace, construction, consumer goods, sports equipment, medical, and energy industries.

By understanding the importance of impact testing and its applications, manufacturers and researchers can develop safer, more reliable, high-performing materials and products that meet industry standards and consumer expectations. As technology advances and new materials are developed, the role of impact testing will continue to evolve, driving innovation and progress across various fields.