Impact resistance is an essential characteristic for materials used on surfaces in high-traffic areas. When selecting from different options for projects, such as hotels or retail, it is crucial to choose those that offer greater resistance to impact damage.

What will you learn in this article?

• What determines a material's impact resistance
• How impact resistance is measured
• Which materials tend to be more resistant to impact

What determines a material's impact resistance?

A material's impact resistance is influenced by a number of factors that determine how it will react when a load or impact is applied to it. These include the internal composition of the material, its properties, and other factors. Below, we detail the main elements that influence this characteristic.

Internal composition and structure

The internal composition of a material is a fundamental factor that determines its ability to resist external forces. Those with a homogeneous structure efficiently distribute the energy generated by impacts, thus reducing the risk of fractures or significant damage. On the other hand, those with a porous structure or internal cavities tend to be more vulnerable, as the energy is not dispersed evenly, increasing the possibility of breakage or deformation.

Toughness vs. hardness: different concepts

Although they are related terms, the hardness and toughness of a material are two distinct properties. Hardness refers to a material's ability to resist abrasion or scratching, while toughness refers to the material's ability to absorb energy without breaking. A material can be hard, such as quartz, but if it does not have sufficient toughness, it can easily fracture under a strong impact. Toughness is essential to ensure that a material does not break under stress.

Other external conditions: temperature, support, geometry, thickness

External conditions can also influence a material's impact resistance. The temperature to which a material is exposed can affect its flexibility or rigidity. In addition, the shape of the material, its thickness, and the type of support on which it rests play an important role in its ability to withstand impact. A thin or poorly supported material may be more prone to fracture when struck.

How is impact resistance measured?

The impact resistance of materials is evaluated using different tests that measure the amount of energy a material can absorb without breaking or suffering permanent deformation. Below, we describe the most common methods for measuring impact resistance.

Pendulum test: Charpy test / Izod test

The Charpy test and the Izod test are standard tests for measuring the toughness of materials against impact. Both tests measure the amount of energy absorbed during the fracture of a material test piece, providing an assessment of its ability to resist impact damage. The key difference between the two lies in the shape of the test piece and the type of support:

• Charpy test: In this test, the test piece has a notch in the centre (usually V-shaped) and is supported horizontally. A pendulum is released from a specified height and strikes the test piece. The energy absorbed is measured from the angle of displacement of the pendulum after impact. This method is suitable for materials that experience a type of fracture that can be easily measured, such as metals.
• Izod test: In contrast, in the Izod test, the test piece is vertical and supported at a single point at its base. The pendulum is also dropped from a specific height and strikes the material. The energy absorbed is calculated in the same way, but the test design allows the material's response to more localised impacts to be studied.

Free fall/ball impact test

The free fall or ball impact test is a method used to evaluate resistance to impact from falling objects or concentrated blows. In this test, a metal sphere is dropped onto the surface of a material from a specific height, according to the standard. In some cases, heavier spheres or greater heights are used to increase the severity of the test.

Compression and flexion test

Although not specifically designed to measure impact resistance directly, compression and flexion tests allow the evaluation of how a material reacts to concentrated or distributed loads, which are common conditions in industrial and commercial environments. These tests focus on a material's ability to resist deformation or breakage when a significant external load is applied.

• Compression test: a test piece of the material is placed between two plates and subjected to an axial load. The load is gradually increased until the material experiences significant plastic deformation or failure.

• Bending test: Here, a test piece of the material is placed on two supports, and a load is applied to the centre of the test piece. As the load increases, the material bends until it reaches a point of breakage or irreversible deformation.

Which materials are typically most impact resistant?

When selecting materials for applications exposed to constant impact or shock, such as countertops or furniture, impact resistance is a key factor. The most common materials used in these applications include natural stone, quartz surfaces, wood, and other composite materials. Below, we will analyse how these materials behave in terms of impact resistance and how they perform in specific tests.