ISO 179 Plastics - Determination of Charpy Impact Properties

The Charpy method for determining impact properties described in the ISO 179 series of standards has a wider range of applications than that given in the ISO 180 standard and is more suitable for testing materials that exhibit interlaminar shear fracture or surface effects caused by environmental factors.

This method is suitable for use with the following range of materials:

• Rigid thermoplastic molding and extrusion materials (including filled and reinforced compounds in addition to unfilled types) and rigid thermoplastic sheets
• Rigid thermoset molding materials (including filled and reinforced compounds) and rigid thermoset sheets (including laminates)
• Fiber-reinforced thermoset and thermoplastic composites containing unidirectional or multidirectional reinforcements (such as mats, woven fabrics, woven rovings, chopped strands, combination and hybrid reinforcements, rovings, and milled fibers) or sheets made of pre-impregnated materials, including filled and reinforced compounds
• Thermotropic liquid crystal polymers.

Notched specimens are not normally suitable for use with rigid cellular materials, long-fiber-reinforced composites, or thermotropic liquid crystal polymers. In these cases, unnotched specimens may be used. This method is suitable for specimens molded to selected dimensions, machined from the center section of a standard multipurpose test specimen, or machined from finished or semi-finished products such as molds, laminates, and extruded or cast sheets.

The “ISO 179 Plastics - Determination of Charpy impact properties” standard, developed by the International Organization for Standardization (ISO), consists of the following subsections published under the same title:

• The standard "ISO 179-1 Part 1: Uninstrumented Impact Testing" describes a method for determining the Charpy impact strength of plastics under specified conditions. This standard defines a number of different specimen and test configurations. Different test parameters are specified depending on the material type, test specimen type, and notch type. This method can be used to examine the behavior of specific specimen types under defined impact conditions and to predict the brittleness or toughness of specimens within the limitations of the test conditions. It can also be used to determine comparative data from similar material types.

The test specimen, supported principally at its ends as a horizontal beam, is struck with a single impactor with the impact line centered between the supports and is bent at a high, nominally constant rate. In the case of edge impact with notched specimens, the impact line is directly opposite the single notch. The method determines the preferred dimensions of the test specimen.

Tests performed on samples of different sizes or with different notches, or on samples prepared under different conditions, may yield non-comparable results. Other factors, such as the instrument's energy capacity, impact velocity, and sample conditioning, may also affect the results.

Consequently, when comparative data are needed, these factors should be carefully controlled and recorded. The method is not intended to be used as a data source for design calculations. However, information about a material's typical behavior can be obtained by testing at different temperatures, varying the notch radius and/or specimen thickness, and testing specimens prepared under different conditions.

• The standard "ISO 179-2 Part 2: Instrumented Impact Testing" describes a method for determining the Charpy impact properties of plastics from force-deflection diagrams. ISO 179-1 defines different types of bar-shaped test specimens and test configurations, as well as test parameters dependent on the material type, test specimen type, and notch type. Dynamic effects such as load cell/striker resonance, test specimen resonance, and initial contact/inertia peaks are addressed in this document.

The ISO 179-1 standard is suitable for characterizing impact behavior solely by impact strength, using devices whose potential energy is approximately equal to the specific fracture energy to be measured. This standard is used to record a force-deflection or force-time diagram for detailed characterization of impact behavior and to develop automated devices that eliminate the need for energy matching.

The method described in this standard is also suitable for:

• To obtain more and different material properties under impact conditions.
• Audit the Charpy test procedure, as this instrumentation allows the detection of typical operational errors, such as the sample not being in close contact with the supports.
• Automatically detecting the type of fracture.
• Pendulum type instruments to avoid frequent replacement of pendulum hammers.
• To measure fracture mechanical properties described in other ISO standards.

The ISO 179-1 standard applies to the range of materials that can be tested by this method.

For general comparability of test results, the ISO 179-1 standard should be consulted.

Information about the typical behavior of materials can be obtained by testing at different temperatures, varying the notch radius or specimen thickness, and testing specimens prepared under different conditions. It is not the purpose of this standard to provide an interpretation of the mechanism occurring at each point on the force-deflection diagram. Such interpretations are a task of ongoing scientific research.

Test results obtained with this method can only be compared if the test specimen preparation conditions and test conditions are identical. Therefore, the impact behavior of the finished products cannot be predicted directly from this test.

In principle, a rod-shaped test specimen, supported at its ends like a horizontal beam, is struck vertically with the impact line centered between the supports and is deflected at a high, nominally constant rate. During impact, the impact force is recorded as a function of time or deflection. Depending on the evaluation method, the deflection of the specimen can be measured directly with appropriate measuring instruments or, in the case of frictionless impact carriers, by calculating the initial velocity and force as a function of time. The force-deflection diagram obtained in these tests describes the high-deflection-rate impact behavior of the specimen, and various aspects of the material's properties can be inferred from this diagram.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, has a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the ISO 179 Plastics - Determination of Charpy Impact Properties standard.