ASTM D790 and ISO 178 Test (Flexural Properties Testing)

Scope

ASTM D790 and ISO 178 are standard test methods used to evaluate the bending properties of rigid and semi-rigid plastics, including fiber composites with reinforcements. These methods establish a framework for measuring a material’s resistance to bending, maximum stress before breaking, and other relevant mechanical properties within bending loads.

The Procedure

ASTM D790 and ISO 178 involve a three-point testing procedure bend test. Here’s a simplified breakdown:

• Specimen Preparation: At this point, samples are meticulously prepared from plastic sheets or plates, adhering to the specified dimensions outlined in the standards.

• Test Fixture Setup: A three-point bend test fixture is employed, featuring two support points on the bottom and a loading point positioned in the center at the top of the specimen.

• Testing Process: A controlled force is steadily applied to the center of the specimen through the loading point, causing it to bend. The force and deflection of the specimen are both measured throughout the test.

• Test Termination: The test ends when the specimen reaches a pre-defined deflection (typically 5%) or fractures.

Data Analysis

The collected data, comprising force and deflection measurements, is then utilized to calculate crucial flexural properties. These factors include:

• Flexural Modulus: This measures the material’s degree of resistance to elastic distortion under the bending force.
• Strength: Representing the maximum pressure the sample can take before giving in during the test.
• Yield Strength: This means the stress level at which the material exhibits a permanent deformation upon bending.

Specimen Size Considerations

While ASTM D790 and ISO 178 share the core principles of three-point bend testing, they differ slightly in preferred specimen size. ASTM D790 recommends a cross-section of 3.2 mm x 12.7 mm, whereas ISO 178 favors a larger specimen with a depth of 4 mm.

Further Analysis

You can employ additional data analysis techniques beyond the fundamental flexural properties to glean further insights into a material’s behavior under bending loads. These advanced methods may involve:

• Stress-Strain Curve Analysis: Illustrating the correlation between applied force and the resulting pressure on the specimen. This provides a visual representation of the material’s behavior throughout testing.
• Fracture Surface Analysis: Here, the examination of specimens using a microscopic technique is conducted, revealing vital information about fracture mode, and potentially indicating material flaws or weaknesses.

Applications of Flexural Testing

The following are some prominent applications:

• Automotive Components: Assess the bending strength of automotive components such as dashboards, bumpers, and interior trim parts.
• Aerospace Industry: Evaluating the flexural properties of lightweight composite materials used in aircraft structures.
• Building and Construction: Characterizing the bending performance of plastic pipes, panels, and roofing materials.
• Consumer Products: Testing the bending behavior of plastic toys, electronic housings, and other consumer goods.

Choosing Between ASTM D790 and ISO 178

ASTM D790 and ISO 178 provide standardized methods for flexural testing of plastics. However, some key factors can influence which standard to choose:

• Industry Standards: Specific industries may have established preferences for one standard. It’s crucial to follow relevant industry standards for consistency and regulatory compliance.
• Specimen Size: If specimen size constraints exist, consider the preferred sizes outlined in each standard (ASTM D790: 3.2 mm x 12.7 mm vs. ISO 178: 4 mm depth).
• Material Type: While both standards apply to various plastics, some specific material types may have established practices favoring one standard only. Consulting relevant material data sheets or industry experts can be helpful.

Conclusion

ASTM D790 and ISO 178 are essential standards for assessing the flexible properties of plastics, providing critical insights that aid in product development and quality assurance. They ensure that materials meet rigorous standards and contribute to innovative and durable products while navigating the complexities of material testing and leveraging trending science for success.

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