ASTM D638

Introducing ASTM D638 – Industrial Physics

ASTM D638 is the definitive test method for determining the tensile properties of plastics, including tensile strength, elongation, tensile modulus, and yield behaviour. It is one of the most widely used mechanical‑testing standards in the plastics industry, providing a reliable basis for material comparison, quality control, and specification compliance.

The method applies to rigid and semi‑rigid plastics, moulded and extruded shapes, and sheet materials — making it essential for manufacturers, converters, and laboratories working with polymer‑based products.

What ASTM D638 Covers

ASTM D638 defines a controlled procedure for evaluating the tensile behaviour of plastic materials using a universal testing machine (UTM). Key elements include:

• Preparing standardized dog‑bone‑shaped specimens (Types I–V)
• Conditioning samples under controlled temperature and humidity
• Applying tensile force at a defined rate of extension

Measuring:

• Tensile strength
• Tensile modulus
• Elongation at break
• Yield stress and strain
• Reporting results in accordance with specimen type and test speed

The method applies to:

• Rigid and semi‑rigid plastics
• Moulded and extruded materials
• Thermoplastics and thermosets
• Filled, reinforced, and composite plastics
• Sheet, plate, and film (above minimum thickness requirements)

ASTM D638 ensures consistent, comparable tensile‑property data across laboratories and production environments.

Where ASTM D638 Is Used

This standard is widely used across the plastics and manufacturing sectors:

• Polymer and resin producers
• Injection‑moulding and extrusion operations
• Automotive and aerospace suppliers
• Consumer‑product manufacturers
• R&D and formulation laboratories
• Quality‑control and compliance testing

It supports both routine material verification and advanced mechanical‑performance evaluation.

Why Tensile‑Property Testing Matters

Understanding tensile behaviour is essential for:

• Ensuring material strength and durability
• Predicting performance under load and deformation
• Validating formulation changes and material substitutions
• Meeting industry, regulatory, and customer specifications
• Supporting design decisions and structural analysis

Tensile testing is a foundational mechanical‑property assessment used alongside impact, flexural, and hardness testing to build a complete material profile.

Your Global Test and Measurement Partner for ASTM D638

Industrial Physics supports plastics manufacturers, converters, and laboratories with the tools and expertise needed to evaluate tensile performance in line with ASTM D638. From universal testing systems to extensometry and sample‑conditioning solutions, we help ensure your materials meet demanding performance and reliability standards.