ASTM D638 Tensile Properties of Plastics
Read about the ASTM D638 standard for plastic tensile testing and evaluating material strength under tension.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
Tensile testing to ASTM D638 describes the determination of plastic material properties under a uniaxial tensile load at ambient conditions up to fracture. This test technique covers results such as tensile strength, yield strength, modulus, and elongation, enabling an engineer to interpret a material’s response to tension.
This test remains one of the most useful in selecting suitable polymers for packaging, automotive, and industrial applications where reliability and safety are concerns. ASTM D638 ensures standardized and consistent evaluation to support material design, process optimization, and quality control.
Contact our experts today to schedule ASTM D638 testing and receive detailed, actionable test reports for your application needs.
Scope, Applications, and Benefits
Scope
ASTM D638 defines the method for determining the tensile properties of plastics using standardized dumbbell-shaped specimens. It provides data on modulus of elasticity, elongation, yield tensile strength, and ultimate tensile strength. This information forms a reliable foundation for material characterization in research, design validation, and quality control.
Applications
- Mechanical characterization of polymers for material selection
- Quality assurance in manufacturing plastic components
- Research and development for comparing formulations
- Evaluating the structural performance of load-bearing plastic parts
- Ensuring compliance with performance and safety requirements
Benefits
- Determine tensile strength, yield strength, elongation, and modulus
- Support informed material selection based on mechanical behavior
- Ensure batch-to-batch consistency in production
- Provide reliable data for product certification and regulatory compliance
- Enable prediction of plastic performance under real-world stress conditions
Test Process
Specimen Preparation
Prepare Type I–V specimens per ASTM D638 and condition for 40 hours at 23°C and 50% RH.
1Mounting & Alignment
Clamp the specimen in the UTM with proper axial alignment; set the appropriate gauge length.
2Controlled Tensile Loading
Apply tensile load at a constant speed (typically 5 mm/min for ductile plastics, 50 mm/min for brittle materials).
3Data Acquisition & Fracture
Record load, extension, and stress–strain data until fracture; capture yield, modulus, and elongation values.
4Technical Specifications
| Parameter | Details |
|---|---|
| Standard | ASTM D638 |
| Specimen Types | Type I, II, III, IV, V |
| Grip Separation | Typically 115 mm for Type I (varies by specimen) |
| Test Speed | 1–500 mm/min depending on material category |
| Force Accuracy | ±1% |
| Strain Measurement | Measured up to break using the extensometer |
| Test Output | Tensile Strength, Elongation at Break, Modulus, Stress–Strain Curve |
Instrumentation Used for Testing
- High-precision Universal Testing Machines (UTM) with calibrated load cells
- Clip-on or non-contact extensometers for accurate strain measurement
- Pneumatic or mechanical grips with aligned jaws to minimize slippage
- Computer-controlled crosshead speed for maintaining a constant strain rate
- Data acquisition software for generating real-time stress–strain curves
Results and Deliverables
- Tensile Strength (Yield and Break)
- Elongation at Yield & Elongation at Break
- Young’s Modulus / Tensile Modulus
- Complete Stress–Strain Curve
- Failure mode observations and comparison with specification requirements
Frequently Asked Questions
ASTM D638 determines the tensile properties of plastics, including tensile strength, yield strength, elastic modulus, and elongation. This helps test whether a specific plastic would be suited to packaging, automotive, or industrial parts.
Sample types vary by thickness: Type I for rigid plastics up to 14 mm, Type II for lower strength materials, Type III for thin materials up to 1 mm, Type IV for films at 0.25 to 1 mm, and Type V for small samples below 4 mm.
Tensile strength is defined as the maximum stress at which a plastic could break, and that's an essential consideration in determining whether it is suitable for a load-bearing application.
By understanding a material's tensile properties, manufacturers may rationally choose a material that meets the demanded quality and performance standards.
A stress-strain curve shows a material's behavior under tensile force. The curves give insight into the kind of elastic and plastic deformation, yielding point, and breaking point, which makes the material selection process significant for applications.
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