ASTM D638–Compliant Tensile Testing of Plastics

ASTM D638–Compliant Tensile Testing of Plastics (Shimadzu AGS‑V)

Significance of the Topic

Tensile testing is a fundamental method to quantify mechanical properties of polymer materials that directly affect performance in service and guide material selection and product design. ASTM D638 provides a standardized procedure and specimen geometry for tensile testing of plastics so that results from different laboratories and conditions are comparable. Reliable tensile properties — tensile strength, elastic (Young's) modulus, and total elongation at break — are essential for assessing stiffness, strength, ductility and predicting deformation or failure under load.

Objectives and Study Overview

This work demonstrates an ASTM D638 (2014 revision) compliant tensile test procedure applied to three common thermoplastics using a Shimadzu AGS‑V precision universal testing machine. The aim was to obtain repeatable stress–strain data and compute tensile strength, total elongation, and elastic modulus for polypropylene (PP), polycarbonate (PC), and polyvinyl chloride (PVC), and to illustrate measurement conditions and data processing used to ensure traceable, comparable results.

Methodology

• Specimens: Dumbbell Type I (ASTM D638), parallel section dimensions: width 13 mm × thickness 3.2 mm. Five replicates per polymer (n = 5).
• Specimen materials tested: polypropylene (PP), polycarbonate (PC), polyvinyl chloride (PVC).
• Preload: 5 N applied to eliminate slacking/initial deflection and improve repeatability.
• Test speed: 50 mm/min. Gauge (parallel) length: 50 mm. Grip separation: 115 mm.
• Strain measurement: non‑contact digital video extensometer (TRViewX 240S) used to record strain; a sticker‑type line gauge marker was placed on the specimen for video tracking. Extensometer output was converted to engineering strain for the plots.
• Cross‑sectional area for stress calculation: average of three width and thickness measurements taken along the parallel section; stresses computed as load divided by this average area.
• Data analysis: For each material, average and standard deviation of tensile strength, total elongation at break, and elastic modulus were computed from five replicates.

Used Instrumentation

• Shimadzu AGS‑10kNVD precision universal testing machine (AGS‑V series), configured with a 5 kN load cell.
• 5 kN pneumatic flat grips with single‑cut file teeth; pneumatic grip actuation at 0.4 MPa.
• TRViewX 240S non‑contact digital video extensometer for strain measurement.
• TRAPEZIUMX‑V (Single) test control and acquisition software; TRViewX used for extensometer data integration.
• Sticker‑type line gauge markers applied to specimens for video tracking.

Main Results and Discussion

Summary of key mechanical properties (averages from five replicates):

• Polypropylene (PP): Tensile strength ~30.4 MPa; total elongation ~156.1%; elastic modulus ~1.76 GPa. Standard deviations indicated low spread in strength (0.23 MPa) and modulus (0.072 GPa), larger scatter in elongation (42.2%), consistent with ductile failure variability.
• Polycarbonate (PC): Tensile strength ~64.6 MPa; total elongation ~65.0%; elastic modulus ~2.19 GPa. Moderate variability in elongation (SD 34.7%) and small variability in strength and modulus (SD 0.19 MPa and 0.11 GPa, respectively).
• Polyvinyl chloride (PVC): Tensile strength ~75.3 MPa; total elongation ~4.8%; elastic modulus ~3.13 GPa. Very low elongation and small standard deviations (SD elongation 0.6%), indicating brittle behavior with highly repeatable stiffness and strength measurements.

Stress–strain curves obtained from the video extensometer show the expected material trends: PP exhibits high ductility with extensive plastic deformation prior to failure; PC combines moderate strength with substantial ductility; PVC is comparatively stiff and brittle with limited strain to failure. The measurement approach — preload, averaged cross‑sectional measurement, and non‑contact extensometry — produced small standard deviations for tensile strength and elastic modulus across replicates, supporting good repeatability of the protocol for comparative material evaluation.

Benefits and Practical Applications

• Standardized, ASTM D638‑compatible testing enables objective comparison of polymers from different suppliers or processing conditions (e.g., molding parameters, additives, reinforcement).
• Quantitative tensile properties support material selection decisions considering stiffness, strength, and ductility requirements for end‑use applications and safety factors in design.
• Non‑contact video extensometry reduces potential artifacts from contact extensometers on thin or low‑stiffness plastics and simplifies alignment and gauge marking for repeatable strain measurement.
• Pneumatic grips and applied preload improve specimen clamping consistency and reduce grip‑related variability, enhancing inter‑laboratory reproducibility when combined with standard specimen geometry and test speed.

Future Trends and Potential Applications

• Integration of higher‑resolution digital image correlation (DIC) methods alongside video extensometry to map local strain fields and detect necking, heterogeneities, or strain concentration near grips.
• Automated specimen dimension measurement and area correction to reduce operator dependence and improve stress accuracy for irregular or composite specimens.
• Expansion of standardized protocols to include rate‑dependent and temperature‑controlled testing for viscoelastic plastics and to better simulate service conditions.
• Use of the standardized tensile data in computational material models (constitutive models, finite element analysis) to predict part performance and failure in engineering designs.

Conclusion

An ASTM D638‑compliant tensile testing workflow using the Shimadzu AGS‑V system, pneumatic gripping, and TRViewX non‑contact video extensometry provides reliable, repeatable measurements of tensile strength, modulus, and elongation for common thermoplastics. The protocol produces low variability in strength and modulus and effectively distinguishes ductile versus brittle material behavior, making it suitable for material qualification, QA/QC, and research comparisons.

References

• Shimadzu Corporation. ASTM D638–Compliant Tensile Testing of Plastics. Application News. First Edition: Jul. 2026.