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Evaluating Chemical Stress Resistance of Polymers: Practical Insights from SAE J2016
Although SAE J2016 has been cancelled and superseded by ISO 11403-3, its methodology remains a cornerstone for screening plastics against environmental stress cracking. This article provides a concise overview of the procedure, key test parameters, and engineering considerations derived from the standard.
Understanding the Standard
SAE J2016, originally issued in 1989 and cancelled in 2008, was a screening procedure for assessing the susceptibility of plastics to environmental stress cracking when exposed to pure solvents or mixtures. The standard was based on ISO 11403-3 and considered redundant, leading to its withdrawal. However, the testing principles are still widely applicable and referenced in material qualification.
The standard focuses on measuring tensile properties (tensile strength at yield or break, and tensile work to break) before and after exposure to chemicals at applied stress levels. These indicative properties help quantify the reduction in material performance due to chemical attack.
Test Specimens and Conditioning
Specimens are prepared from injection-molded multipurpose test bars according to ISO 3167 or ISO 10724. A machined waist region exposes interior material to the chemical. The waist dimensions: radius (r) = 15 mm ± 1 mm, minimum width (b1) = 3 mm ± 0.2 mm. A minimum of five specimens per condition is required. If material anisotropy is expected, specimens should be taken parallel and perpendicular to flow direction.
Conditioning is critical. Specimens must be conditioned at 23 °C ± 1 °C and 50 % ± 5 % relative humidity for at least 88 hours before testing. For moisture-sensitive materials, equilibrium with the conditioning atmosphere is essential.
| Parameter | Requirement |
|---|---|
| Specimen type | ISO 3167 or ISO 10724 with machined waist |
| Conditioning | 23±1°C, 50±5% RH, ≥88 h |
| Indicative properties | Tensile strength (σy or σB) and work to break (wtB) |
| Exposure times | 100 h and 1000 h |
| Stress levels | Minimum 4, targeting 25% reduction in strength and 50% reduction in work to break |
| Chemicals | Refer to Appendix A; choose relevant to service environment |
🛠️ Engineering Design Insight
When selecting test chemicals, always consider the actual service environment. The standard provides a guide list but emphasizes application-specific relevance. Moreover, ensure specimens are machined with cutting direction parallel to the specimen length to avoid stress concentrations that could skew results. For anisotropic materials, test in both flow and cross-flow directions to capture directional sensitivity.
When selecting test chemicals, always consider the actual service environment. The standard provides a guide list but emphasizes application-specific relevance. Moreover, ensure specimens are machined with cutting direction parallel to the specimen length to avoid stress concentrations that could skew results. For anisotropic materials, test in both flow and cross-flow directions to capture directional sensitivity.
Procedure Overview
- Measure reference tensile properties (σuo) using ISO 527-1 and ISO 527-2 at standard conditions.
- Condition specimens again for 24 h under standard atmosphere.
- Expose to chemical at a series of stress levels for 100 h and 1000 h periods.
- After exposure, measure indicative properties at the same test speeds.
- Plot property values vs. stress and determine σsc and σwc values corresponding to 25% reduction in strength and 50% reduction in work to break.
Test speed: for polymers with strain at break <10%, use 5 mm/min; otherwise 50 mm/min.
Common Mistakes to Avoid
- Inadequate specimen conditioning before exposure.
- Using chemicals irrelevant to the service environment.
- Ignoring material anisotropy; must test both directions.
- Insufficient stress levels or number of specimens.
- Machining stress concentrations from improper cutting direction.
⚠️ Important Note
Since SAE J2016 has been cancelled, users should refer to the current ISO 11403-3 for formal testing. However, the practical details from J2016 remain valuable for internal screening and comparative studies. Always validate final designs with prototype parts under realistic conditions.
Since SAE J2016 has been cancelled, users should refer to the current ISO 11403-3 for formal testing. However, the practical details from J2016 remain valuable for internal screening and comparative studies. Always validate final designs with prototype parts under realistic conditions.
Frequently Asked Questions
1. Why was SAE J2016 cancelled?
It was deemed redundant because its scope and procedure were equivalent to ISO 11403-3. The SAE Plastics Committee determined the standard was no longer necessary as an active document.
2. What are the indicative properties to measure?
The standard specifies tensile strength at yield (σy) or at break (σB) for brittle materials, and tensile work to break (wtB). These provide a clear picture of degradation.
3. How many stress levels are required?
A minimum of four stress levels, with at least five specimens per level, are needed to accurately determine the stress that causes 25% reduction in strength and 50% reduction in work to break.
4. Can I test chemicals not listed in Appendix A?
Yes, the appendix is only a guide. The user should choose solvents relevant to the actual application environment. Testing additional chemicals is recommended for comprehensive evaluation.
By following the principles outlined in SAE J2016 and aligning with ISO 11403-3, engineers and material scientists can effectively screen plastic materials for chemical stress resistance and avoid premature failures in service.
