The Silent Killer of Plastic Parts: How to Prevent Long-Term Failures
Plastic parts are everywhere, from household appliances and consumer gadgets to critical industrial components. They’re typically lightweight, versatile, and cost-effective—yet they aren’t invincible. Sometimes, a plastic part that appears perfectly sound when it leaves the factory can fail months or years into its life cycle, seemingly without reason. If you’ve ever experienced this type of failure, you know just how frustrating—and costly—it can be.
In this article, we’ll explore what causes these mysterious, long-term failures in plastic parts and discuss the steps you can take to design components that stand the test of time.
Understanding the Problem
A Real-World Example
Many years ago, I investigated a puzzling product failure. The plastic component had passed all the usual tests: it could handle the required load, fit perfectly within the assembly, and displayed no immediate signs of stress. Yet, after about a year in use, it cracked and became unusable.
Why did it fail when it had initially performed so well?
The short answer: plastics behave differently from metals. They creep, fatigue, and degrade over time. What looked good on paper or in a short-term test slowly succumbed to long-term stresses.
The Plastic Paradox
Plastics are tough—but not in the same way metals are. Under constant or cyclical stress, certain types of plastics experience “creep,” a slow, permanent deformation that can lead to cracks and breaks over extended periods. They also suffer fatigue: micro-cracks develop under repeated loading, eventually leading to sudden failure. On top of that, environmental factors like temperature swings, humidity, and chemical exposure can degrade a plastic’s integrity.
In short, the “silent killer” isn’t just one issue—it’s a host of age-related and environment-related phenomena that weaken plastics over time.
Key Factors in Long-Term Plastic Part Failures
- Creep
Plastics, especially under continuous load, will slowly deform. For instance, a bracket holding up a shelf might hold fine initially, but over months, it could sag and eventually break. - Fatigue
Even small cyclic loads—like vibrations in a vehicle or repeated pressing of a button—can cause micro-cracks to develop and propagate over time. Eventually, these cracks lead to larger, visible failures. - Environmental Degradation
Heat, moisture, UV radiation, Environmental Stress Cracking (ESRC) and chemicals all contribute to the breakdown of polymer chains in plastics. Some plastics are more resistant than others, but no plastic is entirely immune to environmental wear and tear. - Material Selection
Using the cheapest plastic might reduce costs in the short term, but it can lead to expensive recalls or product failures later. Different plastics have vastly different properties in terms of strength, flexibility, thermal stability, and chemical resistance. - Product Design Life
Every product has an intended lifespan—years, maybe decades. If the design doesn’t account for how materials behave over that time, it’s practically inviting premature failure.
Strategies to Prevent Long-Term Failures
1. Factor in Creep and Fatigue in Your Analysis
Modern finite element analysis (FEA) software can simulate long-term loading and cyclic stresses to predict possible weak points. Incorporating creep and fatigue models early in the design helps highlight risk areas.
- Tip: When running FEA, input real-world conditions—like temperature ranges, exposure to chemicals, and repeated loading scenarios—to get the most accurate predictions.
2. Test, Test, Test
There’s no substitute for thorough testing. While it’s impossible to simulate every real-world environment, you can design accelerated tests that expose products to extreme conditions in a shorter time frame.
- Accelerated Aging: Exposing parts to higher temperatures or chemicals can approximate years of normal operation in a matter of weeks or months.
- Cyclic Loading Tests: Repeated stress tests that mimic actual usage conditions can reveal fatigue issues.
- Environmental Chambers: These allow you to control temperature, humidity, and chemical exposure to see how a part behaves under different conditions.
3. Define a Product Design Life
At the very start of a project, clarify how long the product is expected to last. Is it a disposable item meant for short-term use, or an industrial component with a 10-year service life?
- Design and Materials Choice: With a clear target life in mind, you can choose materials and design parameters accordingly.
- Safety Margins: Build additional margins into the design if failure carries significant consequences (e.g., in medical or aerospace applications).
4. Choose the Right Material—Not Just the Cheapest
The upfront cost of higher-grade plastics might be more than baseline materials, but the savings in preventing failures and customer dissatisfaction far outweigh the initial investment. Consider the following:
- Temperature Resistance: Some polymers retain strength at higher temperatures better than others.
- Chemical Resistance: If your product will be exposed to cleaning agents, solvents, or other chemicals, ensure your plastic can handle it.
- UV Stability: For outdoor applications, UV-resistant grades are crucial to avoiding embrittlement or discoloration over time.
Real-World Consequences of Ignoring Long-Term Performance
- Product Recalls: If your plastic part fails after months of use, you may face expensive recalls or warranty claims.
- Brand Reputation: A sudden wave of part failures can damage your credibility in the market.
- Legal Liabilities: In critical applications, such as medical devices or automotive safety components, unexpected failures can lead to serious legal implications.
Have You Seen a Part Fail Over Time?
In the fast-paced world of design and manufacturing, it’s easy to focus on immediate performance tests—after all, those are what get the green light for production. But if you neglect the factors that cause long-term creep, fatigue, and degradation, you risk creating a product that might pass initial tests yet fail miserably in the real world.
The bottom line: A part that works today isn’t always a part that works forever. By carefully considering the lifespan of your product, running thorough tests, and choosing suitable materials, you can prevent the silent killer of plastic parts from quietly undermining your hard work.
Closing Thoughts
If you’ve ever encountered a puzzling part failure—one that took months or years to surface—you’re not alone. The good news is that there are proven strategies to combat these invisible wear-and-tear issues.
Want to learn more? Feel free to reach out if you have questions about designing, analysing, or testing plastic components for longevity. Together, we can ensure your products are built to last and maintain their integrity in the face of real-world conditions.