DESIGN
COMMENT
Michael Paloian, Integrated Design Systems, Inc.
Designing for the Long Term Product design is very fulfilling as well as challenging. It feels great to be able to think of something, sketch it out on a piece of paper, maybe make a model, then translate your idea into an actual product! One of the most challenging responsibilities for a designer or engineer is designing a product for the long term. This process requires in-depth knowledge in materials science, manufacturing, physics, mechanics, aesthetics, human factors, and application. It would help if you had a crystal ball when designing a product to last for 5, 10, or 20 years. Unfortunately, none of us have a reliable means of looking into the future unless you subscribe to a fortuneteller. So how do you design a product to last for a specified minimum timeframe? There are a few basic requirements for designing long-lasting products as listed below: • Know your material • Understand the product application • Manage stresses and loads • Always account for the environment • Never assume anything Understanding Material Properties Knowledge of material properties cannot be over-emphasized. Long-term performance is highly dependent on material properties, and how well matched they are to the applied loads, chemicals, radiation, and thermal conditions to which they are subjected. Engineers need to evaluate the extremes of these parameters based on the specified material and anticipated operating conditions. Although this may appear to be straightforward, it is quite the opposite. An engineer must carefully expect every possible use condition for a given product and evaluate its performance based on a combination of conditions. Unfortunately, most published material data is limited to immediate loads. This limitation requires product designers to conduct accelerated testing based on sound engineering principles. Understand the Product Application Although this may appear to be elementary, it is a critical and often overlooked step in product design. Understanding the application requires understanding the interrelationships between product use, misuse, use environments, maintenance, and safety. For example, a product exposed to sunlight for up to ten years requires excellent UV resistance. Specifying a UV 10 grade of polyethylene means that it will retain a minimum of 50% of its tensile strength and impact after this exposure period. Therefore your device should be designed to withstand a minimum of two times the loads from time zero.
Manage stresses and loads Stresses and loads should also account for creep, which is time and temperature-dependent. For example, a water tank can be filled and perform well at room temperature and time zero. However, it could fail after two or five years under constant load and higher temperatures. This phenomenon is attributed to creep. Creep is a change in modulus over time under constant load. Always account for the environment The environments of use are critical to assess when designing for the long term. Product environments could include harsh chemicals, which could rapidly degrade plastics. Environmental conditions also influence radiation such as UV, or X-rays, gamma rays, etc. Thermal conditions are another common environmental consideration. Electrical energy is also crucial since it will affect designs requiring insulation which is dependent upon dielectric strength. Never assume anything The last important consideration for designing for the long term is never to assume anything. Assumptions often lead to a false sense of security based on omissions of critical design considerations. Omissions lead to errors and premature product failures, which is why the US courts are backlogged with thousands of lawsuits every year based on “Errors and Omissions.” Critical due diligence is essential in any design methodology where long-term product performance is required. I hope this brief editorial was informative and somewhat enlightening. It is intended to alert you to the challenges associated with designing products to last long periods. This topic would be an excellent subject for a book. If you have any comments or would like to reach me, please feel free to contact me at paloian@idsys.com. www.rotoworldmag.com 49
