How to manage stress

Design engineers with considerable experience in metals may overlook the effect creep can have on the long-term performance of a plastic part, particularly when applications involve high operating temperatures. When a stress is applied over a long time, the observed strain is greater than that predicted by the short-term modulus. This additional strain is called creep. It occurs in metals, but is a much more significant design factor in plastics. It can generally be stated that the closer the applied stress is to the ultimate stress (or failure point), the more significant creep becomes for plastics.

“Creep is a phenomenon that must be taken into account when designing with plastics, especially if the application is subjected to thermal cycling,” comments K.C. Desai, CAE manager for Solvay Advanced Polymers, Alpharetta, GA.

The polymer structure, as well as reinforcement and fillers, affect the material’s tendency to creep. Unfortunately, creep cannot be determined directly from data sheet information.

A consequence of creep is stress relaxation. Consider a plastic part attached with a bolt torqued to achieve sufficient compressive stress. Over time the plastic will creep, which in turn lowers the compressive stress. As the stress drops, the tendency to creep is diminished until an equilibrium is achieved at a lower stress level. Because of this, it is usually necessary to increase the initial torque to avoid a loss of bolt tightness.

Issues that can result from a poor understanding of creep range from premature part failure to excessively high safety factors due to overcompensation, such as sections that are too thick.

A graph of apparent modulus versus time should be used as a reference before selecting a material for a given application. Apparent modulus is the ratio of applied stress to creep strain.

Creep properties are evaluated through the measurement of strain as a function of time while a test specimen is subjected to a constant tensile, compressive or flexural stress at specified conditions. The primary caveat of these tests, however, is the same as was stated in the first two parts of the “Designing with Plastics” series: the tests occur under ideal conditions. Understanding the effects of temperature and chemical atmosphere is extremely important.

Homework: How to help your child without too much stress

For homework to be done well (and for the intended learning to be achieved), it’s important that it’s done in a place where your child can concentrate and where they’ve got the right equipment. Spaces to work should be light, airy and quiet, with natural light flowing in. For loads of reasons though, sometimes that’s easier said than done. So if they don’t have a quiet, calm place to work (or need a computer and don’t have one), then you can speak to the school. Homework clubs and after-school help will be very likely available, with teachers and staff on hand to point your child in the right direction and set sail for success!

But at the end of the day, what’s the most important thing? It’s very, very simple. Do your best. That’s all the school will ask. By just being there, taking an interest, checking in and talking to your child about their homework, you’re already doing a great job. And if they don’t do their homework, a little word in their ear to remind them to do it can go a long way to help them see that school and home are working together, and so they need to make sure it gets done! In the vast majority of cases, your child will confidently work through their homework without throwing a page of equations at you – but if they do, I hope you can take a breath, do your best, and get it done…together!


Strategies for managing stress

With week four of the fall semester on its way, the academic workload is beginning to loom over students thus starting a never-ending cycle of stress. Whether we realize it or not, stress can often be managed by how we interact with our own bodies. We feel it in our breathing, head-and-body aches, changing sleep patterns and more. It’s important to make sure you are taking time to take care of yourself, so here are some helpful strategies for managing stress.


It’s easy to get overwhelmed and busy to the point that you aren’t getting a lot of movement, but one of the best ways to decrease stress is by getting exercise. Whether it’s a 20-minute walk through campus or a full-blown workout, moving around can help with relaxing and increasing your mood.

With group exercise classes and personal training options available, McComas Hall is a perfect spot to get all forms of exercise in. McComas is open from 6 a.m. to 11 p.m. Monday-Friday and 10 a.m. to 10 p.m. Saturday and Sunday.


Providing a safe time and place for your mind to relax and unwind is important and easily overlooked. Meditation is often misunderstood as a result of pop culture as being much more difficult than it is. In reality, meditation is whatever works the best for you. Yoga, running, painting, the classic sit-and-think imagery we’re all familiar with; if it soothes your mind, it can be a meditative practice. 

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