As you mention, yes high temperature accelerate drastically the creep of plastic.

I made previously creep test on polypropylene under room temperature and under 50 degree Celsius, the creep was increased 4 to 5 times under high temperature.

In your case, the creep of your plastic must be investigated experimentally unless you find previous experimental results for the same plastic alloy.

As you mention, yes high temperature accelerate drastically the creep of plastic.

I made previously creep test on polypropylene under room temperature and under 50 degree Celsius, the creep was increased 4 to 5 times under high temperature.

In your case, the creep of your plastic must be investigated experimentally unless you find previous experimental results for the same plastic alloy.

https://www.sciencedirect.com/search?qs=metal-plastic%20composite%20beam&show=25&sortBy=relevance

I agree.

I do not know, I was not interested in the interaction of the metal and composite,

with compliments, Adam

Ayman Trad

Thank you for the hint. PA66 is affected by creeping at ambient temperature and relatively low stress already.

https://books.google.at/books?id=TnHJX79b3RwC&pg=PA502&lpg=PA502&dq=creeping+of+PA66+-yang&source=bl&ots=dEM1taKOac&sig=ACfU3U2-0Dk6ObynkAxDuRAUIu3eeXFFlA&hl=en&sa=X&ved=2ahUKEwiBx6CD9ffiAhXql4sKHcrKB4kQ6AEwF3oECAgQAQ#v=onepage&q=%20&f=true

This important links.

Furthermore, another question (1) and 2 more below:

I propose a simple engineering approach for the calculation of shear stiffness, since any precise formulation needs to be based on tests tailored to the specific needs of my question:

The obtained shear (spring) stiffness from a shear test is being reduced by 2 multiplicative factors, kt for temperature and kc for creeping in order to obtain a design resistance, see attached screenshots. (I am only interested in creeping values for a long time duration).

Therefore,

Long term shear stiffness = Shear stiffness from test * reduction factor creeping * reduction factor temperature

1.) Is this simplified approach sensible, which I explain or rather ask about above?

2.) How to account for the loss of material resistance from water absorption?

3.) As PA66 undergoes embrittlement over time - this can result in unwanted local stress peaks ?

I agree

Dear Franz,

Although your problem may look simple at first glance, it is actually very complex. The reason is that there are interactions between aging, temperature, time, stress and moisture effects, not to mention chemical degradation through hydrolysis and oxydation.

I would tend to be very wary of a simple knock down factors approach to such a model, especially for long times.

The problem is that each factor tends to accelerate the other. For example, moisture absorption will reduce the glass transition temperature of the amorphous phase and thus reduce stiffness and increase temperature effects on creep, and aging will be accelerated, and so on. Very non-linear. And that is not accounting for the fact that moisture chemically degrades PA66, and that heat and stress accelerate this chemical degradation!

It is a very interesting problem, but also a very complicated one. You may want to have a look at the seminal work of Struik «Physical Aging in Amorphous Polymers and Other Materials.» as well as the work of Schapery on non linear viscoelasticity.

Also look for the time-temperature stress superposition principle (also variation on the theme adding stress or other variables). If I recall correctly, David Dillard «Creep and creep Rupture of Laminated Graphite/Epoxy Composites.» has an interesting literature review on the subject.

These are old work, but I think they are still quite relevant to your problem.

(You may also have a look at the lit review and last few chapters of my thesis, where I deal with similar subjects, although in dynamic loading rather than creep).

Good luck,

Laurent

Hi;

I totally agree…, of course, high temperatures accelerate significantly the creep of plastic.

My best regards