Is this workable to use DMA 800 for measuring the complex stiffness modulus of woven fabric (carbon fiber) epoxy reinforced composite? DMA has maximum force of 30N. Anyone has tried ever? Thanks
Sure , I have been doing this for many years now.. It delivers very good results on the dynamic properties and tandelta damping coefficient.
Of course you can, obtaining maximum tan delta values and also values of glass transition temperatures
Sure you can. Care should be taken in selecting the amplitude and frequency of the deformation, and appropriate dimensions for the test specimens.
Yes you can.
Maybe you should have a look at ISO 6721-1
For general information see also: ftp://mail.best-tech.com/eBooks/Mechanical%20Engineering/Dynamic%20Mechanical%20Analysis%20-%20A%20Practical%20Introduction%20-%20K.%20Menard%20%28CRC%20Press%201999%29%20WW.pdf
Yes you can. The cross section of your sample is the limiting factor for your hardware below Tg.
Yes you can..and the obtained dynamic properties and E prime values are well satisfactory..!!
I don't see the reason why not. For E', make sure you have enough replications.
Thanks everyone for response. I asked this question because I found some limitations of using DMA for polymer composites in literature. The main concerns of using DMA in literature (Prof. Gibson's book "Principles of Composite Material Mechanics, page 403") are:
i) DMA equations are based on the models ideal for polymers but not for polymer composites. These equations do not take into account coupling effects.
ii) Stiffness of DMA mounting hardware is not enough to handle the polymer composites.
Has anyone compared the damping ratios obtained from DMA with modal analysis or shaker table for polymer composites (reinforced plastics with carbon fiber)?
Thanks in advance
In my opinion it is a clear yes.
Concerning your concerns:
1)The equations used by the device to calculate the real and imaginary part of the modulus are useful for viscoelatic materials but it is mainly a definition. You apply a sinusoidal force/stress and your sample gives a strain answer. The strain is again sinosoidal. The Ratio between the maxima of stress and strain gives you your modulus times a scaling factor depending on your geometry. This modulus is called a complex modulus. Then you check whether there is a phase shift between force and strain. If there is no phase shift you measured a pure hookean Body. If there is a phase shift by an angle delta you measured a viscous or viscoelastic material. Composites are viscoelastic. The measured angle is a value for your damping behaviour.
Due to the high amount of crosslinking they don`t show much of their viscous behavior but it is definitely existing. You can observe very beatiful glass transition effects...
Up to this Point i don't see any material preference concerning the applied equations. Additionally you can split the complex modulus in the storage and the loss part by using the angle Delta. I'm not 100% sure whether here are some simplifications within the mathematics.
2) the stiffness of typical DMA mounting devices is not very high, but it is not necessary as typically the Maximum load is limited. you describe your device with a Maximum force of 30N which is already rather high for an Standard DMA. You should not compare the clamps of these devices with the clamps of an universal testing machine set up for forces in the higher kN or even MN range.
Additionally there are also some DMA-machines available with higher Forces and they also use stiffer clamps (e.g. GABO).
But as some others wrote it is important to use sample dimensions that fit your available Forces. With 30N you won't get much strain from a big sample but DMA is a method of small deformations at different frequencies.
The absolute values of the E' and E'' are of course influenced by the accuracy of Dimension measurement. This becomes harder the smaller your samples are. Depending on your loading mode some Dimensions may hava a much biger influence then others (e.g. thickness in bending). In some cases the smallest Dimension (which has the biggest relative error) has the biggest Impact on you calculated modulus. Therefore everyone should be caution when using absolute values.
We investigated carbon fibre composites by DMA and are very satisfied from the available Information concerning the material properties and their change during curing process.
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