There are several ways to investigate hygrothermal effects including accelerated aging or real exposure tests. Each have its own advantages and disadvantages. Real exposure tests take a lot of time to perform. On the other hand, interpretation of accelerated aging tests is complicated. Moreover, usually accelerated aging tests lead to activation of degradation mechanisms different than to those which are generally activated in real exposure conditions. 

Probably a safe solution is to try to understand (i) the transfer phenomenon (moisture and temperature) inside your material (ii) moisture/temperature dependent material properties and (iii) combine steps i and ii to have a degradation model. Note that this requires a comprehensive test program. 

Would be my pleasure if I can be of more help.

There are several ways to investigate hygrothermal effects including accelerated aging or real exposure tests. Each have its own advantages and disadvantages. Real exposure tests take a lot of time to perform. On the other hand, interpretation of accelerated aging tests is complicated. Moreover, usually accelerated aging tests lead to activation of degradation mechanisms different than to those which are generally activated in real exposure conditions. 

Probably a safe solution is to try to understand (i) the transfer phenomenon (moisture and temperature) inside your material (ii) moisture/temperature dependent material properties and (iii) combine steps i and ii to have a degradation model. Note that this requires a comprehensive test program. 

Would be my pleasure if I can be of more help.

To evaluate the hygrothermal effect on composites, they can be subjected to laboratory ageing test under hot-wet conditions. The samples for hygrothermal aging should be prepared following ASTM test standards specifications for compressive, flexural test, moisture absorption test and so on. Some just put the specimens in environmental chamber at 70°C and 85% relative humidity (RH). But you can also subject the specimens to other cycles according to the ASTM C481-94 (standard test method for laboratory ageing of sandwich constructions). In this case the cycle can be as follows: immersion in water at 50°C for 1 h, heating in dry air at 70°C for 3 h, spraying with hot water at 70°C for 3 h and heating in dry air at 70°C for 18 h (six consecutive cycles and then left at room temperature with 50% humidity up to a constant weight). After this the specimens can be tested to other tests. 

For the water uptake the ASTM D5229/D5229M-92 (standard test method for moisture absorption properties and equilibrium conditioning of polymer matrix composite materials) can also be used.

I agree with the suggestions offered in his answer by Dra. Manila Chieruzzi.

However, for a full study of the behavior of the composite under high humidity and temperature you should:

1. Know the temperature and humidity ranges for the composite is exposed during its service life,

2. Know what properties of the composite are most important for the further technological performance of the material. For example the mechanical strength, wear resistance, etc.

3. To study the change of these properties with increasing wet mass of standard probes at a given temperature for different relative humidity (all HR within the range of moisture that the composite is exposed during its service life and no less than five HR) ,

4. Repeat the previous study for different temperatures (all temperature within the range of temperature at which the composite is exposed during its service life and no less than five temperatures).

5. Correlating the results of the studies proposed in 3 and 4.

To conduct studies proposed in  3 and 4 you should be placed several groups of not less than 5 standard specimens each for testing compressive strength, wear resistance, or any other property which has been determined, in a climate chamber for uptake studies at given HR and temperature. Different groups of samples are extracted and subjected to the appropriate testing, eg mechanical strength compression or other, after being subjected to conditions of humidity and temperatures for different times. This would have the behavior of a particular property of the composite with its increased wet mass in time.

The other study is to perform classical absorption study to determine the diffusion coefficients of moisture in the material, for which you must perform the study suggests by Dr. Chieruzzi in the first part of your answer. I suggest doing this study also at different HR and temperatures which can determine the dependence of the diffusion coefficient of moisture for a given HR with the temperature.

If you wish, you can consult (unfortunately in Spanish):

1.       Difusión de humedad en mezclas de moldeo para machos de fundición., J.E. Hernández-Ruiz, E. Valencia-Morales, E. Villar-Cociña y J. Vega-Leiva,  Bol. Soc. Esp. Cerámica y Vidrio., Vol. 41, N0 2, pp. 41-46, 2002.

2.       Influencia de la humedad en el comportamiento de la resistencia a la compresión en mezclas de moldeo., J. E. Hernández Ruiz, E. Valencia Morales y E. Villar Cociña,  Bol. Soc. Esp. Cerámica y Vidrio, Vol. 40, N0 2, pp.107-111, 2001.

Hi,

I assume you are asking about fiber-reinforced polymer composites here. There are probably hundreds of papers on hygrothermal effects for polymer matrix composites, published in English in many international journals,  and there are chapters in many books dedicated to composites. You can start with the experimental work by Springer, in the late 1970s, and go from there, and one of the editions of the book by Crank ("The mathematics of diffusion") if you are actually studying the problem from the modeling standpoint. A database (Compendex or similar) search will give you literally hundreds of papers to read.

I also like these two papers from the 1990s, with very good reviews of the physical behavior in FRPs (note: pay attention to accelerated aging tests, which are unreliable if there is a chemical transformation in the polymer):

1) Accelerated Test Methods to Determine the Long-Term Behavior of FRP Composite Structures: Environmental Effects, Lawrence C. Bank, T. Russell Gentry and Aaron Barkatt; Journal of Reinforced Plastics and Composites 1995; 14; 559, 30 pp.

2) Environmental durability of glass-fiber composites, by Carol Schutte, Materials Science and Engineering, 1994, R13, pp. 265-324 

To experimentally calculate one-dimensional moisture diffusivities in FRPs use ASTM D5229. There is probably an ISO standard as well. Note that moisture is intended by ASTM as "liquid (water, jet fuel, salt water, or any other liquid) that is either diffused in relatively small quantity and dispersed through a gas as a vapor, condensed on a surface as visible dew, or present in quantity sufficient for immersion of an object.".

i agree with all but we have studied the hygrothermal effect on  glass epoxy composite und high speed sollicitation submitted to composite structure

We published a paper on hygrothermal effect on nanocomposite's properties. I am attaching a link here in case u out want to take a look. Thanks.

http://www.hindawi.com/journals/isrn/2014/489453/