diffusion corrosion simulation software multilayer laminate composite

Current demand for rigorous and efficient material assessments in end-user applications makes the deployment of advanced and reliable simulation programs necessary. However, there is no software which can handle diffusion, chemical corrosion and mechanical retention phenomena of composite, laminate and coating materials in an integrated manner. In recent years, we have developed a new finite difference / element tool, called IDC-SAC. The use of the tool is twofold:

1.	It allows prediction of (residual) service life and material failure modes in all sorts of environmental circumstances, by integration of diffusion and chemical degradation with long term mechanical retention phenomena.
2.	It supports an optimal design of - often rather expensive and labor intensive - accelerated weathering, ageing and fatigue laboratory tests for plastics, coatings, liners, polymer based laminates and composite materials.

Screenshots of IDC-SAC simulation for several material combinations.

IDC-SAC stands for Instationary Diffusion & Corrosion Simulator for Advanced Composites. It is based on recognition and systematic calculation of all known diffusion and corrosion modes using - among others - free volume, gravimetic, thermodynamical and environmental data. By means of embedded 3D multilayer mathematics, real life behaviour of complex and advanced materials can be quantified rigorously. The software is used solely or - in case of complex loading situations and complex structures - in combination with mechanically oriented (finite element) software. The simulation software can handle the following diffusion, corrosion and mechanical modes:

Diffusion Modes

The distinguished diffusion modes have influence on sorption behaviour (thermodynamics), diffusion rates, swelling stress and forthcoming penetration time, time lag (especially time lag for multilayer and laminate materials) and permeation rates. The program can deal with thicknesses of nano barrier layers until structural reinforced composite layers of several centimeters, and endless combinations of multiple layer thicknesses.

1.	Both S (solubility) and D (diffusion coefficient) are independent of chemical activity. In standard conditions this applies for solvents that have very low chemical compatibility with the polymer. Then, solubility is governed by Henry's Law. For mass transfer (e.g. Water Vapour Transmission in Polyethylene or Helium in PTFE / PVDF) and diffusion coefficient calculations, commonly used Fick's first and second laws can be used.
2.	With increasing activity, S increases while D decreases. This behaviour occurs in polymers like PDMS (Polydimethylsiloxane) elastomer and Polyurethane rubber. It results from a tendency of tighter clustering of the polymer by hydrogen bond formation. This behaviour has been observed with Water and Carbon Dioxide in ambient conditions (PDMS) as well as in supercritical conditions (PVDF).
3.	Both S and D increase as a function of chemical activity. This occurs in case of strong solvent - polymer interaction, hence enthalpy and entropy of the solvent have a significant influence on solubility. Then, solubility thermodynamics are for example governed by: Flory-Huggins for liquid solvents, Sanchez-Lacombe for supercritical solvents. Usually effects of swelling of the polymer matrix must be included in diffusivity, time lag and mass transfer calculations. Since chemical potentials must be used, Maxwell-Stefan theory is most appropriate for diffusion coefficient and/or mass transfer calculations. Examples are Gasoline and Toluene diffusion in Epoxy in ambient conditions and Hydrogen Sulfide diffusion in EPDM or Nitrile Rubber in supercritical conditions.
4.	Both S and D increase as a function of chemical activity. However, the sorption isotherms are sigmoidal, governed by Brunauer-Emett-Teller (BET) adsorption isotherm. Examples are: Water absorption in Nylon 4,6 and Nylon 6,6 (mainly due to free Amide groups in the Polyamide). Due to use of chemical potentials, Maxwell-Stefan diffusion equation is most appropriate.
5.	With increasing activity, S decreases while D increases. This is the Dual Mode Sorption and Transport Model. Sorption and diffusion behaviour of carbon dioxide and Water in glassy polymers and matrix composites have been successfully interpreted in terms of this model (to a certain pressure range). Usually Fick model in combination with local accumulation term can be used. Examples are Water absorption in Vinyl Ester or hydrophobic Polyimide.

Corrosion Modes

1.	Surface corrosion driven by external surface concentration of chemicals and radiation. Most commonly used mechanically oriented simulation programmes, think of Ceasar II, Abaqus or Ansys have included this corrosion rate for metals, but not for polymer surfaces.
2.	Chemical activity (chemical potential, fugacity) driven corrosion. Internal chemical degradation (initially) driven by diffusion and chemical activity. May be followed by concentration controlled chemical degradation. Think of Sodium Hydroxide attack of glass fibres, although properly shielded by resin or a thermoplastic materials (e.g. PEEK or PPS).

Mechanical Modes

1.	Laminate debonding and possible subsequent delamination. This can have the following physical-chemical origins: - insufficient initial adhesion (due to voids, improper wetting); - inhomogeneous or reactive surface (osmotic blister driving delamination); - intrinsic stress (temperature, pressure, diffused mass above free volume); - improper shielding of interface due to composite formulation or long term degradation (i.e. UV light) of protective layer (capillary pathways); - external loads and impacts.
2.	Environmental Stress Cracking (ESC), related to available free volume for diffusion in combination with specific hoop / circumferential stress situation. Occurs in crystalline polymers and is dependent on chemical interaction between chemical and material.

The software is written in C++. For solving complex equations the software uses explicit finite difference (FD) or finite element (FEM) routines.

One can use IDC-SAC supplementary to other specialistic - finite element analysis - mechanical software. Currently the IDC-SAC software is not available with an end-user interface. The development of the user friendly program interface will be finalized in February 2011. Composite Agency uses a production version for the assessments and forthcoming reports. See screenshot below (click here or picture to enlarge screenshot).

IDC-SAC screenshot. Click picture to enlarge.

IDC-SAC prediction results show high degree of correlation to - properly carried out accelerated and long term - laboratory durability test results.

For a demonstration also see slide show below. For more information on laboratory facilities also visit the laboratory analysis section. Forthcoming assessments contain the appropriate scientific and laboratory references, as well as applied formulae, equations and industry standards.

IDC-SAC fit (12 years!) of epoxy coating exposed to water at 20, 40 and 70 degrees Celsius.

The database contains raw data from our own experiments (excluding disclosed laboratory analysis for our clients, third parties, etc.) and from reputable scientific articles. The structure of the database can be compared with online databases such as Matweb and Ides. However the IDC-SAC library contains much more specific and independent information on rates of diffusion, corrosion resistance and forthcoming mechanical retention with regard to plastics, laminate materials and composites. Obviously, Matweb and Ides like data such as "1% swelling after 24 hours of ASTM D471 water exposure according to the producer" is insufficient for our assessments. See some examples of the underlying library at tables.

IDC-SAC deals with polymer based composite materials, multilayer and laminate materials including coatings on metal and plastic liners on all sorts of materials including concrete. In an industrial context, the IDC-SAC chemical - physical simulator has been used for the following weathering and extreme processing assessments:

-	Polymer - metal based packaging for electronics and medical packaging.
-	Multilayer (polymer laminate with inorganic plasma barrier layer) Multicomponent Carbon Dioxide (in presence of moisture and other flue gas components) membrane design.
-	Water diffusion life time analysis of flexible polymer based solar cell.
-	Water vapour transmission and chemical degradation assessment of flax - resin based bio composite containment.
-	Service life prediction of glass reinforced composite rod for concrete reinforcement (for bridge, sluice, dam, and road application).
-	Pipeline retrofitting and residual service life assessment.
-	Service life of internal liners / coatings of concrete demineralized Water tanks (nuclear power plant).
-	Pipeline retrofitting and residual service life assessment.
-	Simultaneous migration and diffusion of Oxygen, Water and Acid through multilayer ( Aluminum barrier layer - EVOH and PP polymer) laminate for food packaging.

For free online case studies derived from forum threads on permeability, corrosion and mechanical retention of plastic based materials, take a look at case histories.