Hygrothermal Aging Conditions Research Articles

Effect of hygrothermal aging on the friction behavior and wear mechanism of the multi-filler reinforced epoxy composites for coated steel

Polymer-based composites for steel structure coating are an effective strategy to improve tribological properties and service durability under hygrothermal aging conditions. In the present paper, epoxy resin was improved by mechanical reinforcement and frictional lubrication fillers, and a kind of multi-filler reinforced epoxy composite (MFREC) was successfully prepared. Water uptake behavior, mechanical and thermal property evolution, friction behavior and wear mechanism as well as micro-topography analysis of MFREC under hygrothermal aging were conducted and discussed in detail. The research results showed that the water uptake curve of MFREC after distilled water and 5 wt.% NaCl water solution immersions confirmed the two-stage diffusion model, where the quasi-equilibrium water uptakes were 4.23% and 3.67%, respectively. Additionally, the fundamental reason for the degradation of the mechanical and thermal properties of MFREC was the hydrolysis of the resin and the de-bonding of the fillers/matrix interface. The interface shear strength of MFREC adhesive and steel gradually decreased with the hygrothermal aging, but did not lose the bonding property, because the uniformly dispersed multi-fillers can fill the internal defects of the matrix and prolong the crack propagation path to block the effect. Before hygrothermal aging, MFREC had excellent friction and wear resistance compared to resin matrix, especially under water lubrication conditions. The anti-wear rate of MFREC increased by up to 59.6% compared to the room temperature dry test environment due to the coupling effects of the water lubrication and anti-friction characteristics of modified fillers. Hygrothermal aging had little effect (＜12%) on the friction coefficient of MFREC, but the anti-wear properties decreased significantly, especially the Ws increased by 255.1% under the 60 °C immersion condition. Because the degradation of thermal/mechanical properties was not enough to resist the high shear stress of the steel ball, leading to severe fatigue wear.

Creep behavior of epoxy adhesives subjected to different hygrothermal aging conditions—nanoindentation creep tests and theoretical study

Epoxy adhesives have been extensively used in the aerospace, marine, and automotive industries to join different components. A major concern with the use of epoxy adhesives is their viscoelastic behavior in aggressive service conditions such as hygrothermal ageing. Surveying the creep behavior of adhesives is of paramount importance to increase long-term durability. In this work, nanoindentation creep tests were performed on an epoxy adhesive exposed to distilled water and seawater at 55 °C for various ageing durations (0, 14, 38, 160, 251, 383, 582, and 800 h). The hardness, modulus, creep displacement, and creep rate sensitivity were quantitatively investigated to elucidate the effect of hygrothermal ageing. All the mechanical properties were found to decrease with the ageing time. The adhesive subjected to distilled water showed lower creep resistance due to higher absorption of moisture. In addition, linear relationships were observed between different mechanical properties and moisture contents irrespective of ageing conditions. Subsequently, the generalized Kelvin model was applied to investigate the creep compliance and the dependence of different deformation types (elastic, viscoelastic, and viscous deformation) on the ageing time and ageing conditions. The motion of molecular structures was also discussed. Finally, a modified creep model was proposed based on the generalized Kelvin model and continuum damage theories, which established the relationship between the dry and aged adhesive via the moisture-dependent degradation factors. The predicted creep displacements coincided well with the experimental results for the case, demonstrating the reliability of the creep model.

Degradation of Mechanical Properties of Flax/PLA Composites in Hygrothermal Aging Conditions.

The main advantage of green composites is their biodegradability, but this biodegradability can also be considered a drawback if the degradation appears during the service life of the component. Therefore, the study of the mechanical behavior of green composites after hygrothermal aging tests is necessary to analyze their degradation process. This study aims to comprehensively analyze the hygrothermal aging behavior and aging mechanism of flax-fiber-reinforced polylactic acid (PLA) biocomposites. The fully biodegradable composites are manufactured by compression molding. In addition, the influence of atmospheric-pressure plasma treatment on the mechanical properties of the biocomposite is studied. Specimens are exposed to water vapor and 40 °C environmental conditions in a stove for up to 42 days. Several specimens of each type are taken out at regular intervals and tested to examine the water absorption, mechanical properties, and thermal characterization. The results show that the stiffness was significantly reduced after 24 h due to matrix degradation, while the strength was reduced only after three weeks.

Hygrothermal degradation of MWCNT/epoxy brittle materials under I/II combined mode loading conditions: An experimental, micro structural and theoretical study

The effects of carboxylated multi-walled carbon nanotubes (MWCNTs) are studied experimentally and theoretically on mixed-mode (I/II) fracture behavior of epoxy resin at the presence of hygrothermal aging conditions. In this paper, the mixed-mode fracture of MWCNT/epoxy is experimentally measured using Short Beam Bending (SBB) samples with different crack inclination angles (α) ranging from pure mode I (i.e., α = 0°) to pure mode II (i.e., α = 39°). To examine the effects of hygrothermal aging conditions and water barrier properties of MWCNTs, four groups of samples including a group of neat epoxy specimens, and three groups of MWCNT/epoxy specimens (with 0.1, 0.3, and 0.5 wt% of MWCNTs) were manufactured and immersed into hot deionized water for 15 days at 60 °C temperature and similarly four groups were placed at room temperature conditions (26 °C and 25–35% relative humidity) for 15 days. According to the experimental results, toughening the epoxy resin by incorporating nanotubes with 0.1, 0.3, and 0.5 wt% of MWCNTs improved the fracture toughness at both environmental conditions, but the highest fracture toughness was obtained for composition containing 0.3 wt% nanoparticles. The variations of fracture loads were dependent on the ambient environment, MWCNTs content, and mode mixity. The relationship between the obtained experimental results, microstructure and morphology of fracture in the tested samples was also investigated. In addition, the load-carrying capacity of the SBB samples made of the neat and MWCNTs modified epoxy material was also predicted well using a two-term based fracture model called Generalized Maximum Tangential Stress (GMTS) criterion.

Hygrothermal effect on strength of thermally cured glass epoxy nanocomposite made joints

In today’s scenario, the durability of the fiber reinforced polymer composites is one of the major concern for marine and construction sectors. In this context, the strength of glass-fiber reinforced polymer (GFRP) composite based pin joints was investigated under hygrothermal aging conditions with varying hole diameter. The composite pin joint specimens were made of neat epoxy with no nanofiller material and nanocomposite with nanoclay as nanofiller material. The nanoclay filler varying from 0 to 5 wt% was added into the epoxy, and it was found that at 3 wt% of nanoclay filler, the performance of the composite specimens was maximum. Thereafter, effect of hole diameter in GFRP composite pin joints was investigated for maximum bearing capacity, with optimized specimens further exposed to the hygrothermal aging. Hygrothermal aging of neat and 3 wt% nanoclay configuration specimens was conducted in distilled water (aging medium) at different temperatures, that is, 25°C, 45°C, 65°C and for different durations, that is, 15, 30, 45, and 60 days. It was found that the strength of composites decreases with an increase in aging temperature and duration. Nanoclay modified GFRP composite specimens showed better resistance to water absorption rate and had better strength retention ability than GFRP neat epoxy composite specimens.

The effect of hygrothermal aging on the adhesion performance of nanomaterial reinforced aluminium adhesive joints

Adhesive joints are subjected to various environmental factors such as humidity and temperature, depending on their use in industrial applications. It is important to examine and improve the performance of adhesive joints formed with polymeric adhesives, which are known to be sensitive to humidity and temperature parameters, under these conditions. For this reason, in this study, FPL-etched AA7075-T6 aluminium adherends bonded with nonreinforced and BNNP (boron nitride nanopowder), ANP (alumina nanopowder) and MWCNT (multiwalled carbon nanotubes) reinforced epoxy adhesive as a single lap adhesive joint. Thereafter, performance of the adhesive joints that exposed hygrothermal aging conditions of 1, 2, 4 and 6 weeks at 100% relative humidity (RH) and 60 °C were investigated. Glass transition temperature (Tg) values of nonreinforced and reinforced epoxy adhesives before and after hygrothermal aging were determined by DSC (Differential Scanning Calorimeter) analyses. Depending on the nanomaterial types, the tendency of the adhesive joints to water uptake was determined and compared with nonreinforced adhesive joints. When the shear strength findings were investigated, it was defined that the adhesive joints reached almost saturation after 2 weeks of hygrothermal aging. In addition, the most effective nanomaterial type against hygrothermal aging was determined as MWCNT. After 2 weeks hygrothermal aged, the shear strength decreases of MWCNT reinforced adhesive joints were 21.77% and 16.97% less than BNNP and ANP reinforced adhesive joints, respectively. Although the adhesive deteriorates chemically after hygrothermal aging, its adhesion performance improved with the physical benefits of nanomaterials. However, ANP, which is cheaper in terms of price/shear strength performance in long-term aging times, showed similar results with MWCNT. In addition, fracture mechanisms were examined in more detail with SEM (Scanning Electron Microscope) analyses before and after aging, and the effects of hygrothermal aging on the adhesive joints were determined.

Influence of Hygrothermal Aging on Mechanical Properties and Damage Mechanisms of Hemp-Reinforced Biocomposites

ABSTRACT Biocomposites are being developed for structural applications, particularly in the automotive industry. The use of plant fibers as reinforcement is a first step toward the development of eco-materials, but it is necessary to use also a more eco-friendly matrix. In this paper, woven hemp composites impregnated with two different eco-polymers are compared: hemp/Greenpoxy and hemp/Elium. Greenpoxy is a partially bio-based thermoset resin, and Elium is a recyclable thermoplastic polymer. The influence of various hygrothermal aging conditions on the mechanical properties of these composites is studied, and results are compared with the behavior of samples stored at ambient temperature and humidity. Water immersion was carried out at three different temperatures: 21°C, 60°C and 70°C. A Fick’s law was used to model the water uptake. Modulated DSC was performed to measure the evolution of the glass transition temperatures. Repeated progressive tensile loading tests were carried out and instrumented with acoustic emission monitoring. The evolution of the damage factor, the residual strains and the acoustic events was analyzed. Fracture surface analysis and microtomography observations were also performed. Damage mechanisms are discussed. Results show that mechanical properties are highly affected by the hygrothermal aging whatever the matrix, but the increase in temperature affects the two composites differently.

Investigation of the deleterious effects of low-temperature and hygrothermal aging conditions on the mixed-mode fracture resistance of epoxy resin using a short-beam bend specimen

The effect of different environmental aging conditions on the mixed-mode fracture behavior of epoxy resins was investigated using a sub-size specimen. The short-beam bend (SBB) specimens with different crack inclination angles were manufactured and subjected to low-temperature (-71 °C), hygrothermal (immersion in deionized water at 60 °C) and room-temperature conditions. The deleterious effect of low-temperature and hygrothermal aging conditions on the mode-I, mode-II and mixed-mode I/II fracture responses of the epoxy resin was studied by testing the aged and unaged SBB specimens under three-point bend loading. The experimental results indicated that the hygrothermal aging condition, with a reduction of 49% in the effective fracture toughness, imposed a more severe deleterious effect on the fracture response of the specimens in comparison with the low-temperature condition with a decrease of 35% in the effective fracture toughness. The generalized maximum tangential stress criterion was used to predict the fracture loads of the aged and unaged specimens. Moreover, optical microscopy and scanning electron microscopy techniques were employed to assess the fracture surfaces of the specimens aged under different conditions.

Chemical, mechanical and morphological investigation on the hygrothermal aging mechanism of a toughened epoxy

A systematic investigation was implemented in this work to evaluate the effect of hygrothermal aging on the chemistry, mechanics and morphology of a toughened epoxy resin exposed in a 70°C bath. This resin system reached equilibrium moisture absorption within 2530 h with a saturation water uptake of 3.6%, and the moisture diffusion displayed a non-Fick behavior, but can be illuminated well by the Langmuir model. The influence of hygrothermal aging on the glass transition temperature (Tg) was evaluated by Differential Scanning Calorimetry. Chemical changes were monitored by Fourier Transform Infrared spectroscopy, where the evidence for reversible and irreversible chemical changes was observed. The Dynamic Mechanical Analysis was employed to reveal the effect of hygrothermal aging on viscoelasticity, mainly focusing on the Prony moduli and relaxation time, where an interesting phenomenon was noted that the Prony moduli and relaxation time are not affected by hygrothermal aging. The mechanical properties involving tension, compression, and shear were studied detailedly with respect to the dry, hygrothermal, and redry samples. Finally, the fracture morphology of the epoxy under three different hygrothermal aging conditions was analyzed by using Scanning Electron Microscopy. The mechanical results show that for compression, the pre-yield and post-yield both has been strongly weakened after hygrothermal aging, but the pre-yield performance can be recovered by redry; for tension, the nonlinear behavior before final failure has been weakened; for shear, the shear ductility has been significantly enhanced. And the fracture morphology after hygrothermal aging, the representative regions are reduced to two zones: defect and smooth zone.

Hygrothermal Aging History of Amine-Epoxy Resins: Effects on Thermo-Mechanical Properties

Epoxy systems are widely used as matrix resins for fiber reinforced polymers (FRP) and, therefore, often have to withstand harsh environmental conditions. Especially in marine and offshore environments, moisture or direct water contact leads to water absorption into the epoxy resin. As a result, the mechanical properties change during application. Since diffusion at room or colder temperatures is slow, industry and academia typically use accelerated aging methods at elevated temperatures for durability prediction. However, as the water-polymer interaction is a complex combination of plasticization, physical aging, and molecular interaction, all of these mechanisms are expected to be affected by the ambient temperature. To reveal the impact of aging time and temperature on the thermo-mechanical properties of an amine-epoxy system, this publication includes various hygrothermal aging conditions, like water bath and relative humidity aging at temperatures ranging from 8°C to 70°C and relative humidity from 20% to 90%. Thus, it is demonstrated via long-term aging, DMTA and FTIR investigations that, e.g., strength, stiffness, strain to failure, and the glass transition temperature (Tg) can differ significantly depending on aging time and temperature. For example, it can be shown that water absorption at cold temperatures leads to the strongest and longest-lasting reduction in strength, although the maximum water absorption amount is lower than at higher temperatures. For the application, this means that strength differences of up to 26% can be obtained, depending on the aging method selected. Furthermore, it can be shown that conventional prediction models, such as Eyring correlation, which consider the mobility of the molecular structure for the prediction of thermo-mechanical properties, can only be used to a limited extent for prediction in hygrothermal aging. The reasons for this are seen to be, in particular, the different characteristics of the water-polymer interactions depending on the aging temperature. While plasticization dominates in cold conditions, relaxation and strong water-molecule bonds predominate in warm conditions.

Effect of Fiber Pre-treatment Methods on Hygrothermal Aging Behavior of Agave Fiber Reinforced Polymer Composites

ABSTRACT Three different pre-treatment methods, that is, alkali hornification, water hornification, and alkali treatment, are evaluated for the improvement in durability of agave natural fiber-reinforced polymer composites under the hygrothermal aging conditions. The composite specimens were prepared following the standard test procedures laid for moisture diffusion analysis. To analyze the effect of different treatment conditions, the standard test specimens were subjected to different hygrothermal aging conditions in the accelerated environments. After four subsequent hornification cycles, the alkali hornification resulted in about 27% lower water retention value in the agave fibers. Under similar conditions, water hornification leads to a meager 6% loss of water retention. Under the direct exposure to water, the alkali-hornified composites had a mass gain of 4.1%, 4.3%, and 4.7%, respectively, at 25°C, 50°C, and 75°C. The mass gain of alkali-treated composites was 4.3%, 4.5%, and 5.1%. and water hornification resulted in a mass gain of 5.5%, 5.9%, and 6.1% at similar temperatures. Under the humidity conditions, the alkali-hornified composites had a mass gain of 0.9%, 1.3%, and 1.1%, respectively, at 25°C, 50°C, and 75°C. The mass gain of alkali-treated composites was 0.6%, 1.05%, and 1.2%. and water hornification resulted in the mass gain of 0.66%, 1.07%, and 1.3% at similar temperatures. The present study reveals the influence of fiber pre-treatment methods on moisture durability of agave natural fiber composites. The results are further supported through microstructural investigations.

Study on the mechanical properties of nanoclay-epoxy composites under different hygrothermal aging conditions

The current study objectives to prepare and characterize nanoclay-epoxy composites (NECs) with a varying weight percentage of nanoclay. The NECs are prepared by mixing nanoclay and epoxy resin using a sonicator. The mixture is mold formed using direct casting technique, to make specimens as per ASTM standards. The specimens are treated with three hygrothermal aging conditions viz., cold water soaking, boiling water soaking and thermal shock. The properties of the specimens are characterized based on tensile and flexural tests as per ASTM standards. The results revealed that hygrothermal aging conditions have an adverse effect on the properties of neat epoxy. Addition of nanoclay increased the mechanical properties and decreased the effect of water soaking conditions. SEM images disclosed the reasons for the failure of the specimens. Conclusions are drawn based on comparison done in obtained results of dry specimens, and the specimens that underwent hygrothermal aging conditions.

Effect of hygrothermal aging on the mechanical properties of nanoclay-glass fiber-epoxy composite and optimization using full factorial design

This work emphasis on investigation of effect of hygrothermal aging conditions on the mechanical properties of nanoclay-glass fiber-epoxy composites. Composite laminates are prepared by ‘hand lay-up technique’ with varied nanoclay and glass fiber weight percentage. Composites have undergone different hygrothermal conditions viz, cold and boiling soaking. Composite specimens are experimented for tensile and flexural strengths. The ‘design of experiment (DOE)’ based on full factorial design (33 = L27) is used to optimize the response variables. The design and analysis is done by using ‘MINITAB 16’ software. Results revealed that, hygrothermal aging conditions (42.69% contribution to the tensile strength and 53.87% contribution to the flexural strength) have negative and maximum influence on the composites. Nanoclay (24.75% of contribution to the tensile strength and 29.17% contribution to the flexural strength) and fiber weight parentage (30.23% contribution to the tensile strength and 16.25% contribution to the flexural strength) have positive influence on the composites.

The effect of surface treatment on the creep behavior of flax fiber reinforced composites under hygrothermal aging conditions

Abstract The application of natural FRP (Fiber Reinforced Polymer) is being targeted in various fields due to both environmental and economic benefits. FFRP (Flax Fiber Reinforced Polymer) is one of the major natural FRPs. The durability and long-term performance of FFRP have been proven a key to its practical engineering application. Some experimental works have been conducted to investigate the creep properties of FFRP. However, fewer efforts have been made to improve its creep performance thus far. In this paper, the effect of surface treatment on the creep behavior of FFRP under hygrothermal aging conditions is studied, and a fractional-order creep model is established to predict its creep behavior.

Hygrothermal aging of an epoxy/dicyandiamide structural adhesive – influence of water diffusion on the durability of the adhesive/galvanized steel interface

ABSTRACT In the present work, moisture absorption of an original expanded Epoxy/dicyandiamide solid formulation designed for the automotive industry was studied. The first part of work focuses on the bulk of cured adhesive joints, according to the water absorption under hydrothermal aging. Aging in immersion in distilled water at 40°C, associated to gravimetric, InfraRed, and optical microscope analyses, enables to estimate the coefficient of diffusion of the formulation in the considered conditions and structural modifications induced by the aging. The studied formulation is stable during the aging, as the structural adhesive network does not degrade, even after 1500 h of immersion. The lixiviation of some compounds of the formulation eventually occurs. The water uptake is always reversible and does not strongly impact the integrity of the joint, even in the case of a fully expanded adhesive joint. The hygrothermal aging enables to define three distinct diffusion domains, and to estimate the coefficient of diffusion of the adhesive joint. Results obtained in this study can be used to estimate the durability of a metal/adhesive interface in hygrothermal aging conditions. As the expanded adhesive joint does not seem to be degraded during the aging, the integrity of the joint is supposed to essentially depend on the durability of the interface and the corrosion of the metal substrate.

Characterization of an acrylic pressure-sensitive adhesive blended with hydrophilic monomer exposed to hygrothermal aging: Assigning cloud point resistance as an optically clear adhesive for a touch screen panel

Optically clear adhesive (OCA) is a key material for assembling a touch screen panels (TSP). TSPs are now applied to many devices; therefore, their preparation and adhesion performance examination including durability can be beneficial work. Cloud point resistance means that a material does not have a hazy appearance under any environment, especially under sudden temperature and humidity changes. It is a critical property for an OCA because it is directly related to image display on a TSP. A hydrophilic component needs to be incorporated to the OCA, and 2-hydroxyethyl acrylate (HEA) was selected as the monomeric hydrophilic component. The change in adhesion performance under hygrothermal aging conditions was investigated. The aging behavior was also monitored using infrared (IR) and Raman spectra and chemiluminescence (CL) analysis. The HEA-containing pressure-sensitive adhesive (PSA) exhibited a good cloud point resistance and adhesion performance along with stable adhesion properties during aging. This consequence is considered suitable behavior for the prepared PSA as an OCA.

Characterization of an acrylic polymer under hygrothermal aging as an optically clear adhesive for touch screen panels

Optically clear adhesives (OCAs) are key components of touch screen panels (TSPs). It is important that OCAs do not affect the transparent electrodes in TSPs because OCAs are contacted to the transparent electrodes. Therefore, N-vinyl caprolactam (NVC) was incorporated in the composition of an acrylic pressure sensitive adhesive (PSA) with excluding an acidic component to maintain the cohesion for OCA preparation. With increasing amounts of NVC, the tack and peel strength of UV-cured PSA increased, but high amounts of NVC led to decreased peel strength. The UV-cured PSA films were placed in a high temperature and humidity chamber for 8 weeks to investigate the durability and corrosion property under hygrothermal conditions. In this study, the corrosion test method using copper foil was suggested as a simple and economical method and was used to evaluate the effect of NVC on the corrosion property of PSA. This method helped identify suitable OCAs that do not have corrosive property. PSA films containing more than 20wt% of NVC promoted the corrosion of copper foil under hygrothermal aging conditions. The caprolactam ring was opened by moisture, and the PSA structure morphed into a polar structure during the aging process. This change caused a glass transition shift, an increase in the storage modulus at the rubbery plateau, and an increase in peel strength. The surface free energy of the PSA films also increased due to the increase in the polar property. However, high amounts of NVC caused a decrease in the peel strength after 8 weeks of aging because of increased molecular interactions.

Study on the shear strength degradation of ACA joints induced by different hygrothermal aging conditions

The effect of the different hygrothermal conditions on the shear strength degradation of ACA joints and the difference among them are studied in this paper using experiments and numerical simulations. First of all, several hygrothermal aging tests with different accelerating levels are carried out to explore the hygrothermal environment induced degradation paths of interfacial strength of ACA joints. It is found that the shear strength degradation paths differ from each other when the ACA joints are tested under different hygrothermal conditions, while they are similar to each other. For each case, the shear strength firstly decreases rapidly and then slowly approximates to a fixed value, and the shear strength difference between each other goes to an approximate constant after certain early test hours. After that, to understand the degradation mechanism better, finite element modeling is achieved to study the relationship of moisture concentration in ACA layer and shear strength of the ACA joints, and it is found that moisture saturation and diffusion rate are considered to be the main causes of the shear strength degradation.

Effects of the hygrothermal environment on the mechanical properties of flax fibres

Since flax is the most promising plant for the reinforcement of polymer-based composites in structural applications, we have chosen to investigate its hygrothermal characteristics which can be useful for the understanding of the behaviour of other plant fibres. The flax fibres were exposed to different hygrothermal conditions: in an oven at various controlled temperatures (–40 to 140℃) and measured relative humidity, in a climate chamber at 50% relative humidity for define temperatures between 25℃ and 85℃, or different determined aging conditions. The correlation of these hygrothermal conditions to the evolution of the mechanical properties gives evidence of the prominent influence of water over temperature on the microstructural changes of flax fibres. The mechanical parameters drastically decrease in usually prescribed hygrothermal aging conditions for organic matrix composite materials, the strength being particularly sensitive to the presence of water. These evolutions were correlated to the fibre microstructure modifications induced by water absorption as revealed by electron microscopy analyses. These findings could be useful for understanding the behaviour of polymer matrix biocomposites in severe hygrothermal conditions.

Durability of Closed-End Pressurized GRP Filament Wound Pipes under Hygrothermal Aging Conditions. Part II: Creep Tests

The creep and damage behavior of GRP filament wound pipes are investigated as a function of the resin ductility. To predict the life time of pipes under low pressure levels and hygrothermal conditions, different methods based on the experimental data and approximations have been used. All these methods involve assumptions that have been discussed and examined carefully. Under creep tests the response of preconditioned pipes by immersion in water at 60°C follows a nonlinear viscoelastic behavior. A damage creep law is, also, assessed followed by microscopic observations to identify the creep damage mechanisms. Two stages are observed: the first describes the initiation of cracks and the second is related to the crack's propagation. Decohesions between the mechanical part of the pipe and the liner followed by microcracking of the liner lead to the failure. Also, the pipes' life is governed by the critical creep strain to failure of the liner. From microscopic observations and physicochemical analysis it appears that pipes' failure results for low pressure levels from mechanical damage and chemical bond rupture, otherwise cracking and delamination lead to the failure. Experimental data show that the use of the creep damage law give the more realistic creep lifetime although this criterion is the most pessimistic one. Predictions based on the Eyring-Zhurkov approach and the nonlinear viscoelastic creep law over-estimate the lifetime because assumptions are not appropriate. Moreover it appears using both microscopic observations and extensometric measurements, that the lifetime, the damage kinetics and the failure mechanisms of the pressurized pipes depend strongly on the matrix ductility.