Autohesion is defined as the resistance to separation of two bonded identical films that have been joined together for a period of time under a given temperature and pressure. Studies on the autohesion phenomenon can provide fundamental insights into the physical processes of adhesive bond and failure, as well as the practical engineering issues such as crack healing, elastomer tack, polymer fusion, self-healing, and polymer welding. In the first part of this dissertation work, four ethylene/1-octene (EO) copolymers were used in the present study consisting of molecules with linear polyethylene backbone to which hexyl groups are attached at random intervals. These copolymers have similar number-average molecular weight (Mn) and polydispersity, but different 1-octene content. These hexyl groups act as the short branches and hinder the crystallization, reduce density to some extent in the solid state, lower the melting temperature, and decrease the stiffness of the bulk materials. A full understanding of the autohesion behavior of the ethylene/1-octene copolymers involves investigations at three different length scales: 1) the molecular scale which controls the interfacial structure; 2) the mesoscopic or microscopic scale which can provide information on the formation of interfaces and on how the energy is dissipated during a fracture process; and 3) the macroscopic scale at which the mechanical properties such as fracture energy can be obtained for a particular test geometry. In the present study, the effects of the branch content on the formation and fracture of the interface of these ethylene/1-octene assemblies were evaluated at the bonding temperatures (Tb) and bonding times (tb). The correlation among these three length scales was also investigated and modeled. The adhesion strength of these symmetric interfaces of EO copolymers was investigated by T-peel fracture tests. The fracture of the interface is an irreversible entropy creating process which involved a substantial amount of energy dissipation. The results of such mechanical tests with respect to the bonding temperature (Tb), bonding time (tb) and peel rate indicated this energy dissipation is the result of a complicated interplay between the ability of the interface to transfer stress and its plastic and viscoelastic deformation properties. When Tb is much higher than the characteristic temperature (Tc), the interfaces were completely healed and cohesive failure was observed in T-peel tests. In this case, the fracture strength decreased with increasing branch content. In contrast, when Tb is very close to Tc, the fracture strength showed an increase with the branch content with either interfacial failure or cohesive failure being observed depending on the branch content and Tb. At higher peel rates, it is observed that higher peel energies are required to fracture the surfaces. Transmission electron microscopy (TEM) showed that the interfacial/interphase structure changed from amorphous to crystalline with an increase in the Tb. The results from the bonding time effect studies showed that the peel energy is proportional to tb1/2 regardless of Tb. But the branch content and the Tb play an important role on the seal rate. Thus, higher seal rate was found for higher Tb and higher branch content. These results also suggest that the autohesion of ethylene/1-octene copolymers are strongly associated with the interactions of melted chains. The chain compositions of these Zeigler-Natta EO copolymers are highly heterogeneous with the branches concentrated in the lower molecular weight portion. Long linear chain segments could form large, well-ordered crystals that provide strong anchors for the tie molecules and therefore determine the density of inter-crystalline links. Short chains with lots of branches could behave as protrusions along the chain to obstruct chain disentanglement and limit a chain from sliding through a crystal. Due to these reasons, the short chains with branches would contribute much less than the long linear chains to the full peel strength after complete sealing. However, higher peel strengths could be obtained only at the higher temperatures or longer bonding times at which the long linear chains begin to melt and diffuse across the interface. On the other hand, the higher branch content samples have the lower crystallinity and could obtain the higher chain mobility at the lower bonding temperatures and with shorter bonding times. Therefore, higher seal strength was observed for the higher branch content samples at lower Tb. Following T-peel fracture tests of ethylene/1-octene copolymer assemblies which showed interfacial failures, the fractured surfaces were investigated by using Atomic Force Microscopy (AFM) and characterized by fractal analysis together with the original films. The AFM images showed strong dependence on the peel rate and branch content. Quantitatively, the fractal analyses demonstrated fractal characteristics at the different finite scales. Two regimes showing fractal features were identified for each surface. In regime I (low magnifications) the fracture test did not change the fractal dimensions much. But there were significant changes in regime II before welding and after T-peel fracture tests. The length scale that separated these two regimes is very close to the size of lamellar structures. The characteristic sizes at which the fractal characteristics emerge were shown to appear at larger scales for surfaces fractured at higher peel rates. This suggests that the appearance of fractal behavior at larger scales requires higher fracture energies. The characteristic sizes and fractal dimensions were shown to depend on the molecular structure. Because the fractal analysis suggests at least some crystalline lamellae on the surfaces still existed during T-peel fracture tests, a "Stitch-welding" has been therefore proposed as the autohesion mechanism in which only chains in the amorphous portions could inter-diffuse. In the second part of this dissertation work, a multi-layer lap-shear geometry has been designed and proven as a reliable testing method in evaluation of the dynamical mechanical properties of polyacrylic pressure sensitive adhesive (PSA) in paper lamination for postage stamp applications. In-situ testing of four different PSA stamp laminates constructed by laminating water-based polyacrylic PSAs to the stamp face papers were carried out using a dynamic mechanical analyzer (DMA) in the temperature range from -50 to 60 oC at frequencies 0.1, 1, 10, and 100 Hz. This geometry requires the tension mode on the DMA, but the results which were recorded as tensile properties were converted to shearing properties of the PSA layers in the laminate. The effect of the thickness (layers of laminates) on the dynamical mechanical properties has been studied and the results suggested that a multi-layer geometry with 5-10 layers could be an appropriate structure to produce enhanced responses. Therefore, the geometry with 8-layer laminates was used for frequency sweep/isothermal temperature and frequency sweep/temperature step tests. The results showed three relaxation responses that is, glassy, transition, and flow regions with respect to the frequencies and temperatures. These results also implied the viscoelastic characteristics of these PSA products. The tensile properties of the face papers were also tested using the same parameters as those of the multi-layer geometry. Significant differences were found between the shearing behaviors of the multi-layer geometry and the tensile behaviors of the elastic face paper. This suggests that the tensile deformation of the face paper in the multi-layer geometry could be ignored and the elastic paper did not contribute to the shearing properties of the PSA layers. Time-temperature superposition curves have been produced with reference temperature set at 23 oC, which can be used to predict the long term and short term performances of these samples at this temperature. This method can be utilized as a standard testing method on the PSA adhesives in the laminate form. In addition to the dynamic mechanical properties, it can also be developed to be a general standard method on testing the rheological properties of adhesives, polymer melts and other viscous materials. / Ph. D.

Fiber-metal laminates (FML) are the advanced materials that are developed to improve the high performance of lightweight structures that are rapidly becoming a superior substitute for metal structures. The reasons behind their emerging usage are the mechanical properties without a compromise in weight other than the traditional metals. The bond remains a concern. This thesis reviews the effect of pre-treatments, say heat, P2 etch and laser treatments on the substrate which modifies the surface composition/roughness to impact the bond strength. The constituents that make up the FMLs in our present study are the Aluminum 2024 alloy as the substrate and the carbon fiber prepregs are the fibers. These composite samples are manufactured in a compression molding process after each pre-treatment and are then subjected to different tests to investigate its properties in tension, compression, flexural and lap shear strength. The results indicate that heat treatment adversely affects properties of the metal and the joint while laser treatments provide the best bond and joint strength.

Submitted by Daniele Amaral (daniee_ni@hotmail.com) on 2017-10-09T20:25:42Z No. of bitstreams: 1 DissSBML.pdf: 11036305 bytes, checksum: bfd6a7dc18c9f75ffae64cce4523adf4 (MD5) / Approved for entry into archive by Ronildo Prado (bco.producao.intelectual@gmail.com) on 2018-01-25T12:34:11Z (GMT) No. of bitstreams: 1 DissSBML.pdf: 11036305 bytes, checksum: bfd6a7dc18c9f75ffae64cce4523adf4 (MD5) / Approved for entry into archive by Ronildo Prado (bco.producao.intelectual@gmail.com) on 2018-01-25T12:34:20Z (GMT) No. of bitstreams: 1 DissSBML.pdf: 11036305 bytes, checksum: bfd6a7dc18c9f75ffae64cce4523adf4 (MD5) / Made available in DSpace on 2018-01-25T12:39:08Z (GMT). No. of bitstreams: 1 DissSBML.pdf: 11036305 bytes, checksum: bfd6a7dc18c9f75ffae64cce4523adf4 (MD5) Previous issue date: 2017-08-28 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Aluminum alloys are widely used in transportation industry to reduce structural weight and fuel consumption. The development of advanced alloys and more effective technologies for joining materials contribute to achieve such objectives. AlMgSc alloys emerge as an interesting option to structural applications due to low density and high mechanical performance, as well as an attractive cost. Friction spot welding (FSpW) process is a novel solid state joining technology that has proven to be suitable for joining lightweight materials. This process is carried out in a few steps and in a short time with low thermal cycles and energy consumption as well as without extra materials addition. Thus, this process is an alternative to industrial techniques such as riveting and resistance spot welding. This work presents, for the first time, the application results of FSpW on AlMgSc sheets in overlapping configuration. The effect of the process parameters, such as rotational speed, plunge depth and plunge time, was investigated in order to obtain joints with higher lap shear strength. The Taguchi method and the analysis of variance were applied to study the influence of each parameter on mechanical properties of the joints. In addition, the welds were submitted to microstructural characterization and a material flow analysis provided an initial understanding about the formation of microstructural features. Therefore, the fatigue performance was analyzed for the condition of higher lap shear strength and the S-N curve was drawn. The results indicated a good static performance of the welds, although the fatigue performance was less satisfactory. Finally, failure mechanisms of static and dynamic tests seemed to be strongly related to geometric features, such as hook, bonding ligament and microstructural transition regions. / Ligas de alumínio são amplamente utilizadas em indústrias de transporte visando a redução do peso estrutural e consumo de combustíveis. O desenvolvimento de ligas avançadas e tecnologias mais efetivas de união contribuem para o alcance de tais objetivos. Ligas do sistema AlMgSc surgem como opção interessante para utilização estrutural devido à baixa densidade e alto desempenho mecânico, aliados a um custo atrativo. O processo de soldagem a ponto por fricção (FSpW) é uma tecnologia recente de união de materiais no estado sólido, que tem se mostrado adequado para a união de ligas leves. Tal processo é realizado em poucas etapas e curto tempo, com baixos ciclos térmicos e consumo energético e sem adição de materiais extras, se mostrando, portanto, uma alternativa a técnicas utilizadas industrialmente, como rebitagem e solda a ponto por resistência. Esse trabalho apresenta, pela primeira vez, resultados de aplicação do FSpW em chapas AlMgSc sobrepostas. O efeito dos parâmetros do processo, como velocidade de rotação, profundidade e tempo de penetração da ferramenta, foi investigado visando a obtenção de soldas com maior resistência em ensaios de cisalhamento, dita condição otimizada. Para tal, foi aplicado o método Taguchi e análise de variância para estudar a importância de cada parâmetro na resistência mecânica das juntas. Além disso, as soldas foram caracterizadas microestruturalmente e uma análise do fluxo de material proporcionou um entendimento inicial acerca da formação de algumas características microestruturais. Ademais, o desempenho em fadiga foi analisado para a condição otimizada de soldagem e a curva S-N foi levantada. Os resultados obtidos apontam um bom desempenho estático das soldas, embora o desempenho em fadiga tenha sido menos satisfatório. Finalmente, os mecanismos de falha, de ensaios estáticos e dinâmicos, foram observados e se mostraram fortemente relacionados a elementos geométricos, como cunha, e linha de união, além de regiões de transições microestruturais. / CNPq: 134654/2016-1

Plasma pretreatments are environmentally benign and energy efficient processes for modifying the surface chemistry of materials. In an effort to improve the strength of the titanium alloy/FM-5 polyimide adhesive joint for aerospace applications, oxygen plasma pretreatments and novel thin plasma polymerized (PP) films were investigated as adhesion promoters. Plasma treatments were carried out using custom-built, low pressure, radio frequency, inductively coupled plasma reactors. Ti-6Al-4V coupons were plasma treated and used to prepare miniature single lap shear (SLS) joints. The effects of plasma pretreatments on surface chemistry were studied using x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Fourier transform infrared analysis (FTIR), and contact angle measurements. Relationships between composition, mechanical properties, and adhesion of PP films on Ti-6Al-4V and silicon wafers were investigated. The nanomechanical properties (modulus, hardness and adhesion) were studied using atomic force microscopy (AFM) nanoindentation and nanoscratch testing. A design of experiments (DOE) three factorial model was used to optimize the parameters for oxygen plasma treatments. Oxygen plasma pretreatments enhanced joint strength by cleaning the titanium surface and creating an extended oxide layer. Nanoindentation of oxygen plasma treated substrates showed no change in the surface mechanical properties due to the oxygen plasma treatment. This suggested that the improved SLS strength of the oxygen plasma pretreated substrates was due to the cleaning of the substrate and the removal of carbonaceous contaminants, rather than any changes in the morphology of the oxide layer. PP acetylene films were predominantly carbon, with oxygen as the other main constituent (incorporated mostly as C-O and C=O). For all SLS specimens tested, the adhesion between PP acetylene and FM-5 adhesive was adequate. However, the strength of SLS joints was limited by the adhesion of the PP acetylene to the Ti-6Al-4V substrate. The effects of a large number of plasma parameters, such as substrate pretreatment, carrier gas, input power, flow rate and film thickness were investigated. All samples failed at the PP film/Ti-6Al-4V interface or within the PP acetylene film, and thicker PP films yielded lower SLS strengths. PP films deposited at lower power exhibited higher hardness and reduced modulus than films deposited at higher power. Overall, thinner films exhibited higher hardness and reduced Young's modulus than thicker films. PP films of higher hardness yielded higher critical loads at debond (thickness normalized) during the nanoscratch test. Thin films were developed via the vapor plasma polymerization of titanium(IV) isobutoxide (TiiB). XPS results suggested that titanium was incorporated into the film as TiO2 clusters dispersed in an organic matrix. No evidence for Ti-C was obtained from the XPS spectra. PP films of TiiB were much more compliant than PP acetylene films. This behavior was attributed to decreased fragmentation and lower crosslinking that occurred during PP TiiB film deposition. These PP films did not exhibit sol-gel-like qualities, and because of the way titanium was incorporated into the films, a more appropriate name for these films might be "titanium dioxide-doped plasma polymerized films." / Ph. D.

Adhesive bonding which has been in use for long as a traditional joining method has gained ground in the last couple of decades due to the introduction of advanced composite materials into the aerospace industry. Bonded structures have advantages such as high corrosion and fatigue resistance, ability to join dissimilar materials, reduced stress concentration, uniform stress distribution, good damping characteristics etc. They also have certain limitations like environmental degradation, existence of defects like pores, voids and disbonds, difficulty in maintenance and repair etc. A serious drawback in the use of adhesively bonded structures has been that there are no established comprehensive non-destructive testing (NDT) techniques for their evaluation. Further, a reliable evaluation of the effect of the existing defects on strength and durability of adhesive joints is yet to be achieved. This has been a challenge for the research and development community over several decades and hence, been the motivation behind this piece of research work. Under the scope of the work carried out in the thesis, some of the primary factors such as the existence of defects, degradation of the adhesive, stress and strain distribution in the bonded region etc., have been considered to study the bond integrity in composite to composite lap shear joints. The problem becomes complex if all the parameters affecting the adhesive joint are varied simultaneously. Taking this into consideration, one of the key parameters affecting the bond quality, viz., the adhesive layer degradation was chosen to study its effect on the bonded joint. The epoxy layer was added with different, definite amount of Poly vinyl alcohol (PVA) to arrive at sets of bonded joint specimens with varied adhesive layer properties. A thorough review of different non destructive testing methods applied to this particular problem showed that ultrasonic wave based techniques could be the right choice. To start with, preliminary experimental investigations were carried on unidirectional glass fiber reinforced plastic (GFRP-epoxy) lap joints. The adhesive joints were subjected to non destructive evaluation (NDE) using ultrasonic through transmission and pulse echo techniques as also low energy digital X-ray techniques. The results obtained showed a variation in reflected and transmitted ultrasonic pulse amplitude with bond quality. Digital X-Ray radiography technique showed a variation in the intensity of transmitted x-rays due to variation in the density of adhesive. Standard mechanical tests revealed that the addition of PVA decreased the bond strength. A plot of coefficient of reflection from the first interface and the bond strength showed a linear correlation between them. After obtaining a cursory feel and understanding of the parameters involved with the preliminary experiments on GFRP adhesive joints which yielded interesting and encouraging results, further work was carried on specimens made out of autoclave cured carbon fiber reinforced plastic (CFRP)-epoxy bonded joints. Normal incidence ultrasound showed a similar trend. Analyses of the Acoustic Emission (AE) signals generated indicate early AE activity for degraded joints compared to healthy joints. Literary evidences suggest that the ultrasonic shear waves are more sensitive to interfacial degradation. An attempt was made to use oblique incidence ultrasonic interrogation using shear waves. The amplitude of reflected shear waves from the interface increased with an increase in degradation. Further, a signal analysis approach in the frequency domain revealed a shift in the frequency minimum towards lower range in degraded samples. This phenomenon was verified using analytical models. An inversion algorithm was used to determine the interfacial transverse stiffness which decreased significantly due to increase in degradation. Conventional ultrasonic evaluation methods are rendered ineffective when a direct access to the test region is not possible; a different approach with guided wave techniques can be explored in this scenario. Investigations on CFRP-epoxy adhesive joints using Lamb waves showed a decrease in the amplitude of ‘So’ mode in degraded samples. Theoretical dispersion curves exhibited a similar trend. Frequency domain studies on the received modes using Gabor wavelet transform showed a negative shift in frequency with increased degradation. It was also observed that the maximum transmission loss for the most degraded sample with 40 percent PVA occurred in the range of 650 – 800 kHz. Non linear ultrasonic (NLU) evaluation revealed that the nonlinearity parameter (β) increased with increased degradation. Kissing bonds are most commonly occurring type of defects in adhesive joints and are very difficult to characterize. A recent non-contact imaging technique called digital image correlation (DIC) was tried to evaluate composite adhesive joints with varied percentage of inserted kissing bond defects. The results obtained indicate that DIC can detect the kissing bonds even at 50 percent of the failure load. In addition, to different experimental approaches to evaluate the bonded joint discussed above, the effect of degradation on the stresses in the bond line region was studied using analytical and numerical approach. A linear adhesive beam model based on Euler beam theory and a nonlinear adhesive beam model based on Timoshenko beam theory were used to determine the adhesive peel and shear stress in the joint. Digital image correlation technique was used to experimentally obtain the bond line strains and corresponding stresses were computed assuming a plane strain condition. It was found that the experimental stresses followed a similar trend to that predicted by the two analytical models. A maximum peel stress failure criterion was used to predict failure loads. A failure mechanism was proposed based on the observations made during the experimental work. It was further shown that the critical strain energy release rate for crack initiation in a healthy joint is much higher compared to a degraded joint. The analytical models become cumbersome if a larger number of factors have to be taken into account. Numerical methods like finite element analysis are found to be promising in overcoming these hurdles. Numerical investigation using 3D finite element analysis was carried out on CFRP-epoxy adhesive joints. The adherend – adhesive interface was modeled using connector elements whose stiffness properties as well as the bulk adhesive properties for joints with different amounts of PVA were determined using ultrasonic inspection method. The peel and shear stress variation along the adhesive bond line showed a similar trend as observed with the experimental stress distribution (DIC) but with a lesser magnitude. A parametric study using finite element based Monte-Carlo simulation was carried out to assess the effect of variation in various joint parameters like adhesive modulus, bondline thickness, adherend geometrical and material properties on peel and shear stress in the joint. It was found that the adhesive modulus and bond line thickness had a significant influence on the magnitude of stresses developed in the bond line. Thus, to summarize, an attempt has been made to study the bond line integrity of a composite epoxy adhesive lap joint using experimental, analytical and numerical approaches. Advanced NDE tools like oblique incidence ultrasound, non linear ultrasound, Lamb wave inspection and digital image correlation have been used to extract parameters which can be used to evaluate composite bonded joints. The results obtained and reported in the thesis have been encouraging and indicate that in specific cases where the bond line thickness and other relevant parameters if can be maintained or presumed reasonably non variant, it is possible to effectively evaluate the integrity of a composite bonded joint.

L’assemblage des matériaux composites thermoplastiques tel que le PEEK est l’une des problématiques majeure de l’industrie aéronautique. Actuellement, différentes techniques sont développées pour assurer l’assemblage structural de ces matériaux, tels que : le soudage, le rivetage, le boulonnage et le collage. Les enjeux industriels majeurs sont principalement, à l’heure actuelle, la conception des structures simplifiées au maximum afin de réduire les coûts de production et la réduction des consommations énergétiques. A cet effet, l’industrie aéronautique fait fréquemment appel à l’assemblage par collage en raison de nombreux avantages qu’il offre (gain de poids, distribution régulière des contraintes, absence de trous) par rapport aux autres techniques existantes. Le PEEK (PolyEtherEtherKetone), est un matériau polymère semi-cristallin thermoplastique, à hautes performances. Ce matériau est souvent utilise dans l’industrie aéronautique principalement renforce par des fibres de carbone ou de verre. Cependant, du fait du niveau élevé de sa résistance chimique l’assemblage par collage du PEEK et de ses composites nécessitent des traitements de surfaces appropries et optimises. Or, afin d’obtenir un system collé à haute performance, la problématique scientifique et technique doit être concentrée sur la jonction entre les éléments à assembler. En effet, la qualité de cette jonction est de la plus haute importance car elle doit permettre un transfert optimal des contraintes thermomécaniques lorsque l’assemblage est soumis a ses conditions d'usage. Cette étude concerne donc, l’amélioration des propriétés mécaniques (monotones et cycliques) de l’assemblage par collage PEEK/PEEK. Dans cette optique, un traitement de surface simple de mise en œuvre est proposé. Ce traitement est le sablage, qui permet la modification topographique (morphologique) de surface. La compréhension des différents phénomènes d’interaction aux interfaces intervenant dans l’amélioration du comportement mécanique du joint de colle et qui s’inscrit dans la triptyque : « Rhéologie, Physico-chimie et topographie », est l’enjeu scientifique majeur dans cette thèse. Dans un premier temps, l’influence des paramètres du traitement tels que le temps de projection, la taille des particules, sur la morphologie de surface de différents matériaux à base de PEEK a été analysée, permettant ainsi d’établir la corrélation entre les paramètres morphologiques et les mécanismes de modification topographique de surface intervenant pendant le traitement de surface. L’un des facteurs clefs pour la compréhension des mécanismes d’interaction entre l’adhésif liquide et le substrat solide est la mouillabilité. L’analyse du comportement au mouillage en fonction des différents paramètres du traitement a été réalisée. La mouillabilité des surfaces traitées est fortement affectée par la rugosité de surface créée après ce traitement. La relation entre les paramètres morphologiques et la mouillabilité a été discutée. Enfin, l’influence des paramètres du traitement par sablage sur le comportement mécanique monotone et à long terme (essais de fatigue) sur la résistance du joint colle a été étudié à l’aide d’essais de cisaillement sur éprouvettes à simple recouvrement. Ceci a conduit, à la proposition de paramètres morphologiques surfaciques spécifiques pour l’optimisation du comportement mécanique du joint de colle des matériaux composites à matrice PEEK. / One of most problematic in the aeronautical industries is the structural joining of the high performance thermoplastic composites like PEEK composites. Actually, a lot of technologies are used for joining thermoplastic composites like welding, bolting, riveting, fastening and adhesive bonding. Due to the various advantages that characterize the adhesive bonding method, such an uniform stress distribution along the joint, weight‐light and cost reduction, makes this technique more desirable to join thermoplastic composites materials compared to the other joining techniques. PEEK (PolyEtherEtherKetone) is a semi‐crystalline thermoplastic material with high performance. This material is wildly used in aeronautical industries, principally, reinforced with carbon of glass fibres. However, its high chemical resistance makes the adhesive bonding of PEEK and its composites difficult and therefore an appropriate and optimised surface treatment is necessary. In the aim to obtain a bonded system with high performance, scientific and technical problematic should be focussed on the junction between adherents. Indeed, the quality of this junction is of utmost importance because it must allow optimum transfer of thermomechanical stresses when the assembly is subject to its terms of use. Though, at this time it is well known that thermoplastic composite materials are difficult to bond with‐out surface treatment. This study, therefore, relates to the improvement of mechanical properties (monotonic and cyclic) of the adhesive bonding system PEEK / PEEK. In this context, a surface treatment, easy to implement, is proposed. This surface treatment is sandblasting, which enables surface topographic (morphological) modifications. Understanding of various phenomena of interfaces interaction involved in the improvement of the mechanical behavior of the adhesive joint and is part of the triptych "Rheology, Physico‐chemistry and topography" is the major scientific challenge in this thesis. Initially, the influence of processing parameters such as the projection time, the particle size on surface morphology of various materials based on PEEK was analysed, thus allowing establishing the correlation between morphological parameters and modification mechanisms involved during surface treatment surface. One of the key factors for understanding the mechanisms of interaction between the liquid adhesive and the solid substrate is wettability. The analysis of the wetting behavior as a function of various parameters of the treatment was performed. The wettability of treated surfaces is strongly affected by surface roughness created after this treatment. The relationship between morphological parameters and wettability was discussed. Finally, the influence of sandblasting processing parameters on the mechanical behavior in monotoning and long‐term (fatigue tests) of the adhesive joint strength was studied, using single lap shear tests specimens. This has led to the proposal of specific surface morphological parameters for the optimization of the mechanical behavior of the adhesive joint of PEEK and its composites.