Figure 1 - uploaded by Gilles Lubineau
Content may be subject to copyright.
Source publication
Spatial heterogeneity of adhesion properties is known to result in bridging during debonding of secondary bonded composite joints. The ligaments that bridge both substrates have crack-arrest features and thus significantly enhance the fracture resistance of joints. We have investigated the effect of randomly distributed adhesion properties between...
Contexts in source publication
Context 1
... schematic on Figure 1 represents a general interface whose properties follow a Gaussian ...
Context 2
... i , ln (G c ) i ) ⇠ N ⇢, µ ln(S) , ln(S) , µ ln(Gc) , ln(Gc) (2) in which ⇢ is the Pearson product-moment correlation coecient of ln(S) and ln(G c ), µ ln(S) and ln(S) are the mean and variance of ln(S) respectively, µ ln(S) and ln(Gc) the mean and variance of ln(G c ), respectively. We recall that the mean and variance of logarithm of any variable a following log-normal distribution can be calculated by: xn-1 xn Under a finite number of sampling spatial points as shown in Figure 1, the corresponding adhesion ...
Context 3
... the property parameters presented in Table 2 Coordinate along interface (mm) Figure 11: Typical debonding process of a joint with the adhesion of fluctuated heterogeneity (The variation of the strength contrasts along the interfaces is superimposed). ...
Context 4
... to evaluate the e↵ect of adhesives' properties on the crack-tip transfer and ligament bridging, Figure 12: The applied constitutive models to test the e↵ects of adhesives' properties on the performance of ABJs. ...
Context 5
... R-curves of the joints with di↵erent adhesives are shown in Figure 13, in which the macro-276 scopic toughness was calculated by integrating the area under the R-curve ranging from a =15 mm to a =24 mm. Figure 13a confirms that the crack resistance of the joints increased in the presence of ligament bridging when ✏ u of the adhesives increased. With higher ✏ u , the ligaments become more stretchable and the bridging length of ligament tend to increase. ...
Context 6
... R-curves of the joints with di↵erent adhesives are shown in Figure 13, in which the macro-276 scopic toughness was calculated by integrating the area under the R-curve ranging from a =15 mm to a =24 mm. Figure 13a confirms that the crack resistance of the joints increased in the presence of ligament bridging when ✏ u of the adhesives increased. With higher ✏ u , the ligaments become more stretchable and the bridging length of ligament tend to increase. ...
Context 7
... fully and substantial improvement in ABJs' crack resistance can be achieved. The R-curves 290 in Figure 13b show little di↵erence in the crack resistance for the three joints (nearly overlapped). ...
Context 8
... applying LEFM, the Mode I energy release rate can be expressed as: 4 (B.5) curve as presented in Figure 14, which clearly manifest the unstable crack propagation during the 347 DCB test with fluctuating heterogeneity of adhesion. The P -response is found to exhibit snap-back 348 instability at which a positive slope changes to a negative slope, and then snaps back to a certain 349 value where it is actually corresponding to the lowest bound of the input toughness. ...
Similar publications
Delamination can occur under the effect of compressive loads on structures, the paper focuses on the behavior of delamination which is occurs following of buckling or post buckling, in laminated composites, the adhesion among layers oftentimes fails and weaken causing for the layers to collapse between them, this phenomenon of delamination behavior...
Laminated composites based on polyetheretherketone (PEEK) and polyimide (PI) matrices were fabricated by hot compression. Reinforcing materials (unidirectional carbon-fiber (CF) tapes or carbon fabric) and their layout patterns were varied. Stress–strain diagrams after three-point flexural tests were analyzed, and both lateral faces of the fracture...
This paper presents the problem of shear-wave propagation in an isotropic laminated composite, which is made of titanium/epoxy/ceramic, considering a localized damage in the adhesion. In practical terms, the damage in the adhesion, which influences on the dispersion relation, is evaluated like a delamination between adjacent layers. Based on an asy...
Citations
... Reports using the spatial heterogeneity of adhesion instead of considering the microroughness can also be found. Li et al. [41] assumed that the stochastic adhesion followed a lognormal distribution. The Napierian logarithm of interface roughness and strength can thus be described. ...
Micro-roughness at adhesion surface yields significant influences on the structural behaviour of adhesive joints. Investigations into the micromechanical mechanism are extremely limited. This works developed a novel particle-based model of joints with stochastic microstructural features of roughness, which can capture refined multi-scale responses as first of this kind. Aluminium adherends with mechanical surface treatments were firstly scanned using 3D laser scanning microscope. The statistical features and reconstruction method of micro-roughness profiles were determined. Single lap shear tests on joints made of epoxy adhesive (Loctite EA 9497) and treated aluminium adherends were performed to provide testing data and observations on failure modes. The refined numerical models were subsequently developed to examine the influences of the actual micro-roughness on the micromechanical behaviors and failure mechanism. The mechanical interlocking, mitigation on crack propagation due to the irregular roughness were investigated. It is followed by introducing the reconstructed roughness of various magnitudes and further numerically examining the micromechanical responses by key stochastic parameters such as root mean square roughness and correlation length. The results indicate that the mechanical interlocking contribute more to enhancing the joint strength than the increase of adhesion area by micro-roughness. A rougher surface in either horizontal or vertical directions does not exhibit a consistent improvement of joint strength, which also depends on the threshold of roughness and the surface skewness triggering the transition of failure modes.
... Multiple researchers report that the highest joint strength performance is obtained using co-curing or secondary bonding. 5 Especially joining complex structures, secondary bonding outperforms the other two methods [9][10][11] Researchers further looked into failure mechanisms at the joint interfaces. The most common problem was an adhesive failure which developed due to interfacial bond failure between the adhesive and the adherent 11,12 Researchers observed that increasing the adhesive thickness enhanced the adhering of adhesive to the surface. ...
Adhesive joining of fiber reinforced polymer (CFRP) composite components is demanded in various industrial applications. However, the joining locations frequently suffer from adhesive bond failure between adhesive and adherent. The aim of the present study is improving bonding behavior of adhesive joints by electrospun nanofiber coatings on the prepreg surfaces that have been used for composite manufacturing. Secondary bonding of woven and unidirectional CFRP parts was selected since this configuration is preferred commonly in aerospace practices. The optimum nanofiber coating with a low average fiber diameter and areal weight density is succeed by studying various solution concentrations and spinning durations of the polyamide-6.6 (PA 66) electrospinning. We obtained homogeneous and beadles nanofiber productions. As a result, an average diameter of 36.50 ± 12 nm electrospun nanofibers were obtained and coated onto the prepreg surfaces. Prepreg systems with/without PA 66 nanofibers were hot pressed to fabricate the CFRP composite laminates. The single-lap shear test coupons were prepared from the fabricated laminates to examine the effects of PA 66 nanofibers on the mechanical properties of the joint region of the composites. The single-lap shear test results showed that the bonding strength is improved by about 40% with minimal adhesive use due to the presence of the electrospun nanofibers within the joint region. The optical and SEM images of fractured surfaces showed that nanofiber-coated joints exhibited a coherent failure while the bare surfaces underwent adhesive failure. The PA66 nanofibers created better coupling between the adhesive and the composite surface by increasing the surface area and roughness. As a result, electrospun nanofibers turned adhesive failure into cohesive and enhanced the adhesion performance composite joints substantially.
... Fiber bridging or adhesive ligament is found to be strongly dependent on the statistical distribution of variability in strength over the delaminating interface [35,36,37,38,39]. ...
The mode I delamination properties between carbon fiber reinforced polymer (CFRP) plies are difficult to measure because the coupling between the intralaminar and interlaminar damage makes delamination properties sensitive to the orientation of surrounding plies. In this study, we use an edge effect mitigator to better isolate the role of the coupling effect that mainly originates from interactions among transverse cracking, local delamination, and fiber bridging. Three samples (i.e., 90//90, 60//60, and 30//30) with and without the edge effect mitigator are evaluated by utilizing the double cantilever beam (DCB) test in the mode I fracture. A baseline unidirectional (UD) DCB test is performed for comparison. The experimental results reveal that for all orientations, the edge effect mitigator confines the delamination crack at the designed interface by limiting the formation of a large fiber bridging zone, thus allowing a more objective evaluation of the delamination properties. However, local crack branching or migration is observed in addition to the primary crack, which is responsible for the fiber orientation-dependent extra dissipation. According to the X-ray scan images obtained in the crack tip, a higher mismatch angle between the fiber orientation and the delamination direction is responsible for the stronger local coupling. The samples without a mitigator illustrate the effect of a fully developed fiber bridging on the apparent toughness in the mode I fracture behavior. The edge effect mitigator demonstrates its potential in a more precise identification of interfacial properties.
... Results obtained from these simulations were then meta-modeled using Gaussian process to study the effect of loading and filler dispersion on the breakdown strength, loss functions and the dielectric constant. Li et al.[300] investigated the adhesive properties of polymer composite laminates to understand the debonding behavior. They used adhesives of different properties and followed Gaussian process to predict the toughness and bonding strength. ...
The superior multi-functional properties of polymer composites have made them an ideal choice for aerospace, automobile, marine, civil, and many other technologically demanding industries. The increasing demand of these composites calls for an extensive investigation of their physical, chemical and mechanical behavior under different exposure conditions. Machine learning (ML) has been recognized as a powerful predictive tool for data-driven multi-physical modeling, leading to unprecedented insights and exploration of the system properties beyond the capability of traditional computational and experimental analyses. Here we aim to abridge the findings of the large volume of relevant literature and highlight the broad spectrum potential of ML in applications like prediction, optimization, feature identification, uncertainty quantification, reliability and sensitivity analysis along with the framework of different ML algorithms concerning polymer composites. Challenges like the curse of dimensionality, overfitting, noise and mixed variable problems are discussed, including the latest advancements in ML that have the potential to be integrated in the field of polymer composites. Based on the extensive literature survey, a few recommendations on the exploitation of various ML algorithms for addressing different critical problems concerning polymer composites are provided along with insightful perspectives on the potential directions of future research.
... Tao et al. [16] implemented a simulation work to trigger ligaments by introducing heterogeneity in the framework of secondary bonded joints, and they found that a certain level of spatially-varying interface properties can help in forming adhesive ligaments, leading to bridging zones for crack-arrest. Meanwhile, the numerical research of Li et al. [17,18] showed that the variability in the statistically uniform properties of an interface has a significant influence on the adhesive ligaments in secondary bonded joints. Herráez et al. [19] enhanced the fracture toughness of delamination by introducing small interlaminar defects to promote fiber bridging. ...
... The work by Chris et al. [25] shows that samples cured with a dwell stage have a 22% reduction of mode I fracture toughness compared to samples cured with a single-stage cure cycle. A plausible explanation is that over curing a CFRP plat alleviates the heterogeneity of the fiber/matrix interface toughness, which has been proved as an important factor for triggering ligament in secondary bonding [16,18]. The following section studies the influence of the variability of fiber/matrix interface toughness on the extent of fiber bridging through a simple model. ...
... The previous section illustrated how sensitive is the extent of fiber bridging and the associated toughening effect with respect to the interface curing degree. Aligned with our other works that analyzed the effects of material variability [17,18], our hypothesis is that a lower degree of curing also corresponds to more variables of the interfacial properties, which explains the different bridging responses. ...
Fiber bridging can significantly influence the interlaminar toughness of laminated composites. However, very little is known about to what extent it depends on the processing conditions. In this paper, we performed a back-bonded double cantilever beam (BB-DCB) test to study the curing process influence on the development of fiber bridging for composite laminates with various thicknesses. The BB-DCB sample included a middle core plate and two backing adherends bonded to each side of the core plate. The total thickness of the BB-DCB samples was kept the same to guarantee the same structural effect due to beam curvature. Thus, only the core plate thickness effect was varied and studied. The experimental results showed that the core plate thickness significantly influences fiber bridging, as the samples with thicker core plates triggered more fiber bridging. Differential scanning calorimetry (DSC) was used to evaluate the degree of cure (DoC) for the different thicknesses, and a correlation was shown between the DoC and the fiber bridging extent. An embedded cell approach was also adopted to show that more fiber bridging was triggered with a larger variance of the fiber/matrix interface toughness and strength, which might have resulted from the change in the DoC with the plate thickness.
... Recently, similar concepts have drawn atten-61 tions to enhance the fracture resistance of secondary bonded joints 62 (Maloney and Fleck, 2019). Lubineau and coworkers designed a 63 series of architectural bondline by patterning interface heterogene-64 ity with laser to trigger large-scale ligaments bridging (Tao et al.,65 2020a; Tao et al., 2020b) or by embedding 3D printed thermoplas-66 tic nets in bondline (Yudhanto et al., 2020), which showed remark-67 able potential to control and tailor the fracture resistance curve. ing the potential of application. ...
Adhesive bonding community shows a continued interest in using bridging mechanisms to toughen the interface of secondary bonded joints, especially in the case of laminated composites. Due to snap-back instability that occurs during fracture, confusions may exist when identifying the toughening effect experimentally. The true toughening effect may be overestimated by lumping all energy contributions (kinetic energy included) in an overall effective toughness. Here, fundamentals for bridging to enhance fracture resistance are explored through the theoretical analysis of the delamination of a composite double cantilever beam (DCB) with bridging. Specifically, we establish a theoretical framework on the basis of Timoshenko beam theory and linear elastic fracture mechanics to solve the fracture response of DCB in the presence of discrete bridging phases. We elucidate the crack trapping and the snap-back instability in structural response during the crack propagation. We identify the contribution to the overall toughness observed numerically/experimentally of both the physical fracture energy and other types of dissipation. The associated toughening mechanisms are then unveiled. Furthermore, we study the effects of property of the bridging phases on the snap-back instability, based on which, we propose a dimensionless quantity that can be deployed as an indicator of the intensity of snap-back instability. Finally, we identify the role of geometrical properties, i.e. the substrate thickness and the arrangement spacing of the bridging phases, in the snap-back instability and the macroscopic fracture toughness of a DCB. This work provides, from a theoretical point of view, an essential insight into the physics related to the structural response of DCB with discrete toughening elements.
Enhancing the performance of adhesively joined composite components is crucial for various industrial applications. In this study, polyamide 66 (PA66) nanofibers produced by electrospinning were coated on unidirectional carbon/epoxy prepregs to increase the bond strength of the composites. Carbon/epoxy prepregs with/without PA66 nanofiber coating on the bonding region were fabricated using the autoclave, which is often used in the aerospace industry. The single lap shear Charpy impact energy and Mode-I fracture toughness tests were employed to examine the effects of PA66 nanofibers on the mechanical properties of the joint region. Scanning electron microscopy (SEM) was used to investigate the nanofiber morphology and fracture modes. The thermal characteristics of Polyamide 66 nanofibers were explored by using differential scanning calorimetry (DSC). We observed that the electrospun PA66 nanofiber coating on the prepreg surfaces substantially improves the joint strength. Results revealed that the single lap shear and Charpy impact strength values of the composite joint are increased by about 79 and 24%, respectively, by coating PA66 nanofibers onto the joining region. The results also showed that by coating PA66 nanofibers, the Mode-I fracture toughness value was improved by about 107% while the glass transition temperature remained constant.
Ensuring the progressivity of failure of adhesively-bonded composite joints is necessary to guarantee safety and to optimize maintenance operations. In our previous work, we proposed a novel surface patterning strategy to stop crack propagation by triggering bridging of adhesive ligaments. However, the brittle failure of classical bridging ligaments still releases a large amount of stored elastic energy, leading to a snap-slip crack propagation or even catastrophic sudden fracture of bonded joints. Such technology could be further improved by integrating ductile structures within the adhesive layer, but the detailed failure mechanisms require systematic investigation. In this work, we integrated thermoplastic polyamide structures within the epoxy adhesive layer of double cantilever beams to guide this transition from brittle failure to a stable softening behavior. Weak polyamide/epoxy adhesion and their embedded area fractions were critical since they affected the damage mechanisms and determined energy dissipation within bonded joints.
