Lap Joint Tests Research Articles

Fracture Behavior and Mechanical Properties of Rivet Joint By Using Ultrasonic Vibration with c-Frtp

Fiber Reinforced Plastics (FRP) have been expected to be used for structural materials in various field because of its high specific stiffness and strength. In the case of using FRP for automotive structures, easy and reliable jointing process in a short time must be needed. Most easy jointing processes are adhesive joint with bonding agent or welding joint in the case of FRTP. However mechanical properties of these joint system depend on the interfacial properties between resin and fiber or resin itself, which are relatively poor. In the case of mechanical joint by using bolt and nut, or rivet system with metal materials, whole structure will be heavy. Therefore if FRP parts could be used as a jointing parts instead of rivets, the problems such as a increase of weight and process time of jointing should be overcome.In this study, rivet joint with pultruded c-FRTP (continuous Fiber Reinforced Thermoplastic composite) rods with CF/PA commingled yarns covered with braided GF / PA commingled yarns and were performed by using ultrasonic welding machine with a die forming rivets for a pair of c-FRTP (CF/PA) plates with a joint structure. Mechanical properties of rivet joint were investigated by performing single lap joint test, and fracture behavior was also investigated by stopping the test in each region of the obtained diagram and embedding the sample for cross-sectional observation.

Static and dynamic testing and modelling of aluminium joints with flow-drill screw connections

A new component test suited for quasi-static and dynamic testing of flow-drill screw connections is presented. The component specimen was made of two different aluminium alloys, and included connections with two material combinations. Large-scale finite element simulations were carried out of each test, in which the connections were modelled with a constraint-based macroscopic model. An improvement of the connection modelling technique is presented. The model was calibrated to cross tension, cross mixed and single lap-joint tests, and validated with peeling and the component tests.

A model assessment method for predicting structural fatigue life using Lamb waves

This paper presents a study on model assessment for predicting structural fatigue life using Lamb waves. Lamb wave coupon testing is performed for model development. Three damage sensitive features, namely normalized energy, phase change, and correlation coefficient are extracted from Lamb wave data and are used to quantify the crack size. Four data-driven models are proposed. The average relative error and the probability of detection (POD) are proposed as two measures to evaluate the performance of the four models. To study the influence of model choice on the probabilistic fatigue life prediction, probability density functions of the actual crack size are obtained from the POD models given the Lamb wave data. Crack growth model parameters are statistically identified using Bayesian parameter estimation with Markov chain Monte Carlo simulations. The model assessment and the influence of model choice on fatigue life prediction are made using both coupon testing data with artificial cracks and realistic lap joint testing data with naturally developed cracks.

Experimental and statistical study of three adherence tests for an epoxy-amine/aluminum alloy system: Pull-Off, Single Lap Joint and Three-Point Bending tests

The mechanical resistance of a bonded joint depends on the adhesive interaction onto the substrate and the mechanical properties of the adhesive itself. Many existing tests can be useful for measuring the adherence or evaluating mechanical adhesive response. All these tests do not provide the same information: in particular, adherence measurements can be split into initiation tests and propagation ones. In this paper, three adherence tests have been considered for the evaluation of the fracture initiation between a poly-epoxide adhesive (a mixture of pure epoxy and amine) and an aluminum surface (AA 2024-T3), namely the Pull-Off, Single Lap Joint (SLJ) and Three-Point Bending tests. Various surface preparation protocols before bonding have been tested and optimized for aluminum substrates, including mechanical and chemical surface treatments, followed by the application of an appropriate primer before bonding. This study paves the way for the future development of adhesive systems as it provides reliable surface preparation protocols for aluminum surfaces and gives an insight into the choice of an adequate adherence test dedicated to high-performance adhesives. The load at break (FMax), the experimental error, the failure mode and statistical studies according to the Weibull model and Principal Component Analysis (PCA) were studied on each surface preparation configuration. It has been shown that the application of a primer, especially a sol-gel product increases the load at break and provides more reliable results. Then, this paper shows that the two tests can quantify the failure initiation and distinguish the different surface preparation efficiency, are the Single Lap Joint test (mode II or mode I + II) and the Three-Point Bending test (mode I), with an increase of the results reliability with the latter one. The Pull-Off test (mode I) is useful as a routine checking, and particularly interesting because its response does not depend on the substrate thickness, even though it cannot highlight the difference between all surface preparations.

Humidity Aging Effect on Adhesive Strength of Composite Single-lap Joint

Because adhesively bonded joints are used in many structural systems, it is important to predict accurate adhesive strengths. Composite aircraft with many joints are easily exposed to low temperatures and high relative humidity. This paper presents a humidity aging effect on the adhesive strength of a composite single-lap joint (SLJ). The adhesive strength of the SLJ is predicted using a finite element analysis with a cohesive zone model (CZM) technique. The humidity aging effect is evaluated based on the adhesive strength and CZM parameters. A lap joint test is carried out on the composite SLJ specimens, which are exposed for four months of 100% R.H. at 25°C. The predicted strengths are in good agreement with experimental data, and the actual crack propagation is satisfactorily simulated using the local CZM technique.

Effect of hygrothermal conditioning on the energy release rate and failure mechanism of metal only adherend-glass fibre prepreg co-cured single lap joints

Fibre-reinforced composite materials are extensively used in repair and rehabilitation of oil and gas metal infrastructures which are largely exposed to water and hydrocarbon. An important aspect to this is applying adequate surface preparation to the metal to ensure a durable bond between the composite and metal substrate. In this paper, mild steel surface was prepared using grit blasting and single lap joint (SLJ) test specimens were manufactured and tested to investigate the adhesion in terms of total energy release rate (GT) of the interface between mild steel adherend and glass fibre prepreg. An out-of-water usable epoxy resin primer was incorporated to join mild steel adherend with glass fibre prepreg by curing at a temperature of 55 °C for 48 h. Upon durability testing of the SLJ specimens using hygrothermal conditioning at a temperature of 55 °C for 1000 h, the experimental GT values were seen to reduce significantly. Comparatively lower amount of cohesive failure and increased amount of swelling or delamination of the adhesive was observed for conditioned SLJ specimens when compared to controlled SLJ specimens. Furthermore, the experimental GT values were found to correlate well with an analytical adhesive interface model.

Effect of air dielectric barrier discharge plasma treatment on the adhesion property of sanded polyphenylene sulfide

Air dielectric barrier discharge (DBD) plasma was employed to treat the sanded polyphenylene sulfide (PPS) surface. The plasma-treated PPS samples were bonded with epoxy adhesive, and the adhesion strength was measured by the single lap-joint specimen test. Scanning electron microscopy (SEM), water contact angle analysis, and X-ray photoelectron spectroscopy (XPS) were applied to investigate the effect of the plasma treatment on the PPS surface property. A slight etching trace was detected after the plasma treatment according to the SEM images. XPS and water contact angle analysis indicated that the plasma treatment introduced sulfide oxides (S=O and O=S=O) onto the PPS surface leading to a higher surface energy. A steady improvement of bonding shear strength was achieved with the increase of plasma treatment time or discharge power density, which was consistent with the failure mode study. According to the above analysis, the air DBD plasma treatment could effectively improve the adhesion property of PPS.

Survey of selected adhesive bonding properties of nine European softwood and hardwood species

Due to the increasing interest in applying a wider range of wood species for structural purposes, nine European softwood and hardwood species (ash, beech, birch, hornbeam, larch, oak, poplar, black locust and spruce) were assessed for their ability to be bonded with three different commercial adhesive systems (melamine–urea–formaldehyde, one-component polyurethane and phenol–resorcinol–formaldehyde). Tensile shear strength and delamination tests were conducted according to European standards, for all tests including the corresponding wood species as adhesive joints and as a solid wood reference. When tested in dry condition, the threshold of solid wood tensile shear strength was reached by all species–adhesive combinations. By contrast, testing in wet condition revealed distinct performance reductions for certain combinations. This trend was confirmed by delamination testing. Overall, the results indicate that extrapolation of test results achieved with a specific wood species (as recommended in the current standard for lap-joint tests) towards other species is highly problematic and has to be done with caution.

Effects of hygrothermal and ambient humidity conditioning on shear strength of metal–GFRP single lap joints co-cured in and out of water

Installing and repairing of oil and gas infrastructure is required to be conducted out of water (OW) and in water (IW). In service, this infrastructure is subjected to various environmental ageing which may affect its mechanical performance. In this study the shear strength of metal–glass epoxy prepreg composites was investigated using single lap joint (SLJ) testing. For this, three different surface preparation methods (grit blasting, wire brushing and needle gunning) and two different manufacturing methods (OW and IW) were employed. Results showed that the specimens prepared by grit blasting had superior shear strength followed by these by needle gunning and wire brushed for both OW and IW methods. Manufactured specimens were also subjected to hygrothermal conditioning (WC) and ambient humidity conditioning (HC) to assess the durability of the produced SLJ specimens. The WC specimens absorbed more moisture than the HC specimens and the shear strength of the WC specimens were found to have deteriorated more than the HC specimens. For the conditioned SLJ specimens, the lower loss of shear strength was found with specimens manufactured IW when compared to specimens manufactured OW for grit blasted and needle gunned specimens and an opposite trend was seen for wire brushed specimens. However, the loss of shear strength was found to be varied with the moisture uptake for individual surface preparation technique and the variation was considered to be due to a combination of many factors other than the type of adhesive used such as metal surface profile, failure mode, rust formation and presence of black coloured metallic remnants.

Delamination analysis of woven fabrication laminates using cohesive zone model

A new test method was proposed to evaluate the cohesive strength of composite laminates. Cohesive strength and the critical strain energy for Mode-II interlamiar fracture of E-glass/epoxy woven fabrication were determined from the single lap joint (SLJ) and end notch flexure (ENF) test, respectively. In order to verify their adequacy, a cohesive zone model simulation based on interface finite elements was performed. A closed form solution for determination of the penalty stiffness parameter was proposed. Modified form of Park-Paulino-Roesler traction-separation law was provided and conducted altogether with trapezoidal and bilinear mixed-mode damage models to simulate damage using Abaqus cohesive elements. It was observed that accurate damage prediction and numerical convergence were obtained using the proposed penalty stiffness. Comparison between three damage models reveals that good simulation of fracture process zone and delamination prediction were obtained using the modified PPR model as damage model. Cohesive zone length as a material property was determined. To ensure the sufficient dissipation of energy, it was recommended that at least 4 elements should span cohesive zone length.

Comparison of the bond strength of oak (Quercus L.) and beech (Fagus sylvatica L.) wood glued with different adhesives considering various hydrothermal exposures

The investigation of the hydrothermal exposure effect on the glue-line strength is obvious when outdoor application of wood products is in option. In our research the bonding quality of oak ( Quercus L.) and beech ( Fagus syl- vatica L.) wood was tested in different conditions according to EN 205. After each exposure the lap joint test specified the shear strength of wood bonded with PVAC and PU adhesive. In our research different behaviour concerning both types of adhesives and selected wood species was observed. The most significant decrease (-80%) of the shear strength was found when the PVAC was used to bond oak wood. Therefore the PVAC adhesive is most likely less suitable for the bonding of the block board in outdoor conditions. On the contrary, the best results in the same conditions were obtained by the oak when the polyurethane adhesive was used. It indicates that the PU adhesive is more suitable for the bonding of oak wood. Considering results of beech wood, there were not found this interaction.

Polyelectrolytes to promote adhesive bonds of laser-structured aluminium

Aluminium is one of the most popular construction materials in machine and equipment manufacture as well as vehicle and aircraft construction. Particularly, in automotive and aircraft industries, the adhesive bonding of aluminium requires the pre-treatment of the adhesive surfaces. In this study laser pre-treatments were used to laterally control the surface roughness and clean the substrate surfaces by forming fresh aluminium oxide layers. In order to keep the adhesive properties stable over time, the laser pre-treated aluminium surfaces were subsequently coated with weak polyelectrolytes. The applied polyelectrolytes lower the driving forces for the adsorption of unwanted surface contaminations and provide reactive amino groups for the subsequent coupling of reactive adhesives. The surface topographies of the laser-treated aluminium surfaces were investigated in relation to the applied laser parameters (such as pulse frequency, and laser power) by means of scanning electron microscopy (SEM) and light-microscopic techniques (confocal microscopy). The adsorption of the polyelectrolytes was studied by X-ray photoelectron spectroscopy (XPS). Inverse water contact angle measurements using captive air bubbles were carried out to study the wettability (hydrophilicity/hydrophobicity) of the modified aluminium surfaces. Single lap joint tests carried out on joined AlMg3 sheets showed that the shear strengths can be significantly increased by pre-treatment with laser and coating of the alloy surfaces with weak polyelectrolytes. Furthermore, the application of polyelectrolytes improved the stability against corrosion. The article shows the increase of tensile shear strengths at adhesively bonded single lap shear samples after laser pre-treatment and also an increase in long-term stability due to of the combination of laser pre-treatment and coating with polyelectrolytes. Adhesive bonds of laser treated samples with and without polyelectrolyte coating have a higher stability against corrosion compared to untreated samples.

Macroscopic strength and failure properties of flow-drill screw connections

Force–displacement responses and failure behaviour of connections using flow-drill screws to join aluminium sheets were investigated under various quasi-static loading conditions. This included single connector tests under tensile, shear and combined tensile and shear loadings, using cross test coupons in a new test set-up, and peeling and single lap-joint tests. The strength of the connection increased with the amount of shear loading, while the ductility decreased. No effect of the anisotropy of the sheets on the behaviour in the single connector tests was found. Axial crushing tests of aluminium single-hat sections joined with flow-drill screws were also performed. Two connection failure modes not observed during the single connector test were found in these tests. For comparison, equivalent single connector and component tests were carried out for self-piercing rivet connections. Similar trends with respect to the ductility, maximum force and shape of force–displacement curves were observed for the two connections, but the local failure modes were different.

Observations and analyses of secondary bending for riveted lap joints

The phenomenon of secondary bending in riveted lap joints of the configuration representative of connections of the aircraft fuselage sheets in the longitudinal direction is investigated experimentally and analytically. The experiments involved strain gauge measurements of secondary bending stresses carried out in close proximity to the fatigue critical section of the riveted lap joint and fatigue tests performed to study the effect of secondary bending on the riveted joint fatigue life. The strain gauge measurement results allowed validation of a simple analytical model proposed by Schijve to estimate secondary bending moments induced in mechanically fastened joints with eccentricities. Variables considered in the fatigue tests were several joint geometry related parameters known to influence the magnitude of secondary bending in the fatigue critical location. It was shown that the fatigue test data for joints of various geometries, which were considerably scattered if the fatigue lives were presented against the applied stress amplitude, could become consolidated within common scatter bands when the lives were plotted in terms of the combined tensile stress amplitude including the bending stress computed from the model by Schijve.

Adhesion and Tensile Properties of a Novel Fiber-Metal Laminate Based on Polypropylene Reinforced with Aramid Fibers.

ABSTRACTThe aim of the present study is to analyze interfacial adhesion and characterize the tensile properties of a FML elaborated from thin layers of an aluminum alloy and layers of maleic anhydride modified polypropylene (MAHPP) reinforced with an aramid woven fabric. For the analysis of interfacial adhesion, a microbond test is carried out on the MAHPP-aramid fiber system and a single lap joint test is performed on FML constituent materials, as well as the tensile characterization of the FML and its constituents is conducted accordingly. Microbond testing revealed an improvement in interfacial shear strength for the MAHPP-aramid fiber system in comparison with that of polypropylene-aramid fiber systems reported in the literature. The apparent shear strength between the FML constituent materials is comparable to that for bonding of aluminum with MAHPP. Tensile characterization of the FML and its constituents showed that the FML presented greater tensile strength than the aluminum alloy; and a more ductile behavior in comparison with its individual components due to the degree of adhesion between the constituents which allows the material to deform in unison.

The Influence of Alloying Elements on Adhesive Properties of Epoxy-Quasicrystal Composites

Quasicrystals (QC) are materials that exhibit good surface properties such as high hardness, low surface energy, low friction coefficient, and good resistance to oxidation and corrosion. Despite these properties, QC alloys are highly brittle, discouraging their uses in applications requiring mechanical stresses. Hence, the development of composites using quasicrystalline materials as reinforcement to ductile matrices is an interesting alternative. In this work, Al-Cu-Fe quasicrystals were used as a reinforcement to epoxy resin in order improve adhesion with metallic substrates. Adhesive properties were evaluated by single lap joint (SLJ) tests and the QC/epoxy interface was analyzed by scanning electron microscopy (SEM). Aluminum, copper, and iron, individual elements, were used to investigate the contribution of each element to the adhesive. Results show that it was possible to significantly enhance adhesion properties when 25% QC was added to epoxy and that the effect of QC amount on SLJ bond strength did not follow a linear trend. Moreover, the contribution of each alloying element was important to explain the influence of QC addition on adhesive properties of the epoxy-based composites.

Mechanical characterization of a high elongation and high toughness epoxy adhesive

In this paper, a new epoxy adhesive has been mechanically characterized. The adhesive combines the properties of an epoxy adhesive and typical polyurethane (PU) adhesive, such as high elongation and high toughness. Experimental tests were performed to measure the tensile properties, shear properties, thermal properties and fracture properties. The tensile test shows high tensile strength and high elongation. The single lap joint (SLJ) test shows that the failure load is proportional to the overlap length for hard steel adherends. For the SLJs with mild steel adherends, the failure occurred due to adherend yielding. Impact tests were conducted using SLJ specimens and the results are consistent with the SLJ tested under static conditions. The Tg was obtained using a Dynamic Mechanical Analysis (DMA) type of test. The toughness in mode I was determined using the Double Cantilever Beam (DCB) test and the toughness in mode II using End Notched Flexure (ENF) test.

Tuning the mechanical behaviour of structural elements by electric fields

This work reports on the adoption of electric fields to tune the mechanical behaviour of structural elements. A mechanical characterization procedure, consisting of double lap joint and 3-point bending tests, is conducted on copper-polyimide laminates while applying electric fields of varying intensity. Field dependence and, thus, adaptability of shear strength and bending stiffness are shown as a function of the overlapping length and interfaces number, respectively. Further, the impact of remaining charges is investigated in both testing configurations. The findings herein lay the foundation for the implementation of electro-adaptive components in structural applications.

The potential of moisture content measurements for testing the durability of timber products

Traditionally, the durability of timber is determined in laboratory decay tests or ground contact field tests. Since it is commonly accepted that results from those tests are not directly transferable to less severe above-ground exposures, this study aimed at assessing alternative durability measures related to the moisture performance of wood. Results from above-ground tests including continuous wood moisture monitoring were analyzed. Decay ratings determined in double-layer field tests were compared with time of wetness, and temperature- and moisture-induced dose according to a dose–response model for above-ground decay. Significant differences between European wood species were found in facade, decking, sandwich, lap-joint, and double-layer tests with respect to their moisture performance. It is concluded that for many wood-based products intended for above-ground use, a combination of short-term laboratory decay tests and mid-term moisture performance field tests may serve as time-saving alternative to long-term decay tests in the field.

On the mechanical behavior of BFRP to aluminum AA6086 mixed joints

The aim of this work is to analyze the possibility to join aluminum alloy AA6086 and composite laminates reinforced with basalt fibers, an innovative material which use is growing in several applications as an alternative to glass fibers. To this goal, three joining techniques were investigated: mechanical by Self Piercing Riveting (in the next called SPR), adhesive by co-curing technique and mixed in which the joining techniques (i.e. adhesive and mechanical) were combined. Two manufacturing technologies (i.e. hand lay-up and vacuum bagging) were used both to produce composite substrates and to realize co-curing adhesion between the substrates to be joined. Mixed joints were realized by inserting the rivets in co-cured joints after 48h than the initial phase of the curing process (i.e. the phase of mixing the resin with own hardener). Overall, six lots of joints were realized (two for each joining technique). All joints were characterized by performing single lap joint tests. The mechanical results were analyzed through a two way analysis of variance.The experimental results show that adhesive joints, realized by vacuum bagging method, show average failure load 22.9% higher and standard deviation 70.6% lower than those realized by hand lay-up, respectively. This means that the vacuum bagging technology allows to increase the adhesion strength of the interface between metal sheet and Basalt Fiber Reinforced Polymer (in the next BFRP), allowing the above failure load growth. Furthermore the failure mechanisms change from adhesive mode to partially cohesive one for the adhesive joints realized by hand lay-up and vacuum bagging, respectively. By comparing mixed joints, different results are obtained: i.e. the hand lay-up joints show both higher average failure load (+42.9%) and standard deviation (+208.3%) than those realized by vacuum bagging. The poor performances of the mixed joints realized by vacuum bagging can be considered due to the excessive value of the chosen riveting load. Statistically, two variables were investigated: i.e. joining technology (i.e. mechanical, adhesive and mixed) and manufacturing process (i.e. hand lay-up and vacuum bagging). These can influence the properties of the joints. In particular, the joining technology results a significant factor. Moreover, an interaction between the two variables exists.