Wedge Test Research Articles

Toughness and Durability of Interfaces in Dissimilar Adhesive Joints of Aluminum and Carbon-Fiber-Reinforced Thermoplastics.

The toughness and the durability under a high humidity condition of the interfaces in dissimilar adhesive joints of carbon-fiber-reinforced thermoplastic with a polyamide-6 matrix and Al alloy were evaluated by two test methods, in which a tensile opening load was applied to the specimens to cleave the interfaces apart in two different ways. In the double cantilever beam (DCB) test, the specimens were continuously pulled apart at a constant velocity, while in the wedge test, the specimens are pulled apart at a constant displacement. The crack growth along the interface in the DCB test was dynamically monitored with the assistance of mechanoluminescence for the accurate detection of the phenomena at the crack tip. The wedge test was employed for the evaluation of the durability of the interfaces under high humidity conditions. It was found that the adhesive joints were failed by various failure modes depending on the surface pretreatment and environmental conditions. Throughout the work, discussion was made concerned with the interfacial structures and the adhesion mechanism of dissimilar adhesive joints.

Review of the Wedge Test and Single Curve Initiation Principle Applied to Aluminized High Explosives

AbstractThe experiments have a key role in the initiation and transition studies of solid high explosives. Detonic has forced scientist to improve their experimental approach by designing relevant set‐up and developing accurate metrological devices. For example, the wedge or pop‐plot test was developed in the 50’s and remains a legacy experiment in the characterization of high explosive. However, for 70 years, it has been widely improved, because of the accurate measurements need. This paper aims to review the main improvements performed on the pop‐plot test and analyze a series of results acquired on melt‐cast and cast‐cured high explosives. We first describe the current set‐up with its new metrological devices. Then, we discuss the results and limitations of this test.

Mode I fracture characterisation of rigid and flexible bonded joints using an advanced Wedge-Driven Test

The resistance to fracture of a bonded joint is usually evaluated through the experimental characterisation of its fracture toughness. Different test procedures and data reduction methods are available in the literature, such as the ISO-25217 test standard. The need for crack length measurement has led to inaccurate results when large adhesive thicknesses or flexible adhesives were studied. Advanced test protocols based on the insertion of a wedge, such as the Wedge Test (WT) in ASTM D3762 or the Wedge-Driven Test (WDT), simplify the test procedure, but most such procedures do not allow for the measurement of fracture toughness. Further, experimental results are scarce in the literature, especially when dealing with bonded joints and considerable thicknesses. In the present work, an advanced data reduction method based on the WDT is presented: The Wedge-Driven Test Plus (WDT+). The fracture toughness of specimens made by bonding two aluminium adherends with a rigid and a flexible adhesive was measured, and the effect of wedge thickness and test speed at low displacement rates on the test results was analysed. The results were compared with static tests performed in a double cantilever beam (DCB) following ISO-25217. It has been demonstrated that the proposed data reduction method is less sensitive to test speed and enables different adhesive types, and bondline thickness and wedge thickness configurations, thereby improving the WDT available in the literature.

Characterizing photovoltaic backsheet adhesion degradation using the wedge and single cantilever beam tests, Part I: Field Modules

Photovoltaic backsheets are exposed to harsh outdoor weathering conditions throughout their service lives that can compromise their protective function, through adhesive debonding between their constituent layers and between the backsheet and the module. A large-scale study on adhesive degradation was conducted on 37 field-exposed modules, that spanned 19 different module manufacturers, that were deployed among six Köppen–Geiger climatic zones, and that were fielded between 0 and 28 years. Six outer layer polymer classes were identified among the backsheets: polyamide (PA), polyethylene terephthalate (PET), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), fluoroethylene vinyl ether copolymer (FEVE), and tetrafluoroethylene hexafluoropropylene vinylidene fluoride copolymer (THV). Two adhesion tests were used to measure the adhesive strength: the wedge test and the width-tapered single-cantilever beam (SCB) test. Adhesion energies were compared across exposure time and Köppen–Geiger climatic zone. Many of the PET-, PVF-, and PVDF-based backsheets experienced degradation of the adhesive layer between the backsheet outer and core layers. A consistent trend of decreasing adhesion energy with exposure time was observed in five out of the six backsheet types. Trends among adhesion energy and climatic zone, while expected, were not observed, possibly due to broad ranges in temperature, humidity, and precipitation defining Köppen–Geiger climatic zones. The cantilever beam measurements produced an upper cutoff of approximately 100 J/m2, above which no modules exhibited field delamination. The results are part of a two-part study quantifying adhesion in both field-weathered and indoor-exposed PV backsheets.

Description of the Boundary Layer Behavior of an Aluminum\u2013Carbon-Fiber-Reinforced Polymer Hybrid Compound Using a Cohesive Zone Model

Compounds of light metals and fiber composites have a large potential in the field of lightweight construction. In order to fully exploit the properties of both materials, joining technology is a major challenge. One of the reasons for this is the electrochemical contact corrosion in these materials. By using a high-temperature resistant thermoplastic (PEEK) as a separating layer between the joining partners, it is possible to produce a material composite using the aluminum die casting process, which exhibits both electrochemical decoupling and high composite strength. The description of the failure behavior of this composite plays an important role in the application of this type of joint to structural components. One of the most widely used methods to describe the failure behavior of a composite using the finite element method is the cohesive zone model. With this model, the initiation of a crack, its evolution and finally the failure of the component can be described by means of a bilinear law. In this paper, a methodology to determine the necessary parameters for fracture mode I using a modified wedge test for the cohesive zone model is described.

Significance of the brazing gap in the brazing of aluminium heat exchangers for automotive industry

The paper presents the influence of the brazing gap width on the structure of bonded joints during the production of aluminum heat exchangers, using brazing technology, in tunnel furnaces with controlled atmosphere. Based on the wedge test, an analysis and qualitative assessment of brazed joints was made for the changing width of the brazing gap and the filler metal used. For the received brazed joints, metallographic tests were carried out using light and electron microscopy (SEM) and microhardness measurements in the characteristic areas of brazed joints. Based on the results obtained, the recommended width of the brazing gap was determined.

Durability study of flexible bonded joints: The effect of sustained loads in mode I fracture tests

Adhesives in bonded structures are exposed both to external loads and environmental conditions; durability studies are currently needed to assess their service lifetime. Conditioning strategies differ in considering external load conditions (such as stressed or not stressed) for the durability analysis of double cantilever beam (DCB) bonded joints. Different test procedures such as ASTM D3762 (wedge testing) or ISO-25217 (DCB testing) exist to characterise the evolution of the fracture strength and toughness found in bonded joints. These methods depend on crack-length measurements, however, and achieving an accurate visual determination may be difficult due to the large fracture process zones (FPZs) that develop in the adhesive layer, especially in flexible or degraded bonded joints. To compensate, crack-length-independent data-reduction methods such as the compliance-based beam method (CBBM) or the J-integral method can be used, but experimental research is lacking on the suitability of these methods in ageing tests. A lack of consensus also exists in testing methodologies to evaluate the durability of bonded joints, especially when examining flexible bonded joints. The present work evaluates the influence of damage on fracture toughness within flexible bonded joints exposed to service conditions. Wedge tests and DCB tests are conducted using DCB specimens bonded with a flexible structural adhesive, proving that the degradation of flexible bonded joints exposed to environmental conditions is significantly accelerated when external loads act on them. The findings show that crack length estimation is affected due to environmental effects and thus, that crack-length-dependent test methods are not applicable in ageing tests.

Characterizing photovoltaic backsheet adhesion degradation using the wedge and single cantilever beam tests, Part II: Accelerated tests

Photovoltaic (PV) backsheets provide critical moisture, mechanical, and electrical insulation to the backside of PV modules, but their continued functionality depends upon their ability to remain well adhered over years of harsh environmental exposure. A study of adhesive strength was conducted on several PV backsheet types exposed to indoor accelerated weathering. Two adhesion tests – the wedge test and single cantilever beam test – were used to measure adhesion energy in four backsheets: two with fluoropolymer-based outer (airside) layers – polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF) – and two with non-fluoropolymer-based outer layers–polyamide (PA) and polyethylene terephthalate (PET). The effects of changes in temperature, ultraviolet (UV) irradiance, relative humidity, and a periodic water spray were studied. The PET-, PVF- and PVDF-based backsheets all showed instances of debonding in an adhesive layer, which is commonly reported. For the PA-, PET-, and PVDF-based backsheets, adhesion energy dropped fairly rapidly with exposure, reaching very low levels by 4000 h. The PVF-based backsheet was relatively robust to weathering. Pull-off of an outer chalking layer in the PA- and PET-based backsheets suggested a sensitivity to UV. Adhesion in these two backsheets was also highly sensitive to changes in moisture level. Changes in UV irradiance and temperature did not show a statistically significant effect on adhesion loss for the exposure levels used. The present work is part of a two-part adhesion study on both field-weathered and indoor-exposed backsheets, and forms a basis for understanding adhesion degradation across a variety of backsheet types and degradation factors.

Comparison of experimental methods to evaluate seam welds quality in extruded profiles

Abstract The wedge and bulge expansion tests were compared in the assessment of the seam welds strength in a tubular profile extruded at two ram speeds. In the wedge test, the expansion was determined by moving a conical punch into the tube until the specimen fracture. In the bulge test, a hydrostatic tensile stress state was applied by expanding the specimen with an internal rubber plug. The two methodologies were compared in terms of load and hoop strain at fracture and by detecting the fracture morphology and location. Then, the effect of a number of design parameters was investigated in order to evaluate the robustness of the standard testing conditions. For both tests, ductile fractures appeared in the seam welds location, but the bulge test was more robust and conservative with respect to the wedge test, showing less scattered data. Thus, the performances of a second die for the tube profile, designed to optimize the seam welds quality, have been successfully assessed by the bulge test and results compared to those achieved by a novel numerical quality index, coming to a final good matching.

An analytical model for DCB/wedge tests based on Timoshenko beam kinematics for accurate determination of cohesive zone lengths

In this work, an analytical model consisting of Timoshenko beams coupled with a cohesive zone is used in order to analyze the extent of the cohesive fracture process zone within mechanical systems displaying beam-like features. This is the case, for example, for the double cantilever beam (DCB) specimen or for the wedge test specimen. The predictions of the model are displayed under the form of diagrams and formulas involving non-dimensional parameters, that can be readily used for example in the context of the identification of cohesive parameters from experimental data. The predictions are also compared to those of previous papers using beam models. It appears that in some configurations, for example soft materials with moderate toughness, the kinematic hypothesis of the Timoshenko beam is necessary in order to get accurate estimate of process zone lengths. The influence of the shape of the cohesive law is also discussed.

Numerical Modelling of Shock Initiation of a HNIW‐Based Explosive

AbstractTo investigate shock‐to‐detonation transition (SDT) characteristics of a HNIW‐based explosive, a rate law based on the Forest Fire model was calibrated by conducting five wedge tests. In the wedge tests, initial shock pressure at wedge‐shaped test explosive charges was varied from 5 to 11 GPa. In each test, the shock trajectory along the wedge‐shaped explosive charge was recorded with a streak camera. The streak records showed that sharp SDT occurred in the test explosive. The shock Hugoniot of the test explosive was determined from the free‐surface velocity of PMMA attenuators measured with a VISAR instrument and the early shock velocity in the wedges, determined from the shock trajectories. The Pop plot for the test explosive was obtained from run distances to detonation estimated based on the shock trajectories. The Forest Fire rate of the test explosive was calibrated from the experimental Hugoniot and the Pop plot. The wedge tests were numerically simulated with the calibrated rate by using a one‐dimensional Lagrangian hydrodynamic code. The calculated shock trajectories closely reproduced experimental observations. The rate was further applied to two‐dimensional numerical simulations of large‐scale gap tests (LSGTs). The estimated critical gap thickness by the LSGT simulations was 43.7 mm, which was in good agreement with experimental data of 46.67 mm. The results of these two types of numerical simulations suggested that the calibrated rate could be used to model most SDT‐related applications.

Transmission Laser Welding of Polyamides: Effect of Process Parameter and Material Properties on the Weld Strength

Transmission laser welding (TLW) is an environmentally friendly and versatile process for assembling polymeric parts. Welding by transmission requires the upper element to be transparent to the laser wavelength whereas the inferior part is absorbent to the same wavelength. Thus, the energy of the laser beam is concentrated at the interface, allowing both polymeric parts to be melted. Upon temperature, the interdiffusion of polymeric chains takes place at the interface, creating bridges between both parts, resulting in a strong assembly. Laser welding is in principle applicable to any thermoplastic, provided that it is transparent to the laser wavelength.In the present work, carbon black filled polyamide has been assembled with two types of 2 mm and 4 mm thick partially transparent polyamide specimens. The effect of the process parameters such as energy density, speed of the laser beam and the part thickness have been correlated with the mechanical strength of welds, measured by wedge tests. The thermomechanical and optical properties of the samples have been assessed and correlated to the dimensions of the heat affected zone (HAZ). For a deeper understanding of the effect of optical and thermal properties of the materials on the quality of the welded joint, a numerical modeling is proposed. The ray tracing method is able to determine the light scattering and the absorption at the micro-scale in the polyamide semi-transparent part. The results of the ray tracing are the volume term source and the heat flux that generates temperature elevation.

Effect of surface roughness and chemistry on the adhesion and durability of a steel-epoxy adhesive interface

This work focuses on the effect of surface roughness and surface chemistry on the initial adhesion strength and corrosive de-adhesion properties of adhesive bonds. The adherend used in this study is a S690 low-alloy steel whereas the adhesive is a 2-component epoxy-amine adhesive (Araldite 2015). The steel surface is subjected to different surface pre-treatment methods such as mechanical abrasion, grit blasting, zirconium conversion treatment and silane treatment. The effect of these different pre-treatments on the surface morphology, roughness and chemistry is addressed. Single-lap joint tests were performed at ambient conditions to assess the initial bond strength of the joint. Static wedge tests were performed in saltwater immersions to study the environmental ageing of the adhesive joints. Unloaded delamination of adhesive films from the steel surface was studied by means of scanning Kelvin probe (SKP) at high relative humidity. This unique combination of different techniques allows thorough evaluations of the bond performance under different environmental and loading conditions. Experimental results indicate that surface roughening plays an important role in the initial adhesion in the single-lap joint test but a minor role in the durability of the bonded steel surfaces. The improved initial adhesion is mainly attributed to the increased interfacial bond area at higher surface roughness. The presence of complex texture or morphology shows a more profound effect than the average roughness on both the initial adhesion and the durability of the interfacial adhesion. The results from the static wedge test show the large contribution of mechanical interlocking, caused by texturing of the surface, on the durability of the interfacial adhesion. In the absence of complex texture, surfaces with altered chemistry by zirconium- or silane treatment exhibit a significant increase of the initial bonding strength due to enhanced physicochemical interactions across the interface. Assessment of the interfacial delamination kinetics by SKP show that despite the absence of any surface topography, chemically altered surfaces prove to have higher resistance to delamination.

Formulation of CL‐20‐Based Explosive Ink and Its Detonating Transfer Performance in Micro‐Size Charge

AbstractExplosive ink in the micro‐size charges of explosive circuits for energetic devices has attracted considerable interest. Herein, explosive ink with 90 wt.% of energetic solid was selected by testing the rheological properties of formulations with different CL‐20 concentrations. Explosive ink suspensions with sub‐micro CL‐20 (2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane) as main explosive and fluorine‐containing rubber/polyvinyl alcohol (PVA) emulsion as binder system were prepared. Direct ink writing (DIW) technology was used for the printing of the sample and for the loading of the explosive ink in a micro‐size groove. The morphology and crystal type of the CL‐20‐based composite samples were characterized by SEM and XRD, and its detonating transfer performance in the micro‐size groove were tested. Results show that the CL‐20‐based composite has a good molding effect, and the crystal type has not changed. The critical detonation thickness is around 11 μm at 1.0 mm fixed width in the wedge tests, and the critical detonation size (cross section) is about 0.3 mm×0.3 mm. The detonation wave could continue to propagate around multiple 90° corners. The maximum corner turning ability of the detonation wave is 140° and the CL‐20‐based composite can detonate completely in a complex charge circuit.

Finite element analysis of self-healing ceramics: analysis of wedge test

Finite element analysis of self-healing ceramics: analysis of wedge test

Effect of 3-Piece Golf Ball with Difference Structures on Golf Ball Performance according to Driver and 52 Degree Wedge Shot

[Purpose] This study aims to demonstrate how, in 3-piece golf balls, the structure difference between dual core with single cover (DSB) and single core with dual cover (SDB) balls can affect the performance of drive shots and 52 degree wedge shots. [Method] The differences between the two ball types were determined by conducting drive shots at 80, 90, and 100 mph swing speeds along with 52-degree wedge shots at 70 mph. [Result] No significant differences were observed between the two balls in the drive shot performance at 80 mph swing speed. In contrast to 80 mph, better performances in DSB were observed in the distance to maximal height (p=0.005), carry distance (p=0.001), and total distance (p=0.027) at 90 mph swing speed. At 90 mph, spin rate (p=0.007), maximal height (p=0.032), carry distance (p=0.006), and flight time (p=0.041) in DSB were observed better performance compare with SDB. Launch angle (p<0.001), back spin rate (p<0.001), total spin rate (p<0.001), height, and decent angle (p<0.001) at wedge test were significantly difference between DSB and SDB. The maximal height (p=0.032), backspin rate(p=0.007), carry distance(p=0.006), and flight time(p=0.041) were also significantly difference between DSB and SDB. [Conclusion] These results demonstrated that DSB would be the more favorable option than SDB for golfers or coaches trying to improve their drive distance and shot preciseness.

Durability of polyamide bonded joints: influence of surface pre-treatment

The aim of this study was to evaluate the influence of surface pre-treatment on the durability of bonded joints between polyamide pieces. Various surface preparations of the substrates were carried out and a wedge test was performed to evaluate the joint behaviour over time. Joints composed of polyamide 6 and polyamide 66 were made using a two-component acrylic adhesive. Four different surface treatments were compared: only degreasing, degreasing + abrasion, degreasing + plasma and degreasing + abrasion + plasma. The tests carried out highlighted the extreme importance of choosing the right surface preparation if one wishes to guarantee high performance over time. For both substrates, superficial preparations with cold plasma yielded the best results.

Improved test time evaluation in an expansion tube

Traditionally, expansion tube test times have been experimentally evaluated using test section mounted impact pressure probes. This paper proposes two new methods which can be performed using a high-speed camera and a simple circular cylinder test model. The first is the use of a narrow bandpass optical filter to allow time-resolved radiative emission from an important species to be captured, and the second is using edge detection to track how the model shock standoff changes with time. Experimental results are presented for two test conditions using an air test gas and an optical filter aimed at capturing emission from the 777 nm atomic oxygen triplet. It is found that the oxygen emission is the most reliable experimental method, because it is shown to exhibit significant changes at the end of the test time. It is also proposed that, because the camera footage is spatially resolved, the radiative emission method can be used to examine the ‘effective’ test time in multiple regions of the flow. For one of the test conditions, it is found that the effective test time away from the stagnation region for the cylindrical test model is at most 45% of the total test time. For the other test condition, it is found that the effective test time of a 54 $$^\circ$$ wedge test model is at most a third of the total test time.

Determination of work of adhesion of gelatin hydrogels on a glass substrate

In this article, work of adhesion (wadh) of soft gelatin hydrogels on a smooth glass substrate is determined experimentally using the wedge adhesion test. The results showed that wadh decreases with the increase in gelatin concentration in the hydrogels but the same is found to be independent of thickness of hydrogel specimen. These results are used further for establishing a scaling law between wadh and mesh size (ξ) of the three dimensional structure present in the hydrogel as wadh ∼ ξ8.6. Finite element analysis is also carried out for validating the fracture stability of wedge test in view of analytical prediction. At the end, practical significance of the present study is also discussed.

The Flexible Initiation Test (FIT): A new experimental test to characterize fracture initiation in mode I at the free edge of bonded assemblies

Direct bonding is based on molecular adhesion. This bonding technique consists to join two surfaces into direct contact without the use of any adhesives or additional material. This process requires clean surfaces with a nanometric roughness, sufficiently close together to initiate bonding. Mechanical characterization of this type of assembly with classical mechanical test as for instance wedge test, cleavage test or double shear test present a highly scattering on mechanical results. This paper presents the Flexible Initiation Test (FIT test), an original test designed to characterize fracture initiation in mode I, and to decrease scattering in fracture initiation load measurements, in particular for adhesive with brittle behavior. This new test has to take into account the industrial framework: to be easy to manufacture, easy to execute repeatedly and efficient to provide experimental data for numerical models (stress criteria applications for instance). The paper proceeds first with an explanation of the main initial ideas to introduce the concept of this new test. Next, a numerical analysis is proposed to validate the concept and to determine the optimal geometry of the tests. Then the experimental device is set up and the concept is validated on three different adhesives with the same substrate (a brittle cyanoacrylate adhesive, a ductile and a brittle epoxy adhesives). To conclude, the FIT test is applied on direct bonded samples (an extreme case nanometric interface and very brittle behavior) to determine the fracture initiation load and to compare scattering of measurements.