Search

Aim: This study was designed to compare the retention strength of monolithic CAD/CAM PEEK crowns to that of CAD/CAM monolithic YTZP-zirconia crowns, both resin-cemented to epoxy resin dies resembling lower molar teeth; after thermomechanical aging simulating 3 months of in-vivo service. Materials and methods: 22 identical epoxy dies, resembling the preparation of a lower second molar (4mm height, 6° axial convergence and 1 mm-thick deep chamfer finish line), were produced by replicating one master stainless steel die via 22 polyvinyl siloxane impressions. The epoxy dies were randomly equally distributed into 2 groups (Zr and P groups); 11 dies each. The first (control) group (Zr) received CAD/CAM milled monolithic Y-TZP zirconia crowns (Katana™ ML), while the other group (intervention) received CAD/CAM milled monolithic PEEK crowns (breCAM.BioHPP™). Two opposing, laterally projecting (mesial and distal) arms were included in the design of all crowns for the retention test. The fitting surfaces of crowns of both groups were sandblasted with 110-µm alumina particles. All crowns were cemented over their corresponding epoxy dies using the (hand-mixed) dual-cured, self-adhesive resin cement (RelyX™ U200) (3-kg seating force). Samples were stored in water incubator for 24 hours (37 °C); then, subjected to mechanical aging (37,500 cycles, 49 N load) with simultaneous thermocycling (300 cycles, 5-55 °C, 12 s dwell time). Retention strength was evaluated by vertically pulling-up the crowns from their corresponding dies, through the pull-out test performed via a universal testing machine (UTM). Failure modes were then observed under digital microscope. The mean dislodgment force (retention strength) for each group was calculated, and statistically compared using Student t-test. Statistical analysis was performed with three-way ANOVA. Pair-wise comparison of groups was made with the Tukey test. Pearson’s Chi-Square test was used to analyze the failure modes. Results: PEEK crowns group (P) demonstrated statistically insignificant higher retention strength (171.28 N ± 26.30) than zirconia (Zr) crowns group (150.40 N ± 24.40). “Mixed” failure mode was predominant in both groups, followed by the adhesive “cement on crown” failure-mode.

In the last years, the use of adhesive bonding is increasing as an alternative to traditional joining techniques due to their advantages such as ease of application, low weight and the good mechani...

The bonding of thermal-sprayed coatings largely depends on the substrate surface morphology. This study examines the effect of the substrate surface texture shapes on the adhesion strength of coatings. For that, it used plasma-sprayed Ni-based MoS2 coatings deposited on grit-blasted and laser-textured surfaces, and investigated the coating bonding strength (ASTM 633 pull-off test), and cross-sectional and fracture morphologies, as well as phase compositions and element distribution. The results showed that the surface texture shape has a significant effect on the improvement of coating adhesion. The coatings deposited on sinusoidal-textured surfaces had the highest adhesion strength (50.0 MPa), followed by coatings deposited on groove-textured surfaces, while dimple and dimple–groove textures resulted in the lowest coating adhesion strength. The coating fracture analysis revealed that cohesive failure occurred mainly at the texture positions, while adhesive failure occurred almost always in plain areas. Therefore, it could be concluded that, in the conditions of this study, the existence of plain areas and dimple textures did not improve coating adhesion. Factors such as coating bond mode, contact area ratio, and coating deposition quality should be comprehensively considered in texture design to improve coating adhesion.

Objectives: to assess the pull off of Polyetheretherketone (PEEK) anterior crown after various surface treatments. Materials& Methods: Twenty Polyetheretherketone (PEEK) full coverage crown were constructed on prepared human maxillary central incisors. All of the crowns (n=20) were divided into four groups according to the surface treatment used group I ) Control , 2) 98% Sulphric acid, 3) 9.5% Hydrofluoric acid (HF ) 4) Air Abrasion with 50 μm AL2 O3 .( n=5 in each ) Afterwards, each crown specimens were cementeded to corresponding abutments using self-adhesive resin cement RelyX U200. Then, subjected to thermo cycling (5°C - 55°C,5000 cycles,). A universal testing machine was used to assess pull-off test. Data were collected, tabulated and statistically evaluated. Results: The mean pull off values were ranked as follows: group II (253.81±7.67 N) > group IV (221.18±3.91N) ≥ group III (203.20±8.23N) > group I (135.91±9.92N). The highest and lowest Pull off values was obtained in group II (253.81±7.67 N) and group I (135.91±9.92N), respectively. Conclusions: 98% sulphric acid PEEK surface treatment is recommended to achieve high retentive strength.

PurposeAs an important part of steel bridge deck pavement, if waterproof adhesive layer performance does not meet requirements, numerous kinds of bridge deck pavement distress may be encountered. To study the adhesive behavior of rubber asphalt waterproof adhesive layers in steel bridge gussasphalt pavement, the pull-off and direct-shear tests have been used in the study to mechanically simulate steel bridge deck pavement under vehicles loading.Design/methodology/approachSeveral potentially influential factors associated with the adhesive strength of rubber asphalt are investigated including temperature, spraying quantity and environmental conditions.FindingsResults indicate that rubber asphalt was associated with good performance with respect to its use as a waterproof adhesive layer; simulated performance was negatively correlated with increasing temperatures. A necessary spraying quantity of 0.4 Lm-2 is required for appropriate adhesive strength of the composite structure, with a decrease in adhesive strength noted when spraying quantity is significantly greater or less than this.Originality/valueThe current paper presents an examination of the adhesive performance of a rubber asphalt adhesive layer on steel bridge deck pouring construction, while additionally examining potentially influential factors and conditions via use of both pull-off and shear tests.

Good bond and water impermeability in fiber-reinforced polymer (FRP) bonded/coated systems are essential if the durability of FRP-rehabilitated concrete structures is to be ensured. In add...

Hypothesis Wetting characteristics of epoxy and phenolic resins on metals depend on the molecular interactions between resins’ functional groups and metal surface. Those interactions affect the practical adhesion strength of epoxy-phenolic coatings on metals. Estimation of the theoretical adhesion energies can reveal this system’s microscopic adhesion mechanisms. Experiments Adhesion is estimated theoretically based on resins’ wettability on metals, and experimentally through pull-off adhesion testing of cured coatings. The effect of various functional groups on adhesion is decoupled using epoxy and phenolic resins with different functionalities. To assess the impact of the metal passivation on adhesion, tinplated and tin-free steel substrates are used. Differences in their surface chemical composition and polarity are investigated using XPS. Findings Theoretical adhesion results reveal a superior adhesion of epoxy compared to phenolic resins. Moreover, epoxy resins having a higher content of epoxide-to-hydroxyl groups show improved theoretical and practical adhesion. The importance of epoxides in driving resins’ initial adhesion on metals is attributed to the formation of direct chemical bonds with active hydrogen on metal surfaces. The adhesion of coatings on tin-free steel is found to be higher than on tinplated steel. This is associated to the increased hydroxyl fraction on tin-free steel surface leading to more hydrogen bonds formation.

Surface treatment technologies are constantly evolving. Increasingly, surface functionalisation is of major concern to lighten structures, improve product performance and reduce costs. To f...

The use of Carbon Fiber Reinforced Polymer (CFRP), for both strengthening material and anode for Impressed Current Cathodic Protection (ICCP) system, is being investigated. The focus of this study is to develop the epoxy that has good bond strength and electrical conductivity. Graphite powder is used as conductive pigments with percentage ranges from 7.5% to 17.5%. All specimens were partially submerged in 5% NaCl solution and induced with electrical current of 10 mA/m2 and 20 mA/m2 for 30 days. An average potential increase of 200 mV was recorded using half cell potential test. The application of 30 days ICCP up to current density of 20 mA/m2 did not affect the bond strength significantly and still complies with ACI recommendation. However, graphite content of more than 15% are found to be not workable and the bond strength is greatly reduced to less than 1 MPa This study concluded that the recommended graphite powder content shall be in the range of 10% to 15%.

This study investigates the acoustic emission signals of concrete slab strengthened with carbon fibre reinforced polymer (CFRP) under pull-off test. Three types of surface preparations were prepared namely without surface preparation, normal surface preparation and boring surface preparation. The slabs were then tested under pull-off test in conjunction with acoustic emission technique. The pull-off strength, acoustic signal strength, amplitude, duration and rise time were analysed and discussed. It was found that the boring surface preparation produced the highest pull-off strength compared to other surface preparations, indicating good bonding between the CFRP and the concrete interface. This study is useful in identifying the bonding between CFRP and concrete using acoustic emission technique.

In the present study, a series of pull-off tests is performed to determine the bonding properties of fiber reinforced polymer (FRP) composites applied to a brittle substrate. Pull-off test is simple, fast and cheap and it is generally employed to evaluate the bond strength between the composite and the substrate. It is a procedure that can be easily performed on-site for checking the quality of the reinforcement adhesion.A steel composite made of a unidirectional steel fabric embedded in an organic matrix (bi-component epoxy resin) was applied to the surface of fired-clay bricks. A shallow core perpendicular to the surface was realized in the test specimen, leaving the core attached to the brick. A steel dolly was glued to the external surface of the core using epoxy adhesive. A loading device was employed to apply the tensile force until failure. The effects of moisture presence on the substrate and shape of the cores on the pull-off strength were investigated.

The durability of concrete cast near the conventional formwork (steel or wood) is reduced because of higher water-cement (w/c) ratio as compared with the concrete present in the core of the member. Various controlled permeability formwork (CPF) liners absorb or drain out excess water near formwork, can reduce the increase in w/c ratio of concrete near the formwork. This paper presents a quantitative study showing improvement in the properties of near surface concrete (NSC) by the use of a commercially available CPF liner, and comparing the performance of more easily available and cheaper alternatives to CPF liner used. Two types of concrete mixes with identical w/c ratio but different water contents were used. Three specimens were made for each of the two types of concrete mix and one surface for each of the specimen was cast using one of the CPF liners among a commercially manufactured CPF, particle board, and gunny bag. Four tests: Rapid chloride permeability test, AgNO3 colorimetry test, initial surface absorption test and pull off test were performed to study durability properties of NSC. Study of physical appearance in terms of blowholes and grey area on the concrete surface using image processing is also presented in the paper. Though commercially manufactured CPF produces better surface than the particle board and gunny bag, the improvement in NSC properties by use of gunny bag is also noteworthy.

The quantification of moisture susceptibility has been a major concern for researchers as it adversely affects the performance of asphalt pavements. Several methods have been developed to assess bond strength using asphalt mixtures in loose and compacted state. These tests lack in their ability to study fundamental properties that affect the bond between bitumen and aggregate. In this context, more fundamental techniques have been developed such as pull-off stub tests and direct tension tests. The first group only measures the maximum pull-off strength and second group has problems related to use of consistent binder film thickness and operational difficulties in test itself. This paper presents a new test to evaluate bond strength, in an attempt, to solve problems associated with traditional direct tension tests. The aim is achieved through a review of existing techniques, development of a gap assembly, fabrication of direct tension test moulds, development of Compression Pull-Off Test (CPOT) and evaluation of its results. The key parameters for bitumen and mastics were evaluated. The CPOT shows promising results for use of this technique to study cohesive as well as adhesive bond strength of binder.

In this paper, the moisture susceptibility of different bituminous binders with two substrates (glass and limestone) was investigated. To that end, the tensile strength of different combinations of bituminous binder–substrate bond was measured using a pull-off test. This test was adapted from the pneumatic adhesion tensile testing instrument (PATTI) test to improve repeatability. Samples were tested in dry condition and after a 7-day conditioning in hot water bath (60 °C). An analysis of variance (ANOVA) was performed on the test results. Overall, the results show that in dry condition, the pull-off strength is a function of the bituminous binder type rather than of the substrate type. After water conditioning, an increase in the pull-off strength was observed for the bituminous binder without polymers and coupled with glass substrate. This was associated with an increase in binder stiffness. For the limestone substrate, the effect of water conditioning was significant only for one type of binder.

Wear and corrosion aspect in materials are the main concern in any industrial sector. Co-Ni-Fe coating can be used to protect materials from corrosion and wear. The purpose of this study is to investigate the wear and adhesive performance of Co-Ni-Fe coated onto mild steel. The coating was fabricated by using the electrodeposition method. The slurry erosion test was performed at different speeds, which were 500, 1000 and 1500 rpm for 12 hours at 2 hours interval. The pull off load using epoxy adhesive was applied until the failure of the coating occured. At 500 rpm, there was no significant weight loss. At 1000 and 1500 rpm, the weight loss was increased as the time was increased. The pull off test showed the coating was not removed from the substrate. This showed that the coating was intact with the substrate. As a conclusion, Co-Ni-Fe coating could contribute to industries such as marine, manufacturing, oil and gas sectors where it can enhance the life span of materials and at the same time protect the substrate from the erosion wear attack.

Over the last 30 years, structural reinforcement and retrofitting with externally bonded composite materials have proven to be efficient and cost-effective solutions to increase both the safety and the lifespan of civil engineering structures, including nuclear power plants. The effectiveness of the strengthening system highly depends on the level of adhesion between the fiber-reinforced polymer (FRP) composite material and the concrete surface. Therefore, on-site evaluation of the bond quality is critical to assess the performance and predict the durability of the system in place. The direct tension pull-off test is most commonly used to quantify the adhesion level, but this standardized method has many drawbacks. In the present study, it is proposed to evaluate the bond properties by using a nondestructive test (NDT) derived from the standard pull-off test. This innovative test enables the measurement of an interfacial &ldquo, stiffness&rdquo, which may be used as a bond quality criterion. This paper gives an insight into the performance of the proposed NDT method, when applied in laboratory conditions to concrete slabs reinforced with bonded pultruded carbon FRP plates (CFRP). Three different epoxy adhesive systems with a broad range of Young&rsquo, s moduli were used for the specimens&rsquo, preparation, in order to vary the stiffness of the concrete/CFRP interface. The purpose was to simulate different levels of interfacial adhesion that could be observed for a single adhesive system. It was shown that the test method was able to detect differences in the interface stiffness beyond experimental uncertainties, and it should therefore enable the detection of differences in the bond quality for a given adhesive system as well. The sensitivity of the NDT was then discussed, and its detection capabilities were predicted for standard field conditions. In the last part, strain measurements were collected during the NDT, thanks to distributed optical fiber sensors (DOFS) embedded in the adhesive joints of the strengthened specimens. An analysis of the strain profiles was found to provide complementary information on the quality of the adhesive bond.

The pull-off test (POT) is a tensile strength testing method that is widely used in concrete/mortar and was recently applied to rock mechanics. The POT can be easily performed in both the ...

Present studies deals with comparison of high velocity oxy fuel and flame spray coating process by developing CoMoCrSi (Tribaloy T400) coating on a titanium grade-15 substrate. Prior to coating, feedstock is processed to obtain higher fraction intermetallics through high energy ball milling technique under controlled atmosphere. Processed feedstock material is sprayed on a Ti-15 substrate through HVOF and Flame spray process. The coated specimens are subjected to metallurgical and mechanical characterization using optical microscope, scanning electron microscope, energy dispersive spectroscopy, x-ray diffraction, Vickers mico hardness tester and bond strength using pull off test method. HVOF sprayed coating exhibits superior properties compared to Flame sprayed coating in terms of surface roughness, porosity, micro hardness and adhesion strength. The detailed studies of two coating systems is discussed.

Substrate preparation plays a vital role in the performance of thermal spray coatings. Adherence of the coating to the substrate depends on surface characteristics like; mechanical interlocking, physio-chemical properties of surface and metallurgical bonding. The surface characteristics depend to great extent on the method used for substrate preparation. In the present study, WC-12Co and WC-17Co coatings were deposited on AZ91D samples prepared using laser texturing as substrate preparation technique. Laser textured substrate was characterized using scanning electron microscopy and surface roughness tester. Bond strength of the coating was determined using ASTM 633C pull off test. SEM was used to study the morphology of the coating; XRD/EDAX techniques were used to study the structure of the coatings. Porosity and micro-hardness of the coatings were also measured. Corrosion performance of the coatings was determined using Potentiodynamic and EIS electrochemical corrosion testing techniques. The coatings are found to have good surface and mechanical properties. Both WC-12Co and WC-17Co demonstrated good corrosion performance during electrochemical testing. However, WC-12Co was found to better protect the AZ91D compared to WC-17Co.

The long-term performance of the bond between carbon fibre reinforced polymer composite (CFRP) fabrics and concrete substrate is crucial to estimations of the reliability of externally strengthened concrete structures. This paper presents the experimental results and analysis of 162 pull-off tests using nine concrete slabs under various environmental conditions, i.e., wet/dry cyclic exposure and full-immersion exposure of 3.5% salt-water at a temperature of 60 °C. The main objective of this study was to assess the effects on the bond performance of CFRP-strengthened concrete slabs during 12 months of exposure in a marine environment. Five types of failure modes were observed in the tested samples. The test results confirmed that 12 months of exposure in a marine environment had a low effect on the epoxy performance between CFRP and concrete. The results also indicated the marginal increase of pull-off strength values after 12 months of environmental exposure.

This paper concerned with the replacement of Epoxy with cement base matrixes as bonding agents for CFRP sheets. Many items were investigated to improve the bond strength and decrease slippage in strengthening system. More than 25 plain concrete prisms with low compressive strength (20 N/mm2) were used to act as the original weak concrete members. Two main groups of cement base bonding agents were investigated in this research (Portland cement and Grout matrix’s). Three main items were looked for. Item 1: mixture content; it was represented in (cement content, using silica fumes & using short metallic fibers). Item 2: CFRP sheet modification; represented in either: a) making holes in CFRP sheets -hence the cross section area of the CFRP sheets were kept the same as all other specimens- or b) impregnate the CFRP sheets in latex-base adhesive material just before using). Item 3: the strengthening technique; which was represented by both the bonding agent layer thickness & the Curing pressure; (it is a pressure done with a specific value just after applying the strengthening on the concrete prism along 24 hours). Single shear test (pull off test) was carried out to evaluate each parameter effect and the results showed that the cement-base matrixes were a very good alternative for epoxy as a bonding agent. Applying Curing pressure; almost double the bond strength and prevent the failure from occurrence in the surface interval between bonding agent / concrete interface, using latex and making holes in the CFRP sheet enhance the penetration of the bonding agent within CFRP sheet. Portland cement gives higher results than grout. Using silica fumes and even increasing the cement content; both have a negative effect on bond strength.

Marine paints are complex polymeric systems containing layers of different nature that significantly delay the corrosion failures. In order to obtain a rapid ranking in the corrosion protection provided by the paints, it is important to apply sensitive and non-invasive methods for early detection of under paint corrosion. Scanning Kelvin Probe (SKP) was used to determine the mechanism(s) of corrosion and paint de-adhesion. This technique is sensitive to the metal-polymer interface and gives a quick assessment of cathodic delamination or anodic undermining. Depending on the type of exposure the mode of corrosion de-adhesion was evaluated and compared with SKP data obtained under polarization experiments by impressed current in aqueous electrolyte. After exposure, pull off test and Scanning Electron Microscopy – Energy Dispersive X ray Spectrometry (SEM-EDX technique) were applied to determine the paint adhesion stability around the defect and to analyse the steel-paint interface.

The aggregate-binder bond is one of the main factors that affect the durability of asphalt mixtures. This can be investigated based on the energy required to fracture the adhesive bond between binder and aggregate. In this study, the effects of Sasobit, Rediset WMX and Rediset LQ on the adhesive bond strength of an aggregate-binder system is investigated using the pull-off test. Test data are compared with the nano-scale adhesion force determined using atomic force microscopy (AFM) using the PeakForce Quantitative Nanomechanical Mapping (PFQNM) method. The impact of warm mix additives, test temperature and binder grade on the practical work of fracture was investigated. It was found that Sasobit, Rediset WMX and Rediset LQ increased the practical work of fracture by 170%, 100% and 143%, respectively, for the aggregate-binder system produced using 40/60 Pen binder, and 70%, 25% and 50%, respectively, for the system produced using 100/150 Pen binder. The contribution of warm mix additives in improving the p...

Background Retention is an essential factor in the sustainability of the prosthesis, especially for short abutment. Despite, the availability of several auxiliary applications, achieving a clinically good retention for cast crowns in prepared short teeth remains a major challenge for the practicing dentist. Objectives This study tests a new method for applying frustum-shaped grooves on short prepared abutments and compares them with traditional setting grooves. Methods Forty-eight copper machine-milled short dies with 3.5 mm length and 12o conversion with a chamfer finish line of 0.7 mm were prepared to mimic short prepared molars and distributed into 4 groups. A control group with two opposing setting grooves and two groups with dual opposing frustums, one of which was prepared to receive two integrated metal protrusions inside the casting that fit the frustums. Frustums were prepared with Komet bur No. 807 with dimensions 0.9 mm at the base and 0.7 mm at the occlusal surface. A direct wax-up was carried out on all dies and all castings were cemented with zinc phosphate cement. A pull-off test was applied until separation. Data were analysed to compare the correlation of the four groups using one-way ANOVA and Bonferroni test (p ≤ 0.05). Results The mean retentive values in Newton were as follows: the control group, 457.80; the setting grooves group, 461.07; the frustum group, 597.59; and the frustum group with the two metal protrusions, 919.80. The retention was increased by 65% in frustum group and doubled in frustum group with the metal protrusions. Conclusions The results showed a statistical significance in retention in the frustum groups with and without metal protrusion over the retention of the control and the setting grooves groups., Biomedical engineering; Biotechnology; Dentistry; Quality of life; Occupational health; Dental materials; Oral medicine; Prosthetic dentistry; Retention; Abutment; Cast crown; Frustum; Groove; Metal protrusion; Tooth preparation; Cement key; Short crown; Pull off test

This paper deals with the problem of chemical pre-treatments of hot dip galvanized materials for the adhesion of organic coatings. In the first part of the paper are mentioned new perspective technologies of chemical pre-treatments and the second part is devoted to the comparison of current and modern chemical pre-treatments and their influence on the adhesion of organic coatings and corrosion resistance. The goal of scientific research is to replace the current chemical pre-treatments due to increasing demands to reduce production costs, protect the environment and reduce the total time of these technological processes.

An anticorrosive coating of post-consumer polyethylene terephthalate (PET) was applied on carbon steel by using an industrial press. The PET layer showed a good adhesion on the substrate, evaluated by using a pull off test, when compared with the traditional organic coatings. In addition, scanning electron microscopy (SEM) analysis showed that the PET layer was uniform, homogeneous, and free of cracks or defects. The Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) proved that the PET properties were not affected by the deposition process. The PET organic coating is a promising coating, due to its corrosion resistance evaluated by using salt spray tests, even though the applied thickness of 65 &micro, m was considered thin for a high-performance coating. The electrochemical impedance spectroscopy (EIS) showed that the PET coating has a capacitive effect and its electrochemical behavior was not affected as the exposure time increased, resulting in an impedance modulus value of 1010 Ω&middot, cm2, after 576 h of immersion in an aqueous solution of NaCl 3.0 wt %.

Fabric-reinforced cementitious matrix (FRCM) composites are usually surface-applied for strengthening reinforced concrete (RC) structures. The efficacy of the FRCM strengthening systems is dependent on the FRCM/concrete bond performance. This paper reports on the experimental results of FRCM/concrete bond characterization through pull-off tests. Six FRCM-strengthened RC slabs ( mm) were prepared and enabled conducting 72 FRCM/concrete pull-off tests. The parameters investigated included: (a) FRCM material (carbon or polyparaphenylene benzobisoxazole (PBO)); (b) level of substrate roughness (no/low/high roughening); and (c) specimen's test age (7, 28, 56, and 84 days). All FRCM systems were single-plied. The study revealed a significance of the surface preparation and test age of specimens on the FRCM/concrete pull-off strength. High-roughness specimens showed an average of 74% pull-off strength increase compared to those without roughening. Also, specimens tested at Day 84 showed 54% strength increase compared to those tested at Day 7, on average. PBO-FRCM system showed slightly higher pull-off strength than that of the carbon counterpart. The specimens showed two distinctive failure types at the (i) fabric/mortar interface and (ii) concrete/matrix interface: the latter was more prominent in carbon-FRCM. Nonetheless, the failure mode was most dependent on the fabric geometry and the substrate roughness. Based on a statistical analysis of the tested specimens, prediction models were proposed for the FRCM/concrete pull-off strength and failure mode. This paper was made possible by NPRP grant # NPRP 7-1720-2-641 from the Qatar National Research Fund (a member of Qatar Foundation) and by grant # QUST-CENG-SPR-13/14 from Qatar University . The findings achieved herein are solely the responsibility of the authors. Scopus

Aging changes the chemistry of bitumen and this adversely affects bitumen’s adhesion with aggregate. For this reason, the use of pull-off test was proposed to evaluate bitumen’s adhesion during different aging stages. In this study, the pull-off test method is used to evaluate the effects of aging on a 60/70 penetration grade bitumen and binders modified with 2 and 4% halloysite nano-tube (HNT). The short-term aging (STA) and long-term aging (LTA) of unmodified and modified bitumens were simulated using the rolling thin film oven (RTFO) and pressure aging vessel (PAV) tests respectively. The pull-off test was conducted using the universal testing machine (UTM). Stainless steel and granite substrates moulds were designed and fabricated for this purpose. Dry and wet conditions were simulated to evaluate the loss of bonding strength due to aging. Additionally, consistency tests, namely penetration test, softening point test, and viscosity test, were conducted on all binders. The activation energy (AE) for unaged and aged binders were also evaluated. The results for the consistency test; the pull-off test for stainless steel substrate; and the values for AE showed that the addition of the HNT decreased the effect of aging, which means that modified binders showed decreased temperature susceptibility and this is reflected in improved aging resistance. The result of the pull-off test on granite substrate showed that binders modified with HNT performed better under dry and wet conditions. It can be concluded that HNT is an anti-aging as well as anti-striping agent.

This study aims to study the deformation and failure behavior of the asphalt-aggregate interface using molecular dynamics (MD) simulations. The 12-component asphalt molecular models and the hydrated silica substrate were employed to form a bi-material interface system. Physical properties of asphalt binder were predicted from MD simulations including density and glass transition temperature for model validation with experimental data. Tensile simulations were performed and the stress-separation responses were obtained to analyze the interfacial mechanical behavior. It was found that the interface failure was mainly adhesive failure although large air voids were formed in the bulk asphalt as the loading rate decreases to a certain level. The interface failure strength and post-peak deformation are affected by loading rate and temperature that is consistent the viscoelastic behavior of asphalt binder. The stress-separation responses match the cohesive zone model (CZM) model that is usually observed in the pull-off strength test at the macroscopic scale. The relationship between chemical compositions of asphalt binder and the interface failure parameters was investigated. The MD simulation shows promising results to understand mechanical failure of asphalt-aggregate interface at the atomistic scale.

This study was conducted to investigate the relationship between fluidity and adhesion strength of unmodified and modified bitumens through the use of the consistency and pull-off tests. A universal testing machine (UTM) was used to quantify the adhesion strength of unmodified and modified bitumens where a specially designed mold was fabricated using stainless steel and granite as substrates. Powder cement, hydrated lime and nano-clay were added to bitumen in two different percentages, namely 2 and 4% by the weight of bitumen. The X-ray diffraction (XRD) was used to determine the effects of the additives on the structure of the binders. On the other hand, the scanning electron microscope (SEM) was used to gather surface topography information of the additives scattered within the binder bulk. It was found that the values for adhesion strength varied depending on the types and percentages of additive used, as well as the substrates and their thickness. The use of stainless steel substrate produced a good correlation between adhesion strength and the results of consistency test, although the results for viscosity test showed a weaker correlation in identifying the changes in adhesion strength that was caused by the addition of additives. It can be deduced that the pull-off test can be a useful tool to determine the effects of additives on fluidity and adhesion strength when stainless steel substrate was used.

In this work, the effects of extractives removal on the performance of used varnishes were studied. The experimental samples were prepared using defect-free alder ( Subcordate alnus) and ironwood ( Zelkova carpinifolia) with moisture content of 12% and were coated with polyester and two-part polyurethane (urethane alkyd) varnishes. Removal of extractive materials followed Tappi Test Methods using hot water and ethanol. Variable parameters were based on the solvent type (extraction method), wood species, and varnish type. Other parameters such as moisture content, sanding process, and dimensions were kept constant. Pull-off adhesion and dynamic absorption tests were used to assess adhesion and performance of the two clear varnish coatings. Sanding process was employed prior to coating, which helped prepare surfaces virtually free of damage. In general, the extractive-free samples had better adhesion strength and wettability compared with the untreated (control) ones. Based on the results of this study, it can be pointed out that all the variable parameters, including the type of wood, varnish, and solvent, had significant effect on the adhesion of varnishes, applied on the wood surface. The difference in wettability between extracted and unextracted samples is due to blocking of the free hydroxyl groups by extractive materials. In addition, it was found that the removal of extractives had the effect of increasing the surface wettability of both species, an important consideration for the varnish coating. The highest adhesion was obtained from polyurethane varnish, applied on ironwood specimens. It seems that the diffuse-porous anatomical structure of ironwood along with its high density of 0.79 g/cm3 could be responsible for its higher adhesion strength than alder species.

A common design feature in aircraft to strengthen skin sections is adhesively bonding stiffeners to them. This has been successfully applied in metal aircraft for years. Those adhesive bonds are usually backed up by rivets, because we are not totally confident about adhesives. So it might be a surprise to learn, that while testing stiffeners made of carbon fiber reinforced plastics, Dr. Sofia Teixeira de Freitas discovered that the adhesive bonds were not the weakest link. Download : Download full-size image Sofia Dr. Teixeira de Freitas is an assistant professor in the structural integrity and composites group at the Faculty of Aerospace Engineering of the Delft University of Technology. Her research is mainly on the structural performance of adhesively bonded structures. And she has discovered a flaw in the current method for designing carbon fiber reinforced plastic joints for aircraft structures. Download : Download full-size image Figure 1: Pull off test setup. Download : Download full-size image Figure 2: The different parts of the pull off test setup. A skin made of glare was used. Download : Download full-size image Figure 3: The tests were carried out with three different spans (L): 100, 200 and 300 mm. Download : Download full-size image Figure 4: Pull off test in process.

The bond strength between asphalt and aggregates is a crucial parameter in evaluating the capability of a binder to resist moisture-induced damage. A novel binder bond strength (BBS) test was studied in this paper, and factors affecting the bond strength including pulling rate and asphalt film thickness were investigated to propose a reasonable test procedure. The results showed that there is an equivalent relation between the pulling rate and the asphalt film thickness. Besides, the influences of different additives on the adhesion and self-healing property of two types of asphalt (neat asphalt and SBS modified asphalt) were investigated using this modified pull-off test. Results indicate that different additives including styrene–butadiene–styrene (SBS), polyethylene (PE), polyphosphoric acid (PPA), Gilsonite, bis-stearamide wax (EBS) and rubber processing oil had significant impacts on the adhesion and self-healing properties of neat asphalt and SBS-modified asphalt. The comparison between BBS and DSR tests revealed that the complex modulus of asphalt had a dual effect on the BBS test results while the comparison of the BBS and Hamburg Wheel Tracking Device (HWTD) tests confirmed that the BBS test could address the mixture resistance to water damage.

PURPOSE To investigate the retention loads of differently fabricated secondary telescopic polyetheretherketone (PEEK) crowns on cobalt-chromium primary crowns with different tapers. MATERIALS AND METHODS Cobalt-chromium primary crowns with 0°, 1°, and 2° tapers were constructed, milled, and sintered. Corresponding secondary crowns were fabricated by milling, pressing from pellets, and pressing from granules. For these nine test groups, the pull-off tests of each crown combination were performed 20 times, and the retention loads were measured (Zwick 1445, 50 mm/min). Data were analyzed using linear regression, covariance analysis, mixed models, Kruskal-Wallis, and Mann-Whitney U-test, together with the Benferroni-Holm correction. RESULTS The mixed models covariance analysis reinforced stable retention load values (p = 0.162) for each single test sequence. There was no interaction between the groups and the separation cycles (p = 0.179). Milled secondary crowns with 0° showed the lowest mean retention load values compared to all tested groups (p = 0.003) followed by those pressed form pellets with 1°. Regarding the different tapers, no effect of manufacturing method on the results was observed within 1° and 2° groups (p = 0.540; p = 0.052); however, among the 0° groups, the milled ones showed significantly the lowest retention load values (p = 0.002). Among the manufacturing methods, both pressed groups showed no impact of taper on the retention load values (p > 0.324 and p > 0.123, respectively), whereas among the milled secondary crowns, the 0° taper showed significantly lower retention load values than the 1° and 2° taper (p < 0.002). CONCLUSION Based on these results, telescopic crowns made of PEEK seem to show stable retention load values for each test sequence; however, data with thermo-mechanical aging are still required. In addition, further developments in CAD/CAM manufacturing of PEEK materials for telescopic crowns are warranted, especially for 0°.

U ovom radu obrađena je površinska zaštita metala od korozije pomoću IC sušivih premaza, te ustanovljena razlika u brzini sušenja premaza, svojstvima premaza te količini HOS-a koja se ispušta prilikom sušenja premaza putem IC-a u odnosu na konvencionalno sušenje premaza na sobnoj temperaturi. Jedan od ciljeva ispitivanja je također bio odrediti kako udaljenost od izvora IC zračenja utječe na brzinu sušenja premaza. Za ispitivanje i karakterizaciju takvih premaza korištena je metoda elektrokemijske impedancijske spektroskopije (EIS) te metoda diferencijalne pretražne kalorimetrije (DSC) Za određivanje kvalitete premaza prema standardu ISO 12944-6 korišten je test prionjivosti premaza odnosno pull off test, sukladno s normom EN ISO 4624. Na temelju provedenih ispitivanja, ustanovljene su prednosti i nedostaci sušenja premaza pomoću IC tehnologije u odnosu na konvencionalnu metodu sušenja premaza. Tehnike sušenja uspoređene su s ekonomskog, ekološkog te energetskog aspekta. Napravljena je analiza isplativosti uvođenja takve tehnologije u postrojenja, u odnosu na postrojenje u kojem su premazi sušeni na konvencionalan način. In this thesis, surface protection technology of metal using IR dryed coatings was analyzed, and it was also pointed the difference in speed, characteristics and quantity of VOC released between IR dryed coatings, compared to the coatings dryed in a convencional way on room temperature. Also, the other purpose of these tests was to find how the distance from the IR emiter affects the drying speed of the coatings. For the testing and characterization of such coatings, the method of electrochemical impedance spectroscopy (EIS) and differential scanning calorimetry (DSC) were used. For determinating the quality of the coating, in accordance with the norm EN ISO 12944- 6, pull off test was conducted to determine the adhesion of such coatings, in accordance with the norm EN ISO 4624. Based on the tests that were carried out, the advantages and disadvantages of drying the coatings with IR technology were compared with the conventional method of drying the coatings. The drying methods were compared from the economical, ecological and energy related aspects. An analysis on the feasibility of introducing such technology into plants was made, compared to a facility with a conventional method of drying the coatings.

Objectives The deviation and spread of values measured by tensile strength tests should be significantly reduced by optimized axially pull-off-device. Material and methods Factors like geometry, roughness, surface texture and fit of the specimens, the luting procedure (mixing ratio, compacting pressure) were standardized and the precision of the axially load transmission during the tensile force application optimized. Copings of CoCr–alloy were luted using a provisional zinc-oxide eugenol and a glass-ionomer cement (n = 20 per group each) on 4°, respectively 8° titanium implant abutment analogs. 24 h after luting the copings were pulled off with the improved (IPD) and the previous non improved device (NIPD). Means, std. dev. and t-tests were calculated. Results The stress- strain curves produced by the IPD showed a clear and linear relationship between stress and strain. The curves of the NIPD were ragged and chaotic. For both luting agents the means of the retentive force were considerable higher (p > 0.000) with IPD. However, the standard deviation was unimproved for the zinc oxide eugenol cement: IPD: 27%; NIPD: 27%, but significantly improved with glass ionomer: IPD: 16%, NIPD: 28%. Conclusion The results from luting agents, which react like a solid body, may benefit from the optimized pull-off-device. Despite the fact that many factors in this investigation have been controlled, unknown flow characteristics of non-Newtonian-fluids like luting agents may have a considerable influence on the standard deviation of pull-off tests.

A silver paste was screen-printed on flexible polyethylene terephthalate (PET) substrates, pretreated with different methods. The adhesion quality was evaluated by a modified cross cut test method implementing a motorized cutting device. Additionally, a semi automatized image analysis method was proposed for the evaluation of cross cut patterns in order to quantify the peeled-off area after tape removal. The feasibility of this novel approach is verified by comparing the results with a standard pull off test. The results show that by implementing image analysis methods the area of paste removed by the adhesive tape can be accurately calculated in an automated way, making it possible to gain quantifiable, user independent and therefore more significant results. Furthermore, the results from cross cut test and from pull off test show a similar trend.

T-joints stiffeners made from carbon/epoxy composites have been increasingly applied in aeronautical structures, however as majority of the carbon fiber reinforced structures, they have faced with delamination problems. Through-the-thickness reinforcements for laminate composites have been studied as manner to increase transversal strength, especially reducing delamination. In the present work, carbon/epoxy T-joints reinforced transversally by one side stitching (OSS) and molded on Resin Transfer Molding (RTM) process have been performed as well as the reference (unstitched T-joints). The stitching position were designed after analysis of the unstitched T-joints by means of strain field on Digital Image Correlation (DIC) under pull-off test to better improve the areas submitted to large strain. Also, the stitched samples were mechanically tested in pull-off mode and were analyzed during tests by in situ microscopy and post-failure on Scanning Electron Microscopy .The energy release was better contained in the stitched structures especially in the critical region (delta-fillet), due to crack bridging that improved the delamination toughness. Otherwise, the stitch pattern generated by OSS process changed the strain fields asymmetrically when analyzed on DIC during tests. The stitched T-joints showed greater ultimate strength (25%) and load recovery post ultimate strength (19%) in comparison to the reference.

cited By 0; International audience; Organic photovoltaic devices (OPVs) are one of the most promising applications of organic semiconductors due to their compatibility with flexible plastic substrates resulting in lightweight, inexpensive, ergonomic and aesthetic products. While the electrical failure mechanisms in OPVs have been thoroughly investigated, little is known about their mechanical stability, which is as important and critical to ensure long term reliability. The characteristic thin films stresses of each layer present in organic solar cells, in combination with other possible fabrication, handling and operational stresses, provide the mechanical driving force for delamination of weak interfaces or even their decohesion, leading to a loss of device integrity and performance. In this study, we developed a technique to probe weak layers or interfaces in inverted polymer:PC60BM solar cells, establishing a new set-up for the so-called probe tack making it similar to a pull-off test. With this in hand, the adhesion of a variety of active layers towards a standard water-based poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) formulation was compared against that of a new organic-solvent based PEDOT:PSS. The organic-solvent based PEDOT:PSS formulation showed improved adhesion compared to the standard water-based formulation. Chemical characterization of the exposed surfaces indicated a difference in their composition, suggesting a stronger interaction of the organic-solvent based PEDOT:PSS with the active layer and resulting in a different fracture path. Indeed, all OPVs with water-based PEDOT:PSS showed a delamination localized at the active layer/PEDOT:PSS interface, while those with the organic-solvent formulation were not fractured at this interface but rather, in the active layer.