Adhesive Failure Mode Research Articles

Identification of the Cohesive Parameters for Modelling of Bonded Joints between Flat Composite Adherends with Thick Layer of Adhesive.

The failure of bonded composite materials is accompanied by specific failure modes. These are specifically Mode I, Mode II, Mode III, and their combination (so-called mixed mode). These modes depend on the direction and type of loading. The mechanical properties describing the damage initiation and the damage evolution are unique according to the type of adhesive and present mode of failure. However, a few research studies have focused on an adhesive thicknesses greater than 0.2 mm. The main objective of this research is to investigate the mechanical properties of a bonded joint with large adhesive thickness loaded according to Modes I and II. The observed failure parameters, the cohesive and damage parameters, are identified by minimizing the difference between the force-displacement diagram obtained from the experimental data for both Mode I and Mode II. The finite element model is confronted with these parameters and is evaluated based on their agreement. Compared to other studies with a small adhesive layer thickness, the values of failure parameters are lower. The results show that the adhesive thickness has an influence on the values of cohesive and damage parameters and that these parameter values decrease significantly compared to a small adhesive thickness. The obtained parameters can be further used to predict the fracture toughness of other bonded joints loaded in any direction.

Evaluation of Bonding Adhesion Strength and Failure Modes of Different Types of Cutback Asphalts

Evaluation of Bonding Adhesion Strength and Failure Modes of Different Types of Cutback Asphalts

Flowable composite as an alternative to adhesive resin cement in bonding hybrid CAD/CAM materials: in-vitro study of micro-shear bond strength

ObjectiveTo assess the micro-shear bond strength of light-cured adhesive resin cement compared to flowable composite to hybrid CAD/CAM ceramics.Materials and methodsRectangular discs were obtained from polymer-infiltrated (Vita Enamic; VE) and nano-hybrid resin-matrix (Voco Grandio; GR) ceramic blocks and randomly divided according to the luting agent; light-cured resin cement (Calibra Veneer; C) and flowable composite (Neo Spectra ST flow; F), resulting in four subgroups; VE-C, VE-F, GR-C and GR-F. Substrates received micro-cylinders of the tested luting agents (n = 16). After water storage, specimens were tested for micro-shear bond strength (µSBS) using a universal testing machine at 0.5 mm/min cross-head speed until failure and failure modes were determined. After testing for normality, quantitative data were expressed as mean and standard deviation, whereas, qualitative data were expressed as percentages. Quantitative data were statistically analysed using Student t test at a level of significance (P ≤ 0.05).ResultsGroup GR-F showed the highest µSBS, followed by VE-C, VE-F and GR-C respectively, although statistically insignificant. All groups showed mixed and adhesive failure modes, where VE-F and GR-C showed the highest mixed failures followed by GR-C and VE-C respectively.ConclusionsAfter short-term aging, flowable composite and light-cured resin cement showed high comparable bond strength when cementing VE and GR.

Atmospheric plasma treatment effect on shear strength of GFRP-Aluminum adhesively bonded lap joints

The objective of this study is to investigate the effect of air (dielectric barrier discharge) DBD plasma treatment on the bonding strength of adhesively bonded glass fiber-reinforced epoxy composite-aluminum lap joints. The bonding performance of lap joints produced by the plasma treatment was compared with that of untreated and peel-ply surface treatments. Water contact angles of the substrates were measured for untreated, peel-ply, and plasma surface-treated substrates. Experimental results showed that plasma-treated aluminum and GFRP substrates increased the wettability properties and thus shear strength of adhesively bonded GFRP-Al joints increased. After the shear tests, the fracture surfaces of the substrates were visually examined and three different damage modes were observed, including light fiber tear failure, adhesive failure, and thin layer cohesive failure modes.

Microtensile Bond Strength and Failure Mode of Different Universal Adhesives on Human Dentin

AimThe aim of this study was to compare the microtensile bond strength (µTBS) and failure mode of 4 different universal adhesive systems (UAs) on human dentin. Materials and methodsThe study sectioned the occlusal thirds of 32 human third molars and divided them into 4 groups based on the adhesive system used. Group A: Palfique Universal Bond, Group B: Single Bond Universal, Group C: All-Bond Universal, and Group D: One Coat 7 Universal. The specimens underwent a 10,000-cycle thermocycling ageing process prior to testing (n = 32). Afterwards, 8 beams were obtained per group and subjected to µTBS testing using a digital universal testing machine at a speed of 1 mm/min. The microtensile bond strength values were analysed in Megapascals (MPa), and the failure mode was evaluated using a stereomicroscope. Welch's parametric ANOVA with robust variance and the Games-Howell post hoc test were used for µTBS comparisons, and Fisher's exact test was used to determine the association between adhesive type and failure mode. The significance level was set at P < .05. ResultsGroup D showed a significantly higher µTBS than groups A (P < .001) and B (P < .001), but no significant difference was observed with group C (P= .075). Furthermore, groups B and C showed significantly higher µTBS than group A (P< .001 and P < .001, respectively), but there was no significant difference between groups B and C (P = .132). Additionally, group A exhibited a significant association with an adhesive failure mode (P < .05), whereas groups B, C, and D were significantly associated with a mixed failure mode (P < .05). ConclusionThe One Coat 7 Universal adhesive system showed higher microtensile bond strength values and higher chemical interaction with dentin compared to Palfique Universal Bond and Single Bond Universal. However, no significant differences were observed compared to All-Bond Universal.

Experimental evaluation of atmospheric plasma treatment effects on different textures of CFRP composite for aircraft applications

This article examines the impact of Atmospheric Plasma Treatment (APL) on the chemical composition and fracture properties of various textured surfaces (tool and bag side) of carbon fiber/epoxy (CFRP) composites utilized in aircraft applications. For this purpose, parameters of atmospheric plasma (APL) surface treatment were evaluated in comparison to chemical cleaning and peel-ply applications, taking into account its effects on surface properties and adhesive bond strength. A comprehensive variety of surface characterization techniques were utilized to analyze surface modifications, including water and diiodomethane contact angle measurements for assessing surface hydrophilicity, Fourier Transform Infrared Spectroscopy with Attenuated Total Reflection (FTIR-ATR) and X-ray Photoelectron Spectroscopy (XPS) for analyzing chemical composition and functional groups, and Profilometry, Atomic Force Microscopy (AFM), and Scanning Electron Microscopy (SEM) for evaluating surface topography and morphology. Experimental results indicated that the reduction in the contact angle following plasma treatment correlated with the elevated oxygen concentration and the presence of polar functional groups (e.g. -OH, -NH2, -NH3, C=O, O-C=O) on the composite surface. Plasma treatment, especially at low nozzle speeds, increased surface roughness on the bag side surfaces. This prevented adhesive penetration and led to gas entrapment, resulting in adhesive failure mode and reduced single lap shear strength for the bag side. In contrast, on the tool side surfaces, the plasma treatment led to a remarkable 19.7% enhancement in shear strength, highlighting its effectiveness.

Influence of air DBD plasma treatment on the shear and flexural strength of adhesively bonded glass fiber reinforced epoxy composite joints

In this study, air dielectric barrier discharge (DBD) plasma treatment was applied at various voltages and treatment durations to improve the bonding strength of glass fiber reinforced epoxy composites (GF/EP). In addition, single lap shear and three-point bending strengths of adhesively bonded joints were compared between untreated and surface-treated (sanding, peel ply, and plasma) samples. Surface properties of GF/EP composites were examined using contact angle, surface free energy, X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and Atomic Force Microscopy (AFM). Then, mechanical tests (single lap shear and three point bending) were performed and the damage modes were determined. Surface analyses revealed that wettability and polar functional groups increased on the GF/EP surface after plasma treatment. From the mechanical test results, it was observed that the plasma treatment applied to GF/EP composites increased both single lap shear and flexural strength compared to untreated, sanding and peel ply surface treatments. After both single lap shear and 3-point bending tests, adhesive, and light fiber tear failure modes were observed.

Importance of cohesive failure mode in fracture toughness enhancement of polymer nanocomposites with covalent grafting: A multiscale study

The covalent grafting between the nanoparticles and polymer matrix is considered a useful design factor to control the mechanical properties (e.g., fracture toughness). Meanwhile, in the theoretical viewpoint, the toughening mechanisms of the epoxy nanocomposites with covalent grafting are still unclear. In this study, a new multiscale fracture model is proposed to quantify the toughness enhancement of epoxy nanocomposites induced by the covalent grafting. Especially, it was concentrated on the investigation of the influences of the cohesive failure mode on the fracture toughness and revealed that the failure mode transition (from the adhesive failure mode to cohesive failure mode) near the nanoparticles with increasing grafting ratio is critical factor for the toughening mechanisms of the epoxy nanocomposites with covalent grafting. The theoretically derived multiscale model demonstrated that the cohesive failure mode significantly enhanced the fracture toughness of polymer nanocomposites by dissipating more energy compared to the adhesive failure mode. This study underscores the critical importance of rationally designing nanocomposites with an optimal grafting ratio that properly reflects the cohesive failure mode. It is anticipated that the multiscale analysis approach outlined in this study will provide valuable design guidelines and insights for polymer nanocomposites incorporating covalent grafting.

Fracture Resistance and Push-Out Bond Strength of Three Post Types in the Restoration of Anterior Primary Teeth - A In Vitro study.

Restoration fractures and displacement are the two main causes of failure after the rehabilitation of severely worn primary anterior teeth. Compare the effect of three post types on the fracture and push-out bond strength. Sixty undamaged maxillary anterior primary teeth were allocated into three groups according to post type: (I) Tetric N Ceram composite post, (II) prefabricated glass fiber post, and (III) high viscous glass ionomer post. Each group was further subdivided into two sub-groups depending on the test used: fracture resistance test and push-out bond strength test. The all specimens were mounted in acrylic resin blocks and tested using a universal testing machine. The fracture and failure mode were determined by a stereomicroscope inspection of all the specimens. Data were analyzed by one-way analysis of variance (ANOVA) and the Bonferroni post hoc test ( P < 0.05). There was a statistically significant difference between fracture resistance and push-out bond strength values for the experimental groups ( P < 0.05). The most significant fracture resistance value was in Group II and core/post fracture (restorable fracture) was the most obvious fracture in the three groups with the highest percentage in Group I. The most significant push-out bond strength value was in Group I and adhesive failure between dentin and luting cement/post was the most common type in the groups. The fracture resistance and push-out bond strength were affected by the type of post ( P = 0.000). Prefabricated glass fiber posts showed the highest fracture resistance in this study. However, Tetric N Ceram composite posts had the most restorable fracture. Tetric N Ceram composite posts had the highest bond strength with adhesive failure mode.

Interfacial Enhancement and Composite Manufacturing of Continuous Carbon-Fiber-Reinforced PA6T Composites via PrePA6T Ultrafine Powder.

Semi-aromatic poly (hexamethylene terephthalamide) (PA6T) oligomer (prePA6T) ultrafine powder, with a diameter of <5 μm, was prepared as an emulsion sizing agent to improve the impregnation performance of CF/PA6T composites. The prePA6T hyperfine powder was acquired via the dissolution and precipitation "phase conversion" method, and the prePA6T emulsion sizing agent was acquired to continuously coat the CF bundle. The sized CF unidirectional tape was knitted into a fabric using the plain weave method, while the CF/PA6T laminated composites were obtained by laminating the plain weave fabrics with PA6T films. The interfacial shear strength (IFSS), tensile strength (TS), and interlaminar shear strength (ILSS) of prePA6T-modified CF/PA6T composites improved by 54.9%, 125.3%, and 120.9%, respectively. Compared with the commercial polyamide sizing agent product PA845H, the prePA6T sizing agent showed better interfacial properties at elevated temperatures, especially no TS loss at 75 °C. The SEM observations also indicated that the prePA6T emulsion has an excellent impregnation effect on CF, and the fracture mechanism shifted from adhesive failure mode to cohesive failure mode. In summary, a facile, heat-resistant, undamaged-to-fiber environmental coating process is proposed to continuously manufacture high-performance thermoplastic composites, which is quite promising in mass production.

Lap shear properties of CF/PEKK composites through nanoparticle-enhanced adhesive joints

This study investigates the effects of incorporating halloysite nanotubes (HNTs) into polyetherimide (PEI) adhesive for carbon fiber/polyetherketoneketone (CF/PEKK) composite joints. The CF/PEKK substrate is fabricated through an oven consolidation process, while PEI adhesive films with varying HNTs loadings (0.5, 1 and 3[Formula: see text]wt.%) are prepared using solvent casting with [Formula: see text]-butyrolactone. Homogeneous dispersion of HNTs in PEI is achieved through magnetic stirring and IR heating. The resulting film is hot pressed to form a 100[Formula: see text][Formula: see text]m thick film, and adhesive lap shear joint specimens are manufactured through oven consolidation. Morphology and dispersion of HNTs in PEI are analyzed using SEM and EDS, revealing favorable dispersion at 0.5[Formula: see text]wt.% HNTs and aggregation at higher loadings. Differential scanning calorimetry (DSC) is employed to study the glass transition temperature (Tg) of PEI, showing decreased Tg for solvent-cast PEI and increased Tg with HNTs incorporation. This increase is attributed to the constrained mobility of polymer chains due to HNTs’ influence. Lap shear strength (LSS) is evaluated, demonstrating enhancement with HNTs incorporation: 0.5[Formula: see text]wt.% HNTs (+12.5%) &gt; 1[Formula: see text]wt.% HNTs (+8.33%) &gt; Pure PEI &gt; 3[Formula: see text]wt.% HNTs (−12.5%). The study attributes this enhancement to HNTs’ reinforcement and chemical interactions with PEKK. Aggregation tendencies at 3[Formula: see text]wt.% HNTs lead to decreased LSS. SEM-EDS analysis of fractured specimens indicates a multifaceted bonding joint interface involving PEKK, PEI and HNTs. CF/PEKK composites show adhesive, cohesive and adherend failure modes, with adherend failure being dominant. Notably, fabric-like textures and plastic deformations in PEI with 0.5[Formula: see text]wt.% HNTs contribute to enhanced LSS, while higher HNTs content leads to cohesive failure due to aggregation. This study provides insights into optimizing composite adhesive systems by harnessing nanotube reinforcement and controlling dispersion, thereby influencing interfacial strength.

The Influence of Erbium Laser Pretreatment on Dentin Shear Bond Strength and Bond Failure Modes: A Systematic Review and Network Meta-Analysis.

To systematically review in-vitro studies that evaluated the influence of erbium laser pretreatment on dentin shear bond strength (SBS) and bond failure modes. Electronic databases (PubMed, Cochrane Central, Embase, and Web of Science) were searched. Only in-vitro studies involving erbium laser irradiation of the dentin surface and SBS testing of the bonded resin block were included. The three common modes of bond failure (1. adhesive, 2. cohesive, and 3. mixed) were observed and analyzed. The network meta-analysis (NMA) was performed by Stata 15.0 software, the risk of bias was evaluated, and the certainty of the evidence was assessed by the Confidence in Network Meta-analysis (CINeMA). Forty studies with nine pretreatments (1. blank group: BL; 2. phosphoric acid etch-and-rinse: ER; 3. self-etch adhesive: SE; 4. Er:YAG laser: EL; 5. Er,Cr:YSGG laser: ECL; 6. ER+EL; 7. ER+ECL; 8. SE+EL; 9. SE+ECL) were included in this analysis. The NMA of SBS showed that ER+EL [SMD = 0.32, 95% CI (0.11, 0.98)] had the highest SBS next to ER, especially when using one of the 3M ESPE adhesives, followed by EL, ECL, SE and SE+EL. The Ivoclar Vivadent adhesives significantly increased the SBS of the ECL [SMD = 0.37, 95% CI (0.16,0.90)] and was higher than ER+EL [SMD = 0.25,95% CI (0.07,0.85)]. Finally, the surface under the cumulative ranking curve (SUCRA) value indicated that ER+EL (SUCRA = 71.0%) and EL (SUCRA = 62.9%) were the best treatments for enhancing dentin SBS besides ER. ER+EL (SUCRA = 85.3%), ER (SUCRA = 83.7%) and ER (SUCRA = 84.3%) had the highest probability of occurring in adhesive, cohesive and mixed failure modes, respectively. Er:YAG and Er,Cr:YSGG lasers improved dentin SBS compared to the blank group, especially when the acid etch-and-rinse pretreatment was combined with Er:YAG laser. Shear bond strength and failure mode do not appear to be directly related.

Influence of Application Modes on Increasing Bond Strength Longevity of Self-etching and Universal Adhesive Systems to Enamel.

The present study aimed to evaluate the influence of application mode on the short-term microshear bond strength longevity of self-etching and universal adhesive systems to enamel, the failure mode, and the resulting enamel surface micromorphology. Ninety enamel surfaces were obtained from sound third molars, planed, and randomly assigned to nine groups, according to the application mode and the adhesive system (n=10). There were three primer application modes: according to the manufacturer's recommended application time (control), using double the application time recommended for the primer and selective enamel etching. The adhesive systems used were: Clearfil SE Bond (Kuraray), FL-Bond II (SHOFU), and Futurabond U (Voco). At least two resin-bonded composite cylinders (Grandioso Light Flow, Voco) were placed on each enamel surface, and then evaluated for microshear bond strength at 24 hours and 180 days of storage in solution body fluid (SBF) at pH 7.4. Failure modes were evaluated with a stereoscopic microscope at 20× magnification. A micromorphological analysis of the enamel surface was performed under a scanning electron microscope at 5000× magnification before and after the treatments. Mixed models for repeated measures over time showed significant interaction among application modes, adhesive systems, and time periods (p=0.0331). The bond strength of FL-Bond II adhesive to enamel observed after performing selective enamel etching was significantly higher than that observed after applying the control treatment (p=0.0010) at both 24 hours and 180 days. However, no significant difference was observed between the application of this same adhesive at double the time recommended by the manufacturer and the other two application modes (p>0.05). There was also no significant difference in the microshear bond strength for the enamel treatments applied using Clearfil SE Bond and Futurabond U (p>0.05). A significant reduction in bond strength to enamel was observed at the 180-day storage time for all the adhesive systems when selective enamel etching was performed (p<0.0001). No significant association was observed between the adhesive system failure mode and the enamel treatments (p=0.1402 and p=0.7590 for 24 hours and 180 days, respectively). The most prevalent failure was the adhesive type.

Shear bond strength of MDP-containing light-cured veneer adhesive system to zirconia with different surface preparations

This study aimed to evaluate the effects of different surface preparation techniques on the surface microstructure, the shear bond strength (SBS) between zirconia and an MDP-containing light-cured veneer adhesive system, and the adhesive failure mode. Sixty-four zirconia specimens were divided into four groups based on surface preparation methods (n = 16), including zirconia sandblasting (ZSB), zirconia vitrification or glaze-on (ZVG), zirconia surface architecture technique (ZSAT), and ZSAT-ZVG combined technique (ZSATVG) groups. Sixteen lithium disilicate specimens prepared by etching with hydrofluoric acid (HF) were used as a positive control group (LDE). Surface roughness measurement and scanning electron microscopy (SEM) evaluation were performed before and after surface preparation. All specimens were then bonded with an MDP-containing light-cured adhesive system, followed by SBS testing and adhesive failure mode analysis. The ZVG and ZSATVG groups showed the greatest differential roughness value and microscopic irregularities, while the ZSAT and LDE groups had the least surface change but the most micromechanical retentive structures for resin infiltration. SBS values were significantly different among groups (p < 0.001) with the highest SBS observed in the ZSAT group, followed by the ZSB group, LDE group, ZSATVG group, and lastly, the ZVG group. There was a statistically significant difference in failure types among the surface preparation groups (p < 0.001). The ZSAT group had the highest frequency of mixed failure, followed by the ZSB group, LDE group, and the ZSATVG and ZVG groups. Establishing direct micromechanical retention within zirconia itself yields a higher bond strength than indirect micromechanical retention within a glass ceramic layer.

Evaluation of the marginal adaptation and debonding strength of two types of CAD-CAM implant-supported cement-retained crowns

BackgroundIn-vitro data from a clinically well-known lithium disilicate ceramic reference was used to assess the expected performance of resin-based materials in implant dentistry. The purpose of the study was to compare the bond strength and marginal adaptation of nano-ceramic hybrid composite crowns cemented to stock cement-retained abutments to lithium disilicate crowns.MethodsTwenty abutment analogs were embedded into auto-polymerizing acrylic resin blocks. The blocks were divided into 2 groups according to the restorative crown material. The 2 groups were divided as follows: Resin nano-ceramic group and lithium disilicate group. Abutment analogs in both groups were scanned using a laboratory scanner, and the restorations were designed, manufactured, and cemented with resin cement over the corresponding group. All samples were tested for marginal adaptation and bond strength after storage for 24 hours at 37 °C in 100% humidity. Data were collected, tabulated, and statistically analysed using the appropriate tests. Normality was checked using Shapiro Wilk test and Q-Q plots. Data were normally distributed. Variables were presented using mean, 95% Confidence Interval (CI) and standard deviation in addition to median and Inter Quartile Range (IQR). Differences between groups regarding debonding forces was assessed using independent t test. Two Way ANOVA was performed to assess the effect of material and bonding on marginal gap. All tests were two tailed and p value was set at < 0.05.ResultsMarginal gap and debonding force values were significantly different according to the type of material used (P < .05). Resin nano-ceramic crowns presented lower marginal gap values before (20.80 ± 8.87 μm) and after (52.11 ± 22.92 μm) bonding than lithium disilicate crowns. The debonding force value for resin nano-ceramic crowns (284.30 ± 26.44 N) was significantly higher than that for lithium disilicate crowns (253.30 ± 33.26 N). Adhesive failure mode was detected in all the specimens in both groups.ConclusionsThe type of material used for implant-supported cement-retained crowns had a statistically significant effect on marginal adaptation and bond strength. Resin nano-ceramic implant-supported cement-retained crowns had better marginal adaptation and higher bond strength than those manufactured using lithium disilicate.

Medium-term evaluation of the bond strength and dentin penetration of self-adhesive resin cements to root dentin.

Medium-term evaluate the bond strength and tag formation in root dentin using self-adhesive cements Maxcem Elite (MCE), Relyx U200 (RU2), SeT PP (SPP) and Megalink (MGL) compared to conventional cement Relyx ARC (ARC) for glass fibre post cementation. One hundred bovine incisors roots were endodontically treated and divided into 5 groups (n = 20) according to the cementation system: MCE, RU2, SPP, MGL and ARC. All cementation systems were evaluated at 24 h (1) and 12 months (2) after post cementation. Specimens from the cervical, middle and apical thirds of the root were submitted to push-out bond strength test and confocal laser microscopy to verify the dentin penetration. The adhesive failure mode was classified as adhesive, cohesive and mixed. Data were analysed by one-way ANOVA and Tukey tests (α = 5%). ARC-1 and ARC-12 showed the highest bond strength (P < 0.05). ARC showed the greatest tag extension, regardless of the third (P < 0.05). The most frequent failure mode in the 24-h analysis was cohesive, regardless of the cement used. For the 12-month analysis, mixed failure was the most frequent. Conventional cement (ARC) showed the highest bond strength and tag extension, regardless of the evaluation period. In all cementation systems, the bond strength decreased after 12 months. © 2023 Australian Dental Association.

Numerical Investigation of Failure in Epoxy-Based Adhesive Joints

Currently, adhesive bonding has been increasingly used in various industrial applications such as in automobile lightweight structures for multi-material assembly. However, adhesive joints show a complex failure behavior. Their failure modes can be either adhesive failure, cohesive failure, or mixed mode failure depending on their interfacial strength and also the strength of adhesive layer which also varies with hydrostatic pressure. In this study, the failure of the adhesive joints with an epoxy-based adhesive bonded to metallic substrates are investigated numerically using FEA. The damage evolution model is implemented in the finite element model to predict the failure of adhesive joints. The adhesive strengths under different states of stress for a damage evolution model are characterized using the modified Arcan fixture which is specifically designed to study of hydrostatic pressure effect on an adhesive behavior. The validation of the failure model is carried out with the results of single lap shear test. A good agreement is finally found between FEA and experiments.

Effect Of Surface Treatment on The Shear Bond Strength Between Nickel-Chromium Alloy and Veneering Porcelain

Nickel–chromium (Ni–Cr) alloys, have been used widely, due to their superior physical properties and economic issues in relation to other precious alloys. Many studies have been carried out on porcelain fused to metal restorations to enhance the bonding quality of the porcelain to Ni-Cr alloy, such as mechanical treatment by air abrasion particles or chemical treatment by acid etching to increase the longevity of the restoration. The purpose of this study is to investigate the effect of surface treatments sandblasting with Aluminum Oxide (Al2O3), acid etching with Potassium hydrogen difluoride acid (KHF2) and combination treatment on the shear bond strength between Nickel-chromium alloy substructure and porcelain veneer. Twenty-one cylindrical shaped samples have base of 5 mm in diameter and 1 mm in thickness and a cylinder with 4 mm in diameter and 4 mm in length were prepared from Ni – Cr alloy. The samples were divided into 3 groups (n=7) according to surface treatment: Nickel -chromium treated with sandblasting with 50μm Al2O3 group (c), Nickel – chromium etching with KHF2 group (k), and Nickel – chromium sandblasting with 50μm Al2O3 followed with acid etching with KHF2 group (comb). Then ceramic build up (opaque, dentin, enamel, and glaze Vita VMK Master opaque, dentin, enamel, and glaze Vita VMK Master) and sintering was performed according to manufacturer's instructions and the final dimension of porcelain cylinder (4 X 4X 1) were checked with a metal gauge. All samples were subjected to shear force in a universal testing machine at cross head speed 0.5 mm/min. and recorded in MPa. The fractured samples were checked under (DIGITAL MICROSCOPE) (X50) to evaluate the mode of failure, it was adhesive, cohesive and mixed failure modes. The shear bond strength values were analyzed with one-way ANOVA and LSD. The results showed that the highest mean of shear bond strength values was in Ni – Cr combination surface treatment group (26.11 ± 1.85), while the lowest mean was for Ni- Cr acid etched group (22.02 ± 1.5) and Nic group (20.85 ± 1.5). Within the limitation of the present study, the following conclusion can be drawn: Combination surface treatment produced the highest shear bond strength between Ni – Cr surface and veneering porcelain, followed by etching with KHF2, so combination method would increase longevity of porcelain fused to metal restorations.

Atomistic insights into adhesion characteristics of tungsten on titanium nitride using steered molecular dynamics with machine learning interatomic potential

As transistor integration accelerates and miniaturization progresses, improving the interfacial adhesion characteristics of complex metal interconnect has become a major issue in ensuring semiconductor device reliability. Therefore, it is becoming increasingly important to interpret the adhesive properties of metal interconnects at the atomic level, predict their adhesive strength and failure mode, and develop computational methods that can be universally applied regardless of interface properties. In this study, we propose a method for theoretically understanding adhesion characteristics through steering molecular dynamics simulations based on machine learning interatomic potentials. We utilized this method to investigate the adhesion characteristics of tungsten deposited on titanium nitride barrier metal (W/TiN) as a representative metal interconnect structure in devices. Pulling tests that pull two materials apart and sliding tests that pull them against each other in a shear direction were implemented to investigate the failure mode and adhesive strength depending on TiN facet orientation. We found that the W/TiN interface showed an adhesive failure where they separate from each other when tested with pulling force on Ti-rich (111) or (001) facets while cohesive failures occurred where W itself was destroyed on N-rich (111) facet. The adhesion strength was defined as the maximum force causing failure during the pulling test for consistent interpretation and the strengths of tungsten were predicted to be strongest when deposited onto N-rich (111) facet while weakest on Ti-rich (111) facet.

Interfacial bond strength and failure modes of traditional and modern repair materials for historic fibrous plaster

Many culturally important historic buildings contain fibrous plaster ceilings. The collapse at London’s Apollo Theatre in 2013, which injured 88 people, highlighted the importance of inspecting and restoring ceilings effectively. This study focuses on traditional and modern materials which are applied to the topsides of existing historic fibrous plaster ceiling elements during repair and maintenance. Fibrous plaster ceilings are commonly suspended from primary or secondary structural roof members using fibrous plaster wadding ties or ‘wads’. The application of additional repair material requires the formation of an interface, defining the strength of the repair. Properties of this interface were evaluated through a novel methodology employing pull-off tests’ of approximately 200 specimens consisting of Alpha plaster, Beta plaster, Jesmonite and Aramid gel. Notably, the effect of fibrous reinforcement, and compatibility with historic and degraded material was also investigated. This study has enabled quantification of interfacial properties and evaluated cohesive and adhesive failure modes. Importantly, the extent of redundancy within historic plaster ceiling practice has been demonstrated, with pull-off occurring from 0.5 kN to 2 kN loading, and the ductile behaviour of repair materials evaluated. Results highlight the importance of surface condition, with clean surfaces exhibiting double the tensile loading capacity compared to soiled (dirty) surfaces representative of those encountered on-site. The significance of this study lies in the quantification of repair material performances and consideration of variations in performance, methodology and in-situ environmental factors. Impact stems from the ability of practitioners to make informed decisions relating to adhesion performance when carrying out repairs. A key outcome is more effective preservation of historic elements in heritage buildings, higher levels of safety and serviceability.