Failure Load Values Research Articles

Failure analysis of three rigid block assemblies – A real collapse resulting in death

The failure analysis of three rigid block assemblies is often necessary to assess the stability of architectural and historical assets.An analytical method for the assessment of the overturning stability of assemblies composed by three rigid blocks fitted atop one on another is proposed. The method takes account of several load configurations and all possible collapse mechanisms involving the overturning of one, two or three blocks.In the category of historical assets fall many holy water stoups with pillar, often realized as three rigid block assemblies. A great number of holy water stoups disarticulations occurred in Italy in the last decades, leading, in some cases, to children death.A 7 years old girl died due to the disarticulation of an historical holy water stoup in the Santa Chiara Church, in Udine, Italy, caused by the force applied by the girl on the basin.The stoup is realized as a three rigid block assembly with connections of the type mortise and tenon both between the basement and the shaft and between the shaft and the basin. In the connections the presence of mortar is detected. In order to evaluate the ability of the mortar to stabilize the connections between the three rigid blocks, the mineralogical and petrographic analyses of a mortar sample are performed. Moreover, a loading test is carried out in laboratory to obtain an experimental value of the holy water stoup failure load. This value is determined by applying a vertical force to the outer circumference of the basin.Then, in order to determine the holy water stoup failure load under an inclined force statically applied at the top of the basin, the stoup overturning stability is theoretically analysed. The analysis is performed considering all possible collapse mechanisms of the three rigid block assembly and the variability of the force inclination with respect to the horizontal plane. The performed analysis is suitable because it confirms that the disarticulation of the holy water stoup can be caused by a force applied by the kid at the top of the basin.The presented paper is the first one that analyses the overturning stability of three rigid block assemblies under external forces which do not depend on the single blocks masses and with variable direction.

Effect of Stacking Sequence Variation on First Ply Failure Load of Laminated Composite Skew Plate

The present work aims to study and report the first ply failure load of laminated composite skew plate of different laminations and stacking sequences with a practical boundary condition. The finite element model is developed using eight noded isoparametric curved quadratic shell element with five degrees of freedom per node (with three translations and two rotations). Numerical experiments are conducted considering skew plates of varying skew angles, laminations and stacking patterns. First ply failure loads are evaluated for seven different failure criteria such as maximum stress, maximum strain, Tsai-Wu, Tsai-Hill, Hoffman, Puck and Hashin’s failure criteria. The minimum value of load obtained from different failure criteria is chosen as the governing first ply failure load value. Benchmark problems are solved to validate the correctness of the present approach of evaluation of first ply failure load and incorporation of skew geometry in the present model. The results of authors’ own problems are finally studied meticulously and relative performance matrix of skew plate options of different combination of skew angle and stacking sequences are reported.

Impact of different axial wall designs on the fracture strength and stress distribution of ceramic restorations in mandibular first molar

BackgroundThe purpose of this study was to investigate the fracture strength and stress distribution of four ceramic restorations.MethodsForty human mandibular first molars were collected and randomized into four groups after establishing the distal defect: full crown group with 4 mm axial wall height (AWH) (FC4); short AWH crown group with 2 mm AWH (SC2); occlusal veneer group with 0 mm AWH (OV0); occlusal distal veneer group with only the distal surface prepared, and 4 mm AWH (OD4). The teeth were prepared according to the groups and the ceramic restorations were completed using celtra duo ceramic blocks. The ceramic thickness of the occlusal surface is about 1.5 mm and the edge is about 1 mm. The failure load values and fracture modes of each group were detected by mechanical test in vitro. According to the groups to establish three-dimensional finite element analysis (FEA) models, a 600 N loading force was applied vertically using a hemispherical indenter with a diameter of 6 mm. and compare the stress distribution under the condition of different restorations.ResultsIn vitro mechanical tests showed that the failure load values were SC2 (3232.80 ± 708.12 N) > OD4 (2886.90 ± 338.72 N) > VO0 (2133.20 ± 376.15 N) > FC4(1635.40 ± 413.05 N). The failure load values of the short AWH crown and occlusal distal veneer were significantly higher than that of occlusal veneer and full crown (P<0.05). The fracture modes of the full crown and occlusal veneer groups were mainly ceramic fractures and some were restorable tooth fractures. The short AWH crown and occlusal distal veneer groups presented with three fracture modes, the proportion of non-restorable tooth fracture was higher. The results of FEA show that under the spherical loading condition, the stress of ceramic was concentrated in the contact area of the loading head, the maximum von Mises stress values were FC4 (356.2 MPa) > VO0 (214.3 MPa) > OD4 (197.9 MPa) > SC2 (163.1 MPa). The stress of enamel was concentrated in the area where the remaining enamel was thinner, the maximum von Mises stress values was OD4 (246.2 MPa) ≈ FC4 (212.4 MPa) > VO0 (61.8 MPa) ≈ SC2 (45.81 MPa). The stress of dentin is concentrated in the root furcation and the upper third region of the root. However, stress concentration was observed at the tooth cervix in the full crown.ConclusionUnder certain conditions, the occlusal distal veneer shows better performance than the full crown.

Comparison of biomechanical analysis of four different tibial tunnel fixations in a bovine model

BackgroundTo determine the ideal fixation technique for an ACL reconstruction with a hamstring graft, multiple studies have been undertaken to define the initial biomechanical properties of tibial fixation. PurposeThe aim of this study was to compare the biomechanical properties of tibial fixation methods by creating single or hybrid systems. MethodsBovine tibias and forefoot digital extensor tendons were prepared with four different tibial anterior cruciate ligament fixation methods and compared biomechanically. Fixation materials included polyethylene Ultrabraid high-strength sutures, Biosure interference screws (Smith and Nephew, Memphis, TN, USA), staples (Smith and Nephew, Richards Regular Fixation Staples without Spikes, Memphis, TN, USA), and knotless suture anchors (Multifix-S PEEK) (Smith and Nephew, Memphis, TN, USA). Four groups (n = 5 specimens) were established – group I: single fixation with interference screws; group II: single fixation with knotless anchors; group III: hybrid fixation with interference screws and staples; group IV: hybrid fixation with interference screws and knotless anchors. Each specimen underwent evaluations for cyclic displacement, cyclic stiffness, initial loading strength, ultimate failure load, pull-out displacement, and pull-out stiffness. ResultsAll specimens completed cyclic loading and load-to-failure. The cyclic displacement in group II, which had a single fixation, indicated significantly greater elongation compared with the other groups (P = 0.002). The hybrid systems were more rigid than the single systems in terms of cyclic stiffness, and no statistically significant difference was observed between the hybrid systems (P = 0.461). Group IV was significantly superior in terms of the ultimate failure load (P = 0.004). No statistically significant differences were noted between the groups for pull-out displacement or pull-out stiffness. ConclusionSingle fixation with bioscrews as an in-tunnel tibia fixation method was as successful as hybrid systems. Multifix-S PEEK knotless suture anchors, which can be combined with bioscrews, can be a superior fixation alternative due to its flexibility and ultimate failure load values.

A Biomechanical Comparison of Fixation Techniques in Metacarpal Shaft Fractures.

Background Typically, metacarpal shaft fractures are treated with closed reduction percutaneous pinning, intramedullary nails, or plate fixation. Recently some surgeons have begun using intramedullary headless compression screws. Questions/Purposes The purpose of this study was to compare intramedullary screw fixation to K-wire fixation, which is the standard of care in a transverse metacarpal midshaft fracture, using a cadaveric model. Our hypothesis was that intramedullary screw fixation would have a biomechanical advantage (higher stiffness and peak load to failure) when compared with dual Kirschner wire fixation of transverse metacarpal shaft fractures. Methods Four-point bend testing was performed to compare stiffness and failure load values of seven paired 2nd and 3rd metacarpals instrumented with headless intramedullary compression screw fixation or Kirschner wire fixation. Similar testing was performed on 14 unpaired 4th metacarpals. Results There was no significant difference in peak load ( p = 0.60) or stiffness ( p = 0.85) between fixation groups for the 2nd and 3rd instrumented metacarpals. For the instrumented 4th metacarpals, there was no significant difference in peak load ( p = 0.14), but the stiffness was significantly greater ( p = 0.01) for the compression screw group compared with the Kirschner wire fixation. Conclusions/Clinical Relevance In this study, the load to failure was not different between the two fixation methods and likely both techniques can sustain physiologic loads needed for rehabilitation. The greater stiffness in the 4th metacarpal compression screw group may be related to the smaller canal morphology than in the 2nd and 3rd metacarpals. Larger diameter screws may be needed to obtain a better fit particularly in the 2nd and 3rd metacarpals.

Effect of Sintering Speed and Polishing or Glazing on the Failure Load of Monolithic Zirconia Fixed Partial Dentures.

To evaluate the effect of sintering speed and polishing or glazing on the failure load (FL) of monolithic zirconia fixed partial dentures (FPDs). A total of 40 three-unit FPDs extending from the mandibular first premolar to the first molar were evaluated. The prepared typodont teeth were scanned, and the prostheses were designed. Afterwards, the prostheses were milled from monolithic zirconia blanks. The samples were divided into classic and speed sintering groups (n = 20 each). Half of the samples in each group (n = 10) were polished with an electric handpiece according to the manufacturer's instructions, and the other half (n = 10) were glazed. All of the samples were thermocycled for 3,500 cycles between 5ºC and 55ºC in water baths. The FL was calculated in Newtons with the three-point bending test. The mean ± SD FL values were as follows: classic sintering/polished group = 2,026.5 ± 172.8 N; classic sintering/glazed group = 1,917.58 ± 174.45 N; speed sintering/polished group = 1,787.58 ± 145.81 N; and speed sintering/glazed group = 1,719.6 ± 143.9 N. There was a significant difference in the mean FL between the two sintering methods (P < .001), with the classic sintering group exhibiting the highest FL. Classic sintering of the monolithic zirconia FPDs led to the maximum amount of FL and strength.

Patient-Specific Finite Element Modeling of the Whole Lumbar Spine Using Clinical Routine Multi-Detector Computed Tomography (MDCT) Data-A Pilot Study.

(1) Background: To study the feasibility of developing finite element (FE) models of the whole lumbar spine using clinical routine multi-detector computed tomography (MDCT) scans to predict failure load (FL) and range of motion (ROM) parameters. (2) Methods: MDCT scans of 12 subjects (6 healthy controls (HC), mean age ± standard deviation (SD): 62.16 ± 10.24 years, and 6 osteoporotic patients (OP), mean age ± SD: 65.83 ± 11.19 years) were included in the current study. Comprehensive FE models of the lumbar spine (5 vertebrae + 4 intervertebral discs (IVDs) + ligaments) were generated (L1–L5) and simulated. The coefficients of correlation (ρ) were calculated to investigate the relationship between FE-based FL and ROM parameters and bone mineral density (BMD) values of L1–L3 derived from MDCT (BMDQCT-L1-3). Finally, Mann–Whitney U tests were performed to analyze differences in FL and ROM parameters between HC and OP cohorts. (3) Results: Mean FE-based FL value of the HC cohort was significantly higher than that of the OP cohort (1471.50 ± 275.69 N (HC) vs. 763.33 ± 166.70 N (OP), p < 0.01). A strong correlation of 0.8 (p < 0.01) was observed between FE-based FL and BMDQCT-L1-L3 values. However, no significant differences were observed between ROM parameters of HC and OP cohorts (p = 0.69 for flexion; p = 0.69 for extension; p = 0.47 for lateral bending; p = 0.13 for twisting). In addition, no statistically significant correlations were observed between ROM parameters and BMDQCT- L1-3. (4) Conclusions: Clinical routine MDCT data can be used for patient-specific FE modeling of the whole lumbar spine. ROM parameters do not seem to be significantly altered between HC and OP. In contrast, FE-derived FL may help identify patients with increased osteoporotic fracture risk in the future.

Shear-stud restrained composite slab strength prediction model

The use of shear-stud in composite slab (CS) construction can significantly enhances its longitudinal shear capacity. However, the strength capacity determination of such complex construction is still marred with the capital-intensive challenge resulting from the complex laboratory procedures for establishing its longitudinal shear capacity. To address this challenge, this article develops a simplified numerical function for determining longitudinal shear capacity for CS with shear stud. This study considers slope-intercept method for the longitudinal shear estimate and the adaptation of rational approach in developing the performance function. Furthermore, limit state function was from the use of shear capacity violation that considers experimental failure load (FL) value and design load estimated form the shear contributions. The resulting outputs from the rational analysis facilitated the formulation of numerical function for the determination of FL in a more simplified form. The developed FL algorithm exhibits strong performance in determining the alternate CS failure load though there is stillroom for further improvement especially if span length would be taken into consideration. Further development that incorporates span length might give much favorable result in determining CS strength especially when considering slope-intercept method

Mechanical stability of fully personalized, abutment-free zirconia implant crowns on a novel implant-crown interface

ObjectivesTo test the failure load and failure mode of a novel implant-crown interface specifically designed for the fabrication of fully personalized, abutment-free monolithic zirconia CAD-CAM crowns compared to conventional implant-abutment interfaces involving prefabricated or centrally manufactured abutments for zirconia CAD-CAM crowns. MethodsImplants (N=48) were divided into groups (n=12) according to different implant-abutment interface designs: (1) internal implant connection with personalized, abutment-free CAD-CAM crowns (Abut-Free-Zr), (2) internal conical connection with customized, centrally manufactured zirconia CAD-CAM abutments (Cen-Abut-Zr), (3) prefabricated titanium base abutments from manufacturer 1 (Ti-Base-1), (4) additional prefabricated titanium base abutments from manufacturer 2 (Ti-Base-2). All specimens were restored with a screw-retained monolithic zirconia CAD-CAM molar crown and subjected to thermomechanical aging (1.200.000 cycles, 49 N, 1.67 Hz, 30° angulation, thermocycling 5-50°C). Static load until failure was applied in a universal testing machine. Failure modes were analyzed descriptively under digital microscope. Mean failure load values were statistically analyzed at a significance level of p<0.05. ResultsAll specimens survived thermomechanical aging. The mean failure loads varied between 1332 N (Abut-Free-Zr) and 1601 N (Ti-Base-2), difference being significant between these groups (p<0.05). No differences between the other groups were seen. The predominant failure mode per group was crown fracture above implant connection (Abut-Free-Zr, 75%), abutment fracture below implant neck (Cen-Abut-Zr, 83%), crown fracture leaving an intact abutment (Ti-Base-1/Ti-Base-2 100%). ConclusionsImplant-crown interface with fully personalized, abutment-free monolithic CAD-CAM zirconia crowns exhibited similar failure loads as conventional implant-abutment interfaces (except group Ti-Base-2) involving CAD-CAM crowns with prefabricated or centrally manufactured abutment. Clinical significanceThe new implant connection simplifies the digital workflow for all-ceramic implant reconstructions. The specific design of the implant-crown interface allows the fabrication of fully personalized, abutment-free zirconia implant crowns both in-house and in-laboratory without the need of a prefabricated abutment or central manufacturing.

Influence of zinc coating on nugget development and mechanical properties in dissimilar welded joints DP600 – AISI304 obtained by the RSW process

This paper researches the influence of zinc coating of galvanized DP600 steel (DP600G) on the nugget development and mechanical properties of dissimilar DP600 - AISI304 welded joints obtained by resistance spot welding process (RSW). The RSW evaluations consisted of determining, from the dynamic resistance curves, the different stages involved in nugget formation. The experimental results showed that the zinc coating on the DP600G steel has a significant influence on the time needed for the start of the nugget formation, two times higher than that used for non-galvanized steel. The expulsion time was delayed by 1.12 times. The presence of Zn in the DP600G/AISI304 welded joints produced smaller nugget diameters compared to the DP600/AISI304 joints for the same experimental conditions, however higher peak failure load values were obtained for the first. The causes of this unusual behavior are also analyzed in this paper.

Study of matrix modifications by nano-clay on the mechanical properties of AA3003 honeycomb sandwich panels

Face/core debonding is one of the crucial problems of composite sandwich panels which consist of AA3003 aluminium honeycomb and glass fiber reinforced polymer face sheets. The panel was prepared by a hand-lay process at different nano-clay weight addition of 0%, 2%, 4%, and 6% with the objective of improving face/core adhesion. Interface bonding between face sheets and honeycomb core composite sandwiches and their mechanical behavior were investigated under in-plane compression and bending load. The flexural property of sandwich panels due to the influence of variation in strain rate is further determined. The morphologies of fractured samples were investigated by scanning electron microscope (SEM). The results revealed a significant improvement in mechanical characteristics when nano-clay was loaded to the composites at a concentration from 2 to 4 wt%, and the in-plane compression and flexural failure load values increased by 45% and 81%, respectively, when compared to a pristine sample. It was observed that increasing strain rate led to the increase in failure load of the sandwich panel. SEM images of fractured surfaces showed residual aluminium honeycomb was present in the face sheet, which indicates better adhesion between aluminium honeycomb core and face sheets.

The failure behavior of buckling pin valve: Theoretical, numerical, and experimental study

At present, buckling pin in the bypass of piping as pressure relief valve has been gradually utilized in the low-concentration coal-bed methane (CBM), which bends to release pressure when the main valve fails leading to pipeline blockage. However, current researches mainly focused on the buckling behavior of hydraulic cylinder rod or rod string, and less consideration was given to the operational reliability of buckling pin valves. This paper deduced the calculation formula of the critical failure load based on Euler formula in the buckling pin under buckling load. Besides, three finite element models (FEM) based on Johnson−Cook constitutive model were compared to predict failure strength of buckling pin which were verified by experiment. In addition, the defect sensitivity analysis of the buckling pin under different initial geometric defects rate was carried out. The results showed that a) the experimental value of the critical failure load in the buckling pin was 206.04 N and the bending position was in the middle of the buckling pin; b) the analysis result adopting explicit dynamic method was in best agreement with the experimental results within deviation of 0.24%; and c) the initial geometric defect of buckling pin should be controlled within 1%. This study provides an important reference to predict the critical failure load of the buckling pin valve and achieve safe transportation of low-concentration CBM.

Probabilistic Failure Estimation of an Oblique Loaded Footing Settlement on Cohesive Geomaterials with a Modified Cam Clay Material Yield Function

In this work, a quantitative uncertainty estimation of the random distribution of the soil material properties to the probability density functions of the failure load and failure displacements of a shallow foundation loaded with an oblique load is portrayed. A modified Cam Clay yield constitutive model is adopted with a stochastic finite element model. The random distribution of the reload path inclination κ, the critical state line inclination c of the soil and the permeability k of the Darcian water flow relation, has been assessed with Monte Carlo simulations accelerated by using Latin hypercube sampling. It is proven that both failure load and failure displacements follow Gaussian normal distribution despite the excessive non-linear behaviour of the soil. In addition, as the obliquity increases the mean value of failure load and the failure displacement always increases. The uncertainty of the output failure stress with the increase of the obliquity of the load remains the same. The failure spline of clays can be calculated within an acceptable accuracy with the proposed numerical scheme in every possible geometry and load conditions, considering the obliquity of the load in conjunction with non-linear constitutive relations.

Influence of the Connector Area on the Chipping Rate of the VM9 Veneering Ceramic in a Posterior Four-Unit Yttria-Stabilized Tetragonal Zirconia Polycrystal Fixed Dental Prostheses: A Pilot Study

Abstract Objective The purpose of this study was to evaluate the influence of the connector area on the chipping rate of the VM9 veneering ceramic in a 4-unit yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) framework, using a novel sonographic technique. Materials and Methods The framework was designed as a 4-unit fixed dental prostheses (FDP) with two abutment teeth at the first mandibular premolar and second mandibular molar. The cross-sectional area of the connector was 7.5, 8, or 9 mm2. The prepared teeth were scanned using CAD/CAM technology, and five frameworks were prepared for each design, making a total of 15. The frameworks were divided according to the veneering ceramics: Y-TZP FDPs using Vita VM9 (12 frameworks), and porcelain fused to metal (PFM) FDPs using Vita VM13 (3 frameworks). The specimens were statically loaded until failure. To capture the initiation of the failure within the specimens, a novel sonographic technique, designed for this research, combining acoustic emission and visual monitoring during live load bearing tests, was used to determine the failure load value. Failed frameworks were inspected using a microscope, and failure patterns were identified. One-way ANOVA and Tukey HSD tests were applied for statistical analysis of the results (p-value ≤ 0.05). Results Despite the fact that the chipping strength is proportional to the cross-sectional area of the connector, the effect of the cross-sectional area on chipping load revealed no statistically significant differences, while PFMs showed superior chipping strength relative to the zirconia frameworks regardless of the connector's size. A high rate of catastrophic fracture occurred while loading the specimens. Conclusion The effect of the cross-sectional area on chipping load revealed no statistically significant differences in Y-TZP frameworks. The novel sonographic technique may be a potential method to study the behavior of dental ceramics, including chipping and fracture.

I-fiber implantation robot for composite parts

I-fiber implantation is a new stitching technology that can effectively enhance the interlayer performance of laminated composites. This paper presents and evaluates the design and implementation of the I-fiber robot implantation system integrated for producing high-performance fiber preforms for advanced composites. The system was constructed and validated through I-fiber robot implantation experimentation. It was demonstrated that automated I-fiber implantation could be achieved by use of an industrial robot. The programming method and computer-aided manufacturing software of the I-fiber implantation robot were feasible and effective. The double-cantilever-beam (DCB) experiments showed that the implantation of I-fiber significantly improved the interlaminar fracture toughness of the laminated composite, where the maximum load value increased by up to 106%. The DCB load–displacement curve presented a zigzag shape, where the peaks and valleys were the location points of the I-fiber break. It was also found that for the reinforced laminated composite without an I-fiber head, the delamination failure was manifested as resin cracking and I-fiber pullout, while for the I-fiber with a certain head length, the I-fiber failure mechanism was brittle fracture. I-fiber with a certain head length could significantly improve the interlayer performance of the composite. In addition, DCB experiments also revealed that the implantation matrix had little effect on the interlayer performance of I-fiber reinforced composites, and the failure load value and the I-fiber implantation volume showed an obvious proportional relationship.

A novel approach to modelling the bond characteristics between CFRP fabrics and steel plate joints under quasi-static tensile loads

Carbon fiber-reinforced polymer (CFRP) materials have been effectively used as externally bonded sheets to repair damaged steel structures such as airplanes and ships. In this study, a series of double strap joints with different bonding lengths are considered and examined to experimentally and theoretically assess the effective bond length. Various models exist in the literature which are used to predict the strength of steel and CFRP joints under various loading conditions. Non-linear Lagrange stress method (NLS) which is a novel stress-based method for predicting the failure load values is presented for the first time. This approach is based on 2D and 3D linear elastic finite element analysis. Relying only on two experimental tests, the new approach proposed here can quickly and easily predict the failure load in steel/CFRP samples. In this methodology, it is assumed that the adhesive joint will fail as the normal stress along the adhesive mid-line reaches a predetermined value at a critical distance. In addition, experimental data on steel/CFRP joints gathered from the literature are compared to predictions using the NLS method. It was found that results from the theoretical predictions (NLS) were in good agreement with experimental tests conducted on double strap joints. It was also revealed that the average accuracy of the NLS method is superior to other methods such as cohesive zone model and Hart-Smith. The results revealed that under the best conditions, the NLS model is 5 times more accurate than existing models.

Case study on the mineralogical and petrophysical analysis of reinforced concrete slabs of a highway viaduct of the S.G.C. Orte-Ravenna

For the maintenance of the safety and security of people traveling on the road, renovation of the reinforced concrete is necessary, especially for bridge or viaduct slabs. Being able to quantify the degradation of slabs and propose methodologies for its retrofit or maintenance is crucial not only in the mineralogical-engineering field but also for socio-economic implications. In this study, samples of deck slabs of a viaduct from the highway E45 near the locality of Bagno di Romagna (Emilia Romagna, north of Italy) were subjected to a testing program to evaluate mechanical and mineralogical parameters through thermographic analyses, compression, and Ultrasonic Pulse Velocity tests and morphological observation. The analyses allow to better recognize the damage of the reinforced concrete samples and they have shown that the cause of the detachment of the asphalt has mainly a natural origin, due to temperature variations and precipitation, with a secondary cause in the anthropogenic impact. The work aims to understand the relationships between the structure of the aggregates and the characteristics of concrete to understand the development of degradation. This knowledge could be used to prevent future damages to the highways.Article HighlightsConcrete slabs analysed provided information about the relation between damage level, mechanical behaviour, size and distribution of aggregates.Thermographic analyses were useful to understand how deep the damage was in the slabs and to detect any detachment of the asphalt.Compressive tests, through the failure load value, shown that the ultimate strength level decreased due to formation of microcracks.

Failure Load and Fatigue Behavior of Monolithic Translucent Zirconia, PICN and Rapid-Layer Posterior Single Crowns on Zirconia Implants.

This laboratory study aimed to evaluate the thermo-mechanical fatigue behavior and failure modes of monolithic and rapid-layer posterior single-crowns (SCs) supported by zirconia implants. Methods: 120 all-ceramic crowns supported by one-piece zirconia implants (ceramic.implant; vitaclinical) were divided into five groups (n = 24 each): Group Z-HT: 3Y-TZP monolithic-zirconia (Vita-YZ-HT); Group Z-ST: 4Y-TZP monolithic-zirconia (Vita-YZ-ST); Z-XT: 5Y-TZP monolithic-zirconia (Vita-YZ-XT); Group E: monolithic-polymer-infiltrated ceramic network (PICN,Vita-Enamic); Group RL (rapid layer): PICN-“table-top” (Vita-Enamic), 3Y-TZP-framework (Vita-YZ-HT). Half of the specimens of each group (n = 12) were exposed to fatigue with cyclic mechanical loading (F = 198N, 1.2-million cycles) and simultaneous thermocycling (5–55 °C). Single-load-to-failure testing (Z010, Zwick) was performed for all specimens without/with fatigue application. Data analysis was performed using ANOVA, Tukey’s post-hoc test, two-sample t-test and Bonferroni correction (p < 0.05). Results: All specimens survived fatigue exposure. Significant differences in failure loads were detected among groups (p ≤ 0.004). Materials Z-HT and Z-ST showed the highest failure loads followed by Z-XT, RL and E. The influence of fatigue was only significant for material RL. Conclusions: All types of tested materials exceeded clinically acceptable failure load values higher than 900N and can be recommended for clinical use. Z-HT and Z-ST appear to be highly reliable towards fatigue. Rapid-layer design of PICN and YZ-HT might be an interesting treatment concept for posterior implant SCs.

Nonlinear first ply failure study of laminated composite skew plates

The present work reports the first ply failure investigation of laminated composite clamped skew plates subjected to uniformly distributed transverse static load considering geometric linear and nonlinear strains. An eight-noded isoparametric curved quadratic plate element based on Sanders’ and Von Karman's nonlinearity is employed to develop the finite element code used in the present research. The first ply failure loads are evaluated based on various well-acknowledged failure theories like maximum stress, maximum strain, Hoffman, Tsai – Hill, Tsai – Wu, Hashin and Puck failure criteria. Effect of variation of skew angles on first ply failure loads of laminated composite skew plates for various stacking pattern is reported and studied in depth. The failure criterion corresponding to which the failure load value is minimum, for each skew angle, is only reported in this paper. The effects of skew angle on the first ply failure load are summarised in the form of charts and working equations. The engineers and researchers may use the charts and equations directly to predict the first ply failure load provided the geometry of the plate is known. Besides first ply failure loads the failed plies as well as the failure modes are also reported in the present paper.

Step-stress vs. staircase fatigue tests to evaluate the effect of intaglio adjustment on the fatigue behavior of simplified lithium disilicate glass-ceramic restorations

The aim of the study was to compare the outcomes for the fatigue mechanical behavior of bonded simplified lithium disilicate restorations, with and without an internal adjustment by grinding with diamond bur in running two fatigue tests: Staircase and Step-stress testing approaches. Ceramic discs (IPS e.max CAD) were prepared (Ø = 10 mm; thickness = 1.0 mm), submitted to an in-lab simulation of CAD/CAM milling (#60 SiC paper) and allocated into 2 groups according to the internal adjustment by grinding of the cementation surface: no adjustment (CTRL); or grinding with a coarse diamond bur (GR). Adhesive cementation (Multilink N) was performed onto epoxy resin discs (Ø = 10 mm; thickness = 2 mm) after ceramic/epoxy surface treatments. The cemented assemblies of each group were randomly assigned into 2 subgroups considering two fatigue tests (n = 15): Staircase – SC (250,000 cycles; 20 Hz), or Step-stress – SS (10,000 cycles per step; 20 Hz). Roughness, topographic and fractographic analyses were additionally performed. Statistical analyses were carried out using the Dixon and Mood method for Staircase data, and Kaplan–Meier and Mantel-Cox (log-rank) tests for Step-stress data. Ceramic restorations having its intaglio surface ground (GR group: SC test = 306.67 N; SS test = 646.67 N) presented lower fatigue failure load (FFL) values than the CTRL group (SC test = 879.28 N; SS test = 1090.00 N), regardless of the fatigue testing approach. The percentage of mean FFL decrease comparing the CTRL to GR group was higher for SC (65.1%) than the SS (40.7%) approach. However, a different total number of cycles was applied for each method. Both fatigue tests were able to detect the negative effect of internal adjustments of lithium disilicate glass-ceramic simplified restorations on their mechanical behavior. Therefore, both methods can be applied for similar evaluations (fatigue testing for ceramic restorations).