Monotonic and Fatigue Strength of 3D-Printed Partially Stabilized Zirconia for Monolithic Restorations

To evaluate the laboratory effects of commonly used beverages on the surface roughness and color change of leucite-reinforced Computer Aided Design-Computer Aided Manufacturing (CAD-CAM) material with different laboratory surface finishes. In this study, all the IPS Empress CAD-CAM ceramic block specimens were treated with a glaze layer and then randomly divided into three groups. The samples (n=25) in Group 1 (Control) were not treated (glaze layer was left). The glaze layer of the other samples (n=50) was abraded by the same researcher. While the samples in Group 2 were treated with Optrafine (optrafine after glazing); those in Group 3 were subjected to surface treatment with Eve polishing kits (Eve kit after glazing). The samples were then immersed in five different beverages (cola, coffee, tea, fruit juice and distilled water) and color (ΔE₀₀) and surface roughness (Ra) measurements were repeated after 18, 36 and 54 hours. Color measurements of all specimens were measured using a dental spectrophotometer and surface roughness (Ra values) through profilometry. ANOVA revealed that the interactions of time, time and surface finishing protocols, time and solution, and the combination of time, surface finishing process, and solution were statistically significant (P< 0.001). The least color change (ΔE₀₀= 0.16) and smoothest surfaces (Ra= 0.38) µm were observed in samples with the glaze surface finishing protocol, while the highest color change (ΔE₀₀=2.54) and surface roughness (Ra=2.17 µm) values were found in samples with the Eve surface finishing protocol. The leucite-reinforced CAD-CAM ceramic samples with a glazed surface finish showed the highest color stability and the lowest surface roughness. Color change was measured within clinically acceptable limits in all groups (AT, ΔE₀₀≤ 1.8 ), except for Eve surface-finished tea group (2.54) between 18-36 hours. The esthetic and functional quality of prosthetic restorations is closely related to the surface properties of CAD-CAM ceramic materials. Clinicians must be familiar with the properties and performance of various CAD-CAM materials to make the best choice for their patients.

To evaluate the effect of erosive-abrasive challenge on the optical properties, microhardness, and surface morphology of CAD-CAM ceramics with different surface finishing protocols. CAD-CAM ceramics used were: IPS e.max CAD (DIS), IPS Empress CAD (LEU), Cerec Blocs (FEL), and Celtra Duo (CEL). Specimens were divided into five groups (n = 10): Polishing (P), Conventional Glaze (CG-control), Conventional Glaze with 2 firings (CG2), Extended Glaze firing (EG), and Extended Glaze with 2 firings (EG2). An erosive-abrasive challenge was performed with citric acid and simulated toothbrushing. Color change (ΔE00), translucency, contrast ratio, gloss, Vickers microhardness, and surface morphology were evaluated. The evaluations were performed before and after the erosive-abrasive challenge. ΔE00 was analyzed with one-way ANOVA with Welch correction and Games-Howell, while the other data were evaluated with two-way repeated measures ANOVA and Bonferroni post-test (α = 0.05%). After the challenge, CG groups showed clinically unacceptable color changes. Translucency decreased in LEU-P, FEL-P, FEL-EG, and CEL-EG groups, but increased in DIS-CG2, DIS-EG2, and CEL-EG groups. The contrast ratio was close to 1. No gloss reduction was observed in CG groups. Microhardness decreased in DIS-EG, DIS-EG2, LEU, FEL, and CEL groups, but remained unchanged in LEU-CG, FEL-CG2, and CEL-EG2 groups. Erosive-abrasive challenge affected the properties of CAD-CAM ceramics with different behaviors depending on the surface finishing protocol used. The optical properties and microhardness of CAD-CAM ceramics are negatively affected by erosive-abrasive conditions. Manual polishing showed similar performance in maintaining these properties and may represent a viable and effective alternative to glaze application.

• Selective laser melted Ti6Al4V with three different surface conditions was tested. • Quasi-static, high- and low-cycle fatigue behaviours were characterized. • The theoretical fatigue limit in ideal surface finish conditions was found. • The effect of roughness on fatigue limit was quantified through reduction factors • Fracture mechanics analysis provided further insight about failure mechanisms. Ti6Al4V has emerged as one of the most promising materials for Additive Manufacturing (AM). In this work, three series of AM Ti6Al4V samples were employed to assess the material fatigue behavior and its dependency on surface finish. One series was left in as-built conditions, one was machined, and one was finely polished. No samples underwent heat treatment, and their dimensions were chosen to be representative of the characteristic strut size of AM reticular structures. The as-built and machined series were characterized in terms of roughness, monotonic, Low-Cycle Fatigue (LCF) and High-Cycle Fatigue (HCF) behaviors. The polished series was intended to determine the fatigue limit under ideal surface finish conditions, undergoing roughness and HCF tests only. This allowed the determination of the fatigue limit reduction factors due to surface finish, providing designers with a practical tool for evaluating the effect of surface roughness on the fatigue performance of AM Ti6Al4V. Besides, scanning electron microscopy and fracture mechanics analysis through Kitagawa-Takahashi diagrams, based on Murakami’s theory, were performed. Different laws correlating defect size and fatigue limit of defective components were compared. By transforming roughness into an equivalent defect, further insight into the effect of surface finish on fatigue performance was gained.

Surface factor assessment in HCF for steels by means of empirical and non destructive techniques

PurposeThe goal of the present work was to provide a large set of detector‐specific output correction factors for seven small volume ionization chambers on two linear accelerators in four megavoltage photon beams utilizing perpendicular and parallel orientation of ionization chambers in the beam for nominal field sizes ranging from 0.5 cm2 × 0.5 cm2 to 10 cm2 × 10 cm2. The present study is the second part of an extensive research conducted by our group.MethodsOutput correction factors kQclin,Qreffclin,fref were experimentally determined on two linacs, Elekta Versa HD and Varian TrueBeam for 6 and 10 MV beams with and without flattening filter for nine square fields ranging from 0.5 cm2 × 0.5 cm2 to 10 cm2 × 10 cm2, for seven mini and micro ionization chambers, IBA CC04, IBA Razor, PTW 31016 3D PinPoint, PTW 31021 3D Semiflex, PTW 31022 3D PinPoint, PTW 31023 PinPoint, and SI Exradin A16. An Exradin W1 plastic scintillator and EBT3 radiochromic films were used as the reference detectors.ResultsFor all ionization chambers, values of output correction factors kQclin,Qreffclin,fref were lower for parallel orientation compared to those obtained in the perpendicular orientation. Five ionization chambers from our study set, IBA Razor, PTW 31016 3D PinPoint, PTW 31022 3D PinPoint, PTW 31023 PinPoint, and SI Exradin A16, fulfill the requirement recommended in the TRS‐483 Code of Practice, that is, 0.95<kQclin,Qreffclin,fref<1.05, down to the field size 0.8 cm2 × 0.8 cm2, when they are positioned in parallel orientation; two of the ionization chambers, IBA Razor and PTW 31023 PinPoint, satisfy this condition down to the field size of 0.5 cm2 × 0.5 cm2.ConclusionsThe present paper provides experimental results of detector‐specific output correction factors for seven small volume ionization chambers. Output correction factors were determined in 6 and 10 MV photon beams with and without flattening filter down to the square field size of 0.5 cm2 × 0.5 cm2 for two orientations of ionization chambers — perpendicular and parallel. Our main finding is that output correction factors are smaller if they are determined in a parallel orientation compared to those obtained in a perpendicular orientation for all ionization chambers regardless of the photon beam energy, filtration, or linear accelerator being used. Based on our findings, we recommend using ionization chambers in parallel orientation, to minimize corrections in the experimental determination of field output factors. Latter holds even for field sizes below 1.0 cm2 × 1.0 cm2, whenever necessary corrections remain within 5%, which was the case for several ionization chambers from our set.TRS‐483 recommended perpendicular orientation of ionization chambers for the determination of field output factors. The present study presents results for both perpendicular and parallel orientation of ionization chambers. When validated by other researchers, the present results for parallel orientation can be considered as a complementary dataset to those given in TRS‐483.

Based on the world wide fatigue test database, The Design Fatigue Curve (DFC) Phase 1 and 2 subcommittees established in The Japan Welding Engineering Society (JWES) have been developed new design fatigue curves which are applied for the nuclear component materials, in air environment. The effects of the design factor, such as mean stress, size effect and surface finish, etc. on the fatigue curves are also discussed with the fatigue database in order to construct fatigue evaluation method for the new design fatigue curves. The subcommittees also have studied the applicability of newly developed fatigue evaluation method to the nuclear component materials. This paper reports the fatigue test results of machined finished small-scale test specimens which are used for the verification of proposed fatigue evaluation method. The materials subjected to the fatigue tests are austenitic stainless steel SUS316LTP, low-alloy steels SQV2A and SCM435H, and carbon steel STPT370. Specimens finished with lathe machining are subjected to the tests. The planed maximum height roughness of the specimen are 25 and 100 μm. The fatigue test results show that the surface finish effect on the fatigue strength in the high cycle region of the austenitic stainless steel can be negligible. On the other hand, fatigue strength of the carbon steel and low alloy steel is decreased as increasing the surface roughness of the specimen. Especially, decrease of fatigue strength for the specimens with more than 100 μm maximum height roughness is larger than that of conventional estimation. It is presumed that severe roughness introduced by lathe machining tends to behave as notches and increase the stress concentration at the specimen surface, and resulted in unexpected decrease of fatigue strength.

The aim of this study is to investigate the influence on the high cycle fatigue behaviour of high strength steels of the surface micro-geometry induced by their machining. The machining process considered herein is high speed finishing milling with a ball-end tool. The micro-geometry of the machined surface is characterized by 2- and 3-D roughness parameters. The studied material is a 25MnCrSiVB6 resulphurized steel with a bainitic matrix. The high cycle fatigue behaviour of this material is characterised by its endurance limit evaluated from symmetric tension-compression (Rσ = −1) tests performed according to standard staircase method. This endurance limit was compared to the results of so-called self-heating tests as well as rupture tests performed according to Locati approach. It appears that the difference between the endurance limits measured on the machined or the polished specimens is not fully accounted for by the self-heating measurements. Furthermore, the Arola–Ramulu model also appears as being unable to predict the influence of the surface integrity induced by the milling process on the high cycle fatigue life of this material. Last, a sensitivity analysis of the lead angle of the tool on the anisotropy of the machined surface micro-geometry proves that the roughness of surfaces milled with ball-end tools must be characterized by surface—and not linear—parameters.

In this study, the effect of whisker orientation on monotonic and fatigue strength of aluminium cast alloy locally reinforced by SiC particles and Al2O3 whiskers are investigated. The material is monotonically and cyclically deformed to failure at room temperature. A significant effect of reinforcement orientation on the monotonic strength and fatigue strength are observed experimentally and numerically. With respect to the stress direction the whisker orientation gives significant difference in strength of this material. SEM analysis shows almost all whiskers are transversely debonded when whisker direction is perpendicular to the stress direction and almost all whiskers are broken when the whisker direction is parallel to the stress direction. A three-dimensional single whisker unit cell model of cylindrical shape whisker in the periodic boundary condition is conducted using finite element method (FEM) to describe the overall behavior of the composite. The prediction results based on FEM analysis is found to be in reasonable agreement with the experimental observations.

This paper presents the results of an experimental investigation into the tensile monotonic and fatigue behaviour of symmetric fibreglass-epoxy coupons using three ply angle orientations, 45°, -45° and 0° which were interchanged in three different configurations: [452, -452, 02]s, [452, 02, -452]s and [02, 452, -452]s. The results show that there is significant sequence effect on the monotonic strength and the fatigue performance. The monotonic results demonstrate an increase of 11% in the strength and 6% in stiffness between the weakest laminate, [02, 452, -452]s, and the strongest laminate, [452, -452, 02]s. The fatigue performance depends on lay-up and stress level. At higher stresses, the trend in stacking sequence effect on fatigue strength is the same as for monotonic loading. In contrast, at lower stresses the trend is opposite. The sequence effect observed in the monotonic and fatigue loading is discussed subsequently based on the numerical analysis of interlaminar stresses induced by the free-edge and constraint effect of 0° ply on damage development.

The purpose of this paper is to provide a comprehensive state of the art of fatigue and cyclic loading of natural rock materials. Papers published in the literature are classified and listed in order to ease bibliographical review, to gather data (sometimes contradictory) on classical experimental results and to analyse the main interpretation concepts. Their advantages and limitations are discussed, and perspectives for further work are highlighted. The first section summarises and defines the different experimental set-ups (type of loading, type of experiment) already applied to cyclic/fatigue investigation of rock materials. The papers are then listed based on these different definitions. Typical results are highlighted in next section. Fatigue/cyclic loading mainly results in accumulation of plastic deformation and/or damage cycle after cycle. A sample cyclically loaded at constant amplitude finally leads to failure even if the peak load is lower than its monotonic strength. This subcritical crack is due to a diffuse microfracturing and decohesion of the rock structure. The third section reviews and comments the concepts used to interpret the results. The fatigue limit and S–N curves are the most common concepts used to describe fatigue experiments. Results published from all papers are gathered into a single figure to highlight the tendency. Predicting the monotonic peak strength of a sample is found to be critical in order to compute accurate S–N curves. Finally, open questions are listed to provide a state of the art of grey areas in the understanding of fatigue mechanisms and challenges for the future.

To examine the effects of the surface finish and defects on fatigue limit, specimens differently finished, i. e., sand paper (Grade #600, #80) finish and electrolytic polish, were prepared. Moreover, to simulate surface defects, a small artificial hole of which diameter is varied from 40 to 200 μm is introduced on the specimen surface. Both as-received and annealed specimens were applied so as to extract the effect of the work-hardened surface layer on the fatigue limit. Through examination of the fatigue limit and ten non-propagating crack the following results are obtained: (1) the surface roughness slightly influences the fatigue limit, while the work-hardened surface layer has a primary effect on the fatigue limit. (2) An increase in the diameter of the small hole decreases the fatigue limit and results in the prolongation of the non-propagating crack. (3) For the non-propagating crack, the threshold stress intensity factor range ΔKth decreases with a decrease in the crack length.

The effect of glaze on porcelain strength

PurposeThe purpose of this paper is to estimate the acceptable defect size amax after needle peening (NP) and predict the fatigue limit improvement through the use of NP for an austenitic stainless steel welded joint containing an artificial semi-circular slit on a weld toe.Design/methodology/approachResidual stress and hardness distribution were measured. Microstructures around the weld toe were observed to clarify the cause for the change in hardness after NP. Finite element method analysis was used to analyze the change in the stress concentration following NP. Fracture mechanics was used to evaluate amax after NP. The fatigue limits before and after NP were predicted by determining amax for several levels of stress amplitude.FindingsThe tensile residual stress induced at the surface of the weld toe prior to NP changed to a compressive residual stress after NP. The residual stress near the surface layer after NP exceeded the yield stress prior to NP due to the increase in yield stress as a result of work hardening as well as the generation of a deformation-induced martensitic structure. The stress concentration was reduced due to the shape improvement caused by NP. The estimation value of amax after NP and the prediction results of fatigue limits were in good agreement with the fatigue test results.Practical implicationsThe proposed method is useful in improving the reliability of welded joints used in large steel structures, transportation equipments and industrial machines.Originality/valueFrom an engineering perspective, it is essential to estimate amax and the fatigue limit of welded joints with crack-like defects. However, it is unclear as to whether it is possible to predict amax and the effects of NP on the fatigue limit for stainless steel welded joints.

Shot Peening is a well established mechanical surface treatment to induce compressive residual stresses and work hardening into the surface layer of components exposed to cyclic loading. Due to the induced changes in the surface layer, the fatigue limit increases significantly. The concept of local fatigue strength is based on the comparison of the locally effective fatigue limit with locally active loads in order to estimate the maximum outer loading that will not exceed fatigue limit. In this paper an approach of using simulated surface characteristics after shot peening for the determination of the local fatigue strength will be presented. The complex stress distribution due to cyclic bending of notched geometries will also be determined by FEM. Finally the simulated estimation of the fatigue limit of differently notched specimens of AISI 4140 will be verified with experimentally determined fatigue limits.

The influence of deep cryotreatment before and after double tempering on hardness, wear rate, surface finish and fatigue limit of AISI H21 tool steel has been examined. In the present work, H21 tool steel has been subjected to heat treatment at 1195 °C, double tempering at 540 °C, deep cryotreatment at − 185 °C and soft tempering at 100 °C. The microstructure of samples has been characterized for the number density of carbides, hardness, wear rate, surface roughness and fatigue limit. The fatigue test has been carried out using a rotating bending fatigue machine to study the fatigue strength of the material. The obtained results show that the HTTC24 specimen reduces the wear rate by ≈ 24% and surface roughness by ≈ 21% with an increase in fatigue limit by ≈ 13% compared to HTT specimens. This has been attributed to the increased number density of carbides and hardness; and approximately the complete conversion of retained austenite content into martensite.