Higher Stress Values Research Articles

The effect of attachment types and implant level on the stress distribution in a mandibular overdenture: a 3D Finite Element Analysis

Objective: The objective of this study was to evaluate the stress distribution in bone-surrounding implants placedin different levels in a mandibular overdenture. Material and Methods: A Computerized Tomography (CT) scanof an edentulous mandible was used to generate the models. Two implants with an internal connection wereplaced perpendicular to the occlusal plane in the Canine sites of the mandible. The implant in the left side wasplaced 1mm higher than the other side. Dolder bar and ball attachments were designed. Loading was performedby clenching the teeth with reconstruction of the muscles. In the anterior loading condition, force was appliedto the central incisors and in the posterior loading conditions, it was applied to the molars and premolars. Thenthe Maximum Principal Stresses in the peri implant bone was evaluated with finite element analysis. Results:In both models, the highest stress values were recorded in the cortical bone surrounding the higher implantexcept in the ball model with unilateral load application on the right side (64.7 MPa). In almost all loadingconditions the stress value differences in models with bar and ball attachments were low. Only in the anteriorloading condition, the stress magnitude was higher in two implants of the ball model (60.5 MPa in the left sideand 21 MPa in the right side) compared to the bar model (54.5 MPa in the left side and 17.5 MPa in the rightside). Conclusion: The stress concentration did not affected considerably by the attachment system. High stressvalues were found adjacent the implant with a higher level. To reduce the amount of stress, bilateral balanceocclusion should be considered. KEYWORDSStress; Finite element analysis; Overdenture; Dental implants.

A study of tensile and bending properties of 3D-printed biocompatible materials used in dental appliances

In the last years, a large number of new biocompatible materials for 3D printers have emerged. Due to their recent appearance and rapid growth, there is little information about their mechanical properties. The design and manufacturing of oral appliances made with 3D printing technologies require knowledge of the mechanical properties of the biocompatible material used to achieve optimal performance for each application. This paper focuses on analysing the mechanical behaviour of a wide range of biocompatible materials using different additive manufacturing technologies. To this end, tensile and bending tests on different types of recent biocompatible materials used with 3D printers were conducted to evaluate the influence of the material, 3D printing technology, and printing orientation on the fragile/ductile behaviour of the manufactured devices. A test bench was used to perform tensile tests according to ASTM D638 and bending tests according to ISO 178. The specimens were manufactured with nine different materials and five manufacturing technologies. Furthermore, specimens were created with different printing technologies, biocompatible materials, and printing orientations. The maximum allowable stress, rupture stress, flexural modulus, and deformation in each of the tested specimens were recorded. Results suggest that specimens manufactured with Stereolithography (SLA) and milling (polymethyl methacrylate PMMA) achieved high maximum allowable and rupture stress values. It was also observed that Polyjet printing and Selective Laser Sintering technologies led to load–displacement curves with low maximum stress and high deformation values. Specimens manufactured with Digital Light Processing technology showed intermediate and homogeneous performance. Finally, it was observed that the printing direction significantly influences the mechanical properties of the manufactured specimens in some cases.

The effects of bar holder material, cantilever and vertical misfit on stresses in implant supported overdentures: Three dimensional finite element analysis

Background/Aim: The aim of this study is to examine with finite element analysis the distal bar extension, the bar substructure material type and the amount of bar substructure-abutment mismatch, and the stress caused by the implant at the surrounding bone tissue in bar-retained prostheses. Material and Methods: A bar-retained prosthesis model has been designed on three implants placed in the fully toothless lower jaw at the places of both canines and the midline. Bar holder according to distal cantilever lengths was modeled to be 0 mm, 8 mm and 14 mm. The vertical incompatibility of the bar holder substructure with the abutment was modeled to be 0 µm, 100 µm and 200 µm. A total of twenty-seven (3x3x3) different models were obtained with three different bar infrastructure materials (titanium, gold and chromium-cobalt). 150 N occlusal force was applied to the central fossa of the left 1st molar tooth with a rigid food stuff. Results: In the cortical bone, the highest maximum principle stress value (2.78 MPa) was analyzed around the anterior implant socket in the model 13 (gold, cantilever 0mm, misfit 100 µm). The highest von Mises stress value (343.43 MPa, which occurred at the selected joints in bar holders) was observed in model 27 (chrome-cobalt, cantilever 14mm, misfit 200 µm). Conclusions: When the length of the cantilever is 14 mm, it causes a significant increase in stress around the implant, especially near the cantilever. It has been observed that bar infrastructures with high elastic modulus create higher stress values.

A viscoelastic in-plane damage model for fibrous composite materials

This work presents a viscoelastic in-plane damage model for fibrous composites. The material behavior is modeled as linear viscoelastic, with brittle failure in the fiber-dominated direction, and progressive degradation of the matrix-dominated properties, when the composite is loaded perpendicularly to the fibers or in in-plane shear. An evaluation procedure has been performed by comparing computational stress-strain curves against tensile tests curves under three different displacement rates. In addition, a calibration of the viscoelastic properties, by means of the response surface methodology, is also presented. The proposed material model has shown reasonable performance up to the material reaching an experimentally-verified modulus transition zone. Besides, the viscoelastic calibration procedure has produced a good agreement with the experimental results, concerning maximum stresses. It was observed that the computational stress-strain curve has deviated from the experimental one for higher stress values, indicating that it is necessary to improve the assessment of the nonlinear phenomena, which occur within the material.

Stratigraphically Controlled Stress Variations at the Hydraulic Fracture Test Site-1 in the Midland Basin, TX

We investigated the relationship between stratigraphy, stress, and microseismicity at the Hydraulic Fracture Test Site-1. The site comprises two sets of horizontal wells in the Wolfcamp shale and a deviated well drilled after hydraulic fracturing. Regional stresses indicate normal/strike-slip faulting with E-W compression. Stress measurements in vertical and horizontal wells show that the minimum principal stress varies with depth. Strata with high clay and organic content show high values of the least compressive stress, consistent with the theory of viscous stress relaxation. By integrating data from core, logs, and the hydraulic fracturing stages, we constructed a stress profile for the Wolfcamp sequence, which predicts how much pressure is required for hydraulic fracture growth. We applied the results to fracture orientation data from image logs to determine the population of pre-existing faults that are expected to slip during stimulation. We also determined microseismic focal plane mechanisms and found slip on steeply dipping planes striking NW, consistent with the orientations of potentially active faults predicted by the stress model. This case study represents a general approach for integrating stress measurements and rock properties to predict hydraulic fracture growth and the characteristics of injection-induced microseismicity.

Novel Tough and Transparent Ultra-Extensible Nanocomposite Elastomers Based on Poly(2-methoxyethylacrylate) and Their Switching between Plasto-Elasticity and Viscoelasticity.

Novel stiff, tough, highly transparent and ultra-extensible self-assembled nanocomposite elastomers based on poly(2-methoxyethylacrylate) (polyMEA) were synthesized. The materials are physically crosslinked by small in-situ-formed silica nanospheres, sized 3–5 nm, which proved to be a very efficient macro-crosslinker in the self-assembled network architecture. Very high values of yield stress (2.3 MPa), tensile strength (3.0 MPa), and modulus (typically 10 MPa), were achieved in combination with ultra-extensibility: the stiffest sample was breaking at 1610% of elongation. Related nanocomposites doubly filled with nano-silica and clay nano-platelets were also prepared, which displayed interesting synergy effects of the fillers at some compositions. All the nanocomposites exhibit ‘plasto-elastic’ tensile behaviour in the ‘as prepared’ state: they display considerable energy absorption (and also ‘necking’ like plastics), but at the same time a large but not complete (50%) retraction of deformation. However, after the first large tensile deformation, the materials irreversibly switch to ‘real elastomeric’ tensile behaviour (with some creep). The initial ‘plasto-elastic’ stretching thus causes an internal rearrangement. The studied materials, which additionally are valuable due to their high transparency, could be of application interest as advanced structural materials in soft robotics, in implant technology, or in regenerative medicine. The presented study focuses on structure-property relationships, and on their effects on physical properties, especially on the complex tensile, elastic and viscoelastic behaviour of the polyMEA nanocomposites.

Stress distribution of a novel bundle fiber post with curved roots and oval canals.

The aim of this study was to compare the stress distribution of teeth with curved and straight roots with oval and round canals restored with the bundle and conventional post systems. Six three-dimensional premolars were modeled with round and oval canals, and curved roots using the software. The bundle post and the round posts were modeled. All post models were placed on the canals. The models were subjected to 200 N oblique loading. The results were evaluated by von Mises stresses. This study demonstrated that the bundle post showed higher stress values compared to the conventional post. The stresses in the oval canal were higher than those in the round canal. The highest stress values were found in the curved roots. The stress distribution on the curved roots was observed in the middle and apical third of the canal. The bundle post presented higher stress compared to conventional posts. Besides, a more uniform stress distribution was observed in the bundle groups. When a post was required in extremely irregular, wide canals and curved roots, the bundle post was the material of choice. Canal and root morphology influenced stress distribution.

Experimental simulation of proppant permeability in hydraulic fracturing at extended time under bottom-hole conditions

During hydraulic fracturing treatment, huge quantities of gel are pumped into the formation to initiate the fracture, maintain it open and transport the proppant. The fracture dimensionless conductivity (Fcd) is a key parameter to optimize the fracturing design, to estimate the productivity Index (PI) and the folds of increase (FOI). However, these parameters are affected by the gel residues which decrease the fracture conductivity; thus, the proppant cleanup is a very important step to avoid additional damage caused by fracturing fluid due to high gel concentration and the extended time of gel staying in the fracture before cleanup. Throughout the life of Hassi Messaoud, Algeria field, hydraulic fracturing technique has been aggressively used mainly in four producing formations in the Cambrian, with hard formation characteristics, an average permeability range and low reservoir pressure (0.15–0.45 psi/ft) and high stress value between 6000 and 9000 psi. In this paper, an experimental simulation is applied using a self-made cell to determine the effect of different parameters on the fracture conductivity under various bottom-hole conditions where different variables were used: effect of Proppant type, guar gel concentration, temperature, breaker concentration and closure pressure at extended time. An important drop in fracture conductivity was observed varied between 10 and 80% under stresses at interval of 2000 psi and 8000 psi, gel concentration up to 200 lb/1000 gal at extended time and temperature.

Influence of Resin Cement Thickness and Elastic Modulus on the Stress Distribution of Zirconium Dioxide Inlay-Bridge: 3D Finite Element Analysis

The mechanical properties and the thickness of the resin cement agents used for bonding inlay bridges can modify the clinical performance of the restoration such as debonding or prosthetic materials fracture. Thus, the aim of this study was to evaluate the stress distribution and the maximum strain generated by resin cements with different elastic moduli and thicknesses used to cement resin-bonded fixed partial denture (RBFPD). A three-dimensional (3D) finite element analysis (FEA) was used, and a 3D model was created based on a Cone-Beam Computed Tomography system (CBCT). The model was analyzed by the Ansys software. The model fixation occurred at the root of the abutment teeth and an axial load of 300 N was applied on the occlusal surface of the pontic. The highest stress value was observed for the Variolink 0.4 group (1.76 × 106 Pa), while the lowest was noted for the Panavia 0.2 group (1.07 × 106 Pa). Furthermore, the highest total deformation value was found for the Variolink 0.2 group (3.36 × 10−4 m), while the lowest was observed for the Panavia 0.4 group (2.33 × 10−4 m). By means of this FEA, 0.2 mm layer Panavia F2.0 seemed to exhibit a more favorable stress distribution when used for cementation of posterior zirconium-dioxide-based RBFPD. However, both studied materials possessed clinically acceptable properties.

Direct Synthesis of Functional Thermoplastic Elastomer with Excellent Mechanical Properties by Scandium-Catalyzed Copolymerization of Ethylene and Fluorostyrenes.

Herein, we report copolymerizations of ethylene (E) and ortho-/meta-/para-fluorostyrenes (SF =oFS/mFS/pFS) by using quinolyl methylene fluorenyl scandium complex (Flu-CH2 -Qu)Sc(CH2 SiMe3 )2 . The copolymerizations proceed in a controlled fashion to afford copolymers composed of "soft" ethylene-fluorostyurene (E-SF ) random segments (Tg =-22.2-5.1 °C) and "hard" crystalline ethylene-ethylene (E-E) segments (Tm =42.3-130.2 °C). The copolymers behave like thermoplastic elastomers at room temperature by showing high stress values up to 39.5 MPa under elongation-at-break above 774 % with elastic recovery over 75 %. The excellent mechanical properties are mainly attributed to the microphase separation of the nanoscale crystalline E-E domain from the amorphous E-SF copolymer matrix proved by AFM, WAXD and SAXS. The mechanism investigation by the density functional theory (DFT) simulation reveals that the steric bulky and electron-withdrawing ligand of the catalytic precursor prefers E propagation to generate long E-E segments, while the incorporation of SF is thermodynamic control.

Direct Synthesis of Functional Thermoplastic Elastomer with Excellent Mechanical Properties by Scandium‐Catalyzed Copolymerization of Ethylene and Fluorostyrenes

AbstractHerein, we report copolymerizations of ethylene (E) and ortho‐/meta‐/para‐fluorostyrenes (SF=oFS/mFS/pFS) by using quinolyl methylene fluorenyl scandium complex (Flu‐CH2‐Qu)Sc(CH2SiMe3)2. The copolymerizations proceed in a controlled fashion to afford copolymers composed of “soft” ethylene‐fluorostyurene (E–SF) random segments (Tg=−22.2–5.1 °C) and “hard” crystalline ethylene–ethylene (E–E) segments (Tm=42.3–130.2 °C). The copolymers behave like thermoplastic elastomers at room temperature by showing high stress values up to 39.5 MPa under elongation‐at‐break above 774 % with elastic recovery over 75 %. The excellent mechanical properties are mainly attributed to the microphase separation of the nanoscale crystalline E–E domain from the amorphous E–SF copolymer matrix proved by AFM, WAXD and SAXS. The mechanism investigation by the density functional theory (DFT) simulation reveals that the steric bulky and electron‐withdrawing ligand of the catalytic precursor prefers E propagation to generate long E–E segments, while the incorporation of SF is thermodynamic control.

Tuning the stress state in Nb-thin films by lateral size confinement

For 5 nm thin Nb films adhered to a rigid substrate, hydrogen absorption leads to ultrahigh mechanical stress of about -8 GPa. This is related to a purely elastic behaviour. The high mechanical stress destabilizes phases and even suppresses conventional two-phase regions known for the Nb-H bulk system. These unique thin film properties can be preserved to thicker films, by lateral confinement. Nb-Fe films provide a laterally confined columnar domain structure of well-separated α-Nb(Fe) and μ-FeNb phases. While the α-Nb(Fe) absorbs hydrogen at low chemical potentials, the μ-FeNb phase does not, separating the two phases into a hydrogen active and a hydrogen passive one. The behaviour of 75 nm Nb-Fe films was studied by in situ mechanical stress measurements, in situ x-ray diffraction and transmission electron microscopy. With increasing Fe-content, Nb-Fe films show a strong increase in the yield stress upon hydrogen absorption. This allows for an extended elastic range and high maximum stress values of -4.6 GPa, for 75 nm Nb-Fe films. X-ray diffraction pattern collected upon hydrogen loading of Nb-Fe films show peak shifts and intermediate peak broadening. This indicates the presence of a two-phase region and preservation of the lattice coherency between the α-Nb(Fe)-H phase and the hydride phase. Peak shifts indicate a reduced vertical expansion of the hydrogen absorbing α-Nb(Fe) lattice. This is attributed to the presence of the µ-FeNb phase. FEM simulations on Nb-Fe-H films confirm reduced overall expansions and lateral stresses, when compared to pure Nb-H films. High vertical stresses arise upon H-loading due to the link between the two Nb-Fe phases. These stresses are tensile for µ-FeNb and compressive for the α-Nb(Fe) domains and also reach values of several GPa. Conservation of the exceptional thin film properties to thicker films by lateral confinement is suggested to be a powerful strategy for many different applications like sensor technologies or energy storage.

Influence of Plunger Stress on Resilient Modulus of Forest Subgrade Soils Obtained from Cyclic CBR Test

The low load-bearing capacity of subgrade soils is typical for forest roads. For the determination of the resilient modulus Mr of unbound natural as well as recycled materials, a laboratory triaxial test with cyclic loading is generally preferred. For low volume roads, including forest roads, an alternative method of the cyclic CBR test, which uses standard CBR devices for repeated loading, is being tested and applied in practice. For forest subgrade soils, the procedure for determining the modulus Mr based on cyclic loading of the specimen to a constant penetration depth of 2.54 mm was verified. This procedure was tested on an extensive dataset obtained from 11 forest roads in the Czech Republic, which was then statistically evaluated. The obtained results showed disproportionately high mean values as well as high random variability. Further data analysis revealed that the reason seemed to be the chosen test methodology. When using this procedure for forest soils, high values of plunger stress can occur, which for many types of soils greatly exceed their maximum load-bearing capacity. As result, the modulus Mr is determined at unrealistically high plunger stress values and in many cases on the disrupted specimen. The necessary solution to this shortcoming is to censor the results of the cyclic CBR test, i.e., to exclude unrealistic values of the modulus Mr determined at plunger stresses exceeding the limit values.

Analisa Pengaruh Parameter Proses Terhadap Uji Tarik Produk Hasil 3D Printing Berbahan Polylatic Acid

<p>Fused<em> Deposition Method (FDM) is one of the additive manufacturing methods or methods used by 3D printers. This FDM technology can produce models with a fairly good level of accuracy and strength. However, until now information about the magnitude of the value of accuracy, and the value of strength is very minimal. Because of this, it is necessary to do a test to determine the strength value of the specimens produced using 3D technology printing. The tests carried out aim to obtain settings optimal parameters on a 3D printer using PLA material which is measured by the magnitude of the tensile strength value of the resulting product. The test is carried out by measuring the amount of stress that occurs when the tensile test is carried out. The test was carried out using 81 samples that were printed using the parameters of infill print speed, fill density, extruder temperature, and layer height. Based on the test results, the highest stress value is 1.092 N/m2 with a combination of parameters infill print speed 60 mm/s, fill density 40%, extruder temperature 200oC, and layer height 0.1 mm. The results of the analysis show that the parameter extruder temperature has the greatest influence on the magnitude of the tensile test value, while the layer height parameter has the smallest effect on the value of the test specimen.</em></p>

Comparative biomechanical analysis of rigid vs. flexible fixation devices for the lumbar spine: A geometrically patient-specific poroelastic finite element study

Background and ObjectiveLumbar spinal stenosis (LSS), or the narrowing of the spinal canal, continues to be the leading preoperative diagnosis for adults older than 65 years who undergo spine surgery. Although the treatment of LSS depends on its severity, the optimal surgical technique towards decreasing the risk of adjacent segment disease (ASD) remains elusive. This study aimed to comparatively analyze spinal biomechanics with rigid and flexible fixation devices (i.e., rigid and dynamic posterolateral fusion (PLF) and interspinous process (ISP) devices) during daily activities. MethodsUsing a validated parametric poroelastic finite element modeling approach, 8 subject-specific pre-operative models were developed, and their validity was evaluated. Parametric FE models of the lumbar spines were then regenerated based on post-operation images for (A) rigid PLF (B) dynamic PLF (C) rigid ISP device (Coflex) and (D) flexible ISP device (DIAM) at L4-L5 level. Biomechanical responses for instrumented and adjacent intervertebral discs (IVDs) were analyzed and compared subject to static and cyclic loading. ResultsThe preoperative models were well comparable with previous works in literature. The postoperative results for the PLF and Coflex rigid systems, demonstrated greater ROM; higher values of stress and strain in the AF region; and increased disc height and fluid loss at the adjacent levels, as compared with the pre-op models and the post-op results of the flexible systems (i.e., dynamic PLF and DIAM). The calculated forces on the facet joint were of smaller magnitude for the ISP devices as compared to the PLF, particularly during extension. ConclusionsThis study demonstrates that the dynamic PLF construct and DIAM implants could be effective to maintain the natural poroelastic characteristics of adjacent IVDs, which could be beneficial for enhancing long-term clinical outcomes. FEM provides clinicians with an invaluable patient-specific quantitative tool for informed surgical planning and discerning follow-up management.

Pengaruh Pola Susunan Laminasi Terhadap Distribusi Tegangan Dan Regangan Tarik Pada Komposit CFRP Yang Berlubang

The development of material technology is growing rapidly, especially in the manufacturing industry. One of the materials that are most often used and developed today is composite materials. The purpose of this study was to determine the effect of the pattern of laminate arrangement on the distribution of stress and tensile strain in perforated CFRP composites. The research method carried out is tensile testing using abaqus software, the specimen is designed with 8 laminates and the fiber direction is varied. The specimens were made with the ASTM D 5766 test standard and the properties used were carbon fiber composite type T800S/3900-2B. From the tensile test simulation results, it is found that the highest stress value in the composite with variations in fiber direction 0°, 45°, -45°, 90°, 90°, -45°, 45°, 0° the maximum stress value reaches 356.9 N/ mm², while the smallest stress occurs in the composite fiber direction 0°, 0°, 0°, 0°, 0°, 0°, 0°, 0° with the maximum stress value reaching 165.7 N/mm. The highest stress and strain that occurs in each specimen is located at the edge of the hole perpendicular to the direction of the force, the stress and strain increase based on variations in the direction of the fiber in the composite, the farther the orientation of the fiber direction to the direction of the applied force, the greater the stress concentration that occurs also.Keywords: Tensile test, CFRP composite, abaqus software

Molecular dynamics study on creep behavior of montmorillonite

Clay-rich rocks are widely used in high temperature and stress environment in a very long term like disposal of high-level radioactive waste, exploring its creep deformation mechanism is essential. Clay minerals, as the essential components of clayey rocks, have a crucial influence on the creep behavior. However, it is of great challenge to experimentally investigate the mechanical property of a single crystal mineral due to its small size. In recent years, molecular dynamics (MD) simulations are widely used to address a series of scientific issues including creep mechanism from atomic level. In this study, we selected montmorillonite (MMT), a representative clay mineral in clayey rocks, as the principal object to explore the creep behavior in different temperatures and stresses. The temperature varies from 300 K to 1200 K while the stress is applied in the range of 14GPa to 32GPa. Meanwhile, the anisotropic creep behavior along the two orthogonal crystal orientations is studied as well. It is found the atomic numerical results show a good agreement with macroscopic data that the deformation increases with the temperature raise and applied stress, the creep curve contains two different phases under low temperature and stress while three phases are observed under high values of temperature and stress. Besides, the creep deformation exhibits an obvious anisotropic trend, due to oriented atomic structures. This study provides a better understanding of the creep mechanism of single crystal of MMT and an atomic insight on macroscopic time-dependent deformation of clayey rocks.

Examination of the stresses of the implants applied to the atrophic edentulous maxilla on the maxillary bone

Aim: In advanced atrophy of the posterior maxilla, applied zygoma implants increase the success of the surgical procedure by reducing morbidity and procedure time. In our study, using tomographic records, a model with posterior atrophy was obtained in a computer environment, and zygomatic and dental implants in different numbers and localizations were applied to this model. The aim of our study was to choose the most accurate surgical planning according to the stresses arising from the applied forces.
 Methodology: In our study, one zygoma implant on the right and left in Group 1, two zygoma implants in Group 2, one zygoma implant in Group 3 and one dental implant in the first premolar tooth area, one zygoma implant in Group 4 and one dental implant in the lateral tooth area and one zygoma implant in Group 5 and one dental implant in the lateral and a first premolar tooth area were applied. 150 N were applied vertically to the prosthetic superstructure from the lateral tooth, 1st premolar tooth, 1st molar tooth and 2nd molar tooth. As a result of the applied forces, the maximum stress values ​​in the maxilla molar region were examined by finite element stress analysis.
 Results: In our study, it was observed that Group 1 had the highest stress value, followed by Group 3. Stress values in Groups 2, 4 and 5 were low and they were measured close to each other.
 Conclusion: As a result of our study, it was seen that zygomatic and dental implants applied in addition to the zygomatic implant reduce stress and the localization of dental implants affect the stress values.
 
 How to cite this article: Gülsün B, Çetindağ A. Examination of the stresses of the implants applied to the atrophic edentulous maxilla on the maxillary bone. Int Dent Res 2021;11(Suppl.1):210-5. https://doi.org/10.5577/intdentres.2021.vol11.suppl1.30
 
 
 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

Structural performance of composite tidal turbine blades

Tidal turbine blades experience a significant bending moment in the root area during their long-term operation in a sea water environment. This necessitates using fibre reinforced polymer as the blade material to provide the required strength/stiffness. In this study, a design methodology based on hydrodynamic and Finite Element models with a view to examine the mechanical properties of composites was developed to evaluate the structural response of two commercial scale turbine blades (1.5 and 0.35 MW). Using the output from the hydrodynamic model, Finite Element stress analysis was conducted in order to determine the likelihood of blade failure. To incorporate appropriate failure modes with the blade model, failure analysis was conducted on the composite test coupons. The results of stress analysis show that the blade root area experiences high stress values with failure modes such as resin cracking, fibre/matrix interfacial de-bonding, delamination and fibre breakage. It is also predicted that the glass fibre composite blades require three times thicker laminates than a carbon fibre composite blade of similar design to maintain the same safety factor. Reasonable agreement between the numerically and experimentally determined strain fields on a small-scale blade indicates that the result of Finite Element stress analysis is valid.

Fatigue Analysis of Threaded Components with Cd and Zn-Ni Anticorrosive Coatings

The influence of the electrodeposition of cadmium and zinc-nickel and the stress concentration effect on the fatigue behavior of AISI 4140 steel threaded components were studied. Axial fatigue tests at room temperature with a stress ratio of R = 0.1 were performed using standard and threaded specimens with and without nut interface under base material, cadmium, and zinc-nickel-coated conditions. Finite element analysis (FEA) was used, considering both elastic and elastoplastic models, to quantify the stress distribution and strain for threaded specimens with and without a nut interface. The numeric results were correlated to the experimental fatigue data of threaded components with and without the nut interface, to allow the oil & gas companies to extrapolate the results for different thread dimensions, since the experimental tests are not feasible to be performed for all thread interfaces. Scanning electron microscopy (SEM) was used to analyze the fracture surfaces. The stress concentration factor had a greater influence on the fatigue performance of threaded components than the effect of the Cd and Zn-Ni coatings. The fatigue life of studs reduced by about 58% with the nut/stud interface, compared to threaded components without nuts. The elastoplastic FEA results showed that studs with a stud/nut interface had higher stress values than the threaded specimens without a nut interface. The FEA results showed that the cracks nucleated at the regions with higher strain, absorbed energy, and stress concentration. The substitution of Cd for a Zn-Ni coating was feasible regarding the fatigue strength for threaded and smooth components.