Fillet Region Research Articles

Failure and root cause analysis of vehicle drive shaft

This paper investigates the failure mode and root cause of drive shaft failure in a vehicle through examination of the macroscopic and microscopic morphologies of the fracture surface, the chemical composition, metallographic analysis, and mechanical properties of the material, and theoretical finite element calculations of the drive shaft. The results show that fatigue was the dominant mechanism of drive shaft failure due to obvious benchmarks on the fracture surfaces. Fatigue cracks initiated from the root fillet region of the spline gear. The absence of material defects in this region indicates that the main cause of fatigue cracks is attributable to a high stress concentration owing to the small geometrical dimensions of the root fillet. Meanwhile, the poor quality of the root fillet due to relatively high manufacturing tolerances also produces a higher stress concentration, and thus accelerates crack initiation and propagation. Furthermore, all the fatigue fractures occur on the right splines owing to higher stress amplitudes at this location. Improper stiffness matching between the left and right smooth shafts, which results in a larger torque transmitted to the right spline, is the root cause of the drive shaft failure. These results indicate that re-evaluating drive shaft design to ensure an equal stiffness between the two smooth shaft sections is recommended for a longer service life.

Tooth contact analysis of crown gear coupling with misalignment

In this paper, manufacturing methods are presented for crown gear coupling composed of a hub with longitude crowning and tip sphere teeth, and a sleeve with straight internal teeth. Complete geometrical mathematical models of tools are proposed, including the flank and tip fillet regions. The flank and root fillets of the hub and sleeve generated by the cutters are obtained based on the theories of differential geometry and gear mesh. An accurate method based on a tooth contact analysis technique is presented to determine the contact points (locations of the maximum interference or minimum clearance) and to analyze the crown gear coupling meshing with angular misalignment. In addition, the effects of misalignment angle and crowning depending on the displacement circle radius on the maximum interference, interference distribution and locations of the maximum interference in every angular position of the hub are discussed with an example. It is observed that the side edge contact of the hub tooth can be avoided by modifying the misalignment angle or displacement circle radius and that the location of the maximum value of the maximum interference during one rotation cycle of the hub tooth is around the pure tilted area.

Deposition and mobilization of lipids varies across the rainbow trout fillet during feed deprivation and transition from plant to fish oil-based diets

Identifying aquaculture feeding strategies that reduce the consumption of fish oil without sacrificing the cardioprotective lipid profile of the salmonid fillet will improve aquafeed economics and sustainability. Transitioning fish from a plant oil-based diet to a finishing diet rich in fish oil and long chain n-3 fatty acids (LCn3) for several weeks prior to harvest is effective at boosting the fatty acid profile of the whole salmonid fillet. This study determined whether the response to short-term feed deprivation and a finishing diet varies across different regions of the triploid rainbow trout fillet. Fish were placed on one of three feeding treatments: 1) FO: a fish oil (FO) diet for the entirety of the 20-week study, 2) VO/FO: a vegetable oil (VO) diet between weeks 1–12 then the FO diet for the final eight weeks, or 3) VO/fd/FO: the VO diet between weeks 1–12 followed by a two week period of feed deprivation before transitioning to the FO diet for the final six weeks. Fillets were divided horizontally into three sections (ventral, central, and dorsal) and the fatty acid profile of each was determined. There were unique responses to feed deprivation across fillet regions; the central region exhibited a loss of fatty acids, the dorsal region gained fatty acids, but there was no net gain or loss of fatty acids in the ventral region. The ventral and dorsal regions responded similarly to a high-FO finishing diet, increasing concentrations of fatty acids and LCn3, although not to levels observed in the FO treatment group. In contrast, the fatty acid profile in the central region remained largely unaffected by the finishing diet, with the exception of LCn3 in the VO/FO group that increased to levels comparable to the FO-treatment group. Expression of genes related to muscle atrophy (fbxo32) and LCn3 metabolism (fads5) also varied across different fillet regions and in response to dietary treatments. This study provides evidence for spatially distinct regulation of muscle growth and lipid metabolism that support region-specific physiological and metabolic responses to feeding strategies.

Experimental Investigation on High-Cycle Fatigue of Inconel 625 Superalloy Brazed Joints

The high-cycle fatigue performance and crack growth pattern of transient liquid phase-brazed joints in a nickel-based superalloy Inconel 625 were studied. Assemblies with different geometries and types of overlaps were vacuum-brazed using the brazing paste Palnicro-36M in conditions such as to generate eutectic-free joints. This optimal microstructure provides the brazed assemblies with static mechanical strength corresponding to that of the base metal. However, eutectic micro-constituents were observed in the fillet region of the brazed assembly due to an incomplete isothermal solidification within this large volume of filler metal. The fatigue performance increased significantly with the overlap distance for single-lap joints, and the best performance was found for double-lap joints. It was demonstrated that these apparent changes in fatigue properties according to the specimen geometry can be rationalized when looking at the fatigue data as a function of the local stress state at the fillet radii. Fatigue cracks were nucleated from brittle eutectic phases located at the surface of the fillet region. Their propagation occurred through the bimodal microstructure of fillet and the diffusion region to reach the base metal. High levels of crack path tortuosity were observed, suggesting that the ductile phases found in the microstructure may act as a potential crack stopper. The fillet region must be considered as the critical region of a brazed assembly for fatigue applications.

Implications of Substrate Geometry and Coating Thickness on the Cracking Resistance of Polymer-Based Protective Coatings

Welded steel T-sections of different weld fillet geometries coated with water ballast tank protective coatings were subjected to thermal cycling with a temperature range from 60°C to -10°C. Cracks developed in the coatings at the weld line, propagating longitudinally along it. The number of cycles required to create 1 mm cracks was strongly dependent on the weld geometry and the coating Dry Film Thickness (DFT). Finite Element Modelling (FEM) was employed to calculate thermally induced strain fields in the coatings subjected to the same temperature range. FEM predicted that the greatest strain concentrations are present at the coating surface within the weld fillet region. Increased DFT and decreased fillet radius leads to increased maximum principal strains. Numerical analysis predicts that greatest strain ranges promoting the earliest cracking/failure are found in thicker coatings applied to smaller weld radii. Experimental observations confirm this.

Influence of heat treatment conditions on bending characteristics of 6063 aluminum alloy sheets

Bending deformation behaviors of solution treated (ST), natural aged (NA) and T6 tempered 6063 aluminum alloy sheets were studied by three-point bending tests. The changes of bending force, interior angle, bending radius and sheet thickness in the fillet region were analyzed by experimental measurements and numerical simulations. The results showed that the bending characteristics were strongly dependent on the heat treatment conditions. The T6 alloy sheets were bent more sharply and local plastic deformation occurred severely in the fillet region. However, the ST and NA alloy sheets exhibited relatively uniform bending deformation and large bending radius. The bending force of T6 alloy was the highest, followed by the NA alloy and that of the ST alloy was minimum. After unloading, as compared with the ST and NA alloys, the springback of T6 alloys was markedly larger. The aging time showed a positive sensitivity on the springback and non-uniform bending deformability. The bending characteristics are attributed to the combined effects of yield strength, yield ratio and coefficient of neutral layer.

Optimization of Spur Gear Design to Reduce Stress

The objective of the study is to reduce the stress created in the root fillet region as the maximum stress concentration in gears occurs in the fillet. Therefore, stress relieving features have been created at an offset distance from the root fillet to reduce the stress. A Spur gear with involute profile is taken for the study. The application taken for the study is the gear used in terrain vehicles. The material of the gear is EN-353 grade Steel. Based on the compressive strengths and bending strengths, the spur gear is designed to the required application. The gear is modelled using the specifications obtained from the design calculations. The forces acting on the gear is calculated considering the application in which it is used. The gear is then analysed using the ANSYS WORKBENCH 14.0 software. It has been found that the maximum stress acts near the root fillet region. Hence, stress relieving features of circular and elliptical shapes are created at an offset distance from the root fillet. It has been found that the gear with elliptical stress relieving hole has the minimum stress than those of gears with other combinations. The next objective which is to reduce the mass of the gear is done by creating larger holes in the lower stress regions of the gear. The mass reducing features are created in the gears with stress relieving features and each gear has been subjected to analysis for the minimum amount of stress. It has been found that the value of stress is less in the gear with mass reducing holes but with no stress relieving feature. Thus, the stress acting on the root fillet region has been reduced by 20% by creating circular and elliptical holes. The other objective of mass reduction is satisfied by creating larger holes.

Effect of Fillet Rolling Load on the Fatigue Performance of a Micro-Alloy Steel Diesel Engine Crankshaft

Fillet rolling process is an effective method used to improve the fatigue performance of crankshafts by hardening the fillet region and inducing compressive residual stresses. This paper summarizes the work conducted to investigate the effect of rolling load on fatigue behaviour of a micro-alloy steel crankshaft used in diesel engine applications. Based on the staircase test methodology, component-scale resonant bending fatigue tests were conducted to obtain stress versus number of cycles curves and to evaluate the fatigue endurance limits of the crankshaft at un-rolled condition and fillet-rolled conditions at three different loads. Test data was analysed by Dixon-Mood method to calculate the endurance limits. Results showed that the endurance limit increased significantly with fillet rolling process in comparison to un-rolled condition. Endurance limit further increased with the increasing rolling load however with a limited extent above which excessive hardening deteriorates the fillet region; that is the workability limit. The outcomes of this study has shed light on the fillet rolling process to select the optimum rolling load for the used design and material conditions.

Finite Element Simulation of Bending Stress on Involute Spur Gear Tooth Profiles

This study investigated bending stress distribution on involute spur gear tooth profiles with pressure angle of 20 ̊ but different modules 2.5, 4.0 and 6.0 mm, using a finite-element-based simulation package - AutoFEA JL Analyzer. The drafting of the geometry for the three gear tooth profiles were implemented on the platform of VB-AutoCAD customized environment, before importing to the package. These were separately subjected to analysis for bending stresses for a point at the tooth fillet region with appropriate settings of material property, load and boundary conditions. With the same settings, the bending stresses were computed analytically using American Gear Manufacturers Association (AGMA) established equation. The results of the two approaches were in good agreement, with maximum relative deviation of 4.38%. This informed the confidence in the implementation of the package to investigate the variation of bending stress within the gear tooth profile. The simulation revealed decrease in the bending stresses at the investigated regions with increase in the module of the involute spur-gear. The study confirms that Finite element simulation of stresses on gear tooth can be obtained accurately and quickly with the AutoFEA JL Analyzer.

Deep drawing of cup shell by powder cavity flexible forming technology

A forming method named powder cavity flexible forming was proposed. It is a forming technology which uses powder medium instead of rigid punch or die to form sheet metals. Cup shells were successfully obtained by this technology. The theoretical calculation equation of forming load was obtained through mechanical analysis and the stress state in cup shells was analyzed by finite element simulation. The results show that powder cavity flexible forming technology can improve the forming limit of sheet metal. Compared with rigid die forming process, the thickness reduction in the punch fillet area significantly decreases and the drawing ratio increases from 1.8 to 2.2. The thinning compressive stress in the bottom of cup shell emerges, which makes the bottom of the cup shell in three-dimensional stress state and the stress in punch fillet region decrease due to powder reaction force, which can effectively inhibit the sever thinning of the sheet and prevent the generation of fracture defects.

Fatty acid partitioning varies across fillet regions during sexual maturation in female rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) are commonly reared as diploids (2N, two sets of chromosomes) or triploids (3N, three sets of chromosomes). Sexual maturation in 2N has negative effects on production efficiency, nutrient retention, and fillet quality. On the other hand, 3N female rainbow trout fail to develop gonads, thus enabling an efficient extended growth period when production of larger fillets is desired. The objective of this study was to determine how fatty acid (FA) profiles of various tissue types change throughout development in 2N and 3N rainbow trout, with an emphasis on the response of different fillet regions. Diploid and 3N female rainbow trout were comingled and harvested at 10, 18, and 22months post hatch (mph) and FA profiles of the viscera, fillet sections, and fillet trimmings were analyzed. Diploid fish were larger (P<0.05) than 3N at all sampling periods. Fillet yield was similar between 2N and 3N at 10 and 18mph, while fillet yield was greater in 3N at 22mph (P<0.05). Fillets were divided into four sections; ventral, central, dorsal and caudal. In the ventral, dorsal, and caudal fillets, FAs continued to accumulate with age (P<0.05), regardless of ploidy. However, in the 2N ventral fillet the rate of muscle growth outpaced deposition of saturated FAs between 18 and 22mph (P<0.05). In the 2N central fillet the concentration of most FAs decreased between 18 and 22mph (P<0.05) while they continued to increase in 3N. A similar interaction occurred in viscera tissue, in which there was no net accumulation of FAs in 2N between 18 and 22mph while 3N continued to deposit FA. Saturated FAs were most susceptible to reduced concentrations during sexual maturation, suggesting an increased reliance upon these lipids as a source of energy to support gonad development. In conclusion, there was a disproportionate mobilization of FAs both across and within tissues, with lipids in the viscera and central fillet being particularly vulnerable to mobilization during sexual maturation.

Effect of Adjacent Teeth Load on Bending Strength of High Contact Ratio Asymmetrical Spur Gear Drive

This paper describes methodology for predicting the bending stress of the spur gear accurately by including the load on the adjacent teeth for high contact ratio asymmetric spur gear drive. Higher contact ratio is obtained by enlarging the addendum from the standard addendum value where as the asymmetric is achieved by keeping various pressure angles (170, 200 and 220) at non drive side while the drive side pressure angle was kept as 200. The bending stress developed for the given load according to the load sharing calculated by using stiffness based method along with the effect of adjacent teeth loads are explored in this work. Computer aided design tool is used for generating the gear tooth profile and ANSYS is used to carry out the finite element analysis. The result shows that the maximum bending stress level in a mesh cycle is increased when the load on adjacent teeth are taken into account. The higher pressure angle at the non-drive side yields lesser stress at the fillet region when compared to the lower pressure angle.

Effects of tooth plastic inclination deformation due to spatial cracks on the dynamic features of a gear system

Spatial cracks may occur in the gear tooth fillet region due to the presence of non-uniform load distribution, local non-homogeneity of material quality, and potential misalignment of gear shafts and bearings, among other things. Previous researchers have discussed the tooth plastic inclination deformation due to a uniform depth planar crack. To the best of the authors’ knowledge, the non-uniform depth spatial crack has not been included in previous analyses. This paper presents a tooth plastic inclination model to analytically calculate the three-dimensional distributions of tooth plastic deformations due to spatial cracks based on the slicing principle. In addition, their influence on the dynamic performance of a spur gear pair was studied by building six-degrees-of-freedom model. The simulated results reveal that the non-uniformity of the crack depth along the tooth width direction could lead to uneven dynamic load distributions on the cracked tooth flank, which may excite a tilting motion of the gears. The larger the tooth plastic inclination angle, the higher the amplitude of the tilting motion that would be excited.

A Study on the Fatigue Life of a Composite T-Joint Subjected to Transport Aircraft Spectrum Loads

In this study, an experimental study was carried out on the fatigue life of a carbon fiber composite (CFC) T-joint under a standard transport aircraft spectrum load sequence and compared with predictions based on empirical methods. The co-cured CFC T-joints of size 175 mm × 150 mm × 2.7 mm skin (flange) and centrally placed 2 mm thick, 120 mm high web, were fabricated by autoclave process. The fatigue life in terms of number of load blocks required to fail was experimentally determined under a standard transport aircraft spectrum load sequence, mini-TWIST at various reference loads. All the tests were conducted in a 100 kN servo hydraulic test machine using a specially designed test fixture. The stiffness degradation of the T-joint was monitored during the spectrum fatigue test at regular intervals from the load–displacement data. The fatigue life was observed to increase with decreasing reference load of the spectrum load block. The fatigue damage was observed to initiate as cracks in the fillet region and grow in both flange and web directions. The stiffness was observed to gradually decrease with load blocks indicating the initiation and growth of fatigue damage in the T-joint. Further, the fatigue life under mini-TWIST load sequence was predicted by empirical method using constant life diagram of the material and was observed to correlate reasonably well with experiments.

The effects of spur gear tooth spatial crack propagation on gear mesh stiffness

Due to the presence of non-uniform load distribution, local non-homogeneity of material quality and potential misalignment of gear shafts and bearings, etc., spatial cracks may occur in the fillet region of spur gear teeth. These cracks will eventually propagate in three distinct directions either individually or simultaneously. These directions are the crack depth direction, the tooth width direction and the tooth profile direction. In this paper, an analytical investigation of the influence of spatial crack propagation on the time-varying Gear Mesh Stiffness (GMS) and also the Load Sharing Ratio (LSR) is presented. In order to quantitatively define the spatial crack propagation scenario, the involute spur gear tooth geometry cut with a typical double rounded rack is first determined using two parametric equations. The effects of some gear design parameters and initial crack locations on GMS and LSR are determined and compared with the results from previous papers that used Finite Element Analysis (FEA) in order to verify the proposed analytical model. Finally, a quasi-parabolic crack propagation scenario is assumed, in which 7 propagation cases and 3 typical crack growth paths on the tooth surface are investigated to determine their effect on the maximum reduction of GMS when compared to normal conditions. The results are important for the dynamic simulation of gear transmission behavior, and consequently helpful for the monitoring of gearbox working condition and detection of early crack damage that may exist in gear sets.

Experimental and numerical investigation of composite bolted π-joint subjected to bending load

This present work investigated the failure mechanism of a novel composite bolted π-joint subjected to bending load by experimental and finite element simulation. A test sample manufactured by resin transfer moulding process (RTM) was tested. A 3D progressive damage model developed in ABAQUS/Standard was used to simulate the failure of the π-joint. Based on good correlation of failure load and damage distribution between experimental results and FE prediction, further investigation was extended to the effect of two primary assembly clearances on mechanical behavior of the π-joint. The study results reveal that delamination of the fillet region in L-preform is the π-joint's failure mode. Moreover, the assembly clearances have little effect on the failure load of the joint.

Static mechanical properties of hybrid RTM-made composite I- and Π-beams under three-point flexure

This paper deals with three-point flexure tests on hybrid I- and Π-beams, made out of multi-layer carbon fiber/epoxy resin (including twill woven fabric CF3031/5284 and unidirectional cord fabric U3160/5284) reinforced composites, processed using the RTM (resin transfer molding) technique. Static bending properties were determined and failure initiation mechanism was deduced from experimental observations. Failure mode of the tested hybrid RTM-made I-beams can be reckoned to be characteristic of the delamination from the cutout edge within the web and the debonding propagation along the interface between the inverted triangular resin-rich zone and the adjacent curved web until local buckling within the curved webs around the conjunction fillet region. In contrast, as distinct from hybrid RTM I-beams subjected to three-point bending loading, hybrid RTM-made Π-beams in three-point flexure tests experienced the resin debonding in the inverted triangular resin-rich zones and the debonding propagation along the interface between the inverted triangular resin-rich zone and the adjacent curved web until complete separation of the curved web from the flange. Progressive damage models (PDMs) were presented to predict failure loads and process of hybrid RTM-made I- and Π-beams under three-point flexure. Good correlation was achieved between experimental and numerical results.

Crankshaft failure analysis of a boxer diesel motor

This paper reports a failure mode analysis of a boxer diesel engine crankshaft. Crankshafts are components which experiment severe and complex dynamic loadings due to rotating bending combined with torsion on main journals and alternating bending on crankpins. High level stresses appear on critical areas like web fillets, as well as the effect of centrifugal forces and vibrations. Since the fatigue fracture near the crankpin-web fillet regions is one of the primary failure mechanisms of automotive crankshafts, designers and researchers have done the best for improving its fatigue strength. The present failure has occurred at approximately 2000 manufactured engines, and after about 95,000km in service. The aim of this work is to investigate the damage root cause and understand the mechanism which led to the catastrophic failure. Recommendations for improving the engine design are also presented.

OPTIMIZATION OF A CRANKSHAFT IN CRANK-PIN WEB FILLET REGION FOR IMPROVING FATIGUE LIFE

a crankshaft is often designed with a fillet radius to improving fatigue life of crankshaft. The fatigue life of crankshaft is depending on the proper fillet radius. This fillet radius is changes than fatigue life is also changes of crankshaft. In most of the time fatigue failure is occur in crank-pin web fillet region. The crankshaft fillet rolling process is one of the ommonly adopted methods in engineering to improve fatigue life of the crankshaft. A finite element analysis is implemented to approximate the stress distribution induced in the crankpin fillet region. The modelling of crankshaft is created by Creo-parametric. Finite element analysis is performed to obtain the variation of stress at critical locations and fatigue life of the crank shaft using the ANSYS software and applying the boundary conditions. Existing crankshaft results from finite element analysis is comparing with the experimental result after that boundary conditions are satisfied than only changes in model of crankshaft to improvement in fatigue life. This work in doing for optimization of a crankshaft in crank-pin web fillet region with fatigue life as well as to study a relation between fillet radius/diameter of crankpin to fatigue life.

Fatigue Failure of LP Compressor Blade in an Aero Gas Turbine Engine

Failure of low-pressure compressor rotor blade in an aero gas turbine engine is analyzed to determine its root cause. Forensic and metallurgical investigations are carried out on the blade failed. The failure of the first stage rotor blade is found to be the first in the chain of events that led to the engine failure. The mode of failure in the blade is found to be fatigue and has originated from the mounting lug fillet region due to high stress concentrations. The failure has caused extensive damages in low-pressure compressor module and also in downstream modules as a secondary effect. Remedial measures are also suggested to prevent such failures.