Failure of planetary pinions in earth moving equipment—a failure analysis approach

A series of failures of planetary pinions occurred in the final drive epicyclic gearbox of large trucks used in underground mining. A metallurgical analysis indicated that failure had occurred by internal rupture of the gear. This was attributed to poor heat treatment procedures used in case hardening the gear. This had induced high residual stresses just below the case/core interface, leading to the internal rupture of the gear.     

Fracture failure analysis of hard–thick sandstone roof and its controlling effect on gas emission in underground ultra-thick coal extraction

In underground coal extraction of fully mechanized caving, the overlying hard–thick sandstone main roof could control the failure extent and the movement evolution of the entire overburden strata. The instantaneous failure of the hard–thick sandstone main roof possibly causes strata pressure behaviors, rock-bursts and abnormal gas emissions, which may result in equipment damages and casualties. Tashan coalmine was chosen as a field case study base because of its super great mining height (SGMH) and the overlying hard–thick sandstone roof (HTSR). This mine has experienced a great deal of damaging hydraulic support and abnormal gas emission accidents caused by strata pressure behavior. The fracture failure analysis was analyzed based on “Key Strata Theory” and numerical simulation results. The hard–thick sandstone main roof could perform as a very large double-sided embedded rock beam in the primary fracture and as a cantilever-articulated rock beam in periodic fracture, simultaneously generates a huge hanging space in the gob. The fracture failure of the hard–thick sandstone main roof causes a permeability enhancement in the adjacent rock-coal strata and near face coal seam. The substantial amounts of gas stored in the remaining coal, surrounding rock strata and adjacent coal seams rush out and aggregate in the caved and fissure zone of the gob, thereby forming a huge gas cloud. The disasters due to coupled strata pressure behavior and abnormal gas emissions, which primarily occurred after primary and periodic fracture failure, are predominantly caused by the instantly fracture of main roof. When the main roof reached the ultimate broken span and underwent, rotation and collapse, substantial amounts of gas accumulating in the gob escaped to the working face under the extrusion and impaction of the caving rock strata, which easily produced abnormal gas emissions, some of which exceeded the statutory limit. Shortening the length of the HTSR failure span using hydraulic presplitting and decreasing the gas content of the coal seam using gas drainage technology are recognized as two effective approaches to solve this issue.     

Composites fractography without an SEM — the failure analysis of a CFRP I-beam

This paper describes the fractographic analysis of a typical aerospace structural element made from CFRP. The methods of fracture characterization and failure sequencing are described in detail and the cause of ultimate failure successfully determined using low-power optical microscopy only.     

Impact failure of beams using damage mechanics: Part II—Application

The analytical model developed in Part I (Int J Impact Eng 2002;27(8):837–61) using continuum damage mechanics is used in this paper to predict the displacement to failure of beams subjected to static or dynamic loads producing large plastic strains. The beams, which were made of a ductile, strain rate sensitive material, were loaded at different positions on the span, by two tup geometries travelling with initial impact velocities up to 15 m/s. A reasonable correlation is obtained between the theoretical predictions and the experimental results for the displacements to failure.     

Voltammetry as a tool for monitoring micellar structural evolution?

Self-assembled systems such as micelles and liquid crystals are currently of interest as templates for the controlled formation of nanoscale structures. Knowledge of the mesophase structure, structural evolution, and interparticle interaction is of great importance in understanding the behavior of such systems especially for applications such as nanoreactors. Here, we compare the use of cyclic voltammetry, chronoamperometry, and the rotating disk electrode (RDE) for the determination of micellar hydrodynamic radii and show that only the steady-state RDE yields values directly comparable with nonelectrochemical techniques. The RDE is applied for the determination of cetyltrimethylammonium chloride micellar structure and observing micellar structural evolution as well as evaluating the usual intermicellar interactions. The results clearly show (a) the collapse of the micellar shear plane toward the hard-sphere surface with increasing electrolyte concentration, (b) the electrolyte-dependent spherical expansion of the micellar hard-spheres due to increasing aggregation (N) number, (c) the structural transition from spherical to rodlike micelles, and (d) micellar elongation. As well as structural evolution, the evolutionary changes in interaction processes are also observed, i.e. the transition from Coulombic interactions to excluded volume interaction. This paper describes in detail the voltammetric measurement of these processes and explicates the necessary experimental conditions for successful observation of micellar structural evolution.     

Safety analysis in design—Evaluation of a case study

Safety analysis was applied in the design of a section at a paper mill. The case study involved analysis of layout, transport system, machines, and a number of different activities. The purpose of the analysis was to find measures to decrease occupational accidents. Three years after the installation was finished the occurrence of accidents was investigated. There was a 56% decrease in the number of accidents; the number of working days lost due to accidents was diminished by 75% as compared to 4 years preceding. The results of the safety analysis were also evaluated with respect to the accidents which had occurred. The methods for safety analysis seem to have been efficient in identifying hazards. The general conclusion of the study is that safety analysis can be an effective tool to decrease occupational accident risks.     

Impact failure of beams using damage mechanics: Part I—Analytical model

A simple theoretical method, which is based on ductile damage mechanics and which retains strain rate effects, is presented for predicting the failure of beams made from a perfectly plastic material and subjected to impact loads. For this class of materials, the strains can be estimated by defining a hinge length. The definition adopted here leads to reasonable predictions for the plastic strains and the strain rate, as shown by comparing the results with numerical calculations and experimental data. The equivalent strain and the strain rate can be used in the damage model to predict the failure of beams, as shown in a companion paper (Alves, Jones, Int J Impact Eng 2002;27(8):863–90).     

Buoyancy-driven fluid flow and heat transfer in a square cavity with a wavy baffle—Meshless numerical analysis

The meshless local Petrov–Galerkin method is implemented to simulate the buoyancy-driven flow and heat transfer in a differentially-heated enclosure having a baffle attached to its higher temperature side wall. To execute the proposed numerical treatment, the stream function–vorticity formulation is employed and a unity weighting function is applied for the weak form of the governing equations. In this meshless numerical approach, the field variables are approximated using the MLS interpolation technique. Being attested through comparing the results of two test case simulations with the results of either an analytical or a conventional numerical approach, the MLPG method is applied to investigate the buoyancy-driven flow and heat transfer in the baffled cavity. The present analyses involve a parametric study to implicate the effects of the baffle undulation number, amplitude, location on the wall, and the system Rayleigh number. The investigation reveals the eminent participation of the baffle in transferring heat from the hot wall. The analyses disclose an increase of the hot wall average Nusselt number by elevating the location of the baffle on the hot wall. This average Nusselt number descends with increasing the baffle amplitude. The cold wall average Nusselt number increases as the baffle number of undulation augments.     

Mechanics of crack curving and branching — a dynamic fracture analysis

A comparative study on crack curving and branching criteria in dynamic fracture mechanics shows that the criteria based on advanced cracking concept correlated best with available experimental data. The crack branching criterion requires as a necessary condition, a critical dynamic stress intensity factor, K _Ib, and a sufficient condition involving the crack curving criterion. The criteria are used to predict crack curving and crack branching in dynamic photoelastic experiments involving Homalite-100 and polycarbonate fracture specimens, as well as bursting steel and aluminum pipes.

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Résumé Une étude comparative sur les eritères d'incurvation et d'arborescence d'une fissure en mécanique de rupture dynamique montre qu'un critère basé sur le concept de fissuration avancée présente la meilleure corrélation avec les données expérimentales disponibles. Le critère d'arborescence d'une fissure requiert comme condition nécessaire un facteur d'intensité de contrainte dynamique critique, K _Ib, et comme condition suffisante un critère tenant compte de l'incurvation de la fissure. Les critères sont utilisés pour prédire l'incurvation et l'arborescence d'une fissure au cours d'expériences photo-élastiques en condition dynamique mettant en oeuvre de l'Homalite 100 et du polycarbonate ainsi que des tubes d'acier et d'aluminium en cours d'explosion.

     

Mathematical and physical aspects of material failure: A tribute to Jean-Baptiste Leblond’s odyssey in fracture mechanics

International Journal of Fracture -     

Gifford-McMahon cycle — a theoretical analysis

A theoretical analysis of the Gifford-McMahon cycle is presented. Expressions for the ideal refrigeration produced and the figure of merit are developed. Various losses occurring in a real machine are considered and equations to account for these losses are derived. Results are presented in graphical form.     

Multiscale tool–fabric contact observation and analysis for composite fabric forming

This paper provides measurements and analysis at the meso and microscopic scales of the real contact area between twill carbon fabric and a flat glass counterface. The mesoscopic contact area associated with tow contacts is about 55–75% of the nominal area. However, the total real contact length within the tow contacts, associated with microscopic contact at the fibre level, is only 4–8% of the idealised contact conditions with parallel touching fibres, for a nominal contact pressure of around 2 kPa. The dependence of real contact area on fabric shear angle is also investigated. The estimated real contact pressure is 15,000 times higher than the nominal contact pressure. Models or experiments of friction in composites forming which do not take into account the real contact situation, which is very far from an idealised packing arrangement, may fail to capture the essential tribological mechanisms.     

Preparation and evaluation of a timolol maleate drug–resin ophthalmic suspension as a sustained-release formulation in vitro and in vivo

Abstract

The aim of this work was to assess the performance of resin as an ocular delivery system. Timolol maleate (TM) was chosen as the model drug and an ion exchange resin (IER) as the carrier. The drug–resin complex was prepared using an oscillation method and then characterized regarding particle size, zeta potential, morphology, and drug content. After in vitro drug release study and corneal permeation study were performed, in vivo studies were performed in New Zealand albino rabbits using a suspension with particles sized 4.8?±?1.2?μm and drug loading at 43.00?±?0.09 %. The results indicate that drug released from the drug–resin ophthalmic suspension permeated the cornea and displayed a sustained-release behavior. Drug levels in the ocular tissues after administration of the drug–resin ophthalmic suspension were significantly higher than after treatment with an eye drop formulation but were lower in body tissues and in the plasma. In conclusion, resins have great potential as effective ocular drug delivery carriers to increase ocular bioavailability of timolol while simultaneously reducing systemic drug absorption.     

Stress and failure analysis of crimped metal–composite joints used in electrical insulators subjected to bending

Experimental and numerical investigations are carried out on metal/fibreglass-reinforced-plastic joints integrated in electrical insulators subject to bending. Numerical stress and strain distributions through the bond are calculated with a solid 3D finite element model and the damage initiation in the composite is highlighted. The simulations are compared to experimental data obtained from several joint specimens tested under bending on an experimental setup equipped with strain gauges and a six-channel acoustic emission system. Good correlation between the finite element predictions and the test results is found. The investigations have identified the stress concentrations in the rod, the onset of damage when the load–displacement curve characterizing the bending test deviates from linearity, and the different failure mechanisms.     

Atomistic Simulation of Phase Transformation and Fracture in Ordered Intermetallics

A review of computer simulations carried out at our Center for Materials Simulation applied to stud-ying the different atomistic processes of fracture and displacive (martensitic) transformations is pres-ented.Since these processes can happen extremely rapidly and involve only a small number of atomsinitially,they are ideally suited for molecular dynamics type simulations which can currently onlyspan times of the order of one nanosecond and involve at most a million atoms.A method is alsopresented for simulating much larger samples for much longer times through the use of theMonte-Carlo technique combined with a Ginzburg-Landau free energy functional,where the rele-vant material parameters are determined from molecular dynamics runs on the same alloy system.Asummary of studies on fracture simulations in the ordered intermetallics NiAI and RuAl is given,aswell as a discussion of the observation and analysis of the heterogeneous nucleation of themartensitic transformation in NiAI which shows localized soft mode phenomena.It is concluded thatcomputer simulations,whether of the atomistic molecular dynamics type or of the larger scaleMonte-Carlo variety,are rapidly becoming of greater and greater use in understanding the propertiesof solids under a wide rancle of temperature and stress conditions.     

Fracture analysis of turbine disks and computational–experimental background of the operational decisions

In this paper, fatigue crack growth under operation conditions for rotating disks of aircraft gas turbine engines is analyzed. Initiation and growth of surface cracks for compressor disks made from two-phase titanium alloy has occurred in a disk and blade attachment. Damage accumulation and growth for turbine disks made from steel took place on the inner surface of hole in a hub of wheel. Suggested approach of simulation modeling is used for an analysis and prevention of operation failures of engine rotating components. In the approach described, finite-element models (FEMs) in two and three dimensions were applied to the study of stress–strain state and stress intensity factors for the basic configurations of compressor and turbine disks and their operational damage. Proposed design modifications and repair technologies to existing in-service aircraft gas-turbine engine rotating components are analyzed and substantiated on a static strength and fatigue life basis.     

Mechanical property of magnesium alloy sheet with hardening deterioration at warm temperatures and its application for failure analysis: Part II – failure analysis

The mechanical properties of a thin AZ31B Mg alloy sheet (with the thickness of 0.5 mm) were characterized for its anisotropy, temperature-dependent hardening (including its deterioration) and strain rate sensitivity based on simple tension test data measured at 100 °C, 150 °C, 200 °C, 250 °C, respectively, in Part I. As for anisotropy, simple tension tests were performed along three (rolling, transverse and in-between) directions to calibrate the Hill1948 yield function. As for temperature-dependent hardening, hardening as well as its deterioration (or softening) behavior observed beyond the uniform elongation limit was numerically characterized based on the inverse calibration method, in which strain rate sensitivity was also considered. The mechanical properties were confirmed to properly predict failure by strain localization for all the simple tension tests involved in the characterization procedure. Ultimately, the mechanical properties characterized in Part I were applied in Part II to analyze the failure by strain localization in the cross-shaped cup drawing tests developed as the benchmark problem for the NUMISHEET2011 conference [1]. The results showed that the mechanical properties with hardening deterioration properly predicted failure, while hardening without deterioration (obtained following the common practice) did not, confirming the importance of including the hardening deterioration in tensile property characterization, especially to predict forming failure by strain localization.     

Microstructure and Fracture Morphology in the Welding Zone of T91 Heat—resisting Steel Used in Power Station

Microstructure performance in the welding zone of T91 heat-resistant steel under the condition of TIG welding was researched by means of metallography, X-ray diffraction and scanning electron microscope (SEM). Experimental results indicated that microstructure of T91 weld metal was austenite + a little amount of S ferrite when using TGS-9cb filler wire. Substructure inside the austenite grain was crypto-crystal lath martensite, on which some Cr23C6 blocky carbides were distributed. The maximum hardness (HRC44) in the welding zone is near the fusion zone. There existed no obvious softening zone in the heat-affected zone (HAZ). For T91 steel tube of $63 mmx5 mm, when increasing welding heat input (E) from 4.8 kJ/cm to 12 5 kJ/cm, fracture morphology in the fusion zone and the HAZ changed from dimple fracture into quasi-cleavage fracture (QC). Controlling the welding heat input of about 9.8 kJ/cm is suitable in the welding of T91 heat-resistant steel.     

High Temperature Creep and Fracture Behavior of a Directionally Solidified Ni-base Superalloy

The tensile creep-fracture properties of DZ17G. a directionally solidified superalloy, were inves-tigated at 830~ 900℃. The results show that all of the creep curves exhibit negligible primary creep, relatively little steady-state creep and dominant tertiary creep stage. The higher apparent activation energy for creep (540 kJ/mol ) suggests that the creep is controlled by Orowan bowing process. A large ratio of the fracture time to the onset time of tertiary creep is the consequence of microstructure change, i.e., γ particles oriented coarsening parallel to the applied stress axis.The creep fracture data follow the Monkman-Grant relationship. The transgranuIar fracture mechanism proposed on the basis of the metallographic examinations is the linkage of the creep cracks which initiate at the discontinuities with the microstructure (such as the cast porosity,and the carbide/matrix intedece) and also at the specimen surface, that propagate along the γ/γ intedece with perpendicular to the applied stress axis, and the process of crack propagation can be described by the Tien model.