Main Damage Mechanisms Research Articles

Microscopic investigation of failure mechanisms in AA5182-O sheets subjected to electro-hydraulic forming

In this study, damage mechanisms in AA5182-O aluminium sheets are investigated using quasi-static (QS) Marciniak tests and high strain-rate electro-hydraulic forming (EHF) process. The results confirm that void nucleation, growth and coalescence are the main damage mechanisms of AA5182-O at both high and low strain rates. The EDS analysis suggests that cracking of Al3(Fe-Mn) intermetallic particles is the main source of void nucleation, whereas Mg2Si particles do not majorly influence void formation. Void growth analysis suggests that specimens deformed under QS conditions contained more voids in areas away from the sub-fracture surface but specimens deformed at high strain rate exhibit more significant rate of void growth close to sub-fracture areas. Void formation is suppressed by increasing the applied energy in EHF. And more significantly, the growth of voids is suppressed due to the high-velocity impact of the sheet against the die which plays an important role in increasing formability of AA5182-O aluminium sheet in EHF process. When the void percentage increase remains less than about 0.5% AA5182-O can be formed safely. However, when the void percentage increases beyond 0.6–0.8% fracture becomes inevitable.

A study on friction and wear reduction due to porosity in powder metallurgic gear materials

It has been widely acknowledged that controlled texturing on a surface can contribute to friction and wear reduction at lubricated sliding contact interfaces. This paper investigates the influence on friction and wear of different pore size distributions of powder metallurgy gear materials. The pore sizes are controlled by different densities of the powder metallurgic materials. Two different kinds of powder metallurgy (PM) gear materials were applied and a standard gear material are used as a reference. The friction and wear coefficients of PM materials sliding on PM materials increase with increasing pore size. The friction and wear coefficients of regular steel sliding on PM materials decrease with increasing pore size. No matter what the material of the disc, peeling is one of the main damage mechanisms of powder metallurgy pins with the biggest porosity.

Removing Fines-Migration Formation Damage in the Putumayo Basin in Colombia

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 178996, “Removing Formation Damage From Fines Migration in the Putumayo Basin in Colombia: Challenges, Results, Lessons Learned, and New Opportunities After More Than 100 Sandstone-Acidizing Treatments,” by Wildiman Reinoso, Fredy Torres, and Manuel Aldana, Grantierra, and Pablo Campo, Emilce Alvarez, and Erika Tovar, Halliburton, prepared for the 2015 SPE International Conference and Exhibition on Formation Damage Control, Lafayette, Louisiana, USA, 24–26 February. The paper has not been peer reviewed. To date, more than 100 sandstone-acidizing treatments have been performed in several Colombian oil fields, targeting the Villeta and Caballos Formations in the Putumayo Basin. Fines migration has been the main damage mechanism treated with this type of chemical stimulation. This paper summarizes a wide variety of sandstone-acid-stimulation case histories, highlighting aspects such as mechanical conditions and operational practices. Introduction The Putumayo Basin is located in south-ern Colombia. The Putumayo Basin shows a stratigraphic sequence containing Early Cretaceous (marine) to Miocene/Pliocene sediments (fluvial). Fig. 1 illustrates the location of the Putumayo Basin. Sand Villeta Formation The T Sand samples examined are fine-to medium-grained sandstones. They are composed primarily of quartz grains cemented primarily with quartz overgrowths and authigenic clays. Rare-to-minor cements include solid hydro-carbon, pyrite, and dolomite. X-ray-diffraction (XRD) analyses show that all of the sandstone samples are composed primarily of quartz and clay minerals. Feldspars are absent from all but one sample. Given that virtually all of the framework grains are quartz, with possibly minor argillaceous grains, the sand-stone is classified as quartzarenites. Scanning-electron-microscope (SEM) photographs show authigenic kaolinite filling intergranular zones and possibly replacing grains. Caballos Formation Samples in this formation are all sand-stones. Estimated average grain size ranges from very fine sand to medium sand. The framework grain suite is dominated by quartz. The grains are cement-ed primarily by quartz overgrowths and authigenic clays. XRD determined that all of the samples are composed primarily of quartz and clay minerals. Feld-spars are rare to absent from these sand-stones, confirming that virtually all of the framework grains are quartz and the sandstones should be classified as quartzarenites. Clay-mineral content averages 7.8%, with illite and mixed-layer illite/smectite more common than kaolinite. SEM photos show that these clays are authigenic.

Formation and growth of voids in dual-phase steel at microscale and nanoscale levels

Due to forming processes of the upcoming manufacturing technology of sheet-bulk metal forming, where bulk forming operations are applied to sheet metal, ductile damage occurs due to high triaxial stress and strain states in the material. To consider this type of damage in models for an optimized process design, a description of the critical material state is required, taking the main damage mechanisms into account. In comparison to single-phase materials, where voids nucleate mainly at grain boundaries and triple junctions, in dual-phase materials also phase boundaries or the movement of different hard phases due to forming process contribute to ductile damage. In this study, the mechanisms of nucleation and growth of voids were analyzed in a dual-phase steel DP600 at different strain states and forming temperatures. By specimen preparation using ion-beam slope cutting and scanning electron microscopy, it was possible to observe at nano- and microscale voids, cracks, and elements of deformation reliefs. A correlation between the shape of voids and their location in the crystal lattice was found, whereby the mechanisms of their nucleation, growth, and coalescence could be described.

Pathogenetic aspects of the development of acute focal cerebral ischemia

Current concepts on the main mechanisms of brain damage in ischemic stroke are considered. Chemical regulation of physiological and pathological processes of maintaining cellular pool is supported by a multistep system that included compounds of different structure and complexity. A complex assessment and comparison of the processes taking place during the development of acute local cerebral ischemia (necrosis, apoptosis, autoimmune inflammatory reaction, neuroplasticity) can help in the objectification and prognosis of individual characteristics of the course and outcome of ischemic stroke. Understanding of the cascade of events that occur during the acute ischemic damage is critical for determining current and future diagnostic and therapeutic approaches.

Damage micromechanisms in a hot dip galvanized steel

Abstract: Hot-dip galvanizing is one of the most used methods to apply zinc-based coatings on steels in order to provide sacrificial protection against corrosion over all the steel surface. The aim of this work is the analysis of the hot dip zinc coated steel plates mechanical properties by means of a non-standardized bending test performed minimizing both the bending moment differences along the bending axis and the interactions between the clamping system and the specimen coating. Bending tests are performed both on non-coated and on hot dip zinc coated plates, correlating the measured variables (applied load and crosshead displacement) with the bending moment and the specimen bending angle. Tests are characterised by a good repeatability. Results show that the main damaging mechanisms depend on the different mechanical behaviour of the intermetallic phases and on their thickness. For all the investigated coating conditions, radial cracks are observed. They initiate corresponding to the Γ phase and propagate up to the ζ-η interface. The coating thickness increase implies both an increase of the importance of the cracks in δ and ζ phases and the presence of cracks at ζ-η interfaces.

Compressive behavior and damage evaluation of a PBX substitute material

ABSTRACTIn this work, a polymer-bonded explosive (PBX) substitute material was made of sugar granules and polymer binder with a weight proportion of 90:10. The damage evolution and mechanisms under monotonic and repeated compression were studied in detail by adopting radiation x-ray computed tomography, scanning electronic microscopy, and a laser particle size analyzer. It is found that the initial pores and cracks from the granule breaking represent the main mechanisms of damage. The granule size and porosity decrease, while the damage parameter increases with the increasing applied strain. They are responsible for the damage evolution described by damage parameter D as a function of applied strain. The microscopic observation and macroscopic measurements are correlated quantitatively, which reveals the compressive behavior of the PBX substitute material.

The role of the surface morphology and segmented cracks on the damage forms of laser re-melted thermal barrier coatings in presence of a molten salt (Na2SO4 + V2O5)

Hot corrosion behaviour of yttria-stabilized zirconia thermal barrier coatings (TBCs) with various segmented cracks and surface morphologies, obtained using ultrasonic-assisted laser re-melting, was investigated during exposure to Na2SO4+V2O5 salt at 1100°C. It is demonstrated, that the damage types of TBCs were significantly affected by segmented cracks and surface morphology. Four main damage mechanisms: (i) chemical reaction, (ii) Coefficient thermal mismatch stress, (iii) oxidation of bond coating and (iv) intergranular corrosion, based on the observed transport behaviour of oxygen and molten salt, stress-tolerance and self-healing of various segmented cracks, were discussed to account for the failure behaviour.

Experimental study on microscopic formation damage of low permeability reservoir caused by HPG fracturing fluid

Hydraulic fracturing has become an important stimulation technique for low/ultra-low permeability reservoirs. Research on formation damage caused by fracturing fluid has mainly focused on permeability, sensitivity, fracturing fluid and clay minerals. However, little attention has been devoted to the microscopic changes in pore structure and properties. In this paper, nitrogen gas-adsorption techniques were introduced to characterize the microscopic changes in pore structure. Meanwhile, contact angle testing and Scanning Electron Microscope (SEM) observations were also used to show the changes in wettability and surface morphology of cores, respectively. The results showed that the pore size distributions (PSDs) of low permeability cores were wide, with approximately 75% macropore volume. The obvious changes in PSDs of damaged samples occurred in the range of 2–5 nm and 30–80 nm. The specific surface area decreased, and the adsorbability of damaged samples declined, as well. Concentrated gel and solid residues were confirmed to be the main damage mechanisms for gel breaking liquids, which resulted in changes in composition and roughness, making the cores more hydrophilic. Based on the results of the analysis, the N2 adsorption technique is deemed appropriate for the study of reservoir formation damage when a certain amount of mesopores are present. Additionally, a new method of determining contact angles for porous media is also recommended.

Molecular Pathogenesis of Leprosy

Leprosy is a chronic infectious granulomatous disease caused by the obligate intracellular bacteria Mycobacterium leprae. M. leprae causes symptoms in the skin, peripheral nerves, and other tissues. Type 1 (reversal reaction) and type 2 (erythema nodosum leprosum) lepra reactions are the main mechanisms of skin lesions, nerve damage, and other types of tissue damages. Susceptibility to mycobacterial infection and the clinical presentations of the disease are associated with aberrant host immune response, which forms the spectrum and pathologic manifestations of the disease.

Swing Friction Behavior of the Contact Interface Between CoCrMo and UHMWPE Under Dynamic Loading

CoCrMo alloy and UHMWPE have been widely used in knee joint prosthesis implantation materials. In this paper, swing friction behavior of the contact interface between CoCrMo alloy and UHMWPE is studied under dynamic loading. Swing friction characteristic and damage mechanism are discussed. The results show that swing friction coefficients increase with the rising of maximum normal load and swing angular amplitude. Unloading-standing could play alleviative roles in friction and wear to a large degree. As the cycle number gradually increases, the surface roughness of UHMWPE decreases, while the roughness of CoCrMo increases. During the swing friction, the main damage mechanism of CoCrMo is abrasive wear and the main damage mechanisms of UHMWPE are abrasive wear, fatigue wear and plastic deformation. Besides, it is easier to generate surface damages with small angle and heavy load.

Dynamic analysis of fiber pullout mechanism in cementitious composites under harmonic pullout displacement: analytical approach

Fiber pullout from the concrete matrix is a main characteristic damage mechanism which is observed in cementitious composites, like textile reinforced concrete and fiber reinforced cement composites, and it affects their mechanical behavior under static and dynamic loads. In this paper, an appropriate analytical model of the fiber pullout mechanism is proposed and closed-form analytical solutions are provided under a dynamical excitation of prescribed harmonic pullout displacements at the fiber tip. The constitutive behavior of the matrix-fiber interface is provided by considering the damage behavior, where an elastic damage material model of the interface is employed. For comparison purposes, derived solutions from corresponding Finite-Element simulations of the fiber pullout mechanism are provided and compared with the obtained analytical solutions.

High Heat Flux Laser Testing of HfB2 Cylinders

Hafnium diboride (HfB2) is one of a family of ultra‐high temperature ceramics (UHTCs) which are being considered for application in environments with a substantial heat flux such as hypersonic flight. In order to characterize transitions in the material response with heat flux and therefore predict the in‐service behavior of UHTCs, a range of tests were conducted in which small cylindrical bars of HfB2 were laser heated using heat fluxes from 25 to 100 MW/m2. After testing, the external damage as well as damage observable in cross sections through the cylinders was characterized using photography, optical, and scanning electron microscopy. Experimental results were compared with finite element modeling of the heat flow, temperature distribution, and phase transition. Heat flux rather than total deposited heat was found to be the strongest determinant of the way in which damage develops in samples; for lower heat fluxes, the main damage mechanism is oxidation, progressing to oxidation‐induced melting and finally, at the highest heat fluxes, substantial ablation by melting irrespective of oxidation. The agreement between calculations and experimental observations indicates that such calculations can be used with confidence to guide the design of components.

A combined experimental and modelling study of indentation damage test on thin-film stacked structures

A combined experimental and modelling approach is developed to study the indentation damage test on the thin-film stacked structures. The mechanical properties of the top metal layer, the intermediate dielectric layer and the Si substrate in the structures are obtained through fitting the force-displacement curves from the modelling to those experimental results. The modelling of the thin-film stacked structures under indentation loading and unloading processes is then conducted to analyse the stress field and explain their indentation damage mechanisms. It is found that during the indentation loading stage, the fracture of mode II is the main damage mechanism for the through-thickness cracks in the intermediate Si3N4-Si dielectric layer. The locations of the maximum principle stress and shear stress correspond to the Si damage regions as observed in the experiment results. During the unloading stage, the fracture of mixed modes I and II is the main damage mechanism responsible for the delamination at the intermediate SiO2 dielectric layer and Si substrate interface. This study provides an understanding of the indentation damage mechanisms of the thin-film stacked structures, where cracking normally occurs at the brittle Si substrate or/and at the intermediate layer underneath the top metal layer. The application can be found in the area of the integrated circuit (IC) packaging, where those structures represent the metallization bond pad system in an IC device.

Nanomorphology of graphene and CNT reinforced polymer and its effect on damage: Micromechanical numerical study

Abstract The effect of morphology, shapes and distribution of nanoscale carbon reinforcement in polymers on their strength and damage resistance is studied using computational micromechanical modeling. A new software and approach were developed for the automatic generation of finite element unit cell models of nanocomposites with inclusions of arbitrary and complex shapes. The effect of curved, zigzagged, snake-like shapes of real carbon nanotubes, as well as re-stacking of graphene on the damage evolution was studied in the computational experiments based on the developed code. The potential of hybrid (carbon nanotubes and graphene) nanoscale reinforcement was studied with view on its effect of damage resistance. It was demonstrated that idealized, cylinder like models of carbon nanotubes in polymers lead to an underestimation of the stress concentration and damage likelihood in the nanocomposites. The main damage mechanisms in CNT reinforced polymers are debonding and pull-out/fiber bridging, while in graphene reinforced polymers the main role is played by crack deviation and stack splitting, with following micro-crack merging. The potential of hybrid (carbon nanotubes and graphene) nanoscale reinforcement was studied with view on its effect of damage resistance.

Rupture of intermetallic networks and strain localization in cast AlSi12Ni alloy: 2D and 3D characterization

Damage development during tensile straining of a cast AlSi12Ni alloy has been characterized by in situ SEM imaging and synchrotron X-ray microtomography. Two main damage mechanisms consisting of intermetallic particle rupture and decohesion of Al-Si interfaces were revealed. Particle rupture takes place already from the beginning of the deformation, while decohesion of Al-Si interfaces is more characteristic at later stages. It is shown that damage evolution in the alloy is closely related to the underlying geometry of the intermetallic phase, its clustered structure playing a double role in controlling strain localization in the matrix as well as the rupture sequence of the intermetallic phase itself. The latter shows that small clusters break-off from the complex intermetallic network before large clusters, in good agreement with their load carrying capacity determined by the local volume fraction of the intermetallic phase. Finite element modeling of the alloy's tensile behavior evidences that deformation bands formed in the alloy with complex structure are similar to those developed in a model particle reinforced metal-matrix composite, where the particles correspond to the clustered regions of the intermetallic phase.

OPTIMIZED DISTANCE FOR NON-DAMAGING IN LASER CLEANING PREPARATION

Laser Technology has wide application in industry as well as in scientific research. Semiconductor industry also interested to use laser for cleaning contaminant. However, until today, no laser has been deployed to take over the traditional method due to lack of intension on it. As a first step to embark into industrial solution, initiative has been carried out to do fundamental experiment. Optimization has been established to find out the best position for cleaning without associated with damage. A Q-switched Nd:YAG laser was focused to create breakdown in the air. This is an indicator for plasma formation and shock wave generation as the main mechanisms of damage. Pure aluminium was used as a substrate and mounted on précised a 3D linear translational stage. The defocused distance was varied in the range of 0-25 mm. The damage image was recorded and analysed via the aid of ImageJ software. Small and deep dense deformation was observed as the target located at the focal point. As the defocused distance move further away, the damage tend to be eliminated and its depth approaching the same level as original.

Numerical evaluation of the seismic behavior of façades of Mexican colonial churches

The seismic assessment of façades of churches built during the colonial era in Mexico is presented. This study takes into account two typologies of churches of the center of Mexico, which are far away of the epicenters of the subduction zone, but they both are subjected to frequent earthquakes. The first one corresponds to churches built near to local faults. The second typology corresponds to churches built far away of the local faults. The façades of the first typology are low-rise and have thick walls and some buttresses. The façades of the second typology are taller and slender. Both typologies have only one bell tower attached to the façade. The seismic behavior was studied by means of non-linear dynamic analyses, by using several real earthquake records. These seismic records were registered by stations located near and far of the epicenter zone. According to the numerical results, the façades of the churches built near the local faults can support high accelerations with moderate damage. While the façades of the churches built far away from the local faults present considerable damage for medium accelerations. For both typologies, the belfries are the most vulnerable elements. Besides, the main damage mechanism is a vertical crack on the joint of the tower and the wall of the façade; since the body of the tower tends to separate of the façade wall.

Effect of gamma irradiation on the wear behavior of human tooth dentin.

The objective of this study was to evaluate the effect of gamma irradiation on the wear behavior of human tooth dentin in terms of possible alterations in crystallinity, grain size, and composition. Human premolars (n=19) were collected to obtain the perpendicular or parallel to the direction of the dentin tubule specimens. Each specimen was subjected to 60Gy of gamma irradiation, in daily increments of 2Gy. The nanoscratch tests were conducted. The scratch traces were observed via scanning electron microscope (SEM) and surface profilometer. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to investigate the alteration of crystallography and chemical composition of dentin after irradiation. The change of surface microhardness (SMH) was also evaluated. The nanoscratch results showed that the friction coefficient of dentin after irradiation became higher, and the depths and widths of scratch were greater than that of dentin before irradiation. Additionally, irradiation decreased the crystallinity of dentin and induced the formation of bigger crystals. The carbonate/mineral ratio was increased. Furthermore, a significant reduction in microhardness after irradiation was observed. The main damage mechanisms consisted of the formation of delamination and crack in both the specimens cut perpendicular and parallel to tubule dentin after irradiation. Irradiation affected directly the wear behavior of tooth dentin, accompanied by the alterations in crystallography, chemical composition, and surface microhardness of dentin. This would help extend understanding the influence of irradiation on dentin and provide suggestions for selecting more suitable materials for irradiated tooth.

Risk assessment and economic appraisal of protection methods for the Tarascon-Arles railway embankment

The coordination of flood management practices and the reduction of flood risk as proposed under the Plan Rhone project has led to a vast program of flood defence modernization and construction in the lower Rhone valley. One key element of the project involves the construction of a new 9km levee structure parallel to an existing railway line between the towns of Tarascon and Arles (Bouches-du-Rhone, France ) on the left bank of the Rhone, which has historically been an obstacle to the propagation of flood flows. The new levee is designed to protect the towns of Arles and Tarascon up to the 10−2 annual probability flood event, after which floodwater will flow over a 5km spillway which will be integrated into the structure. In case of overtopping of the spillway via a spillway structure, floodwater is collected in the space between the two embankments and will subsequently flow towards one of ten newly constructed flood discharge structures, spaced at regular intervals in the railway embankment. The levee will form part of a global system of defence which is designed against flooding on the Rhone with an annual probability of occurrence of 10−3 . In the event of overtopping of the levee, the railway embankment will be subjected to hydraulic loading and is at risk of damage from flood flows. During the detailed design phase of the project, options were explored for optimizing the permanent protection for the railway embankment. Using results from 2D and 3D hydraulic numerical modelling, a detailed risk assessment of the railway embankment was undertaken to evaluate its vulnerability under different hydraulic loading conditions and for different failure mechanisms using various parameters including water depth, hydraulic load, the duration of flood exposure and flow velocity. A comprehensive understanding of the main mechanisms of embankment damage under hydraulic loading (internal/ external erosion, overtopping, rotational failure etc.), existing geotechnical conditions and the railway embankment structure were required to undertake the risk assessment. For each hydraulic loading scenario, a detailed economic appraisal was undertaken for each method of protection involving the evaluation of damages associated with disruption to train services and the associated costs to repair the structure. The final stage of the project involved integrating the economic assessment into a wider reaching multi-criteria analysis including indicators for train security, maintainability and environmental impact aspects. The multi-criteria approach was tested under two management strategies to evaluate the effectiveness of each embankment protection system. This paper outlines how the risk assessment, economic appraisal and management-strategy based multi-criteria approach resulted in a highly optimized system of embankment protection with significant gains in terms of both reduced cost of implementation and environmental enhancement whilst maintaining the high levels of railway security required by SNCF-RESEAU.