Surface Spalling Research Articles

Necrogeomorphology and the life expectancy of desert bedrock landforms

This paper presents the first estimates for the life expectancy of the very surface of bedrock desert landforms, such as bornhardts, cliff faces, fault scarp, inselbergs, ridge crests, and slickrock. The correlative dating method of varnish microlaminations yields minimum ages for the timing of the last spalling event caused by the physical weathering process of dirt cracking. Minimum percentage of a bedrock surface spalled per thousand years is a metric that can be estimated using multiple varnish lamination ages. Understanding rates of surface spalling provides a quantitative measure of Gilbert’s (1877: 105) weathering-limited ‘rate of disintegration’, because this metric directly links to the rock disintegration process of dirt cracking. Rates of percent surface spalled then translate into estimates of how long it takes for the very surface of a desert bedrock landform to die. For a variety of example landforms in the southwestern USA, the maximum time required to completely resurface a desert bedrock landform by spalling from dirt cracking ranges from 89 to 600 ka.

Influences of local laser quenching on wear performance of D1 wheel steel

For wheels and rails during actual service process, due to the combined impact of heat generated by friction and plastic deformation, martensite white etching layers (M-WELs) tend to form on the wear surface of wheel/rail materials. However, M-WELs are regarded as a double-edged sword: their relatively high hardness enhances wear resistance, but during wear process, cracks initiate easily due to great amounts of substructures inside M-WELs. Therefore, local laser quenching is adopted to simulate the wheel surface on which M-WELs form. Investigating the effects of M-WELs on wheels’ tribological properties is conducive to the improvement of high-speed trains’ wheel service longevity. The quenched spot with depth of 250 µm and diameter in 4 mm can be formed after local laser quenching on the specimen surface of D1 wheel steel and the hardness is about 930–997 HV0.1. The effect of the quenched layer on tribological properties of specimens was studied by rolling wear test. The results show that the main fatigue damage of non-quenched specimens is shallow spalling, and cracks propagated along the fibrous structure can be observed. There are striking differences for local quenched specimens. It's obvious that cracks initiate easily at the edge of the quenched layer as well as the quenched layer surface, and then propagate along the heat-affected zone at the early worn stage. This leads to spalling of the edge of the quenched layer. Cracks initiated on the surface can extend towards the bottom of the quenched layer with the increase of rotation cycles and the convergence of cracks would result shallow spalling of the quenched layer. After the edge of the quenched layer falls off completely, cracks initiate in the heat-affected zone and propagate along the heat-affected zone or along the fibrous structure of the matrix, leading to shallow spalling. In the subsequent process of rolling wear, cracks extend to the heat-affected zone and continue to propagate along this zone to the area where the maximum shear stress exists; under the impact of the maximum shear stress, the cracks further expand to the matrix. However, if these cracks converge other ones before arriving at the heat-affected zone, large pieces of the quenched layer fall off. The quenched layer can not only accelerate the surface spalling damage of the specimen and wear unevenly, but also can promote the formation of polygonization and reduce wear resistance of the specimen under axial vibration condition.

CONDITION ASSESSMENT OF MARINE STRUCTURES USING FUNCTIONAL CONDITION INDEX APPROACH

Marine structures are subjected to damage and deterioration during their service life because of continuous exposures to aggressive environment. As a result the performance and the intended functions of the structure are affected. This paper presents the development of a condition assessment system for assessing the status of concrete marine structures in Malaysia. The assessment system is based on the Condition Index (CI) method developed by the U.S Army Corps of Engineers. The assessment took into account the level of deterioration observed during inspection work. The Functional Condition Index (FCI) approach was used to calculate the CI of the structure. Field data through visual inspection on concrete wharf structure was collected. Three types of deterioration were considered in the assessment: (1) corrosion of reinforcement, (2) cracking, and (3) spalling of concrete surface. The results show that the calculated CI values based on the proposed method is relatively close to the expert opinion values. The condition assessment system based on the CI method is found to be reliable and efficient hence can be used to monitor the performance of marine structures in Malaysia.

Numerical simulation and experimental comparison of flaw evolution on a bearing raceway: Case of thrust ball bearing

Abstract Bearings are essential elements in the design of rotating machines. In an industrial context, bearing failure can have costly consequences. This paper presents a study of the rolling contact fatigue damage applied to thrust ball bearings. It consists in building a dynamic three-dimensional numerical model of the cyclic shift of a ball on an indented rolling surface, using finite element analysis (FEA). Assessment of the evolution in size of a surface spall as a function of loading cycles is also performed using FEM coupled with fatigue laws. Results are in good agreement with laboratory tests carried out under the same conditions using a fatigue test cell dedicated to ball bearings. This study may improve knowledge about estimating the lifetime of rolling components after onset of a spall using FEA and accounting for structural damage state. Highlights The experimental apparatus and damaged thrust ball bearing are described. We model a portion of the thrust ball bearing featuring a spherical indent. Numerical results in terms of stress field are compared to analytical results from the literature. A fatigue software is used to assess the evolution of spalling size. Good agreement is obtained between experimental test campaigns at different loads and FEA results.

Rail surface spalling detection based on visual saliency

The rail surface images captured by line‐scan cameras are susceptible to nonuniform illumination, stray light, smoothness variations of the rail surface, and so on, which degrade the detection accuracy of the rail surface spalling. To solve this problem, we propose an optical rail surface spalling detection algorithm based on visual saliency. First, the rail surface area is located to eliminate the interference of the surrounding area. Then, a two‐dimensional difference of Gaussian (2D DoG) filter is used to reduce the noise. The filtered images are processed by means of a block local contrast measure (BLCM) estimator, which enhances the contrast of the spalling areas and produces the saliency map. Finally, a threshold is applied to locate the spalling areas. Experimental results demonstrate that the proposed algorithm achieves a detection accuracy of 93.5% and shows good robustness under nonuniform illumination and various rail surface smoothness conditions. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Role of Presulfidation and H2S Cofeeding on Carbon Formation on SS304 Alloy during the Ethane–Steam Cracking Process at 700 °C

The influence of presulfidation and H2S cofeeding on the carbon formation on SS304 alloy in the ethane–steam cracker was investigated in a laboratory-scale quartz reactor setup. SS304H coupons and SS304L powder samples were exposed to ethane–steam and dry ethane in varying H2S content (0–50 ppm), and the SS304 samples were characterized by scanning electron microscopy. This study shows that H2S cofeeding decreases catalytic carbon formation; while it increases the pyrolytic carbon formation during ethane–steam cracking. Preoxidation, presulfidation, and addition of steam to ethane feed also reduces the amount of catalytic carbon formed on the SS304H surface in short-term experiments (4 h). Presulfidation and addition of H2S to ethane feed significantly influences the shape and size of the carbon formed on the surfaces of investigated metal alloys. Presulfidation and H2S cofeeding reduced spalling of the SS304H coupon surface during coking/decoking and thermal cycling.

Service life extension of state highway 16 bridges – New Zealand’s first hybrid corrosion protection application

State Highway 16 (SH16) is an existing motorway of significant strategic importance connecting central Auckland to the city's western suburbs and beyond. It carries, on average, some 90,000 vehicles per day, and runs through an environmentally sensitive coastal marine reserve. Two highway bridges, namely Whau River Bridge and Causeway Bridge are currently being refurbished due to extensive chloride contamination as a result of exposure to a tidal marine environment and exhibit surface cracking, spalling and reinforcement corrosion. A hybrid corrosion protection system has been selected as the preferred corrosion management solution to arrest corrosion and to ensure a residual service life of 50 years. The hybrid corrosion protection (HCP) system comprises discrete zinc anodes which were installed on both the reinforced and pre-stressed concrete piles from the Lowest Astronomical Tide (LAT) level, up to the soffit of the crossbeams. The anodes operate in two phases, initially energised using low voltage DC power to arrest ongoing corrosion and thereafter in galvanic mode to provide corrosion prevention for the residual service life. HCP minimised physical works on site, negated the requirement for extensive replacement of chloride contaminated concrete, allowed work to take place accommodating incoming and outgoing tides and offers protection against chloride induced corrosion to the substructures. This is the first HCP system designed and installed in New Zealand, and it is believed to be the first of its kind for pre-stressed concrete in tidal water in the world.

Characterization and modelling of the degradation of silicon nitride balls with surface missing-material defects under lubricated rolling contact conditions

Hybrid bearings in which ceramic rolling elements are used in combination with hardened steel rings outperform the conventional full-steel bearings in some demanding applications where high speed, high temperature, electric current, and thin-film or medium lubrication are involved. Despite the continued effort and progress made to improve the toughness, ceramics are regarded as brittle solids that can suffer in general from lack of damage tolerance in the form of sensitivity to pre-existing features that are seen as being potentially harmful. Under specific conditions, these imperfections may become critical for the reliability of hybrid bearings.This paper reports on a study of the degradation of silicon nitride ceramic balls, caused by surface missing-material (MM) defects under lubricated rolling contact conditions. Rolling contact fatigue test is conducted on the ceramic balls containing artificial defects of different configuration and sizes. Numerical simulation by means of finite element analysis indicates that the lubricant entrapped inside the MM cavity will be pressurized under rolling contact. The hydraulic pressure of the entrapped lubricant can result in significant tensile stress at the corner of the cavity that may cause crack initiation, initial crack propagation, and eventual spalling of the ball surface. Such a degradation mechanism is confirmed by the characteristics of the fatigue damage observed from the tested balls. Based on the understanding of the failure mechanism, a model based on the nonlocal approach to crack initiation at a V-notch is developed to describe the damage tolerance of the silicon nitride balls with the MM defects of specific geometry with respect to the rolling contact load. The prediction of the tolerance limits agrees well with the endurance limits of the silicon nitride balls tested under lubricated rolling contact conditions.This research has contributed to a fundamental understanding on what type and size of the MM defects can be tolerated in hybrid bearings in relation to used application running conditions.

Dynamic mechanism modeling for dual-impulse behavior excited by a spall on outer race of ball bearing

Fatigure in rolling element bearings results in spalling of the raceways or rolling elements which is the most common bearing fault. The size of the spalling area, however, has close relationship with dual-impulse behavior produced by a localized surface spall. Based on the Hertzian contact theory and investigation of the excitation mechanism of dual-impulse behavior excited by a localized surface spall, a new coupled non-linear dynamic model of the ball bearing with a localized surface spall on outer race is developed, which considers the time-varying displacement and contact force excitation. The solution to the differential equations is obtained applying the Runge-Kutta numerical integral method. The time interval of dual-impulse behavior is investigated in this paper. Comparisons of the stimulated and theoretical results and the experimental and theoretical results show the effectiveness of the proposed model.

Chloride penetration resistance and frost resistance of fiber reinforced expansive self-consolidating concrete

The objective of this paper is to investigate the chloride penetration resistance and frost resistance of fiber reinforced expansive self-consolidating concrete (ESCC). Fibers and expansive agent were used to decrease shrinkage, control cracks and enhance microstructure of the concrete. Steel fibers with three volume fractions (0.25%, 0.50% and 0.75%) of the total volume of concrete and monofilament polypropylene fibers with two volume fractions (0.05%, 0.10%) were used in the test. This study established levels of chloride penetration of fiber reinforced ESCC. The frost resistance was determined by rapid freezing and thawing test. Results indicated that PP shows more sensitivity on slump flow than SF but less impact on T500. Chloride content increased with the incorporation and increase of fibers at depths less than 17.5 mm. However, chloride penetration resistance along the depth was enhanced with increasing fiber factor. SF0.50PP0.05 exhibits the best chloride penetration resistance, and SF with a volume fraction of 0.50% and PP with a volume fraction of 0.05% show mutual beneficial effect on the chloride penetration resistance of ESCC. The relative dynamic modulus of elasticity (RDME) of ESCC in the presence of fibers decreased slightly when compared with ESCC in the absence of fibers, and decreased with the increasing fiber factor. It also shows that the increase of fiber content decreased the speed of surface spalling of the specimens as well as the mass change.

Fracture evolution and failure behaviour of marble specimens containing rectangular cavities under uniaxial loading

To analyse the fracture coalescence behaviour around hole-like flaws in rock, rectangular cuboid marble specimens containing a single rectangular cavity or two rectangular cavities with different layouts were tested under uniaxial compression. Failure characteristics of specimens and strain concentration regime (SCR) evolution on specimen surfaces were measured by means of acoustic emission (AE) and digital image correlation (DIC) techniques respectively. Numerical simulations were further conducted on specimens with the same specimen and cavity dimensions using the discrete element method (DEM), and the inclination angle between centroids of two cavities with respect to the horizontal direction was varied to investigate its influence on failure modes and mechanical properties of specimens. Results showed that both cavity number and layout have a significant influence on mechanical behaviour of marble specimens. The existence of two cavities leads to more degradation of mechanical properties than a single cavity. For specimens with two cavities, the strength first decreases and subsequently increases with increasing inclination angle, and the specimen with two vertically aligned cavities has the maximum strength. Four failure modes were observed in specimens, namely splitting failure, shear failure, mixed tensile/shear failure, and surface spalling. In addition, absorbed energy per unit volume e was introduced to characterise the fragmentation of different groups of specimens. Specimens containing cavities absorbed less energy per unit volume, and thus were less fragmented after failure.

Fatigue and surface spalling of cemented carbides under cyclic impact loading – Evaluation of the mechanical properties with respect to microstructural processes

Cemented carbides used in excavation tools have to feature particular mechanical properties to withstand impact loads and abrasive degradation processes. It is assumed that a high fracture toughness is important to counteract brittle material failure due to forced rupture (supercritical loads) or material fatigue caused by subcritical impacts or cyclic loads. The fatigue-induced failure mechanism on a microstructural scale (evolution of fracture) in cemented carbides is discussed controversially in the literature. We are thus focusing on fatigue-initiated surface degradation of cemented carbide grades during ground excavation. Various cemented carbide grades were loaded with cyclic subcritical impact loads that lead to microstructural damage. The crack path was analyzed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The number of endured load cycles is further correlated with the microstructural composition and the resulting mechanical properties of the tested grades. The results demonstrate that the commonly used correlation between resistance against fatigue load and fracture toughness KIC does not seem to be suitable for describing subcritical crack growth in cemented carbides due to cyclic loads that lead to surface spalling and microfatigue. The cemented carbide grades with the highest KIC values do not possess the highest resistance against surface spalling and thus the highest fatigue resistance. The influence of the microstructural properties (dWC, VCo, λCo) on the results has been shown. Furthermore, the correlation between fatigue sensitivity and crack path fractions was analyzed.

The Influence of Concrete Strength on the Effect of Synthetic Fibres on Fire Resistance

Numerous studies have verified that increased concrete strength reduces its resistance to fire, leads to a higher degree of strength reduction and higher chances of spalling of concrete surfaces.The risks of spalling of concrete surfaces can be reduced by adding synthetic polypropylene fibres. Numerous experiments have shown that the risk of spalling of the concrete surface is significantly lower when using short, small diameter fibres of polypropylene synthetic, because the pore structure created by the burning of fibres reduces the risk of cracking.However, the question arises whether other types of fibres of greater diameter and length are still able to prevent spalling of concrete surfaces without drastically reducing the strength and if so, in what range of concrete strength it is true.The experiments are aimed to determine the effects of micro and macro synthetic fibres on the post-fire residual compressive strength, flexural strength and porosity of concrete.Nine kinds of mixture were prepared and tested. Three of them are without fibers (reference concretes) with diverse strength, three with synthetic micro-fibres with diverse strength and three with synthetic macro-fibres of diverse strength. The experiment was conducted with three concretes with different strength. Each type had a reference concrete without fibre reinforcement, one with micro- and one with macro-fibres.

Run-out based crossed roller bearing life prediction by utilization of accelerated testing approach and FE numerical models

Surface wear and spalling phenomena are the most important factors affecting roller bearing performance and operational lifetime, in terms of number of cycles the bearing can operate. Although bearing life has been traditionally defined by the onset of spalling, as specified by international standard ISO 281, this definition does not always reflect the real operational conditions, since bearing wear can also represent a failure criterion when excessive run-out occurs. In such cases, bearing life needs to be predicted according to the amount of bearing run-out resulting from wear due to load and number of cycles. In the current study, the wear phenomenon has been modeled using the Archard wear and Lemaitre damage models, both included in a numerical simulation of a roller bearing assembly. Wear and damage models, along with the results of accelerated life experiments, have been used to develop a reliable method enabling bearing life prediction with a minimal number of material characterization tests. Accelerated life testing experiments on real bearings have been performed to confirm the reliability of the methodology, showing good correlation with numerical simulation results and proving that the developed model can be utilized for prediction of the lifetime of bearings.

Visual inspection of fire-damaged concrete based on terrestrial laser scanner data

Visual condition survey and inspection is typically the initial method employed in the assessment of concrete damaged by fire, and it is among the most significant non-destructive testing methods. In spite of visual inspection being simple in principle, it is capable of providing cardinal information about the condition of the fire-damaged structure and act as a basis upon which subsequent and detailed assessment methods can be founded. When concrete is exposed to various elevated temperatures, it undergoes change in its physical characteristics among others, and indicators such as change in surface texture, cracks, spalling and colour change become evident. These indicators of fire-damaged concrete can be assessed using visual inspection methods and further assessed with more advanced methods in a case where detailed investigations are needed. In this study, visual inspection of terrestrial laser scanner data of fire-damaged concrete was investigated by modelling and analysing laser intensity. An analysis of the generated intensity images from laser intensity data has proved useful and valuable in the visual inspection of concrete before and after heating. Furthermore, laser scanner geometric data has been used in the assessment of concrete surface roughness before and after heating.

Influence of high temperature on the residual physical and mechanical properties of foamed concrete

To study the influence of high temperature on the properties of foamed concrete, four densities of foamed concrete (300kg/m3, 450kg/m3, 600kg/m3 and 800kg/m3) were taken into account in a series of tests. The change laws of appearance, mass, compressive strength and elastic module at ambient temperature and after undergoing different high temperatures (200°C, 400°C and 600°C) were presented. The results indicate that the appearances for all of four different densities were different. The cracks to be observed at the higher densities foamed concretes (i.e., 800kg/m3 and 600kg/m3). However, the pore connectivity and surface spalling phenomenon are easier to be observed at lower densities foamed concretes (i.e., 300kg/m3 and 450kg/m3). With temperature increasing, the density, compressive strength and elastic modulus became lower and lower for all samples, however some details are different. Furthermore, two predicting models to reflect the change laws of compressive strength and elastic modulus with different densities and temperatures are obtained and are verified by comparing the results with the experimental data and other proposed models in previous works.

Surface Corrosion and Microstructure Degradation of Calcium Sulfoaluminate Cement Subjected to Wet-Dry Cycles in Sulfate Solution

The hydration products of calcium sulfoaluminate (CSA) cement are different from those of Portland cement. The degradation of CSA cement subjected to wet-dry cycles in sulfate solution was studied in this paper. The surface corrosion was recorded and the microstructures were examined by scanning electron microscopy (SEM). The results show that SO42-, Na+, Mg2+, and Cl− have an effect on the stability of ettringite. In the initial period of sulfate attack, salt crystallization is the main factor leading to the degradation of CSA cement specimens. The decomposition and the carbonation of ettringite will cause long-term degradation of CSA cement specimens under wet-dry cycles in sulfate solution. The surface spalling and microstructure degradation increase significantly with the increase of wet-dry cycles, sulfate concentration, and water to cement ratio. Magnesium sulfate and sodium chloride reduce the degradation when the concentration of sulfate ions is a constant value.

Experimental Laboratory Validation of Reproducing Road Viaducts Concreting Processes

In the latest period, hundreds of concrete viaducts were built in Poland within a short time range. Their characteristic feature was the use of high class concrete containing the CEM I 52.5 cement. The concreting works often took place during winter time. Despite successful laboratory tests, the concrete prepared on the concreting site often did not achieve the assumed freeze-thaw resistance.The lack of freeze-thaw resistance in concrete had an unusual course. A higher than normative decrease of strength with simultaneous high tightness was observed. There was no surface spalling, typical for the low freeze resistance concrete, no edge curvature, etc. In addition, on the sample surface, a characteristic mesh of white leakage of unknown chemical compounds around big aggregate grains was identified. Those compounds were thoroughly investigated with the use the SEM analysis.It was found that the direct reason of lowering the concrete strength after 150 cycles of freezing and defrosting was the occurrence of numerous micro-cracks formed during the hydration of high amount of clinker cement in concrete block. Moreover, these phenomena were enhanced by the occurrence of white, needle-shaped, hard-soluble salts localised in the boundary between aggregate and cement paste. Based on the EDS analysis, these salts were identified as nickel and calcium phosphates, ettringite ana thaumasite formations and others, which delayed cement hydration [1,2,7–9].The variety of occurring white salts forced the commencement of model laboratory tests on a specially built station for reproducing the processes taking place during concreting and developing recommendations for the construction workmanship.

An experimental investigation on strength, deformation and crack evolution behavior of sandstone containing two oval flaws under uniaxial compression

To increase the understanding of strength and failure mechanism of fractured rock, a series of uniaxial compression tests on red sandstone specimens containing two pre-existing oval flaws was carried out using a rock mechanics servo-controlled testing system. On the basis of the experimental results, the influences of the coplanar flaw angle and ligament angle on the mechanical parameters and fracture process of sandstone specimens containing two oval flaws were analyzed in detail. The mechanical parameters including peak strength, peak strain and elastic modulus of pre-flawed specimens are all much lower than those of the intact specimens. For the specimens containing two coplanar oval flaws, the peak strength is distinctly related to the coplanar flaw angle, while the peak strain and elastic modulus are not obviously dependent on the coplanar flaw angle. For the specimens containing two non-coplanar oval flaws, the peak strength, peak strain and elastic modulus all have a nonlinear relationship with the ligament angle. By adopting photographic and AE monitoring techniques, the crack initiation, propagation and coalescence process and the AE evolution behavior of sandstone specimens were all observed and characterized. The stress drops in the stress-time curve correspond to a sudden increase in accumulated AE counts in the accumulated AE-time curve, resulting from the initiation and coalescence of cracks. The ultimate failure modes of sandstone specimens containing two pre-existing oval flaws are a mixture of several cracks (wing crack, anti-wing crack, secondary crack, shear crack and far-field crack and surface spalling), which depend on the flaw geometry. The failure patterns of pre-flawed specimens can be identified as the following four distinct modes: no crack coalescence failure, indirect crack coalescence outside the bridge area failure, single crack coalescence inside the bridge area failure and tensile crack coalescence outside the bridge area failure. The last failure mode was only observed in the specimens containing two non-coplanar oval flaws for β=120°and 150° due to the two pre-existing overlapping flaws.

A New Approach for Fatigue Damage Modeling of Subsurface-Initiated Spalling in Large Rolling Contacts

Large bearings employed in wind turbine applications have half-contact widths that are usually greater than 1 mm. Previous numerical models developed to investigate rolling contact fatigue (RCF) require significant computational effort to study large rolling contacts. This work presents a new computationally efficient approach to investigate RCF life scatter and spall formation in large bearings. The modeling approach incorporates damage mechanics constitutive relations in the finite element (FE) model to capture fatigue damage. It utilizes Voronoi tessellation to account for variability occurring due to the randomness in the material microstructure. However, to make the model computationally efficient, a Delaunay triangle mesh was used in the FE model to compute stresses during a rolling contact pass. The stresses were then mapped onto the Voronoi domain to evaluate the fatigue damage that leads to the formation of surface spall. The Delaunay triangle mesh was dynamically refined around the damaged elements to capture the stress concentration accurately. The new approach was validated against previous numerical model for small rolling contacts. The scatter in the RCF lives and the progression of fatigue spalling for large bearings obtained from the model show good agreement with experimental results available in the open literature. The ratio of L10 lives for different sized bearings computed from the model correlates well with the formula derived from the basic life rating for radial roller bearing as per ISO 281. The model was then extended to study the effect of initial internal voids on RCF life. It was found that for the same initial void density, the L10 life decreases with the increase in the bearing size.