Subcritical Crack Propagation Research Articles

Single fluid-driven crack propagation in analogue rock assisted by chemical environment

During the operation of hydraulic fracturing as used in many geo-energy and geo-environment applications, chemical stimulation is often incorporated for cracking enhancement in low-permeability geological formations for the purpose of an optimization of energy recovery. The mechanism of subcritical crack propagation in a chemically reactive environment is essential for understanding of the involved coupled chemo-mechanical process and a better control of acid-assisted hydraulic fracturing. It has been postulated that the rate of crack propagation under environmental loads is inherited from the chemical processes involved including the reaction and the diffusive transport. However, laboratory explorations focusing on the evolving interplay between the propagation of a fluid-pressurizing individual crack and the environment it is subject to via a variable chemical intensity imposed have been rare. Here we present an experimental investigation on a single tensile crack propagation in alginate hydrogel as an analogue material for brittle rocks, driven by the injection of a chemically reactive fluid kept at constant pressure using a Hele-Shaw cell setup. We show that an intensified chemical environment can accelerate tensile crack propagation in both subcritical crack growth and fracturing regimes, while leading to the Region III fracturing of less brittle characteristics. During the experiment, crack-tip blunting upon injection of reactive solutions was observed, suggesting a competing mechanism between the crack-tip geometry induced toughening and the chemically induced softening within the process zone as the crack advances. Our results provide quantitative insights into how a chemically reactive environment facilitates the growth of a single macroscopic crack of mode I opening in a low-permeability matrix through coupled chemo-mechanical feedback. The imposed chemical environment promotes crack propagation while alleviating the stress concentration at the advancing crack tip, suggesting a more energy-efficient method compared to pure water fracturing. We anticipate our experimental investigation presented here to be a starting point of sound laboratory support for future studies towards a more controllable technique of chemical stimulation in geomaterials as well as complementing the ongoing modeling efforts in reactive chemo-mechanics.

ATZ composites with enhanced mechanical reliability and lifetime

Tetragonal zirconia demonstrates very good mechanical properties in rapid tests but reveals the strength decrease over time typical for oxide materials. If the material is loaded for a long period of time, the subcritical crack propagation occurs. Introducing additional phases into the zirconia matrix can both limit the grain size growth and introduce residual stresses, which can retard or even stop the crack run. The base of this work is a composite from the family of alumina toughened zirconia (ATZ) ones with a dispersed small content of alumina (1.5 wt%). The matrix was obtained via common sintering of different zirconia powders with various yttria content, which resulted in the material of a very small grain size. Incorporating additional alumina (8.4 or 15.8 wt%) led to the independence of strength from the loading time. Other calculations were made in order to estimate the survival time of the material working under load.

Application of Statistically Similar Representative Volume Elements of Metal Matrix Composites for the Efficient Simulation of Crack Propagation on the Microscale

AbstractThe efficiency of various drilling and cutting processes is strongly determined by the wear resistance of the applied tools. For example in mechanized tunnel drilling, metal matrix composites, used as reinforcements on the chisels, are primarily exposed to surface spalling. This wear mechanism is governed by subcritical crack propagation through the material's microstructure, which consists of brittle carbide inclusions surrounded by a ductile matrix. The microstructure morphology strongly influences the crack propagation and thus, the resistance against wear. In order to improve the material's microstructure regarding wear, numerical simulations on the microscale are an important tool to gain knowledge about the influence of the morphology on the crack propagation. The investigated microstructure is given as voxel data obtained from a µCT scan. Because of the high complexity of the microstructure, simulations of crack propagation through it are computationally costly, in particular under cyclic loads. Hence, simplified artificial microstructures are constructed which resemble the morphological as well as mechanical properties of the full microstructure. Here, these less complex microstructures are constructed according to the method in [1,2] for the generation of so‐called Statistically Similar Representative Volume Elements (SSRVE). For the efficient simulation of crack propagation through heterogeneous microstructures based on voxel data, the framework in [10] is applied on the SSRVEs. In numerical simulations, the capability of the SSRVEs to represent the crack behavior of the full microstructure is investigated by comparing with the results are compared to simulations on a cutout of the full microstructure.

Subcritical crack propagation in glacial quarrying during subglacial water pressure variation

AbstractGlacial quarrying stems from the fracturing of subglacial bedrock. Much evidence shows that subcritical crack propagation of bedrock is closely related to subglacial water pressure fluctuations. Here we employ a model that assesses the impact of subglacial water pressure fluctuation on cavity length and subcritical crack propagation, while analyzing the effect of a pre-existing crack location using a phase-field model (PFM). Our results indicate that the cavity length is reduced during diurnal fluctuations in water pressure. There are two patterns of subcritical crack propagation on the corner of the step. The first stems from a rapid drop in water pressure. The second occurs after the water pressure recovers from the fluctuation to the initial steady state. This pattern is a consequence of enhanced stress concentration on the step since the modeled cavity length exceeds its steady value and has higher efficiency in promoting subcritical crack propagation. Additionally, based on the PFM results, we speculate that the subcritical crack initiation and propagation happen on a broader scale, including the ice-bed contact region and its adjacent region. Our findings imply that the duration of subcritical crack propagation is short and typically ceases once the cavity length adjusts to reduced water pressure levels.

Subcritical crack growth and fracture behavior of rocks and long-term strength estimation

Understanding the potential subcritical fracture behavior is very essential to assess the perennial stability of rock engineering. The purpose of this study is to reveal the fracture characteristics and subcritical crack propagation of rocks with different lithologies, emphasizing that the influence of time-dependent fractures on the long-term strength of rocks cannot be ignored. The fracture toughness, KI-V curves and subcritical growth index of five types of rocks were obtained by the double-torsion (DT) technique. Subcritical fracture propagation exists in the rock as the stress intensity level is between K0 and KIC, and the ratio of the two values is between 0.73 and 0.83. Using a three-dimensional digital image correlation (3D-DIC) technique and a plane mirror, the evolution of tensile strain and crack propagation process on the bottom surface of specimens were observed successfully. The granite and basalt showed a faster growth rate of subcritical crack propagation, with fracture rate ranging from 10-2.5 to 10-6.9 m/s. The long-term strength of rocks was estimated based on the tensile strength, fracture toughness, SCI and A values. In a short term, basalts with the highest tensile strength have the highest long-term strength, while granites show the highest long-term strength when the time-to-failure exceeds 408.2 years. Therefore, the time-dependent cracking behavior of rock engineering must be considered when assessing the long-term stability.

Characterization of IASCC crack tips extracted from neutron-irradiated flux thimble tube specimens in view of a probabilistic fracture model

This study reports the properties of irradiation assisted stress corrosion crack tips extracted by means of focused-ion beam from 60 to 80 dpa neutron-irradiated O-ring specimens tested under straining conditions under a pressurized-water reactor environment. Various crack tip morphologies and surrounding deformation features were analyzed as a function of applied stress, surface oxidation state and loading form - constant versus cyclic. All investigated cracks exhibit grain boundary oxidation in front of the crack tip, with the extent of oxidation being proportional to applied stress. These findings clearly demonstrate that, under the subcritical crack propagation regime, the grain boundary oxide grows faster than the crack. On the other hand, crack tips appertaining to specimens with removed oxide layer at the outer surface show comparatively less oxidation at the crack tip, which could indicate towards crack initiation from regions that exemplify lower stress, such as the O-ring inner surface. Cyclic loading is found to have a more pronounced effect on the crack tip microstructure, demonstrating increased deformation twinning and α′-martensitic transformation, which signifies towards an increased susceptibility to intergranular failure. Still, the extent of crack tip grain boundary oxidation in this case agrees well with expected values for maximum stress applied during cyclic loading. All results are interpreted based on the probabilistic subcritical crack propagation mechanism and provide strong support to a stress-driven internal oxidation model.

Simulation of ductile crack propagation in metal matrix composites ‐ Comparison with cyclic experiments

AbstractThe efficient operation of mechanized tunnel drilling machines is strongly determined by the wear resistance of the applied mining tools. Especially in chisels, but also partly in cutting disks, metal matrix composites are used. Their wear mechanism is dominated by surface spalling, i.e. subcritical crack propagation through the material's microstructure, mainly consisting of a ductile metal matrix and carbide inclusions. Since this process is primarily governed by the morphology of the microstructure and the mechanical behavior of the individual phases, simulations at the microscale enable the design of improved materials. In this contribution, a method for the modeling of this process is presented. The approach is based on the eigenerosion framework introduced in [1] and an algorithmic scheme for large strains is given, which extends the small strain implementation in [2]. For the phases at the microscale, the finite strain plasticity formulation [3] is applied. Examples according to [4] are shown in order to demonstrate the mesh independence of the framework for ductile crack propagation. Furthermore, simulations are carried out on the microscale by applying the Finite Cell Method [5] on metal matrix composite microstructures. Here, a specific cell arrangement is constructed which minimizes the required number of cells for a given microstructure morphology. Additionally, an experimental setup for the validation of the eigenerosion framework on the microscale is presented. By evaluating the results of these simulations, failure of the material can be investigated on a microscopic level and improvements of the material morphology regarding wear can be realized.

Modeling the subcritical spread of cracks grown by fatigue / Modelando a propagação subcrítica de rachaduras crescidas por fadiga

The objective of this article is to mathematically model the subcritical propagation of fatigue-grown cracks. Three fatigue specimens were used, made of ASTM A 36 structural steel, which were notched in the center of the specimen to simulate a stress concentrator, and for the crack to propagate in the same plane. A three-point bending fatigue machine was used which is equipped with computer data acquisition equipment.The subcritical propagation of fatigue cracks was monitored, using the strain gage technique, and it was verified with the beach marking technique; which guaranteed the reliability of the method. With the data obtained, a vs N graph was made, and the empirical equation that governs this phenomenon was found; Likewise, derivatives were applied and the crack advance speed versus crack size was calculated; and to calculate the stress intensity factor, the Newman Raju method was applied, which is being verified by many researchers in recent years.In this way, it is possible to find a mathematical expression that modulates the fracto-mechanical behavior of the subcritical propagation of a crack, which relates the advance speed of the crack as a function of the fracture toughness evaluated as a function of the intensity factor of tensions K. With which a model similar to the one proposed for the Paris model is achieved, with the values for the parameters C = m / Cycle and m = 2.0252 that are close to the values obtained by researchers in similar materials.

Effect of thermal treatment on the fracture toughness and subcritical crack growth of granite in double-torsion test

An understanding of the fracture behavior and subcritical crack propagation of hard rock under different temperatures is necessary for the design and stability of nuclear waste disposal projects. The aim of this study was to understand the thermal effect on the fracture behavior of granite, which had been heated at 25 (untreated), 100, 200, 400, and 600 °C, respectively. A series of uniaxial compressive tests and double-torsion tests were performed on granite specimens. The three-dimensional digital image correlation technique was used to investigate the strain evolution and fracture pattern in granite specimens during subcritical crack propagation. According to the results, the uniaxial compression strength, Young’s modulus and fracture toughness of the granite specimens increased and then decreased with an increase in treatment temperature. These parameters dropped sharply as the treatment temperature exceeded 400 °C, mainly because of the thermally-induced destruction of the quartz crystal structure and a generation of wider intergranular fractures. A comparison of the subcritical crack length by theoretical calculations and experimental observations from digital image correlation showed that the two values were consistent. At a treatment temperature of 400 °C and 600 °C, the velocity of the subcritical crack propagation was accelerated, so the length of the subcritical crack during the relaxation test was 4.14 times and 5.25 times that at 25 °C, respectively. The subcritical crack growth and fracture process of the double-torsion tests were visible by the three-dimensional digital image correlation system. A subcritical crack growth index (n) can be used to characterize the susceptibility of the subcritical crack propagation in rock relaxation tests, which helps to evaluate the long-term stability of nuclear waste disposal projects.

An experimental and theoretical investigation of time-dependent cracking and creep behavior of rocks under triaxial hydro-mechanical coupling

Subcritical crack propagation and rock creep deformation are the main factors affecting the long-term stability and strength characteristics of rocks under hydro-mechanical coupling. Triaxial creep tests were performed on rock-like mortar specimens containing a pre-existing 3-D crack to investigate the time-dependent mechanical behavior of the cracked rock. A modified theoretical model for the irreversible deformation of rocks based on subcritical crack propagation was used to analyze the creep mechanism of the specimens and the effects of water pressure. The specimens with creep damage mainly exhibited a tensile-shear failure mode, and the macrofracture presented more tensile characteristics with increasing water pressure. The water pressure promoted the prefabricated crack propagation, inhibited the formation of microcracks, increased the creep rate, and accelerated specimen failure, which had a negative effect on the long-term stability of the specimens. The modified model accurately predicted the variation in irreversible axial strain and time required for specimen failure, especially under higher water pressures. The creep deformation of the specimens was much larger than the instantaneous deformation at the same crack propagation length, indicating that subcritical crack propagation is the main factor leading to the failure of rocks.

A two-scale time dependent damage model for preferential gas flow in clayey rock materials

Understanding of the gas migration within the host rock is critical for the safety assessment of a deep geological repository for radioactive wastes. However, localized gas flow in clayey host rock materials is a complex behavior associated with dynamic and unstable network of dilatant pathways, which are accompanied by micro-cracking that indicates macroscopic tensile fractures. The subcritical crack propagation at the microscale may represent the mechanism of time dependent damage observed at the macroscale. A two-scale damage model is developed in this study to explicitly simulate the preferential gas flow in clayey rock materials. A homogenization method based on asymptotic developments is employed to deduce the macroscopic damage behavior coupled with the poroelastic system, which initiates from the periodically distributed microstructures with micro-cracks. A time dependent damage evolution law is constructed based on the microscopic phenomena and the corresponding intrinsic permeability model is proposed which implicitly accounts for the fracture opening induced permeability change. The local macroscopic response of the model is analyzed and validated against the experimentally measured direct tensile strength, which illustrates the homogenized elastic and permeability coefficients, and highlights the influence of several parameters, i.e., the initial damage, the microstructural size and the strain rate. Numerical examples are presented in order to illustrate the global macroscopic response, in which a pure mechanical test, i.e., uniaxial tension test is simulated and verified against the laboratory results, then the simulation of preferential gas flow is illustrated together with the comparison of experimental explanation. The numerical results showed that the proposed two-scale model can explicitly simulate the gas induced fracturing, in which the damage propagation and the dilatant gas pathways are well captured.

Chemo-mechanical modeling of static fatigue of high density polyethylene in bleach solution

High density polyethylene (HDPE) is increasingly used in infrastructure applications with a design service lifetime of several decades. In many cases, the HDPE member is exposed to a corrosive environment, such as in pipes carrying potable water, where the dissolved bleach selectively attacks the loosely packed amorphous phase of the polymer. The failure mechanism of HDPE transitions from a ductile to a brittle mode as the corrosion level increases. This leads to subcritical crack propagation, which deteriorates the load capacity of the structure. In this study, we develop a coupled chemo-mechanical model to simulate stress corrosion cracking (SCC) in HDPE members exposed to a bleach solution. The mechanical response of the polymer is described by a constitutive model that separately considers the individual deformation and damage behaviors of the amorphous and the crystalline phases. The model accounts for the intermolecular deformation and homogeneous void growth in the crystalline and amorphous phases, along with the resistance of the entangled network and craze damage in the amorphous phase. The embrittlement due to corrosion is captured by relating the constitutive parameters of amorphous phase to the molecular weight of the polymer. The diffusion and chemical reaction of bleach are described by a reduced order kinetics model that links the extent of polymer oxidation to the reduction of the molecular weight. The material constitutive model and diffusion–reaction model are combined in a single finite element (FE) code to investigate the SCC behavior of double edge notched HDPE specimens. The simulation yields the stress-life curves and fracture kinetics under different environments. The predicted stress-life curve qualitatively matches the measured stress-life data of polymer pipes. It is shown that the stress-life curve exhibits different regimes corresponding to distinct failure mechanisms, as indicated by the stress and strain distributions in the specimen.

Extension of the eigenerosion approach to ductile crack propagation at large strains and its application on hard metal microstructures

AbstractThe efficient operation of mechanized tunnel drilling machines is strongly determined by the wear resistance of the applied mining tools. Especially in chisels, but also partly in cutting disks, hard metals are used. Their wear mechanism is dominated by surface spalling, i.e. subcritical crack propagation through the material's microstructure mainly consisting of a ductile metal matrix and carbide inclusions. Since this process is mainly governed by the morphology of the microstructure and the mechanical behavior of the individual phases, simulations at the microscale enable the design of improved materials. In this contribution a method for the modeling of this process is presented. The approach is based on the eigenerosion framework introduced in [1] and an algorithmic scheme for large strains is given, which extends the small strain implementation in [2]. For the phases at the microscale the finite strain plasticity formulation [3] is applied. Furthermore, simulations are carried out on the microscale by applying the Finite Cell Method [4] on hard metal microstructures. Here, a specific cell arrangement is constructed which minimizes the required number of cells for a given microstructure morphology. By evaluating the results of these simulations, failure of the material can be investigated on a microscopic level and improvements of the material morphology regarding wear can be realized.

How the risk of failure in lifetime of tempered glass depends on the size of NiS inclusions and heat soak test duration

AbstractThe probability of breakage in service lifetime of heat‐tempered glass panes contaminated by nickel sulfide inclusions is estimated with a multiscale micromechanically motivated statistical theory, which considers the effects of the heat soak test (HST). Short and long HSTs differently affect the phase transformation of NiS of diverse chemical composition, whose increase in volume can break the glass. The main hypothesis, corroborated by experiments, is that there is a lower limit for the size of NiS stones below which no crack can be initiated from the volumetric expansion. The catastrophic propagation of nucleated fractures in the long term is modeled through a rescaled critical stress intensity factor, which accounts for the subcritical crack propagation and the slow phase transformation of NiS. A parametric analysis evidences how the failure probability is strongly affected by these parameters, depending on the holding time in the HST. Tailored experimental activity is suggested for the proper calibration of the model.

An Atomistic Study of the Stress Corrosion Cracking in Graphene.

Using molecular dynamics (MD) simulations, we study the mechanism of stress corrosion cracking in graphene. Two sets of modelings are conducted. In the first one, large graphene sheets with cracks in the armchair and zigzag directions are exposed to oxygen molecules. The crack growth as a result of chemical reactions between carbon radicals and oxygen molecules at different mechanical tensile stress levels is studied. In the second set of simulations, MD simulations are combined with the density functional-based tight bonding method to enhance the accuracy. This set of modelings focuses on a smaller zone in the vicinity of the crack tip. The impact of initial crack orientation on corrosion is studied by investigating corrosion of cracks in both armchair and zigzag directions. We investigate the subcritical crack propagation occurring as a result of the combined effects of both mechanical loading and chemical reactions. Our results show that cracks in graphene can grow due to chemical reactions with the environmental molecules. The MD modelings also predict that reaction of carbon atoms with oxygen molecules might lead to a stress relaxation at the crack tip, hence preventing further crack propagation. The results show that subcritical crack growth can happen by two mechanisms, which include the failure of C-C bonds or by removing the carbon atoms from graphene sheets in the form of CO or CO2 molecules.

Low Friction Coefficient of Phyllosilicate Fault Gouges and the Effect of Humidity: Insights From a New Microphysical Model

AbstractFault slip is often localized in phyllosilicate‐rich fault gouges in a manner consistent with the relatively low friction coefficients measured for dry and especially wet phyllosilicates in laboratory experiments. However, the microphysics controlling these low friction coefficients remains unclear. Here, we propose a microphysical model, inspired by microstructural observations, for the prediction of the absolute value of the friction coefficient of pure dry and wet phyllosilicates. Experimentally produced phyllosilicate gouges suggest that shearing is controlled by sliding along (001) grain/platelet interfaces operating in series with removal of overlapping grain edge barriers by basal cleavage. We derive a model incorporating a subcritical crack propagation equation for the latter, constrained by subcritical crack growth data for muscovite. Model predictions for muscovite show similar trends regarding the effects of humidity and slip velocity on friction coefficient as do experiments at room temperature. The absolute value predicted for the friction coefficient is difficult to compare with experimental values, as it critically depends on atomic scale (001) sliding resistance, which is poorly constrained by available experimental data. Further discrepancies with experimental data can be explained by effects of varying grain size, grain aspect ratio, and porosity on the friction coefficient. While numerous qualitative explanations have been proposed previously for the low friction coefficient exhibited by phyllosilicates, especially in the presence of water, our study provides a new step toward a quantitative, physically based model.

Role of Impurity Sulphur in the Ductility Trough of Austenitic Iron-Nickel Alloys.

The role of impurity sulphur in the ductility trough of iron–nickel (Fe–Ni) alloys is investigated using hot tensile tests. A strong detrimental effect of some ppm levels of sulphur is demonstrated. In addition, it is shown that, in the ductility trough, material failure occurs through subcritical grain boundary crack propagation, involving dynamic embrittlement at the crack tip, due to the sulphur. Very high intergranular crack growth rates are observed. This is possible because plastic deformation accelerates the transport of sulphur to the crack tip, by several orders of magnitude, compared to normal bulk diffusion. The ductility is recovered at high strain rates, which correlates with a decrease in the sulphur concentration measured on the fracture surface. It is suggested that the main mechanism of sulphur transport is dragging by moving dislocations.

Time-Dependent Propagation of 3-D Cracks in Rocks Under Hydromechanical Coupling

Crack propagation and rock failure under hydromechanical coupling have typical time-dependent characteristics, and the subcritical crack propagation is one of the most important causes of rock instability. Rheological tests based on mortar specimens containing single internal 3-D cracks and the corresponding numerical simulations are carried out to investigate the time-dependent characteristics of the crack propagation, the failure mode of rocks, and the effects of water pressure and crack dip angle. The mortar specimen exhibits a tensile-shear failure mode under the hydromechanical coupling as observed in rheological tests, and a macro-fracture penetrates the upper and lower ends of the specimen. The propagation rate of the crack decreases first and then increases. The crack propagation can be divided into three stages according to the relationship between the propagation rate and fracture parameters. The water pressure significantly reduces the time required for rock failure due to its promoting effect on the crack propagation rate, which has negative effects on the long-term stability of rocks. Cracks with a dip angle of 45° are more likely to cause rock failure under hydromechanical coupling, while cracks with larger dip angles exhibit a better long-term stability.

The Role of Chemistry in Fracture Pattern Development and Opportunities to Advance Interpretations of Geological Materials

AbstractFracture pattern development has been a challenging area of research in the Earth sciences for more than 100 years. Much has been learned about the spatial and temporal complexity inherent to these systems, but severe challenges remain. Future advances will require new approaches. Chemical processes play a larger role in opening‐mode fracture pattern development than has hitherto been appreciated. This review examines relationships between mechanical and geochemical processes that influence the fracture patterns recorded in natural settings. For fractures formed in diagenetic settings (~50 to 200 °C), we review evidence of chemical reactions in fractures and show how a chemical perspective helps solve problems in fracture analysis. We also outline impediments to subsurface pattern measurement and interpretation, assess implications of discoveries in fracture history reconstruction for process‐based models, review models of fracture cementation and chemically assisted fracture growth, and discuss promising paths for future work. To accurately predict the mechanical and fluid flow properties of fracture systems, a processes‐based approach is needed. Progress is possible using observational, experimental, and modeling approaches that view fracture patterns and properties as the result of coupled mechanical and chemical processes. A critical area is reconstructing patterns through time. Such data sets are essential for developing and testing predictive models. Other topics that need work include models of crystal growth and dissolution rates under geological conditions, cement mechanical effects, and subcritical crack propagation. Advances in machine learning and 3‐D imaging present opportunities for a mechanistic understanding of fracture formation and development, enabling prediction of spatial and temporal complexity over geologic timescales. Geophysical research with a chemical perspective is needed to correctly identify and interpret fractures from geophysical measurements during site characterization and monitoring of subsurface engineering activities.

Monitoring thermal barrier coating delamination progression by upconversion luminescence imaging

Upconversion luminescence imaging provided contrast for monitoring thermal barrier coating (TBC) delamination progression during interrupted furnace cycling to 1163 °C, with sensitivity even for early stages of subcritical delamination crack propagation. Image contrast for delamination monitoring is obtained because delamination cracks introduce an interface between a higher (TBC) and lower (air) index of refraction medium so that total internal reflection beyond a critical incident angle occurs for both the excitation and emission wave-lengths. Therefore, considerably greater luminescence emission is observed from regions containing delamination cracks. Upconversion luminescence produces exceptional image contrast because background fluorescence is very low when the detected emission is at a substantially shorter wavelength than the excitation. The upconversion luminescence emission was excited within a 6 μm thick Er3+/Yb3+ co-doped yttria-stabilized zirconia YSZ (YSZ:Er,Yb) layer beneath a 130 μm thick undoped YSZ layer, sequentially deposited with no interruption by electron-beam physical vapor deposition (EB-PVD) onto a NiPtAl bond-coated superalloy substrate. Excitation at 980 nm produced upconversion luminescence emission from Er3+ at 562 nm after two sequential energy transfers from Yb3+ co-dopant ions. Upconversion luminescence imaging, supported by scanning electron microscope inspection of interfacial damage, revealed that delamination progression proceeded by the formation of isolated microdelaminations with large separations between the TBC and thermally grown oxide (TGO) along with small-separation microcracks that propagated in the regions between the microdelaminations. In addition, upconversion luminescence imaging of the extent of delamination produced by Rockwell indentation clearly showed that the TBC becomes increasingly susceptible to mechanically induced damage throughout its cyclic life.