Failure Regime Research Articles

Atypical Presentation of Multiple Myeloma: From Heart Failure to Multiple Myeloma

Multiple myeloma (MM) is a hematological malignancy commonly associated with bone pain, hypercalcemia, and renal failure. However, its presentation can occasionally mimic other medical conditions, which may delay diagnosis. This case report describes a patient who was initially diagnosed and treated for heart failure but was later found to have MM, highlighting the importance of considering MM in the differential diagnosis of heart failure. A 56-year-old lady presented with recurrent episodes of shortness of breath, orthopnea, paroxysmal nocturnal dypsnea and bilateral lower limb swelling which she had been treated for decompensated heart failure with optimal therapy. She denied any family history of cardiovascular disease personal history of underlying medical condition and was a nonsmoker. This patient was diagnosed with multiple myeloma and probability of concomitant cardiac amyloidosis and commenced on bortezomib, thalidomide and dexamethasone (VTD) regime and standard optimal therapy of heart failure but her condition deteriorated. After a few days of starting chemotherapy, patient demised despite all the resuscitative effort. Multiple myeloma is common hematological malignancy with its distinct clinical features of “CRAB”, however, more attention and alertness should also be exercised by clinicians as to be able to diagnose it early.

Displacement residuals reveal landslide regime shifts

AbstractDespite significant progress in the development of advanced technologies for detecting and monitoring unstable slopes, accurately predicting catastrophic landslides remains a challenge. To tackle this challenge, our research integrates advanced prediction models and granular systems theory to provide insights into regime shifts within slow-moving deep-seated landslide dynamics. Our approach is designed to discern exceptional departures from historical landslide dynamics. The approach leverages the “group dynamics,” crucial for identifying precursory failure indicators, according to the generic dynamics of the precursory failure regime in granular systems. We select three different monitored slow-moving landslides as test cases. We employ an error correction cointegration vector autoregression model together with an exogenous regressor to encode historical spatiotemporal landslide dynamics and predict displacement at multiple locations by considering the historical landslide motion and relationship with external triggers. Displacement residuals are obtained by computing the difference between predicted and measured displacement for a given historical calibration time window. Threshold values for the displacement residuals are determined by analyzing the historical distribution of these residuals. Lastly, persistence in time of the threshold exceedance and the number of monitoring points that exceed the threshold at the same time are considered to encode the group dynamics. This approach offers several advantages, including the effective identification of critical regime shifts, adaptability, and transferability, and it introduces regime shift information into local landslide early warning systems. This approach can enhance confidence in the resultant alert, particularly when integrated with conventional alert systems, thereby improving the reliability of landslide warning systems.

Structural stability of China’s asteroid mission target 2016 HO3 and its possible structure

ABSTRACT Asteroid 2016 HO$_3$, a small asteroid (<60 m) in super fast rotation state ($\sim$28 min), and is the target of China’s Tianwen-2 asteroid sample-return mission. In this work, we investigate its structural stability using an advanced soft-sphere-discrete-element-model code, dembody, which is integrated with bonded-aggregate models to simulate highly irregular boulders. The asteroid body is numerically constructed by tens of thousands particles, and then is slowly spun up until structural failure. Rubble piles with different frictions, cohesions, morphologies, grain size distributions, and structures are investigated. We find a 2016 HO$_3$ shaped granular asteroid would undergo tensile failure at higher strengths as opposed to shear failure in lower strengths, regardless of its shape and constituent grain size ratio. In the tensile failure regime, the critical tensile strength is proportional to the square of the spin rate, but surprisingly, is independent of the internal friction angle. Such relations indicate that the Maximum Tensile Stress criterion emerges as superior paradigm for investigating the failure behaviour of fast-rotating asteroids. We predict that the high-spin rate of asteroid 2016 HO$_3$ requires a surface strength over $\sim$3 Pa and a bulk tensile strength over $\sim$10–30 Pa. Through comparing these strength conditions with the latest data from asteroid missions, we suggest a higher likelihood of a monolithic structure over a typical rubble pile structure. However, the possibility of the latter cannot be completely ruled out. In addition, the asteroid’s surface could retain a loose regolith layer globally or only near its poles, which could be the target for sampling of Tianwen-2 mission.

A comparative analysis of compressive and wear failure of laser-powder bed fused Stainless Steel 316L produced with different hatch spacing in stripe and contour patterns

The selection of hatch spacing is crucial in additive manufacturing processes to produce a defect free Stainless Steel 316L (SS) components, especially in laser powder bed fusion (LPBF) process. Improper selection of hatch spacing could lead to various failure regimes (like vertical cracking, porosity, and un-melted particles) in Stainless Steel 316L (SS) component produced through laser powder bed fusion (LPBF). Further, the failure regimes have a direct impact on the hardness, compression strength, friction, and wear properties of LPBF SS components. The present study has taken substantial efforts to analyse the impact of various hatch spacing (0.08 mm, 0.10 mm. and 0.12 mm) in stripe and contour patterns, in terms of morphology, mechanical, and tribological properties of LPBF SS components. Also, the present study elucidates how variations in hatch spacing influences the features like particle fusion, crack formation, density, hardness, surface roughness, compression, and wear properties. The stripe pattern with low hatch spacing of 0.08 mm showed better particle fusion and high surface roughness; whereas the high hatch spacing has produced voids, un-melted powder particles, and cracks in the stripe and contour pattern. High densities and hardness values were attributed to the stripe patterns with more effective melting and fusing of powder particles. XRD analysis revealed the stable phase compositions across various hatch spacing with a predominant FCC crystal structure. Residual stress distribution was significantly influenced by the hatch spacing for both stripe and contour patterns. Importantly, the low hatch space leads has promoted the tensile residual stress formation and vice versa for the higher hatch spacing. Stripe patterns showed higher compression strengths with buckling and shear mode as a compression failure. The stripe pattern demonstrated a low specific wear rate (SWR) and coefficient of friction (COF) compared to the contour pattern, with respect to the various hatch spacing. Furthermore, the simulated body fluid (SBF) lubrication regime played a significant role in reducing the COF. Patches, groves, furrows, and craters demonstrated the abrasive and adhesive failure for both stripe and contour pattern, which is further detailed in the article.

Rock fines breakage by flow-induced stresses against drag: geo-energy applications

The paper presents a strength-failure mechanism for colloidal detachment by breakage and permeability decline in reservoir rocks. The current theory for permeability decline due to colloidal detachment, including microscale mobilisation mechanisms, mathematical and laboratory modelling, and upscaling to natural reservoirs, is developed only for detrital particles with detachment that occurs against electrostatic attraction. We establish a theory for detachment of widely spread authigenic particles due to breakage of the particle-rock bonds, by integrating beam theory of particle deformation, failure criteria, and creeping flow. Explicit expressions for stress maxima in the beam yield a graphical technique to determine the failure regime. The core-scale model for fines detachment by breakage has a form of maximum retention concentration of the fines, expressing rock capacity to produce breakable fines. This closes the governing system for authigenic fines transport in rocks. Matching of the lab coreflood data by the analytical model for 1D flow exhibits two-population particle behaviour, attributed to simultaneous detachment and migration of authigenic and detrital fines. High agreement between the laboratory and modelling data for 16 corefloods validates the theory. The work is concluded by geo-energy applications to (i) clay breakage in geological faults, (ii) typical reservoir conditions for kaolinite breakage, (iii) well productivity damage due to authigenic fines migration, and (iv) feasibility of fines breakage in various geo-energy extraction technologies.

Evaluating failure regime of an active landslide using instability and rockfall simulation, NW Himalaya

Evaluating failure regime of an active landslide using instability and rockfall simulation, NW Himalaya

Failure in articular cartilage: Finite element predictions of stress, strain, and pressure under micro-indentation induced fracture

Articular cartilage is found at the distal end of long bones and is responsible for assisting in joint articulation. While articular cartilage has remarkable resistance to failure, once initially damaged, degeneration is nearly irreversible. Thus, understanding damage initiation is important. There are a few proposed mechanisms for articular cartilage failure initiation: (A) a single collagen fibril stress-based regime; (B) a rate-dependent regime captured by brittle failure at slow displacement rates (SDR) and ductile failure at fast displacement rates (FDR); and (C) a rate-dependent regime where failure is governed by pressurization fragmentation at SDR and governed by strain at FDR. The objective of this study was to use finite element (FE) models to provide evidence to support or refute these proposed failure mechanisms. Models were developed of microfracture experiments that investigated osmolarity (hypo-osmolar, normal osmolarity, and hyper-osmolar) and displacement rate (FDR and SDR) effects. Cartilage was modeled with a neo-Hookean ground matrix, strain-dependent permeability, nonlinear fibril reinforcement with viscoelastic fibril terms, and Donnan equilibrium swelling. Total stress, solid matrix stress, Lagrange strain, and fluid pressure were determined under the indenter tip at the moment of microfracture. Results indicated significant rate dependence across multiple outputs, which does not support (A) a single failure regime. Larger solid and fluid pressures at FDR than SDR did not support (C) a rate-dependent regime split by pressurization at SDR and strain at FDR. Consistent solid shear stresses at SDR and consistent third principal solid stresses at FDR support (B) the ductile-brittle failure regime. These findings help to shed light on the underlying mechanisms of articular cartilage failure, which have implications for the development of osteoarthritis.

Ultra-tough architected adhesive joints for integrated composite processing and bonding

Deployment of advanced polymer-based composites in critical structures requires, among others, breakthroughs in adhesive bonding solutions. Indeed, available methods still suffer from limited fracture toughness of adhesives and from time-consuming bonding processes. Here, we demonstrate a novel concept of architected thermoplastic joints with exceptional fracture resistance up to 5000 J/m2, fully integrated with the composite resin transfer molding process, hence simultaneously targeting both limitations. This extreme toughness is activated through controlled 3D printed hollow pattern within a Nylon bondline. A synergetic combination of plastic dissipation, crack deflection, branching and arrest is tuned by changing the pattern characteristics. Three failure regimes are unraveled through fractographic analyses and finite element models. A stress-at-a-distance fracture criterion, identified for each constituent, quantitatively predicts the toughness variations along the crack path. This approach, amenable to dissimilar bonding between metals and composites, paves the road towards novel and higher performance structures and manufacturing approaches.

A modeling study of elastoplastic rock failure regime based on finite discrete elements

Numerical simulation has become a pivotal method in geotechnical engineering for analyzing rock failure. However, traditional model lacks comprehensive elastoplastic rock characterization. Therefore, a new finite-discrete element model using the Drucker-Prager criterion and cohesive elements based on a traction-separation law to accurately simulate elastoplastic rock breaking has been built. A scratch test simulation is conducted to describe the mechanical response and failure characteristics of the rock during the cutting process. Rock failure characteristics derived from numerical simulations align closely with experimental observations. These simulations successfully replicate both the ductile and brittle regimes observed during scratch tests. Furthermore, they provide insights into the primary driving factors behind rock failure under different regimes. Variation of cutting force and specific energy obtained from the model are entirely consistent with experimental results, with the specific energy decreasing following a −0.5 power law, thus explaining the energy dissipation rule of the specific energy decrease. In brittle regime, crush zones and the resulting rough shearing surface are observed, plastic damage is also found, revealing that the cutter tip is the key structure influencing them. The model established in this paper holds significant importance for rock mechanical property evaluation and the optimization design of cutter structures.

Modelling the effect of layer strength distribution on the brick-and-mortar failure regimes and properties

Brick-and-Mortar structures are of high interest because their staggered multi-material arrangement can result in a remarkable combination of high strength and high toughness. Synthetic replication of these structures with high geometric control has been made possible recently with the advances in multi-material Additive Manufacturing (AM). However, very little is known on how inherent material variation in the constituent materials, which can be significant in AM, affects the structure response.In this work, we use a semi-analytical model to theoretically show that a variation in the strength of the layers in a Brick-and-Mortar structure has a significant effect on the failure response of the structure. It can lead to changes in failure regimes and negatively impact the mechanical properties, such as decrease the strain to failure or decrease the yield stress. This is particularly pronounced when the material behaviour is situated close to the transition point between failure regimes. We then present an experimental method to capture strength variability in the layer material and demonstrate that the incorporation of this variability into the semi-analytical model improves our prediction of the failure response of the structure, as compared to experiments.

Experimental study on solid particle migration and production behaviors during marine natural gas hydrate dissociation by depressurization

Sand production is one of the main obstacles restricting gas extraction efficiency and safety from marine natural gas hydrate (NGH) reservoirs. Particle migration within the NGH reservoir dominates sand production behaviors, while their relationships were rarely reported, severely constrains quantitative evaluation of sand production risks. This paper reports the optical observations of solid particle migration and production from micrometer to mesoscopic scales conditioned to gravel packing during depressurization-induced NGH dissociation for the first time. Theoretical evolutionary modes of sand migration are established based on experimental observations, and its implications on field NGH are comprehensively discussed. Five particle migration regimes of local borehole failure, continuous collapse, wormhole expansion, extensive slow deformation, and pore-wall fluidization are proved to occur during depressurization. The types of particle migration regimes and their transmission modes during depressurization are predominantly determined by initial hydrate saturation. In contrast, the depressurization mainly dominates the transmission rate of the particle migration regimes. Furthermore, both the cumulative mass and the medium grain size of the produced sand decrease linearly with increasing initial methane hydrate (MH) saturation. Discontinuous gas bubble emission, expansion, and explosion during MH dissociation delay sand migration into the wellbore. At the same time, continuous water flow is a requirement for sand production during hydrate dissociation by depressurization. The experiments enlighten us that a constitutive model that can illustrate visible particle migration regimes and their transmission modes is urgently needed to bridge numerical simulation and field applications. Optimizing wellbore layout positions or special reservoir treatment shall be important for mitigating sand production tendency during NGH exploitation.

Dwell-fatigue crack growth behaviour of Alloy 709

Dwell-fatigue crack growth behaviour of an advanced austenitic stainless steel Alloy 709 has been investigated and compared with that of a conventional Type 316H stainless steel. The test procedure employed alternation of 1 h dwell-fatigue loading and 0.25 Hz fast cycling so that crack growth rates (da/dN) obtained from dwell-fatigue loading can be compared to those purely result from fatigue mechanism on the same test-piece. Tests were conducted at 550, 650 and 750 °C in air using 0.5 T compact tension test-pieces under a fixed maximum load of 8 kN and a stress ratio, R, of 0.1. For the investigated temperature and ΔK ranges, crack growth mechanisms of fatigue alone, creep alone and mixed fatigue-creep have all been observed. Detailed fractographic and metallographic observations were conducted to interpret failure mechanisms and regimes of different failure modes. Compared to crack growth rates obtained under 0.25 Hz fatigue loading, dwell-fatigue produces: no obvious increases in crack growth rates at a test temperature of 550 °C; a moderate increase (∼ 2–5 times) at a test temperature of 650 °C; and, over a tenfold increase at a test temperature of 750 °C. Compared to 316H, Alloy 709 has much improved resistance against creep-fatigue crack growth, here confirmed at the single test temperature of 650 °C.

Small‐Scale Characterization of Shock Sensitivity for Non‐Ideal Explosives Based on Imaging of Detonation Failure Behavior

AbstractThe plethora of potential homemade explosive (HME) formulations combined with the fact they often exhibit large critical diameters make them expensive to characterize with traditional large‐scale tests. A relatively new method for small‐scale characterization was investigated using non‐ideal explosive charges consisting of ammonium nitrate (AN) and various fuels. Here, we extend this method using an optical characterization technique that utilizes the decay rate of the reaction wave velocity in failing detonations of sub‐critical diameter charges as a metric for the shock sensitivity of an explosive. The conditions required for successful detonation initiation and failure have long been used to investigate shock sensitivity (critical diameter, gap tests, run‐to‐detonation experiments); however, the failure regime still remains largely unexplored. The utility of this small‐scale characterization technique lies in its ability to determine the relative shock sensitivity of explosive with minimal material and experiments while simultaneously providing transient velocity data for potential use in modeling efforts. In this work, high speed imaging was used and analyzed to determine rates of reaction wave velocity decay in the AN‐fuel samples. Among the fuels tested with AN were diesel (ANFO), nitromethane (ANNM), and aluminum (AN−Al). It was found that nitromethane was the most effective at sensitizing the AN of the systems considered. In both ANNM and AN−Al, maximum shock sensitivity (here measured as the minimum reactive wave velocity decay rate) occurred at fuel percentages below stoichiometric mixtures. This was interpreted to be due to the competing effects of stoichiometry and hot spot criticality. Sensitivity results were compared to run‐to‐failure (RTF) distances and published critical diameter trends which showed good correlation.

Dynamic fracture regimes forinitially prestressed elastic chains.

We study the propagation of a bridge crack in an anisotropic multi-scale system involving two discrete elastic chains that are interconnected by links and possess periodically distributed inertia. The bridge crack is represented by the destruction of every other link between the two elastic chains, and this occurs with a uniform speed. This process is assumed to be sustained by energy provided to the system through its initial configuration, corresponding to the alternating application of compression and tension to neighbouring links. The solution, based on the Wiener–Hopf technique and presented in Ayzenberg-Stepanenko et al. (Ayzenberg-Stepanenko et al. 2014 Proc. R. Soc. A 470, 20140121 (doi:10.1098/rspa.2014.0121)) is used to compute the profile of the medium undergoing failure. We investigate when this solution, representing the steady failure process, is physically acceptable. It is shown that the analytical solution is not always physically applicable and can be used to determine the onset of non-steady failure regimes. These arise from the presence of critical deformations in the wake of the crack front at the sites of the intact links. Additionally, we demonstrate that the structural integrity of the discrete elastic chains can significantly alter the range of speeds for which the bridge crack can propagate steadily.This article is part of the theme issue ‘Wave generation and transmission in multi-scale complex media and structured metamaterials (part 2)’.

Effect of osmolarity and displacement rate on cartilage microfracture clusters failure into two regimes

Articular cartilage is a poroviscoelastic (PVE) material with remarkable resistance to fracture and fatigue failure. Cartilage failure mechanisms and material properties that govern failure are incompletely understood. Because cartilage is partially comprised of negatively charged glycosaminoglycans, altering solvent osmolarity can influence PVE relaxations. Therefore, this study aims to use osmolarity as a tool to provide additional data to interpret the role of PVE relaxations and identify cartilage failure regimes. Cartilage fracture was induced using a 100 μm radius spheroconical indenter at controlled displacement rates under three different osmolarity solvents. Secondarily, contact pressure (CP) and strain energy density (SED) were estimated to cluster data into two failure regimes with an expectation maximization algorithm. Critical displacement, critical load, critical time, and critical work to fracture increased with increasing osmolarity at a slow displacement rate whereas no significant effect was observed at a fast displacement rate. Clustering provided two distinct failure regimes, with regime (I) at lower normalized thickness (contact radius divided by sample thickness), and regime (II) at higher normalized thickness. Varied CP and SED in regime (I) suggest that failure in the regime is strain-governed. Constant CP and SED in regime (II) suggests that failure in the regime is dominantly governed by stress. These regimes can be interpreted as ductile versus brittle, or using a pressurized fragmentation interpretation. These findings demonstrated fundamental failure properties and postulate failure regimes for articular cartilage.

SIMULATION OF HOMOGENEOUS HYDROGEN-AIR DETONATION INTERACTION WITH POROUS FILTER

Calculations of the interaction of a cellular detonation wave (DW) with an inert porous filter were carried out based on the developed physical and mathematical model of the mechanics of heterogeneous medium which takes into account the detailed chemical kinetics of chemical reactions in the gas phase. Under an inert porous filter, a motionless lattice of inert particles is considered. The following flow regimes were revealed: propagation of attenuated cellular DW at velocities less than the Chapman-Jouguet velocity and detonation failure with the destruction of the cellular structure. Critical volume concentrations of filter particles corresponding to the detonation failure regime were calculated. Dependences of the normalized DW velocity and detonation cell size on the volume concentration of particles in filters were calculated. The concentration limits of detonation (critical volume concentrations of particles lead to detonation failure) in filters with diameters of 50, 100, and 200 µm were determined. The dependences of the normalized DW velocity and size of detonation cell on the volume concentration and diameter of particles in filters were calculated.

The Brittle–Ductile Transition and the Formation of Compaction Bands in the Savonnières Limestone: Impact of the Stress and Pore Fluid

Carbonate sediments play a prominent role on the global geological stage as they store more than 60% of world’s oil and 40% of world’s gas reserves. Prediction of the deformation and failure of porous carbonates is, therefore, essential to minimise reservoir compaction, fault reactivation, or wellbore instability. This relies on our understanding of the mechanisms underlying the observed inelastic response to fluid injection or deviatoric stress perturbations. Understanding the impact of deformation/failure on the hydraulic properties of the rock is also essential as injection/production rates will be affected. In this work, we present new experimental results from triaxial deformation experiments carried out to elucidate the behaviour of a porous limestone reservoir analogue (Savonnières limestone). Drained triaxial and isotropic compression tests were conducted at five different confining pressures in dry and water-saturated conditions. Stress–strain data and X-ray tomography images of the rock indicate two distinct types of deformation and failure regimes: at low confinement (10 MPa) brittle failure in the form of dilatant shear banding was dominant; whereas at higher confinement compaction bands orthogonal to the maximum principal stress formed. In addition to the pore pressure effect, the presence of water in the pore space significantly weakened the rock, thereby shrinking the yield envelope compared to the dry conditions, and shifted the brittle–ductile transition to lower effective confining pressures (from 35 MPa to 29 MPa). Finally, permeability measurements during deformation show a reduction of an order of magnitude in the ductile regime due to the formation of the compaction bands. These results highlight the importance of considering the role of the saturating fluid in the brittle–ductile response of porous rocks and elucidate some of the microstructural processes taking place during this transition.

Size effects and failure regimes in notched micro-cantilever beam fracture

Fracture tests using notched micro-cantilever (MC) specimens are increasingly being used to measure the fracture toughness of materials at the micro-scale. Detailed finite element analyses (FEAs) of loading of self-similar micro- and bulk cantilever beam fracture specimens using isotropic, elastoplastic constitutive models, are conducted to critically examine the validity of the toughness data obtained using MC specimens. From the simulated normalized load versus load point displacement and the corresponding normalized energy release rate versus load curves, the transition of the failure regimes from crack propagation to plastic collapse of the uncracked notch ligament are identified. While the crack propagation regime allows for the estimation of valid fracture toughness of the probed material, the plastic collapse regime does not. The effects of specimen aspect ratios, material hardening, and yield criteria on the master curves and transition point are examined. A method to interpret the failure regimes, assess the validity and size effects in micro-cantilever fracture tests is proposed. An expression is derived for the minimum size requirements of MC fracture specimens in order to get a valid fracture test. The data reported in the literature from fracture tests on bulk metallic glasses, nano-crystalline materials and ultra-fine grained materials are assessed using the proposed methodology. The present work has important implications for specimen design, interpretation of failure regimes, and potential size effects in MC fracture tests.

Probabilistic analysis of cleavage fracture in commercial polycrystalline tungsten

Polycrystalline tungsten is a promising candidate as plasma-facing armour material in future fusion reactors. Below the DBTT tungsten shows brittle or semi-brittle behaviour with no or little plastic deformation before cleavage fracture. Moreover, tungsten has an inherent low fracture toughness as well as a large scatter within the strength properties. This requires a statistical treatment of the strength values. Therefore, four-point bending tests in the temperature range of room temperature (RT) to 400 °C were performed to allow the Weibull analysis in brittle failure regime and/or the Beremin model analysis in case of onset of plastic behaviour while approaching the DBTT temperature. The analyses are supported by FE simulations. Weibull and Beremin parameter values are determined from the simulation results using post-processing codes.

Effect of angled layers on failure regimes in brick-and-mortar structures

Brick-and-Mortar structures can exhibit exceptional combinations of properties, such as high strength and toughness. The properties are highly dependent on the failure regime, namely the ability to distribute damage prior to failure. In our recent work on rectangular Brick-and-Mortar structures, we have identified a transition from localised damaged (called ‘two-peak’ failure) to distributed damage (called ‘peak-plateau-peak’ failure), depending on the brick aspect ratio and the relative normal and shear layer material properties. However, the effect of non-rectangular brick shapes on these failure regimes has not yet been explored. In this work we predict with semi-analytical modelling, and validate with experiments, that introducing an angle into the ‘shear’ layers of the Brick-and-Mortar structure to create ‘diamond’ and ‘inverse diamond’ brick shapes results in a transition from ‘two-peak’ to ‘peak-plateau-peak’ failure for low aspect ratios. It is further shown that the angle required to transition to ‘peak-plateau-peak’ failure decreases with increasing aspect ratio, and that introducing an out of-plane angled layer in the form of an osteomorphic brick shape can further decrease the angle required for the transition. Our work demonstrates that the transition from ‘two-peak’ to ‘peak-plateau-peak’ failure significantly increases the toughness of the structure, without compromising strength or stiffness, highlighting the importance of understanding and controlling the parameters that affect the failure regimes.