Propensity For Damage Research Articles

Self-healing thermally conductive polymer composites based on polyvinyl alcohol with dynamic borate ester and hydrogen bonds

Traditional thermally conductive polymer materials exhibit a propensity for damage when applied in dynamic environments, which leads to shortened service life and suboptimal utilization of resources. Herein, polyvinyl alcohol (PVA)-based thermally conductive composites with a self-healing capability are prepared based on dynamic borate ester bonds and hydrogen bonds. Poly(dopamine) functionalized graphene oxide (denoted as PGO) is used as a thermally conductive filler to achieve a high thermal conductivity (TC) of 0.79 W/(m·K) for the PGO/PVA composites, which is 527% of pure PVA (0.15 W/(m·K)). The improved TC of PGO/PVA composites is mainly attributed to the reduction in interface thermal resistance and the construction of heat conduction channels. Additionally, the PGO/PVA composites display a self-healing efficiency higher than 60% at room temperature without external simulation. Furthermore, the as-prepared PGO/PVA composites exhibit excellent mechanical properties, with a tensile strength of 409 kPa and an elongation at break of 479%, respectively. This work provides a promising strategy for fabricating thermally conductive polymer composites, which can be deployed as thermal interface materials for long-term applications.

Analysis of hydraulic parameters in determining the occurrence of cavitation in the spillways of the Furnas, Luiz Carlos Barreto de Carvalho and Batalha hydroelectric power plants

Analysis of hydraulic parameters in determining the occurrence of cavitation in the spillways of the Furnas, Luiz Carlos Barreto de Carvalho and Batalha hydroelectric power plants

Spherical indentation test for quasi-non-destructive characterisation of asphalt concrete

The indentation test is a promising technique for the viscoelastic characterisation of asphalt concrete (AC). Indentation measurements are primarily influenced by the material properties in the direct vicinity of the indenter-specimen contact point. Accordingly, it may become a useful alternative for the characterisation of thin asphalt layers as well as for a quasi-non-destructive AC characterisation in the field. In this study, the spherical indentation test is used to measure the linear viscoelastic properties of AC mixtures extracted from a road test section. The measured complex moduli are compared to those obtained by the shear box test and are found to exhibit a linear correlation. The measurements are further analysed using the Gaussian mixture model to assign each indentation test to either aggregate-dominated or mastic-dominated response. The measurements attributed to mastic-dominated response are found to be more sensitive to the temperature and AC’s binder properties as compared to the average measurements. Accordingly, the proposed test method may provide a promising tool to measure AC viscoelastic properties and monitor the changes in AC binder phase in a non-destructive manner. A finite element micromechanical model is used to identify a representative scale for the response measured in mastic-dominated tests as well as to quantify the effect of measured properties on the AC damage propensity.

Backside polyethylene wear in reverse shoulder arthroplasty.

Aseptic loosening from implant-associated osteolysis in reverse shoulder arthroplasty (RSA) may contribute to premature implant failure. Although articular side polyethylene (PE) damage has been well documented in the literature, no studies to date have investigated backside wear in RSA. The aims of this investigation were to (1) document and compare the damage between the backside and articular surface in explanted RSA components, (2) assess whether certain quadrants have a greater propensity for damage, and (3) report the most common mode(s) of backside PE damage. Twenty-one RSA humeral liners retrieved during revision procedures between 2005 and 2014 were included for analysis. The mean time between implantation and extraction was 16 months (10 days-88 months). Diagnoses at the time of revision included dislocation (10), infection (4), mechanical failure (3), loosening (2), and unknown (2). Liners were examined under light microscopy (×10-30 magnification) and damage on the articular and backside of the liner surface was graded using the modified Hood score. The location and damage modality were compared between the articular side and backside of the implant. Damage was noted on the articular surfaces of all 21 liners and on the backside surface of 20 liners. The total damage in all the quadrants was higher on the articular surface than on the backside of the component, with a mean difference in total quadrant damage scores of 11.74 ± 3.53 (P < .001). There was no difference in damage among the quadrants on the backside (P = .44) or the articular surface (P = .08). The articular side exhibited greater scratching, abrasion, and surface deformation than the backside (P < .001). This short-term retrieval study demonstrated that backside PE damage occurs on the humeral component of RSA implants. There was greater damage to the articular side of the liner but wear to the backside was present in almost all liners. The clinical importance of backside wear in RSA and its overall contribution to PE particulate disease and osteolysis needs further investigation.

Effects of temperature and microstructure on low cycle fatigue behaviour of a PM Ni-based superalloy: EBSD assessment and crystal plasticity simulation

The macro and mesoscale deformation and damage of the PM nickel-based superalloy FGH4098 under low cycle fatigue loading at elevated temperatures were investigated using both SEM/EBSD characterization and crystal plasticity finite element (CPFE) simulations. The results indicate that higher temperature leads to more severe macroscale damage i.e. larger areas of hysteresis loops and shorter fatigue life with transgranular failure mode at both 650 °C and 750 °C. The misorientation parameters derived from EBSD characterization show similar deformation at both temperatures, but more intense localized deformation in the crack initiation region at 750 °C. Based on the accumulated shear-strain energy dissipation density and Fatemi-Socie fatigue indicator parameter, the distribution and evolution of fatigue damage are shown to be strongly affected by local stress–strain state and temperatures, and more severe and homogeneous damage is found at 750 °C. The CPFE simulation results also show higher damage propensity, as indicated by the fatigue indicator parameters used here, in the vicinity of annealing twin boundaries with high difference in elastic modulus.

Prediction of vibration induced damage in photovoltaic modules during transportation: finite element model and field study

The transportation of the photovoltaic (PV) modules involves excessive vibrations and shocks. These dynamic loads can crack the solar cells and glass of the PV modules. The cracks generated in solar cells during the transportation phase may not always have immediate implications on the electrical performance of the PV modules. However, in the long-run, cracks generated during transportation of the modules may propagate during operation in field due to wind load, snow load and thermal stresses. The propagation of cracks may create electrical isolation in the cells of a PV module, which can cause loss of electrical power. Therefore, it is important to minimize the damage in PV modules due to transportation and mechanical handling. In this work, PV modules have been transported in packaging following the industry practices to cover a distance of 270 km with accelerometers attached on several modules. Finite element (FE) modelling has been used to calculate natural frequency of vibration for the assembly of the PV modules by simulating the conditions close to the actual transportation experiment. This study shows that transportation makes the modules vibrate at their natural frequency. The first four natural frequencies of vibration calculated through the FE simulations match well with the peaks observed in the power spectral density profiles experienced by PV modules during transportation. Mode shapes corresponding to the first four natural frequencies have also been visualized to identify the contours with maximum displacement. It is hypothesized that out of all the cells, those falling within the contour of maximum displacement would have higher propensity for damage during the transportation. The results presented here can be useful for PV community to improve the packaging methodology, dimensions and material selection of the photovoltaic modules.

Importance of microstructure modeling for additively manufactured metal post-process simulations

This work investigates the significance of microstructure-level modeling by simulating the material response of an inhomogeneous selective laser melted (SLM) Inconel 625 specimen subjected to two different post-process operations, namely micro-milling and laser shock peening (LSP). A physics-based thermal finite element simulation is executed to obtain the SLM thermal history from which a 3-dimensional inhomogeneous microstructure representative volume element (RVE) is generated via the Dynamic Kinetic Monte Carlo predictive model. A Johnson–Cook plasticity definition coupled with Hall–Petch strengthening is used to define unique yield surfaces for individual grains based on their major diameters. Micro-milling and LSP simulations are subsequently executed with and without considering an inhomogeneous microstructure RVE in attempt to elucidate differences in the plastic strain, temperature, induced stress magnitude and distribution, as well as differences that arise during material removal for the micro-milling only. The micro-milling simulations reveal a greater volumetric distribution of plastic strain and temperature for the inhomogeneous case, although the homogeneous case with isotropic assumption reveals greater heat dissipation at the tool-workpiece interface with 27% greater contact pressure and 39% greater frictional shear stress. Examining the ductile and shear damage progression at a specific time increment reveals that the inhomogeneous model has a slightly lower damage propensity in comparison the homogeneous case, despite having identical damage models and boundary conditions. Variation in the SLM process-dependent yield surfaces, for grains at different locations, results in spatial variations of the computed stress triaxiality, which influences the material removal, as well as the stress concentrations developed near the tool-workpiece interface. Thus, a process-structure-property relationship is captured with the microstructure modeling. This work is the first to illuminate the importance of capturing SLM-induced anisotropy, considering the additively manufactured grain structure subject to micro-milling and LSP post-processes.

An analysis of fracture in staggered mineralized collagen fibril arrays

Fracture resistance of bone arises from various toughening mechanisms at multiple hierarchical levels. Despite considerable effort devoted to identification of fracture mechanisms associated with the ingenious hierarchical structure of bone, how the structural elements at the submicroscale contribute to the toughness of bone is largely unknown. In this study, the calculations are carried out for a biological composite consisting of mineralized collagen fibrils (MCFs) embedded in an extrafibrillar matrix (EFM), and the individual effects of the parameters associated with energy dissipation in the EFM are elucidated. The intrafibrillar plasticity through mineral/collagen sliding, the interfibrillar sliding and the mechanism of energy dissipation of the EFM are incorporated in the computational model. Furthermore, the staggered arrangement of MCFs and the fracture of the interfaces between MCFs and the EFM are accounted for. It is found that high stiffness of the EFM gives rise to enhanced energy dissipation in the EFM and reduced damage of the MCF/EFM interface. In addition, plastic deformation in MCFs is activated by the high stiffness of the EFM, which promotes energy dissipation, thereby enhancing toughness of the MCF arrays. The low initial yield stress of the EFM plays the roles in increasing energy dissipation in the EFM, promoting plastic deformation in MCFs and mitigating fracture of the MCF/EFM interface. The fracture behavior of MCF arrays is also influenced by the post-yield strain hardening behavior of the EFM; strong strain hardening enables diffuse damage of the MCF/EFM interface. We further reveal that strong post-yield strain hardening of MCFs increases the propensity of damage of the MCF/EFM interface and delays plastic deformation in MCFs. The findings of this study can not only shed new light on the fracture mechanisms of the staggered MCF arrays, but also provide mechanistic insights into bioinspired materials design.

Measurement and analysis of vibration and mechanical damage to bananas during long-distance interstate transport by multi-trailer road trains

Mechanical damage induced by vibration is a known cause of quality deterioration and wastage of fresh produce in post-harvest supply chains. The need to minimize visual defects in fruits, such as bananas, is being driven by the growing consumer preference for high quality produce. Transport of produce interstate and internationally from the growing regions to major retail markets, however, increases the risk of exposure of fruits to injurious vibration excitation. This study measured the vibration, and consequential mechanical damage, to bananas stacked at different stack heights and positions in a multi-trailer road train during an interstate road transport of over 3000 km in distance. Significantly different damage levels in bananas were observed in different pallet positions of the road train with the highest damage propensity revealed at the most rear pallet position. The damage levels in each pallet position were found to closely correspond with the Root-Mean-Square (RMS) acceleration of the vibration excitation on the trailer floor. The highest energy Power-Spectral Density (PSD) peaks were revealed to be concentrated in the lower frequency range (0.1–5 Hz). The cartons stacked in the top tiers of each pallet showed significantly increased mechanical damage followed by the bottom tiers with the middle-tiers exhibiting minimal damage. Palletized banana cartons subjected to simulated vibration, on a laboratory vibration simulator, demonstrated that vibration in the high frequency range (>30 Hz) was attenuated with the height of the carton in the pallet. However, the transmissibility of vibration energy in the range of 3–20 Hz was the greatest in the top-tier cartons, resulting in excessive mechanical damage to the bananas. The characterization of damage to bananas at different stack positions\\heights of multi-trailer road trains is an integral step for the development of damage reduction mechanisms. These would require the design, optimization, and simulation testing of better packaging alternatives targeted at minimizing the occurrence of mechanical injury in-transit.

Crystal plasticity assessment of inclusion- and matrix-driven competing failure modes in a nickel-base superalloy

Two competing failure modes, namely inclusion- and matrix-driven failures, are studied in a Ni-base superalloy, RR1000, subjected to fatigue loading using crystal plasticity finite element (CPFE) simulations. Each individual factor related to the inclusion, which may contribute to crack initiation, is isolated and systematically investigated. Specifically, the role of the inclusion stiffness, loading regime, loading direction, a debonded region in the inclusion-matrix interface, microstructural variability around the inclusion, inclusion size, dissimilar coefficient of thermal expansion (CTE), temperature, residual stress, and distance of the inclusion from the free surface are studied in the emergence of two failure modes. The CPFE analysis indicates that the emergence of a failure mode is an outcome of the complex interaction between aforementioned factors. We observe the possibility of a higher probability of failure due to inclusions with increasing temperature, if the CTE of the inclusion is higher than the matrix, and vice versa. We do not find any overall correlation between the inclusion size and its propensity for damage, based on an inclusion that is of the order of the mean grain size. Finally, the CPFE simulations indicate that the surface inclusions are more damaging than the interior inclusions for similar surrounding microstructures.

Hemodynamics Characteristics of a Four-Way Right-Atrium Bypass Connector

Currently, the surgical procedure followed by the majority of cardiac surgeons to address right ventricular dysfunction is the Fontan procedure, which connects the superior vena cava and inferior vena cava (IVC) directly to the left and right pulmonary arteries (LPA and RPA, respectively) bypassing the right atrium. The goal of this study is to develop a patient-specific four-way connector to bypass the dysfunctional right ventricle and augment the pulmonary circulation. The four-way connector was intended to channel the blood flow from the inferior and superior vena cava directly to the RPA and LPA. By creating a connector with proper hemodynamic characteristics, one can control the jet flow interactions between the inferior and superior vena cava and streamline the flow toward the RPA and LPA. The focus for this study was on creating a system that could identify the optimal configuration for the four-way connector for patients from 0 to 20 years of age. A platform was created in ANSYS that utilized the design of experiments (DOE) function to minimize power-loss and blood damage propensity in the connector based on junction geometries. It was confirmed that as the patient's age and artery size change, the optimal size and shape of the connector also changes. However, the corner radius did not decrease at the same rate as the opening diameters. However, it was found that power losses within the connector decrease, and average and maximum blood traversal time through the connector increased for increasing opening radius.

特異な腐食環境下での配管腐食減肉に関する損傷の起こり易さの感受性抽出方法(ベイズの定理)の研究

A piping plan depends on inspection history or inspection data in order to extract propensity of damage mechanism. The inspection data are ①Periodic maintenance inspection record (SDI), ②On-stream inspection data (OSI), ③Unplanned stop or extraordinary inspection records and ④corrosion-loop database visualized by evaluating corrosion rate as a corrosion system. Each of injury site of corrosion thinning with an organic acid as a specific injury mechanism, operating temperature conditions as a condition for extracting parts, fluid corrosion factor, structure factor, and material is quantified qualitatively or semi-qualitatively. It states that priority order by data visualization of damage propensity (Bayesian theorem) is required.

Landslide susceptibility and risk assessment in a non-mountainous region – a case study of Koronowo, northern Poland

The study deals with landslide threats in a low-relief region which exemplifies an area rarely perceived as prone to such geohazards. Actually, in the gently undulated landscape in the vicinity of Koronowo at the Brda River (South Pomeranian Lake District, northern Poland) intensified landsliding was observed in the recent years. The field mapping and examination of air photos showed that endangered terrains are fairly extensive and cannot be limited to initially identified slope failure incidences (hot-spots). The devised landslide susceptibility and hazard map is an outcome of predictive modelling using empirical likelihood ratio function ( LR ) with respect to seven evidential layers: elevation, slope angle, slope aspect, flow accumulation, surface deposits, depth to glacial raft, land cover as well as the landslide scars. The values of potential losses were calculated based on the mapped land-use categories and current market prices of estates and services. The final map, which resulted from combining landslide hazard with potential losses, shows damage propensity in a spatial scale of the town surroundings. It is meant as a supportive tool for decision-making with regard to allocating funds for stabilization measures or planning placement of new investments. On this background, stabilization solutions for selected sites are assessed in a cost-benefit context.

Determining optimum air-void spacing requirement for a given concrete mixture design using poromechanics

The frost resistance of concrete is a function of the concrete constituent properties, entrained air-void system parameters and environmental exposure history. However, only a single maximum value for the void spacing factor is specified for all types of concrete by code writing bodies for successful protection against freezing damage. The advent and utilisation of new materials over the recent years warrant reevaluation of the validity of this single pass/fail criteria established more than 50 years ago. Here, a poromechanical model, capable of incorporating concrete constituent properties, environmental exposure and air-void spacing factor, has been used to determine the role of various concrete constituents and air-void system on the damage propensity of concrete exposed to freezing temperatures. It is found that a maximum threshold of acceptance, for instance a 0.2 mm spacing factor, may not be adequate for all concrete mixture designs subject to various cooling conditions. The model also suggests that concrete with low-porosity, low-permeability mortar matrix, a characteristic property of mortar containing supplementary cementitious materials and/or low water to cement ratio, can perform satisfactorily under freezing temperatures even with a spacing factor greater than the recommended value. If utilised for design, this model will give more freedom to practitioners in ensuring concrete durability by controlling multiple factors including the concrete mixture components and proportions rather than just satisfying a single pass/fail criterion for void spacing factor for all concrete mixtures.

Quasi-continuum photoluminescence: Unusual broad spectral and temporal characteristics found in defective surfaces of silica and other materials

We previously reported a novel photoluminescence (PL) with a distribution of fast decay times in fused silica surface flaws that is correlated with damage propensity by high fluence lasers. The source of the PL was not attributable to any known silica point defect. Due to its broad spectral and temporal features, we here give this PL the name quasi-continuum PL (QC-PL) and describe the features of QC-PL in more detail. The primary features of QC-PL include broad excitation and emission spectra, a broad distribution of PL lifetimes from 20 ps to 5 ns, continuous shifts in PL lifetime distributions with respect to emission wavelength, and a propensity to photo-bleach and photo-brighten. We found similar PL characteristics in surface flaws of other optical materials, including CaF2, DKDP, and quartz. Based on the commonality of the features in different optical materials and the proximity of QC-PL to surfaces, we suggest that these properties arise from interactions associated with high densities of defects, rather than a distribution over a large number of types of defects and is likely found in a wide variety of structures from nano-scale composites to bulk structures as well as in both broad and narrow band materials from dielectrics to semiconductors.

Stress concentration factors and stress-gradients due to circular holes in radially functionally graded panels subjected to anti-plane shear loading

Closed-form expressions for the elastic fields (stresses, stress-gradients, strains, and displacements) in radially graded continua without and with circular holes are derived. The conventional definition of the stress concentration factor, which is the ratio of the maximum tangential stress on the circumference of the hole to the far-field applied traction, leads to physically unrealistic interpretations in functionally graded materials. A novel definition is derived for the stress concentration factor in graded panels. The stress concentration factor increases when the rigidity modulus progressively decreases away from the center of the hole (softening materials). The stress concentration desirably reduces in hardening materials in which the rigidity modulus progressively increases away from the hole. The gradient of the tangential stress ahead of the circular hole introduces an affected zone that is size-dependent (depends on the size of the hole, even in homogeneous media). The affected zone size decreases, while the stress-gradients increase with increase in the inhomogeneity length-scale and results in the increasing propensity of damage in softening materials. In hardening materials, the propensity of damage reduces with increase in the inhomogeneity length-scale due to the stress dilution.

Edge‐loading severity as a function of cup lip radius in metal‐on‐metal total hips—A finite element analysis

While favorable tribological properties and allowance for larger femoral head sizes have made metal-on-metal (MoM) bearings an increasingly popular choice for total hip arthroplasty, concerns have mounted regarding adverse reactions to metal wear debris and ions. MoM cups differ from conventional polyethylene cups in terms of edge profile design and reductions from full hemisphericity, suggesting differences in loading at or near the cup edge, especially during subluxation events. Finite element analysis was used to investigate the effects of cup orientation and lip edge curvature on damage propensity for edge or near-edge loading during subluxation. Increased cup lip radius (resulting in reduced articular arc) had a detrimental effect upon subluxation-free hip range of motion and upon dislocation resistance. Contact stresses near the cup edge demonstrated complex relationships between edge radius and cup orientation, with peak stresses being influenced by both variables. The tendency for scraping wear at the egress site demonstrated similarly complex dependencies. These data indicate that acetabular cup design is an important determinant of edge and near-edge loading damage propensity.

Complex relationships between salt type and rock properties in a durability experiment of multiple salt–rock treatments

AbstractA laboratory salt weathering experiment was performed using five salts to attack eight types of rocks to determine the relative significance of rock durability and salt aggressivity to salt crystallization damage. The influence of individual rock properties on the salt susceptibility of the rocks was also evaluated. To study the relation between pore characteristics, salt uptake, and damage, the pre‐ and post‐experiment pore size distributions of the rocks were also examined. It is observed that both salt type and rock properties influenced the damage pattern. The durability ranking of the rocks became significantly altered with the salt type while the variation in salt efficacy ranking with rock type was less pronounced. Of the five salts used, sodium chloride and aluminium sulfate were invariably ineffective with all rock types while sodium carbonate, sodium sulfate, and magnesium sulfate, were markedly more effective in damaging most types of rock used. Of the rock properties investigated, the microporosity (of pores smaller than 0·05 or 0·1 µm) showed the most significant influence on deterioration of the rocks associated with salt crystallization, whereas microporosity of pores smaller than 5 µm played a more important role in salt uptake. Pore size distribution was thus the key factor controlling salt uptake and damage. Rocks with a large number of pores (&lt;5 µm) and a high proportion of pores (&lt;0·05 or 0·1 µm) were particularly susceptible to salt crystallization damage. However, anomalies arose that could not be explained in terms of rock properties or salt efficacy alone. Overall, the relative influences of salt type/efficacy and rock type/properties on salt damage propensity were not clear enough to draw a reasonable conclusion. Salt crystallization damage appears to be influenced by the individual interactions between salts and rocks, which could explain the anomalous results. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Acid-Rich Peptides are Prone to Damage under Fenton Conditions - Split-and-Mix Libraries for the Detection of Selective Peptide Cleavage

Acid-rich peptides are damaged under Fenton conditions to a greater extent than others as revealed by combinatorial screenings. The higher damage propensity is due to Fe-complexation that leads to the generation of radicals in close vicinity and thereby to the cleavage of the backbone of acid-rich peptides.

Analysis of tablet compaction. II. Finite element analysis of density distributions in convex tablets

A Drucker‐Prager/cap constitutive model, where the elastic and plastic model parameters are expressed as a function of relative density (RD), was presented in a companion article17 together with experimental calibration procedures. Here, we examine the RD distribution in curved‐faced tablets with special reference to the die wall lubrication conditions. The compaction of powders is examined using finite element analysis, which involves the following factors: constitutive behavior of powder, friction between powder and tooling, geometry of die and punches, sequence of punch motions, and initial conditions that result from die fill. The predictions of the model are validated using experimental RD maps. It is shown that different die wall lubrication conditions induce opposite density distribution trends in identical tablets (weight, height, and material). The importance of the internal tablet structure is illustrated with respect to break force, failure mode, and friability: it is demonstrated that for a given average tablet density the break force and failure mode are not unique. Also, tablet regions having lower density locally have higher propensity for damage. The applicability of finite element analysis for optimizations of formulation design, process development, tablet image, and tool design is discussed.