Effects Of Material Degradation Research Articles

Degradability of Biodegradable Soil Moisture Sensor Components and Their Effect on Maize (Zea mays L.) Growth.

Inexpensive and no-maintenance biodegradable soil moisture sensors could improve existing knowledge on spatial and temporal variability of available soil water at field-scale. Such sensors can unlock the full potential of variable-rate irrigation (VRI) systems to optimize water applications in irrigated cropping systems. The objectives of this study were to assess (i) the degradation of soil moisture sensor component materials and (ii) the effects of material degradation on maize (Zea Mays L.) growth and development. This study was conducted in a greenhouse at Colorado State University, Colorado, USA, by planting maize seeds in pots filled with three growing media (field soil, silica sand, and Promix commercial potting media). The degradation rate of five candidate sensor materials (three blends of beeswax and soy wax, balsa wood, and PHBV (poly(3-hydroxybutyrate-co-3-hydroxyvalerate))) was assessed by harvesting sensor materials at four maize growth stages (30, 60, 90, and 120 days after transplanting). All materials under consideration showed stability in terms of mass and dimension except PHBV. PHBV was degraded entirely within 30 days in soil and Promix, and within 60 days in sand. Balsa wood did now show any significant reduction in mass and dimensions in all growth media. Similarly, there was no significant mass loss across wax blends (p = 0.05) at any growth stage, with a few exceptions. Among the wax blends, 3:1 (beeswax:soy wax) was the most stable blend in terms of mass and dimension with no surface cracks, making it a suitable encapsulant for soil sensor. All materials under consideration did not have any significant effect on maize growth (dry biomass, green biomass, and height) as compared to control plants. These results indicated that 3:1 beeswax:soy wax blend, PHBV, and balsa wood could be suitable candidates for various components of biodegradable soil moisture sensors.

Optimization of preparation of montmorillonite nanometer zero-valent iron and the degradation of amoxicillin by response surface methodology

Abstract Three-factor and three-level tests were carried out by Box–Behnken response surface methodology, with amoxicillin as the target pollutant, nanometer zero-valent iron (nZVI) materials loaded with montmorillonite prepared by liquid phase reduction method and the concentration of FeSO4 and NaBH4 and montmorillonite dosage as influencing factors. It revealed that the interaction between FeSO4 concentration and NaBH4 concentration had a significant effect on the preparation of montmorillonite-loaded nanometer zero-valent iron material, playing a key role in the removal of amoxicillin, and the effect of FeSO4 concentration was even more significant. In addition, the shape, structure and characteristic groups of the prepared materials were analyzed by means of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), etc. The nanometer zero-valent iron loaded with montmorillonite can effectively slow down the nZVI agglomeration effect and improve the effect of material degradation of pollutants. For the same concentration of amoxicillin wastewater, the removal rate of amoxicillin wastewater, after 1 h reaction, is as follows: Mont/nZVI > nZVI > Mont. The optimal conditions for the reaction are: pH is 3, the initial concentration is 60 mg/L, and the dosage is 2 g/L. The higher the temperature, the more amoxicillin is degraded by Mont/nZVI.

Durability of natural fibre epoxy composite structural columns: High cycle compression fatigue and moisture ingress

Many studies have investigated durability effects on the mechanical properties of natural fibre composite laminates using material tests, notably tension coupon tests. Few studies have investigated durability effects on the structural properties of natural fibre composite load-bearing structural members. In the case of thin-walled structural columns in compression, the degradation of mechanical properties may also influence structural properties such as compression buckling and post-buckling, which cannot be assessed via material testing. The present paper investigates the effects of high cycle compression fatigue and moisture ingress on the structural properties of natural fibre-epoxy composite structural columns of flax and jute, tested in pure compression. It is shown that up to one million cycles of compression load equivalent to one half of the ultimate compression load, has negligible influence on the (post-fatigue) compression strength. Conversely, moisture ingress notably effects the compression stiffness, buckling behaviour and strength. The compression stiffness of saturated columns reduced by up to 44%, the buckling load reduced by up to 48%, and the ultimate strength reduced by up to 45%. The large strength reduction is attributed to the combined effects of material degradation and increased susceptibility to compression buckling in moisture affected columns.

Electrospun polyester-urethane scaffold preserves mechanical properties and exhibits strain stiffening during in situ tissue ingrowth and degradation

Consistent mechanical performance from implantation through healing and scaffold degradation is highly desired for tissue-regenerative scaffolds, e.g. when used for vascular grafts. The aim of this study was the paired in vivo mechanical assessment of biostable and fast degrading electrospun polyester-urethane scaffolds to isolate the effects of material degradation and tissue formation after implantation. Biostable and degradable polyester-urethane scaffolds with substantial fibre alignment were manufactured by electrospinning. Scaffold samples were implanted paired in subcutaneous position in rats for 7, 14 and 28 days. Morphology, mechanical properties and tissue ingrowth of the scaffolds were assessed before implantation and after retrieval. Tissue ingrowth after 28 days was 83 ± 10% in the biostable scaffold and 77 ± 4% in the degradable scaffold. For the biostable scaffold, the elastic modulus at 12% strain increased significantly between 7 and 14 days and decreased significantly thereafter in fibre but not in cross-fibre direction. The degradable scaffold exhibited a significant increase in the elastic modulus at 12% strain from 7 to 14 days after which it did not decrease but remained at the same magnitude, both in fibre and in cross-fibre direction. Considering that the degradable scaffold loses its material strength predominantly during the first 14 days of hydrolytic degradation (as observed in our previous in vitro study), the consistency of the elastic modulus of the degradable scaffold after 14 days is an indication that the regenerated tissue construct retains its mechanical properties.

On-Site Identification of the Material Composition of PV Modules with Mobile Spectroscopic Devices

With the increased development of portable and handheld molecular spectrometers within recent years, new fields of applications have opened up, such as their use (i) for material identification of samples contained in large and non-portable components and (ii) the detection of material degradation effects and failures directly in the plant. The usability and transferability of well-established analytical characterization techniques, such as attenuated total reflection (ATR) Infrared (IR)-, Raman, and Near-Infrared (NIR)-spectroscopy as mobile devices for the in-field characterization of Photovoltaic (PV) modules, are described and discussed. Material identification of the polymeric compounds incorporated in the PV modules (encapsulants, backsheets) is often an important task, especially when degradation and failures occur. Whereas the knowledge of the bill of materials is one challenge, the detection of material degradation effects is another important issue. Both tasks can be solved nondestructively by the application of mobile spectrometers. Raman spectroscopy is the best-suited method for the identification of the encapsulant within the module (measurement through 3-mm glass), while NIR measurements allowed for the nondestructive determination of the composition of the multilayer backsheet. Surface degradation effects (e.g., oxidation, hydrolysis) are best detectable with IR-spectroscopy. The application of mobile devices allows for direct material analysis in the field without dismantling PV modules, transporting them to the lab, cutting them in smaller pieces, and analyzing them in conventional bench-top spectrometers.

Temperature-Dependent Viscoelastic Model for Asphalt–Concrete Implemented within a Novel Nonlocal Damage Framework

AbstractA viscoelastic constitutive model for an asphalt–concrete (AC) material that accounts for temperature and material degradation effects is proposed. The model is implemented within a finite-...

Error analysis of aged modules with cracked polyamide backsheets

Within the last years, an increased occurrence of backsheet cracking, especially of Polyamide-based backsheets, was observed in PV installations and reported in literature. Thus, a detailed failure analysis on cracked polymeric backsheets was performed in order to identify the drivers leading to the unexpected behaviour of the Polyamide multilayer composites. Using a unique combination of analytical tools allowed for deducing a spatially resolved representation of material degradation effects within a PV module for the first time. The correlation of local material degradation effects with the influence zones of external and internal stresses enables the derivation of the main factors for the formation of different types of cracks in Polyamide backsheets.

Displacement ratios for structures with material degradation and foundation uplift

In this paper, combined effects of material degradation, p-delta, and foundation uplift are incorporated in a soil-structure-interaction (SSI) framework to assess seismic response of a single-degree-of-freedom system. The considered phenomenological systems represent a column with a lumped mass on top is placed on a rigid foundation. The foundation is mounted on Winkler springs and dashpots to take account of soil-foundation compliance and material/radiation damping. The springs are tensionless to guarantee that uplift is properly modelled. The model is verified for two specific limit cases with the code and literature to make sure that the model is capable of capturing SSI and foundation uplift. Three sets of flexural degradations for capturing nonlinear performance of the column are defined to be categorized as low, moderate, and high degradation levels. The response of each system is then compared to the corresponding one with the elastic–perfectly plastic (EPP) material behavior. More than 150,000 analyses are conducted for several dimensionless parameters and twenty time history ground motions. The results including elastic and inelastic displacement ratios are finally compared with those stipulated by seismic codes for shallow foundations with the flexible-based condition. The results reveal that material degradation can significantly increase the displacement ratios of soil-structure systems and in some cases can lead to structural instability, which cannot be captured by conventional EPP models. More specifically, displacement ratios calculated in accordance with ASCE41-17 by assuming fixed-base model and incomplete data about level of material degradation might be underestimated, once compared to the results of more realistic conditions.

Novel Topology Optimization Techniques Adapted to Strengthening of Civil Structures Suffering from the Effects of Material Degradation

Over years, cultural heritage monuments and historical buildings, as well as old civil structures, have been exposed to slow aging processes, material damage and degradation due to climate and environmental changes or problems resulting from poor maintenance. The task of repairing and strengthening of historical structures can be extremely challenging, because of architectural value of buildings, from one side, and selection of appropriate engineering techniques, from the other. The estimation of technical condition of the old structures, from the engineering point of view, is usually difficult or even impossible to carry out in a precise way. Because of a limited knowledge about stiffness of the considered structure, the designing of strengthening elements for historical structures becomes a motivation for developing new concepts and engineering techniques. In what follows some of the well-known, conventional reinforcing methods, like implementation of wood and steel frames or tie rods, have been gradually replaced by innovative approaches, which allow the resulting structures to become lighter, stronger and also attractive from the aesthetic point of view. This paper presents the novel design technique for retrofit strengthening of existing civil structures suffering from the effects of material degradation. The unknown stiffness distribution within weakened structure is modelled by randomly distributed material data, including cracks and reinforcements of original structure. The idea is to adopt topology optimization techniques to find the optimal layout of strengthening elements for loaded, initially and randomly weakened structure. Classical approach to topology optimization is to find within considered design domain the distribution of the material, which is optimal in some sense. The material data for design-active and design-passive regions of the structure are defined first. Then, optimization process, understood as minimization of the structure compliance, is performed and material is removed from the parts of the structure where it is not necessary to the parts, where it is essential. Finally, the considered structure takes on a new shape, while the amount of the material is reduced to assumed volume fraction. The new idea discussed in this paper is to implement into optimization process a random information about the stiffness of the original structure by modelling design-passive regions with randomly distributed values of material data. As a result, the new layout of strengthened structure for which the assumed volume fraction is preserved can be obtained. This approach allows to reduce a mass of strengthening elements, but what is essential, the complete information about the material degradation level of the original structure is not necessary to perform the optimization process.

Fatigue of glued-in rods in engineered hardwood products — Part II: Numerical modelling

ABSTRACTFatigue behaviour of materials is traditionally performed on probes that ensure that stresses (or strains) are very uniform. This is a situation seldom encountered in most adhesively bonded joints, where stresses usually peak at the end of the overlaps. This paper presents a relatively simple model to predict the fatigue behaviour of glued-in rods (GiR) involving hardwood in previously investigated in an extensive experimental campaign. The model is based on strength and stiffness degradation of the components of the GiR, which were experimentally estimated in small scale tests. Based thereupon, Finite Element Analysis (FEA) was used to estimate the effect of material degradation on the residual strength of the GiR, which was then interpreted as S-N-curves. The influence of several parameters, e.g. strength and stiffness degradation rates and the magnitude of the residual strength threshold were numerically investigated. The result showed that it is possible, using a practitioner adapted numerical model, to predict the fatigue behaviour of GiR, based upon comparatively simple fatigue characterisation on their components.

Prediction of the residual lifetime of gas pipelines considering the effect of soil corrosion and material degradation

The calculation model is developed to evaluate the residual lifetime of a pipe with a crack considering in-service degradation of the pipeline steel and the effect of soil corrosion. The model is based on the first law of thermodynamics. The problem of determination of the period of subcritical crack growth in a pipe is reduced to the differential equation subjected to definite initial and final conditions. Obtained equation together with the boundary conditions are used for prediction of the residual lifetime of the pipe made of the X52 pipe steel. The pipe contains external surface semi-elliptical crack. The task consists in the determination of the time of crack propagation through the pipe wall till its decompression. According to the experimental data, cracks in the studied steel under long-term loading and soil corrosion propagate mainly at constant rate, which is different for the as-received pipeline steel and the steel after 30 years in service. Based on these data, the equation for approximate determination of the crack growth rate for arbitrary service time of the pipe made of the X52 steel is proposed. To evaluate the crack propagation time, the energy approach is employed. For a crack that remains semi-elliptical during propagation, the problem is reduced to the differential equation system that determines the variations of the crack semi-axes. The system solution under definite initial and final conditions renders the expression for the pipe residual lifetime. The dependences of pipe residual lifetime on initial crack depth and pipe operation time are derived. The strong influence of the time of steel previous service on the pipe residual lifetime is manifested.

Progress and challenges with local approaches to cleavage fracture

Local approaches (LA) to cleavage fracture incorporate microstructure information and failure mechanisms into mathematical models for calculation of component failure probability. They offer a promising mechanistic alternative to global approaches and have been successfully applied to predict cleavage fracture toughness (CFT) changes due to material degradation and geometry effects. Predicting the dependence of CFT on temperature, specifically in the ductile-to-brittle transition (DBT) regime, remains a challenge. This work offers one avenue for addressing the challenge by revisiting the mathematical basis of LA and demonstrating that changes in continuum mechanical fields due to changes of deformation properties with temperature are insufficient to deliver predictions in agreement with experimentally measured CFT dependence on temperature. This suggests that the process by which cleavage initiators are generated is dependent on temperature separately from the dependence of the deformation properties on temperature. The temperature dependence of the generation process is derived for the material studied in the work. A methodology is described for predicting CFT in the DBT regime, using deformation and fracture toughness properties at one temperature and deformation properties at any other temperature of interest.

Effects of material degradation on electrical and optical characteristics of surface dielectric barrier discharge

In this paper, screen-printed electrodes are asymmetrically fabricated on three different dielectrics (multi-layered polyimide, quartz, and alumina). Supplied with AC power, sustainable surface dielectric barrier discharge (SDBD) plasma is generated in atmospheric pressure. During plasma processing, different changes of material degradation and discharge images are observed. The corresponding electrical and optical characteristics are investigated by optical emission spectra (OES) and Lissajous figure analysis, respectively. It is found that both dielectric degradation and electrode erosion occur on the surface of the polyimide based SDBD device, while there is only electrode erosion for the quartz and alumina based devices, which results in different changes of electrical characteristics. OES calculated results show that with an increase of discharge aging time, electron temperature increases for the polyimide based SDBD device and decreases for quartz and alumina based SDBD devices, while all the gas temperatures of three dielectrics increase with the aging time. Furthermore, compared to vibrational temperature and gas temperature, the distribution of electron temperature is more suitable for evaluating the changes in discharge uniformity during plasma processing.

Thermodynamic formulation of a unified multi-mechanism continuum viscoplastic damage model with application to high-Cr steels

In this paper, a unified multi-mechanism continuum viscoplastic damage model is proposed to simulate the thermomechanical behavior of high-Cr steels at elevated temperatures. To represent the effects of material degradation under external loads, a total damage tensor is incorporated, which is composed of the low-cycle fatigue damage, the creep damage and the ductile damage. Within the small strain framework, the model is established through a thermodynamically consistent approach. First, some kinematic assumptions are proposed and the concept of effective stress is adopted. Then, based on a state potential with proper constitutive form, the constitutive equations can be derived from the second law of thermodynamics. By further considering the postulate of maximum dissipation, a Lagrangian functional is constructed through a regularization scheme. The stationary points of the Lagrangian functional yield the evolution equations of the dissipative variables. For the isotropic damage case, the damage tensor can be represented by a scalar damage variable and the constitutive evolution equations in the model can be simplified. To be prepared for practical applications, numerical integration algorithms are proposed to solve the constitutive evolution equations, and the material parameters in the model are identified based on the experimental data. To demonstrate the efficiency of the current model, it is applied to simulate the thermomechanical response of high-Cr steels under different loading conditions. The simulation results can fit the experimental data at a quantitative level and the damage mechanisms under the different loading conditions can be revealed. Besides that, the model is further modified to take into account the microcracks closure effect of the ductile damage. The current model would be helpful for the safety design and lifetime evaluation of high-Cr steel components in practical applications.

An anisotropic damage model for tensile fatigue

AbstractFatigue damage in materials is considered to be the effect of material degradation, and the dispersion in fatigue life is attributed to variability in microstructure. This paper presents a numerical model to simulate fatigue damage evolution using continuum damage mechanics to characterize material degradation. An explicit microstructure topology representation is achieved using Voronoi tessellations. Unlike conventional models which use a scalar approximation for damage, this model treats the damage variable as an anisotropic tensor. The model is used to simulate tensile fatigue failure in thin steel specimen. The fatigue life estimations from the model compares well with published experimental results. The results predict a high variability in fatigue life that is characteristic of metals and alloys, as compared with the existing isotropic damage models available in the literature. The model was also used to study the influence of material inhomogeneity on fatigue life dispersion.

A Methodology for Quantifying Cell Density and Distribution in Multidimensional Bioprinted Gelatin–Alginate Constructs

Bioprinted tissue constructs can be produced by microextrusion-based materials processing or coprinting of cells and hydrogel materials. In this paper, a gelatin–alginate hydrogel material formulation is implemented as the bio-ink toward a three-dimensional (3D) cell-laden tissue construct. However, of fundamental importance during the printing process is the interplay between the various parameters that yield the final cell distribution and cell density at different dimensional scales. To investigate these effects, this study advances a multidimensional analytical framework to determine both the spatial variations and temporal evolution of cell distribution and cell density within a bioprinted cell-laden construct. In the one-dimensional (1D) analysis, the cell distribution and single printed fiber shape in the circular cross-sectional view are observed to be dependent on the process temperature and material concentration parameters, along with the initial bio-ink cell densities. This is illustrated by reliable fabrication verified by image line profile analyses of structural fiber prints. Round fiber prints with width 809.5 ± 52.3 μm maintain dispersive cells with a degree of dispersion (Dd) at 96.8 ± 6.27% that can be achieved at high relative material viscosities under low temperature conditions (21 °C) or high material concentrations (10% w/v gelatin). On the other hand, flat fiber prints with width 1102.2 ± 63.66 μm coalesce cells toward the fiber midline with Dd = 76.3 ± 4.58% that can be fabricated at low relative material viscosities under high temperature (24 °C) or low material concentrations (7.5% w/v gelatin). A gradual decrement of Dd (from 80.34% to 52.05%) is observed to be a function of increased initial bio-ink cell densities (1.15 × 106–16.0 × 106 cells/ml). In the two-dimensional (2D) analysis, a printed grid structure yields differential cell distribution, whereby differences in localized cell densities are observed between the strut and cross regions within the printed structure. At low relative viscosities, cells aggregate at the cross regions where two overlapping filaments fuse together, yielding a cell density ratio of 2.06 ± 0.44 between the cross region and the strut region. However, at high relative viscosities, the cell density ratio decreases to 0.96 ± 0.03. In the 3D analysis, the cell density attributed to the different layers is studied as a function of printing time elapsed from the initial bio-ink formulation. Due to identifiable cell sedimentation, the dynamics of cell distribution within the original bio-ink cartridge or material reservoir yield initial quantitative increases in the cell density for the first several printed layers, followed by quantitative decreases in the subsequent printed layers. Finally, during incubation, the evolution of cell density and the emergence of material degradation effects are studied in a time course study. Variable initial cell densities (0.6 × 106 cells/mL, 1.0 × 106 cells/mL, and acellular control group) printed and cross-linked into cell-laden constructs for a 48 h time course study exhibit a time-dependent increase in cell density owing to proliferation within the constructs that are presumed to affect the rate of bio-ink material degradation.

Towards standardisation of proof load testing: pilot test on viaduct Zijlweg

Proof load tests of bridges can be very useful for structures with a lack of information, or for structures of which the effect of material degradation is difficult to assess. Contrary to diagnostic load testing, proof load testing is not well-defined in current standards in terms of required load and analysis of measurements. The risk related to the high loads used in proof load testing requires standardisation for these tests. The paper highlights important considerations for proof load testing that may lead to the development of guidelines in the Netherlands, by illustrating a pilot study on the viaduct Zijlweg in the Netherlands. This reinforced concrete bridge rates too low in shear. Topics of interest are the required load that the bridge has to withstand to be approved by the load test and the interpretation of the measurements during the test to avoid permanent damage to the structure. These measurements were compared to the stop criteria from existing codes for buildings, to examine if recommendations for the use with bridges can be formulated. The final result of the test on this case study is that the capacity of the viaduct is proven to be sufficient for shear and bending moment.

Actual Problems of the Safety and Reliability of the NPP Structures in Slovakia

The last accidents of the NPP in Chernobyl and Fukushima give us the new inspiration to verify the safety level of the NPP structures. This paper presents the new requirements to test of the safety and reliability of the NPP structures due to the last accidents in the world. The risk assessment to verify of the safety and reliability of the NPP structures based on probabilistic and nonlinear analysis is presented. The uncertainties of the loads level (long-time temperature and dead loads), the material model (concrete cracking and crushing, behaviour of the reinforcement and liner), degradation effects and other influences following from the inaccuracy of the calculated model and numerical methods were taken into account in the LHS method. The results of the deterministic and probabilistic analysis of the NPP structures are presented.

Influences of Material Degradation Due to Laser Cutting on the Operating Behavior of PMSM Using a Continuous Local Material Model

During manufacturing of electrical machines, shape giving production steps such as punching and cutting introduce plastic deformations and residual stress to the soft magnetic material. As a result, the magnetic properties of the material decrease and locally both static and dynamic hysteresis losses increase in the vicinity of the cut surfaces. For consideration of local permeability deteriorations, different models have been published. These are capable of describing the changing local magnetization and loss behavior. Current approaches subdivide the magnetic core into slices of different magnetic properties, thereby discretizing the continuous deterioration. This paper analyzes the effects of material degradation due to cutting on the performance and machine parameters of a permanent magnet synchronous machine using a continuous material model for efficient numerical modeling of the local magnetization behavior. By replacing inefficient sliced models, the continuous model is independent of the discretization and converges in case of coarse meshes to the sliced model. Influences on the machine behavior are studied in terms of local flux density distributions, iron losses, efficiency, torque, and inductances on the operating map and an exemplary working point.

Safety evaluation of cored rockfill dams under high seismicity using dynamic centrifuge modeling

Dynamic centrifuge modeling was performed for inclined-core rockfill dams under high seismicity to assess their seismic safety and characterize the dynamic response of embankments. Latest techniques including two-stage generalized scaling, shell stiffness matching, and single target g-level shaking were adopted. The effect of rockfill material degradation on the seismic response was investigated. All the inclined-core rockfill dam models indicated that exceptionally strong shaking (0.7–1.0g) does not endanger structural safety although the less competent shell models undergo comparable deformation. Measured data indicated that a counterbalancing effect influences the seismic response of dam models: increased damping from shear strains (material nonlinearity) and amplification from material inhomogeneity. An irregular stiff foundation is believed to affect the attenuation characteristics of motion. The study results/data will contribute to the research of advanced physical modeling of large embankments under seismic areas and help to validate the procedures and results of numerical modeling.