Equivalent Damage Research Articles

Fractional‐order freezing‐and‐thawing damage model for hydraulic concrete subjected to variable temperature processes

AbstractSince research on the freezing‐and‐thawing damage experienced by hydraulic concrete subjected to variable temperatures is currently rudimentary, it is difficult to use existing models to quantitatively reflect the damage of actual hydraulic engineering concrete under such conditions. This study first presents a formula to calculate the equivalent damage age through an analogy with the equivalent age theory, and the results of this formula can comprehensively reflect the relationship between the freezing‐and‐thawing process at variable temperatures and concrete damage. Then, this study establishes a fractional freezing‐and‐thawing damage model for hydraulic concrete subjected to freezing‐and‐thawing cycles at variable temperatures according to fractional calculus theory. New model parameters for freezing‐and‐thawing damage are identified and optimized with existing testing data acquired under variable freezing‐and‐thawing temperatures. Moreover, the applicability of the new model is verified with different freezing‐and‐thawing temperature data obtained from supplemental freezing‐and‐thawing tests performed in this study. The analysis results show that the new concrete freezing‐and‐thawing damage model can accurately reflect the changes in concrete strength during freezing‐and‐thawing cycles at variable temperatures.

Effects of freeze-thaw cycles on fatigue performance of asphalt mixture and development of fatigue-freeze-thaw (FFT) uniform equation

Although it is widely recognized that freeze-thaw cycles can accelerate the performance deterioration and lead to premature failures of asphalt pavements, a quantitative understanding of how it affects the fatigue life is so far still lacking. This study aims to identify the effects of freeze-thaw cycles on fatigue performance of asphalt mixture. For this, the indirect tensile fatigue tests were performed up on the specimens to measure the fatigue life of the freeze-thaw damaged specimens. Results suggest that fatigue life Nf decreases with the increase of saturation and number of freeze-thaw cycles and the decrease rate of fatigue life Nf becomes more pronounced at higher stress levels. The effects of freeze-thaw cycles on fatigue performance of asphalt mixture were quantified by establishing fatigue-freeze-thaw (FFT) uniform equation through two different strategies: the equivalent damage principle-based approach and the direct modification approach. A comparison study indicates that the FFT uniform equation based on equivalent damage principle and exponential shift factor function can best describe the coupling effect between freeze-thaw cycles and fatigue.

A micromechanics based elasto-plastic damage model for unidirectional composites under off-axis tensile loads

Nonlinear properties of composite materials are essential for their engineering application. In this work, a three-phase micromechanics bridging model is employed to evaluate the nonlinear behavior of a composite from properties of fiber, matrix and interphase. It is assumed that the matrix elastoplasticity and the interface damage are two major sources of the nonlinearity. The former is described by the J2 flow rule. The latter is approximated by an interphase with stiffness degradation. For an interphase, an equivalent damage stress is introduced to account for the effect of normal and shear stress on the interface damage growth. Further, an explicit empirical equation is developed to relate the equivalent damage stress and the stiffness degradation of an interphase. The present elasto-plastic damage model is validated by comparing with experimental data of a series of composites under off-axis tensile loads.

A fast and efficient numerical prediction of compression after impact (CAI) strength of composite laminates and structures

Abstract In this paper, an equivalent damage model is proposed to quickly predict the compression after impact (CAI) strength of composite laminates and stiffened panels. Low-velocity impact (LVI) and CAI tests at various energy levels are carried out on laminates. Based on the measured impact damage sizes, the model simplifies the damage area into concentric circles with different stiffness and strength properties by adopting the soft inclusion method. Progressive failure analysis and virtual crack closure technique (VCCT) are used to simulate the intra-laminar and inter-laminar failure of impacted laminates under axial compression in commercial finite element software ABAQUS. The predicted failure modes and CAI strength of laminates are in good agreement with the experiment results from this paper and the literature at various impact energies, which proves the validity of the model. Whilst the numerical model achieves high computational efficiency, the effect of mass scaling on computational efficiency and accuracy is evaluated, which provides a reference for the parameter choice in engineering application. The model is further applied to predict the compressive failure load of the stiffened composite panel with skin bay impact damage as a practical application, showing this modelling approach is also suitable to composite structures.

A note on computing the growth of small cracks in AM Ti-6Al-4V

The certification requirements for additively manufactured (AM) replacement parts requires the ability to predict the growth of small sub mm cracks. To this end, it is shown that the Hartman-Schijve crack growth equation proposed in a prior paper for the growth of small cracks in AM Ti-6Al-4V manufactured specimens also accurately predicts the growth of small cracks in Laser Beam Powder Bed Fusion (LB-PBF) manufactured Ti-6Al-4V specimens. The specimens studied are built with two different LB-PBF machines with different processing parameters. Particular attention is given to the growth of crack from initial sizes that are of the same order of magnitude as the minimum equivalent initial damage size (EIDS) in the US Air Force (USAF) approach to the certification of an AM replacement part.

Degradation characteristics of electron and proton irradiated InGaAsP/InGaAs dual junction solar cell

The degradation characteristics of MOCVD grown InGaAsP/InGaAs dual junction solar cells, irradiated by 1 MeV electron, 3 MeV and 10 MeV proton, have been investigated. Main electrical and optical properties of solar cell degraded seriously with the increase of irradiation fluences due to the irradiation induced defects which are acting as non-radiative recombination centers in the active layers of the solar cell. The remaining factor of Pmax is 0.67, 0.53 and 0.51 for 1 MeV electron, 10 MeV proton, and 3 MeV proton irradiation, respectively, when the displacement damage dose (DDD) is 3.16×1010 MeV/g. The degradation of external quantum efficiency (EQE) of each subcell mainly occurred in the long wavelength region, the integrated current density Jsc of InGaAsP and InGaAs subcells degraded more seriously upon 3 MeV and 10 MeV proton irradiation comparing to 1 MeV electron irradiation. The InGaAsP subcell turned out to be the current limiting unit due to the lower Jsc before and post irradiation. By applying equivalent displacement damage dose model, the relative damage coefficient for 3 MeV proton to 10 MeV proton and 1 MeV electron to 10 MeV proton have been calculated.

Computational evaluation of effectiveness for intratumoral injection strategies in magnetic nanoparticle assisted thermotherapy

PurposeTo investigate, evaluate, and compare the effectiveness of intratumoral magnetic nanoparticle (MNP) injection strategies (single-site and multi-site injection). The comparison is done with respect to a hypothetical case of uniform MNP distribution within tumor volume. MethodsThe injection strategies have been modeled in a three-dimensional tumor surrounded by healthy tissues while considering Gaussian spatial distribution of MNPs. In single-site injection strategy, the MNPs are injected at tumor centre, while in multi-site injection strategy the tumor is compartmentalized and injected at 9 sites (8 sites in compartments and one at tumor centre). The temperature field is computed in tissues during and after the thermo-therapy, by solving Pennes’ Bio-heat model, using finite volume method. From temperature field, effectiveness of each injection strategy is quantified in terms of thermal dosimetry, i.e. Arrhenius thermal damage and CEM 43 in tissues. The analysis has been done with two MNP injection doses (4 mg and 5 mg of MNPs/cm3 of tumor). ResultsTemperature in multi-site injection strategy is more homogenous in comparison to single-site injection strategy. With injection dose of 5 mg of MNPs/cm3 of tumor, multi-site injection strategy thermally affects greater tumor volume than single-site injection strategy (17% in thermal damage, and 14 % in CEM 43). Multi-site injection strategy with 4 mg of MNPs/cm3 of tumor, produces almost equivalent thermal damage to tumor volume as single-site injection strategy with 5 mg of MNPs/cm3 of tumor. The thermal damage produced by multi-site injection strategy is very close to the damage in uniform MNP distribution. However, increased MNP spread in multi-site injection strategy affects greater healthy tissue volume. ConclusionMulti-site injection strategy performs better than single-site injection strategy. However, selection of injection site number, location, and amount of MNPs to be injected at each injection site plays a key role in optimization of this thermotherapy.

Launderability of Conductive Polymer Yarns Used for Connections of E-textile Modules: Mechanical Stresses

E-textile is one of the emerging fields of current era and some dynamic and state of the art products are already available on the market. E-textile products are facing problems related to reliability and difficulty in laundering. This paper is focused on the standards to be proposed for washability of e-textile structures after in depth analysis of wash process. Mechanical forces acting on the e-textile structure during washing are considered the most damaging among all others. Well known textile benchmark tests such as Martindale abrasion and pilling box are supposed to have similar mechanical damages on e-textile structures as in washing. As E-textiles relay on flexible connections (textile motherboard) within textile structure realized by conductive yarns, they are the main target of our investigations. The resultant change in electrical resistance after mechanical tests on silver plated conductive yarns used as connection threads in e-textile structures is co-related with washing results to propose equivalent damage effect without washing of samples.

Damage Evolution Analysis of Rock Slope in Tunnel Entrance Section Under the Seismic Action

Starting from the microscopic heterogeneity feature of the rock material, the paper applies the theory of continuous medium damage mechanics and deduces the constitutive relation for microscopic damage of rock material. Afterwards, this paper sets ANSYS development platform as its main body and puts forward the equivalent damage unit based on the assumption of macroscopic homogeneity to simulate the damage cracking process of the rock side slope at the tunnel portal section based on the principle of microscopic damage mechanics. It is shown in the calculation results that the side slope damage and destruction involve a continuous damaging process from the microscopic perspective. Under the impact of seismic load, there will initially be micro cracks on the side slope structure. As time goes by, these micro cracks will gradually expand into larger ones and finally form penetrated damage area; especially, there will be penetrated damage area formed above the tunnel vault, which can be deemed as that the vault has been completely damaged and poses a negative influence on the safe operation of the tunnel. Therefore, the vault top should be reinforced during design and construction, and the calculation method and analysis results of this paper can be applied to the analysis of damage destruction in similar complex structures.

Degradation analysis of 1 MeV electron and 3 MeV proton irradiated InGaAs single junction solar cell

In this paper we reported the electrical and spectral properties of 1 MeV electron and 3 MeV proton irradiated In0.53Ga0.47As single junction solar cell, which is used as the fourth subcell of wafer bonded GaInP/GaAs//InGaAsP/InGaAs four-junction full spectra solar cell. The equivalent displacement damage dose model was applied to study the radiation effects of solar cell. The results show that the electrical parameters of the solar cell degrade seriously with the increase of irradiation fluences, the reduction of minority carrier life-time and changes of series and shunt resistance caused by irradiation-induced displacement damage are the main reason for the degradation of cell performance. Degradation of spectral response mainly occurred in the long wavelength region of solar cell due to the bigger displacement damage in the base layer of solar cell. Degradation properties of solar cell by electron and proton irradiation can be predicted by electron to proton damage equivalency factor Rep.

Spectral and electrical properties of 3 MeV and 10 MeV proton irradiated InGaAsP single junction solar cell

3 MeV and 10 MeV proton irradiated InGaAsP single junction solar cell have been investigated. Proton fluences are calculated by MUSALISS software based on the equivalent displacement damage method. SRIM simulation is used to analyze the irradiation damage. The result shows that the external quantum efficiency (EQE) and electrical parameters of the solar cell are degraded by both 3 MeV and 10 MeV proton irradiation. The degradation of EQE is larger in the longer wavelength region because of the higher probability of carrier lifetime reduction in the base region of the solar cell, and the 3 MeV proton produced more degradation of the electrical parameters of the solar cell than that of 10 MeV proton irradiation under the same displacement damage dose.

Random fatigue damage accumulation analysis of composite thin-wall structures based on residual stiffness method

The damage accumulation and life prediction for C/SiC composite panels subjected to random vibration loading was studied by using the residual stiffness model in combination with critical failure stiffness ratios in the different stress levels. According to the results of stiffness degradation and material S-N curves for constant-amplitude fatigue loadings, a new residual stiffness model was established and extended to adapt random stress states by using an equivalent damage ratio algorithm in time domain. The stiffness degradation and material S-N curves were obtained by using constant amplitude fatigue experiments. Random vibration tests with limited-bandwidth excitation were conducted to verify the prediction model. Good agreement is observed compared with the results of 2D plain-woven C/SiC composite panel subjected to random vibration loadings.

Effect of Successive Impact Loads From a Drop Weight on a Reinforced Concrete Flat Slab

Lebanon is one of the countries which are at high risk of experiencing rock falls. In order to ensure public safety, engineers must take into consideration this risk. In the past years, numerous researches were conducted on the behavior of horizontal structural elements, slabs, of different types under dynamic impact load. Reinforced concrete flat slabs are commonly used slabs in residential buildings. To build a profound understanding of the structural behavior of the slabs under such loadings, it is important to investigate the effect of energy dissipation on the equivalent impact force, mid-span deflection and damage pattern. In this study a sample reinforced concrete slab of 500 x 1000 x 100 mm dimensions is considered. The aim of this paper is to find how these factors vary with the increase in energy as the drop load resembling the real rock fall is left to drop freely from different heights 0.6 m and 1 m.

Intelligent Time‐Domain Parameters Matching for Shock Response Spectrum and Its Experimental Validation in Active Vibration Control Systems

Shock response spectrum (SRS) test is a kind of vibration test that uses the principle of equivalent damage to simulate complex shock and vibration environment for evaluating product fragility. However, for a certain SRS, neither an analytical nor a unique inverse time‐domain shock waveform (TSW) exists, making the SRS test a very challenging problem. Synthesis of a TSW using a group of wavelets with different frequencies, amplitudes, and phases is considered to be a very promising method. However, it is challenging to find an optimal group of wavelets since there are hundreds of optimization variables and objective functions. In this paper, a novel intelligent parameter matching method for TSW synthesis is proposed for the SRS test. A variable‐weight method has been introduced to combine the effects of hundreds objective functions so that the optimization problem can be solved by using the genetic algorithm. The frequency response function of the shaking system has been taken into consideration in the calculation of the objective function, so the synthesized TSW can be applied directly to the SRS test. In the optimization process, normalized control factors have been formulated for the optimization variables so that they can be tuned in a reasonable small range to avoid irrationality and accelerating convergence in searching process. The effectiveness of the proposed method has been verified experimentally in two active vibration control systems, in which one contains a 500 N minishaker and the other contains a 1‐ton shaking table. It can be seen from the experimental results that the proposed method can accurately synthesize the input TSW for the shaking system, where the output TSW and SRS can accurately meet the time‐ and frequency‐domain specification.

Uncertainty Characterization of Silicon Damage Metrics

A general formulation of silicon damage metrics and associated energy-dependent response functions relevant to the radiation effects community is provided. Using this formulation, a rigorous quantitative treatment of the energy-dependent uncertainty contributors is performed. This resulted in the generation of a covariance matrix for the displacement kerma, the Norgett–Robinson–Torrens-based damage energy, and the 1-MeV(Si)-equivalent damage function. When a careful methodology is used to apply a reference 1-MeV damage value, the systematic uncertainty in the fast fission region is seen to be removed, and the uncertainty for integral metrics in broad-based fission-based neutron fields is demonstrated to be significantly reduced.

Degradation of up-grown metamorphic InGaP/InGaAs/Ge solar cells by low-energy proton irradiation

To gain higher efficiency than that of traditional lattice-matched solar cells, newly designed up-grown metamorphic (UMM) InGaP/InGaAs/Ge solar cells were grown on Ge substrates. The defects in UMM InGaP/InGaAs/Ge can be perfectly controlled, and thus the conversion efficiency exceeds 30%. Similarly, the radiation environment in space could also cause displacement damage in UMM solar cells, causing the degradation of electrical properties. Proton irradiation at 50 keV and 150 keV was tested on the UMM solar cells. Because the top InGaP layer is thick enough, the radiation defects are limited within the top subcell without affecting the underlying subcells. In this research, 50-keV protons cause more serious degradation of short-circuit current, whereas 150-keV protons cause more serious degradation of open-circuit voltage. The difference may be related to the distribution of defects, which is calculated by The Stopping and Range of Ions in Matter (SRIM). Defects in the junction region would cause the decrease in voltage, whereas defects in the surface region could cause degradation of current. As a comparison, lattice-matched GaInP/GaAs/Ge solar cells were also irradiated by low-energy protons. The degradation under 150-keV protons is more serious because the damage peak lies in the middle GaAs layer, which has poor radiation resistance. The degradation under 70-keV proton irradiation proves that a thinner GaInP layer improves the radiation resistance. It is notable that the degradation of short-circuit current and maximum power is influenced by the equivalent displacement damage dose (DDD), but this is not accurate for open-circuit voltage. The artifact signals at 700–750 nm after 50-keV proton irradiation indicate the decrease in shunt resistance of the InGaP subcell during proton irradiation.

Damage constitutive model of single flaw sandstone under freeze-thaw and load

The deterioration of mechanical properties subjected to freeze-thaw action is a determining factor for natural rock masses in cold region engineering. Taking four cases of flaw sandstone as the research object, freeze-thaw cycles experiments and triaxial compression tests were conducted to analyze the mechanical properties after 0, 20, 40 and 60 freeze-thaw cycles. The damage evolution equation of freeze-thaw sandstone under load is established based on the Lemaitre strain equivalent principle and continuum damage mechanics theory. In this regard, the damage model was developed to predict the degradation of triaxial compression strength for single flaw sandstone samples, it takes into account pre-existing cracks, confining pressure, freeze-thaw action and load. The results show that the sandstone damage consists of factors mentioned above, the coupled damage variable acquired from the proposed method well agree with the actual condition, and the damage constitutive model validations are given through comparisons between the calculated and the measured.

Bird Management in Blueberries and Grapes

Bird damage to fruit is a long-standing challenge for growers that imposes significant costs because of yield losses and grower efforts to manage birds. We measured bird damage in ‘Bluecrop’ blueberry fields and Pinot noir vineyards in 2012–2014 in Michigan to investigate how year, grower, and forest cover influenced the proportions of bird damage. We tested whether inflatable tubemen (2013–2014) and a methyl anthranilate spray (2015) reduced bird damage in blueberries, and tested the deterrent effect of inflatable tubemen in grapes (2014). Years when crop yield was lower tended to have a higher damage percentage; for blueberries, bird damage was highest in 2012, and in grapes, damage was highest in 2012 and 2014. Neither blueberry fields nor vineyards with inflatable tubemen showed significantly reduced bird damage, although the blueberry fields showed a non-significant trend toward lower damage in the tubemen blocks. Blueberry field halves treated with the methyl anthranilate spray had equivalent bird damage to untreated halves. Our results correspond to previous work showing that percent bird damage varies by year, which was likely because bird consumption of fruit is relatively constant over time, while fruit yield varies. Fruit growers should expect a higher proportion of bird damage in low-fruit contexts, such as low-yield years, and prepare to invest more in bird management at those times. Investigating patterns of bird damage and testing deterrent strategies remain challenges. Bird activity is spatially and temporally variable, and birds’ mobility necessitates tests at large scales.

A novel energy-based equivalent damage parameter for multiaxial fatigue life prediction

Energy-based damage parameters are widely used, due to their availability, in the prediction of multiaxial fatigue life, usually by integrating the product of stress and strain range into a single scalar quantity. However, in most engineering applications, stress and the strain histories cannot be known simultaneously. Although incremental plasticity methods can be used to estimate the response from measured or specifically designed loads, these processes are too complicated to be employed. In this paper, a novel energy-based Equivalent Damage Parameter (EDP) based on uniaxial fatigue data is proposed to predict the fatigue life under multiaxial fatigue loadings. In this way, the augmentation of uniaxial tensile elastoplastic work can be estimated thanks to the non-proportional (NP) hardening factor FNP and the energy-based material constant αw. Moreover, the contributions to total elastoplastic work from different loading components can be separated and quantified by using the Moment Of Inertia (MOI) method and weighting factor ξ, introduced as a parameter. The efficiency of the proposed parameter is validated by reasonable correlations with the experimental fatigue data of 316L steel tubular specimens subjected to various proportional or NP loadings.

A method of determining test load for full-scale wind turbine blade fatigue tests

Full-scale fatigue test is an effective method for validating the fatigue performance of wind turbine blade. Its primary problem is how to design the test load. The conventional approach to determine test load requires a complicated and time-consuming process. Thus, a simplified method for directly converting load spectrum of blade into test load is proposed in this paper. Firstly, beam theory is used to obtain the relationship between stress, strain and bending moment of blade cross section. Based on the assumption of local stress concentration and linear relationship between stress and strain, M-N curves (applied moment vs. allowable number of cycles to failure) is defined. Secondly, based on Miner's linear cumulative damage theory and constant life diagram, the equivalent fatigue cumulative damage of load spectrum which is equal to the damage of full-scale fatigue test is obtained. Then, in the case of the selected test load ratio and cycles, the mean and amplitude of test load can be solved. Finally, the validity of the proposed method is verified by an illustrative example. The result indicates that the error of the calculated results between this method and the traditional method is close to 5 %, and it can be used for fatigue test and improve the efficiency of test load design.