Effect Of Defect Size Research Articles

Multiscale Simulation of Laser-Based Direct Energy Deposition (DED-LB/M) Using Powder Feedstock for Surface Repair of Aluminum Alloy.

Laser-based direct energy deposition (DED-LB/M) has been a promising option for the surface repair of structural aluminum alloys due to the advantages it offers, including a small heat-affected zone, high forming accuracy, and adjustable deposition materials. However, the unequal powder particle size during powder-based DED-LB/M can cause unstable flow and an uneven material flow rate per unit of time, resulting in defects such as pores, uneven deposition layers, and cracks. This paper presents a multiscale, multiphysics numerical model to investigate the underlying mechanism during the powder-based DED-LB/M surface repair process. First, the worn surfaces of aluminum alloy components with different flaw shapes and sizes were characterized and modeled. The fluid flow of the molten pool during material deposition on the worn surfaces was then investigated using a model that coupled the mesoscale discrete element method (DEM) and the finite volume method (FVM). The effect of flaw size and powder supply quantity on the evolution of the molten pool temperature, morphology, and dynamics was evaluated. The rapid heat transfer and variation in thermal stress during the multilayer DED-LB/M process were further illustrated using a macroscale thermomechanical model. The maximum stress was observed and compared with the yield stress of the adopted material, and no relative sliding was observed between deposited layers and substrate components.

Effects of artificial embedded defect size and position on the fatigue lives of additive manufacturing Ti–6Al–4V alloy

Additive manufacturing (AM) components usually contain various defects with different positions and sizes inside, resulting in the great change of fatigue performance with the defect location and sizes. Therefore, in the evaluation of numerous structural factors, the defect size effect is one of the most typical problems in the AM components. This study for the first time investigated the effects of sizes and positions of the artificial embedded defects on the high-cycle fatigue (HCF) lives of the most widely studied AM Ti–6Al–4V alloy. Samples with artificially embedded defects of two sizes (300 μm and 500 μm) and three positions (center, 1.5 mm from the center and 0.5/0.2 mm from the center) for fatigue tests. The result show that the larger the defect size and the closer it is to the surface, the lower the fatigue life. Through fractographic observations, fatigue lives analysis, and defects statistics, the influences of defect size and position on the HCF lives were discussed. It is found that the Murakami formula can well describe the HCF lives distribution of the AM Ti–6Al–4V alloy with different artificial embedded defects.

Non local multiaxial fatigue modeling of defects : A unified approach to interpret size and shape effects

This paper deals with the effect of defect size and shape under high cycle fatigue for metallic alloys. A large simulation campaign based on a multiaxial fatigue criterion and a non-local approach is presented. A relative defect size based on a ratio between the defect size and a characteristic length introduced by the non-local approach is defined. A normalized Kitagawa–Takahashi diagram is then obtained. A competition between the highly stressed volume size and the local maxima due to the defect is observed and seem dependent on the relative defect size. The effect of the loading mode (uniaxial and pure shear) and of the plasticity are discussed. Finally, a comparison of the simulation results with experimental data on a 316L L-PBF demonstrates the robustness of the proposed approach and explains the negligible effect of the defect morphology compared to its size.

Molecular Dynamics Simulation of the Effect of Defect Size on Magnetostrictive Properties of Low-Dimensional Iron Thin Films

Molecular Dynamics Simulation of the Effect of Defect Size on Magnetostrictive Properties of Low-Dimensional Iron Thin Films

The effect of defect size and location on the fracture risk of proximal tibia, following tumor curettage and cementation: An in-silico investigation

Even though, proximal tibia is a common site of giant cell tumor and bone fractures, following tumor removal, nonetheless very little attention has been paid to affecting factors on the fracture risk. Here, nonlinear voxel-based finite element models based on computed tomography images were developed to predict bone fracture load with defects with different sizes, which were located in the medial, lateral, anterior, and posterior region of the proximal tibia. Critical defect size was identified using One-sample t-test to assess if the mean difference between the bone strength for a defect size was significantly different from the intact bone strength. Then, the defects larger than critical size were reconstructed with cement and the mechanics of the bone-cement interface (BCI) was investigated to find the regions prone to separation at BCI. A significant increase in fracture risk was observed for the defects larger than 20 mm, which were located in the medial, lateral and anterior regions, and defects larger than 25 mm for those located in the posterior region of the proximal tibia. Furthermore, it was found that the highest and lowest fracture risks were associated with defects located in the medial and posterior regions, respectively, highlighting the importance of selecting the initial location of a cortical window for tumor removal by the surgeon. The results of the BCI analysis showed that the location and size of the cement had a direct impact on the extent of damage and its distribution. Identification of critical regions susceptible to separation at BCI, can provide critical comments to surgeons in selecting the optimal cement augmentation technique, which may ultimately prevent unnecessary surgical intervention, such as using screws and pins.

Very High Cycle Fatigue Life Prediction of SLM AlSi10Mg Based on CDM and SVR Models

A novel fatigue evolution model considering the effect of defect size and additive manufacturing building direction based on the theories of continuum damage mechanics and its numerical implementation in ABAQUS is proposed in this paper. First, the constitutive model, fatigue damage evolution model and their parameter calibration methods are presented. Second, using the ABAQUS platform, the proposed model is implemented with user-defined subroutines. After that, based on the proposed model and its numerical implementation, the fatigue life of additively manufactured AlSi10Mg is predicted and its applicability is verified through experimental results. Finally, a support vector regression model is established to predict the fatigue life, and its results are compared to those of the numerical finite element method. The results show that the support vector regression model makes better predictions than the finite element method.

Effects of surface defects on rolling contact fatigue of M50 steel with consideration to both the transgranular and intergranular damage

Surface-initiated pitting and subsurface-initiated spalling of M50 bearing steel were investigated, considering transgranular and intergranular damage. The damage initiation and propagation for contact surface with defects produced by different size particles were analyzed using integrated model combined continuum damage method (CDM) and cohesive zone method (CZM). Pitting and spalling mechanism, and defect size effect on damage evolution were discussed. The results indicated both pitting and spalling include intergranular and transgranular damage evolution. As the defect size increases, the RCF mode change from spalling to pitting. Damage evolution mode of spalling and pitting is the plastic deformation and damage accumulation mode, respectively. Moreover, the prediction accuracy for the damage evolution of the integrated model is higher than single-CDM and single-CZM models.

The Biomechanical Influence of Defected Cartilage on the Progression of Osteochondral Lesions of the Talus: A Three‐dimensional Finite Element Analysis

Osteochondral lesions of the talus (OLTs) are common injuries in the general population. Abnormal mechanical conditions applied to defected cartilage are believed to be the culprits to deteriorating OLTs. This study aims to investigate the biomechanical effects of defect size of talar cartilage on OLTs during ankle movements. A finite element model of the ankle joint was created based on the computed tomography images of a healthy male volunteer. Different defect sizes (S = 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, and 2.0 cm2 ) of talar cartilage were modeled to simulate the progression of OLTs. Mechanical moments were applied to the model to generate different ankle movements, including dorsiflexion, plantarflexion, inversion, and eversion. The effects of varying defect sizes on peak stress and its location were evaluated. The maximum stress on the talar cartilage increased as the area of the defect enlarged. Additionally, as the defect size of OLTs increased, the areas with peak stress on talar cartilage tended to move closer to where the injury was located. High stresses were present in the medial and lateral areas of the talus at the neutral position of the ankle joint. The concentrated stresses were mainly located in the anterior and posterior defect areas. The peak stress in the medial region was higher than on the lateral side. The order of peak stress from highest to lowest was dorsiflexion, internal rotation, inversion, external rotation, plantar flexion, and eversion. Osteochondral defect size and ankle joint movements significantly modulate the biomechanical features of the articular cartilage in osteochondral lesions of the talus. The progression of osteochondral lesions in a talus deteriorates the biomechanical well-being of the bone tissues of the talus.

Fracture Response of X80 Pipe Girth Welds under Combined Internal Pressure and Bending Moment.

In order to determine the effect of defect size on the pipeline fracture performance of girth welds in oil and gas pipelines, ABAQUS was used to simulate the fracture responses of X80 pipelines with girth weld defects under internal pressure and bending moment conditions based on damage mechanics. In particular, the length and depth of defects were parametrically studied; the defect depth range was 20-80% of the wall thickness, and the circumferential length range of the defects was 5-20% of the pipeline circumference. The results show that, under the combined action of internal pressure and bending moment, the defect depth was more associated with adverse effects than the circumferential length of the defect. The failure load did not linearly decrease as the size of the defect increased, but when the depth of the defect reached a certain value, the failure load suddenly decreased.

A linear elastic finite element approach to fatigue life estimation for defect laden materials

This work assumed that the stress-life behaviors of defect-laden materials converge at a certain low life cycle and attempted to estimate fatigue life by applying relative knock-downs to the endurance limit of a reference stress-life data. Linear elastic finite element analysis on small cracks initiated from defects was performed to evaluate the effect of defect size, aspect ratio, and location on endurance limit. While for internal defects size and shape are both influential, size and depth were found to be more important for surface defects. These findings were validated against the fatigue lives of laser powder bed fused Ti-6Al-4V specimens.

Buckling response of subsea pipeline with irregular corrosion defect under external pressure

The subsea pipeline is prone to corrosion due to the combined influence of a complex environment and internal fluid. The corrosion defect results in the local thinning of the wall thickness of the pipeline, affecting the pipeline collapse response under external pressure. In the present study, the buckling response of subsea pipelines with irregular corrosion defect is analyzed. First, a method for calculating the critical buckling pressure of pipelines with irregular corrosion defect is proposed. The accuracy of the proposed method is verified by comparing it with finite element (FE) results and experimental tests. Then, the effects of defect size, steel grade and diameter-to-thickness ratio on the defect interaction and critical buckling pressure of the pipeline are explored. Finally, the application range of the present method is extended by considering defect length, initial ovality and internal pressure.

Effect of defects in adhesive layer on the interfacial bond behaviors of externally bonded CFRP-to-concrete joints

The structural strengthening technique using fiber-reinforced polymer (FRP) composites to strengthen concrete structures has been widely used. For this reinforcement technique, the stress transfer mechanism at the FRP-concrete interface is one of the key factors affecting the reinforcement effectiveness. In practice, the bond layer is prone to defects due to uneven concrete surface, environmental deterioration or external loading during service life, which can weaken the bonding performance of the FRP-concrete system and even lead to unexpected structural failure in severe cases. In this paper, an experimental study on the influence of interface defects on FRP-concrete interface bonding behavior is designed. Based on the digital image correlation (DIC) technique, the effects of defect size, shape and location on the FRP interfacial bonding behavior were investigated separately. It was found that when the defect area was less than 5% of the effective bond area, the reduction of debonding load was similar to the fluctuation of the conventional interfacial debonding process, and the effect of defects on the interfacial bonding performance was relatively limited. The results also show that the degree of influence of defects on bonding performance varies for different configurations. The higher the concentration of defects, the higher the decrease in the FRP-concrete bearing capacity, especially those defects closer to the FRP boundary. Meanwhile, the proposed loading capacity reduction model considering the defect area is compared with the experimental results to assess the severity degree of defects.

Dynamic modelling of swashplate with local defects in axial piston pump and coupled vibration analysis

Local defects in a swashplate usually occur on the contact surfaces between the slipper and swashplate in an axial piston pump. An in-depth analysis of vibrations of a defective swashplate can be useful for the progress of defect detection approaches for the pump. An improved time-varying displacement excitation model considering the effects of defect sizes and bias angle is proposed to study a swashplate with a local defect based on coupling of a piecewise function. The effects of defect sizes and defect bias angle on the vibrations of a swashplate are analysed. A test rig is constructed to validate the dynamic model. The dynamic model can accurately predict the acceleration pulse waveform caused by the swashplate for parallel and bias defect cases with an error of only 0.98% in the frequency domain. The fault characteristic frequency of the swashplate is seven times the rotational frequency. The excitation peak and duration of the pulse waveform excited by the swashplate are related to the defect size and bias angle. The defect width has a significant effect on the acceleration peaks. This study provides a new method for dynamic simulation of a swashplate with a localised defect in an axial piston pump.

Characterization of temperature dependence of fracture behavior of monolithic and laminated ultra‐high temperature ceramic matrix composites

AbstractThe fracture behavior of ultra‐high temperature ceramic matrix composites at high temperature has received increasing attention. However, few studies consider the effect of particle/crack interaction on the high temperature fracture strength of materials. In this work, the effect of particle/crack interaction is introduced into temperature‐dependent fracture strength model of monolithic ultra‐high temperature ceramic matrix composites, which also considers effects of flaw size, grain size, and residual thermal stress. Furthermore, by considering the influence of laminated structure, a theoretical model of the temperature‐dependent fracture strength of laminated ceramic matrix composites is developed. The effect of particle/crack interaction is also included in this model. It should be noted that the predictions of models agree well with the experimental data of both monolithic and laminated materials without using any fitting parameters. The effect of particle/crack interaction is found to have a significant weakening effect on the strength of materials at different temperatures.

Effect of defect size and tooth anatomy in the measurements of a 3D patient monitoring tool

PurposeTo assess the influence of defect size and tooth anatomy on the measurements performed by a 3D patient monitoring tool. MethodsA fully dentate model was scanned to obtain a master digital file. Virtual duplicates received defects created in molars (16, 18, 28) and incisors (11, 12, 22), according to different depths (60, 80, 120 microns) and sizes (small, medium, large) totaling 180 conditions. The surface changes measured by the 3D Patient Monitoring Tool (3Shape TRIOS Patient Monitoring [TPM]) were compared with the reference by 2 calibrated operators. False Positives (FP), and False Negatives (FN) defect were registered. Pearson chi-square test, Multivariate binary logistic regression and Spearman rank correlation were used to evaluate the data (α = 0.05). ResultsA significant association was found between the area and the presence of FP and FN (P < .01). Larger defects had higher chances to present FP or an FN respectively. There was a significant association between the tooth and the presence of a FP value (FP, P = .02; FN, P = .005) specially in molars. No significant association was found between the defect depth and the presence of a FP value. Spearman rank correlation showed a strong association between the presence of an FP and an FN (r = 0.858, P < .01). ConclusionsThe defect size and tooth anatomy significantly affected the virtual follow-up, whereas defect depth did not. Small defects were correctly detected in all cases. An incorrect measurement on one side of the tooth simultaneously resulted in incorrect measurement on the opposite side. Clinical relevanceThe clinician should be aware that different factors related to the characteristics of the defects could affect the quality of the full-arch digital follow-up. Therefore, caution is needed when interpreting the models comparison in cases that a larger area of a tooth has been modified.

A Review of Magnetic Flux Leakage Nondestructive Testing.

Magnetic flux leakage (MFL) testing is a widely used nondestructive testing (NDT) method for the inspection of ferromagnetic materials. This review paper presents the basic principles of MFL testing and summarizes the recent advances in MFL. An analytical expression for the leakage magnetic field based on the 3D magnetic dipole model is provided. Based on the model, the effects of defect size, defect orientation, and liftoff distance have been analyzed. Other influencing factors, such as magnetization strength, testing speed, surface roughness, and stress, have also been introduced. As the most important steps of MFL, the excitation method (a permanent magnet, DC, AC, pulsed) and sensing methods (Hall element, GMR, TMR, etc.), have been introduced in detail. Finally, the algorithms for the quantification of defects and the applications of MFL have been introduced.

Computational Study of the Thermal Rectification Properties of a Graphene-Based Nanostructure.

Thermally rectifying materials would have important implications for thermal management, thermal circuits, and the field of phononics in general. Graphene-based nanostructures have very high intrinsic thermal conductance, but they normally display no thermal rectification effects. The present study relates to a thermally rectifying material and, more particularly, to a graphene-based nanomaterial for controlling heat flux and the associated method determining the rectification coefficient. Thermal rectifiers using a graphene-based nanostructure as thermal conductors were designed. Vacancy defects were introduced into one end of the nanostructure to produce an axially non-uniform mass distribution. Modified Monte Carlo methods were used to investigate the effects of defect size and shape, vacancy concentration, and ribbon length on the thermal rectification properties. Anharmonic lattice dynamics calculations were carried out to obtain the frequency-dependent phonon properties. The results indicated that the nanoscale system conducts heat asymmetrically, with a maximum available rectification coefficient of about 70%. Thermal rectification has been achieved, and the difference in temperature dependence of thermal conductivity is responsible for the phenomenon. Defects can be tailored to modulate the temperature dependence of thermal conductivity. The power-law exponent can be negative or positive, depending upon the ribbon length and vacancy concentration. A computational method has been developed, whereby the numerous variables used to determine the rectification coefficient can be summarized by two parameters: the power-law exponent and the thermal resistance ratio. Accordingly, the rectification coefficient can be obtained by solving a simple algebraic expression. There are several structure factors that cause noticeable effects on the thermal rectification properties. Defect size, vacancy concentration, and ribbon length can affect the thermal conductance of the nanostructure symmetrically and significantly. Graphene-based nanostructure thermal rectifiers can be arranged in an array so as to provide thermal rectification on a macroscopic scale.

Three-dimensional failure behaviour of L-shaped laminated composite with wrinkles and defects

In this paper, three-dimension failure behaviour of L-shaped composite beam with manufacturing defects was studied under four-point bending test condition. First, X-ray computed tomography scan was performed for L-shape laminated composite beam specimen to detect manufacturing defects such as voids, pre-delamination, and wrinkles or ply waviness. The scan images were then converted to three-dimensional volumetric entity through image processing, from which finite element mesh was generated with the detected defects directly incorporated. Next, three-dimensional progressive failure analysis was performed for the finite element model of the L-shaped laminate composite simulating four-point bending test condition with delamination and matrix failure in 90 degree plies accounted for by using cohesive zone modelling. The predicted maximum load was well matched to that obtained by tests validating the analysis modeling. Then a series of parametric studies were performed to investigate the effect of defect size and location on the failure load and delamination propagation pattern. It was found that the maximum load reduction was the largest when the pre-defect was located at the center of the symmetrical portion of the L-beam. In addition, the maximum load and delamination development behavior varied significantly depending on the interlayer and in-plane position of the pre-defect.

Effects of defect sizes at different locations on compressive behaviors of 3D braided composites

This paper reports the effects of defect sizes at different locations on the compressive behaviors of 3D braided composites. A polytetrafluoroethylene (PTFE) particle was embedded into the composite to form a defect. Low-velocity impact compression tests, high-speed photographic observations and micro-computed tomography (micro-CT) analyses were performed. Finite element analysis (FEA) models were developed to reveal stress distributions. We found that the compressive strength decreases and damages deteriorate with the defect size. The size effect of the defect in the center region is more significant than that in the surface region. FEA results show that there is a stress concentration around the defect, where the stress magnitude increases with the defect size. The decrease in compressive strength is attributed to stress changes in the shear region caused by defects. We expect such an investigation could be applied to characterize compressive strength in various composites with defects in different sizes and locations.

Correlations of fatigue strength of additively manufactured metals with hardness and defect size

One of the principal challenges that limits wide adoption of additively manufactured (AM) metals is their ill-understood fatigue behavior. The present study investigated the correlations between material properties, and the defect size effects on the fatigue performance of AM metal samples. Based on these correlations, some methods are proposed for constructing approximate S-N lines. The goal of these approximation methods is to provide reasonable correlation between the fatigue performance of components manufactured of AM metals, and easily and inexpensively obtainable properties like hardness, ultimate tensile strength, and defect characteristics. The proposed methods are shown to produce reasonable first order approximations.