Crack Line Research Articles

Success of Veneers with Indirect Resin Composite

Objective: To evaluate the success of veneers fabricated with indirect resin composite (Ceramage). Method: This Descriptive Case Series was completed at de’ Montmorency college of dentistry/Punjab Dental Hospital, Lahore over the period of 6 months from Jul 2018 to Jan 2019. Patients fulfilling the inclusion criteria of the study were selected. After the informed consent, pre-operative radiographs of the teeth to be veneered were taken to rule out any caries activity or periapical pathology. A total of 60 veneers were fabricated with indirect resin composite. Patients were followed up with 6 months interval and restorations were evaluated for complications like dislodgment, chipping, fracture, sensitivity and bleeding from gums. Results: Out of total of 60 veneers 50 were successful and 10 were unsuccessful. only 4 showed slight postoperative sensitivity,4 showed moderate postoperative sensitivity and 2 showed severe postoperative sensitivity.out of total 5 showed minor crack lines,3 showed minor chipping (1/4 of the restoration) and 2 showed moderate chipping (1/2 of restoration). Success rate of veneers fabricated with indirect resin composite (Ceramage) was 83.3%. Conclusions: The indirect veneers have undergone considerable improvement and refinement over the past few decades and have now matured into a predictable restorative concept in terms of longevity, periodontal response and patient satisfaction. The design of the restoration should take the material properties into account in order to enhance the clinical performance. Key words: Indirect Resin Composite, Veneers, Smile makeover

Study on Crack Development of Concrete Lining with Insufficient Lining Thickness Based on CZM Method.

The most common structural defect of a tunnel in the operation period is the cracking of concrete lining. The insufficient thickness of tunnel lining is one of the main reasons for its cracking. This study studied the cracking behavior of standard concrete specimens and the failure behavior of tunnel structures caused by insufficient lining thickness using Cohesive Zone Model (CZM). Firstly, zero-thickness cohesive elements were globally inserted between solid elements of the standard concrete specimen model, and the crack development process of different concrete grades was compared. On this basis, a three-dimensional numerical model of the tunnel in the operation period was established. The mechanism and characteristics of crack propagation under different lining thicknesses were discussed. In addition, the statistics of cracks were made to discuss the development rules of lining cracks quantitatively. The results show that the CZM can reasonably simulate the fracture behavior of concrete. With the increase in concrete strength grade, the number of cohesive damaged elements and crack area increases. The insufficient lining thickness changes the lining stress distribution characteristics, reduces the lining structure’s overall safety, and leads to the cracking of the diseased area more easily. When surrounding rock does not contact the insufficient lining thickness, its influence on the structure is more evident than when surrounding rock fills the entire lining thickness. The number of cohesive damaged elements and the size of the crack area increases significantly.

Effects of canal damage characteristics on canal seepage based on a three-dimensional numerical model

An increasing number of canals are designed with liners to decrease canal seepage. As the lining material and cracks or holes were previously considered equivalent porous media, few studies have quantified the effects of lining parameters on canal seepage, and the relationships between the reduction factor (β) of the lining and the crack width (df) and hole density (hd) are not explicit, leading to large errors in the estimation of seepage loss. A three-dimensional numerical model is employed to simulate seepage loss from canals lined with concrete and geomembrane material in a total of 1159 scenarios, focusing on the crack locations, saturated hydraulic conductivity (Ks) of concrete material and geomembrane material (Ksc and Ksg, respectively), thickness (Tc), concrete lining df, and geomembrane lining hd. For canals lined with concrete, df is the main factor affecting canal seepage, followed by Ksc and Tc. Cracks with widths smaller than 0.02 mm have minimal influence on β, where β is reduced by a decrease in Ksc or an increase in Tc. When df ranges from 0.02 to 0.2 mm, β increases gradually to a maximum value, while the impacts of Ksc and Tc weaken. For canals lined with geomembranes, β increases slightly with hd from 0 to 4.2 × 10−5, increases nearly linearly with log hd from 4.2 × 10−5 to 8.4 × 10−3, and then approaches 1.0. β is weakly influenced by Ksg for particular hd values when Ksg is smaller than 10−11 m/s, increases rapidly with Ksg from 1 × 10−11 to 1 × 10−8 m/s, and then exceeds 0.938. For a canal lined with both concrete and a geomembrane, the trends in β with changes in df and hd are identical to those of a canal with a single lining. Based on these results, the damage degree is proposed to evaluate the influence of cracks and holes on the lining effectiveness and as an intermediate variable for calculating β from df and hd. Three empirical equations are proposed to calculate the β value of the concrete lining, geomembrane lining and combined lining with different df and hd. The results show that the proposed equation improves the accuracy of the estimation of β compared with the multiplication model and can be further used for calculations of seepage loss from lined canals.

Diagnosis and Management of Fractured Teeth; Review Article

Traumatic damage to the teeth and oral tissues are the most common causes of tooth fracture. Because of their location in the oral cavity, front teeth in the upper jaw are the most commonly fractured. Sports, car accidents, and physical violence are the most prevalent causes. Cracked teeth are often diagnosed by visually inspecting the tooth (preferably utilizing microscopes). The size and form of the fracture plane are not always determined by looking at the crack line. One factor that contributes to the difficulty of effectively making an endodontic diagnosis is the inability to visualize the depth of the fracture through a clinical exam alone. Transillumination, microscopes and dyes are a useful tool for finding and diagnosis of the crack, treatment of the crack depends on the type, extend of the crack as well as the condition of the patient. In this review we’ll be looking at the diagnosis, etiology and management of fractured teeth.

Analysis on ultimate water pressure and treatment measures of tunnels operating in water rich areas based on water hazard investigation

In recent years, the tunnels operating in water rich areas of China occasionally suffer from disasters, such as lining cracking, leakage, and track deformation. To develop reasonable and effective treatment measures for tunnel water hazards, this paper investigates the water hazards in tunnels operating in water rich areas of China, and identifies the causes of these water hazards. Considering the on-site situation of water hazards (e.g., track bulging and lining cracking), FLAC3D simulation was implemented to compute the actual water head on the tunnel during the water hazards, that is, the ultimate water pressure of the tunnel. Based on ultimate water pressure and water hazard investigation, the authors put forward treatment measures for tunnel water hazards, and evaluated whether the treated tunnel can withstand the attack of high-water pressure in future. The research provides theoretical and data references for treating water hazards in tunnels operating in water rich areas.

The Correlation of Crack Lines and Definitive Restorations with the Survival and Success Rates of Cracked Teeth: A Long-term Retrospective Clinical Study

IntroductionCracked teeth frequently require protective adhesive restorations. This long-term, longitudinal retrospective clinical study aimed to evaluate the factors influencing the success and survival rates of cracked teeth with crack lines (CLs) in different directions when restored early with onlays or full-coverage crowns. MethodsThe dental records of 71 patients with a total of 86 cracked teeth with different pulpal and periapical diagnoses and with follow-ups spanning over 1–11 years were included. Data regarding the demographics; clinical symptoms and signs; bruxism; occlusal interferences; eating habits; pulpal and periapical diagnoses; number, direction, location, and extent of CLs; probing depth; and coronary condition before and after the placement of definitive restorations were collected. Univariate associations between tooth survival and explanatory variables were assessed. The long-term survival rate was estimated using Kaplan-Meier analysis and the log-rank test. A multivariate analysis was performed using Cox regression analysis. ResultsThe overall success rate was 93.0%, and the overall survival estimates of cracked teeth restored early were 98.6%, 94.9%, and 55.9% at the 1-, 5-, and 11-year follow-ups, respectively. The direction of the CLs did not influence the survival of the tooth. No significant association was observed between the type of tooth, probing depth, root canal treatment, and tooth loss (P > .05). The multivariate analysis showed that previously treated cracked teeth (P < .05), the provision of onlay restorations (P < .05), and the placement of posts (P < .05) had higher correlations with tooth loss. Additionally, the placement of full-coverage crowns resulted in lower tooth loss compared with the placement of onlays (P < .05). ConclusionsPrevious endodontic treatment in teeth that subsequently develop CLs has a negative impact on the survival rate of the teeth. Moreover, early placement of full-coverage crowns should be implemented for cracked teeth regardless of the direction or the number of CLs because it is associated with a higher cracked tooth survival rate.

Précis of gap test results requiring reappraisal of line crack and phase-field models of fracture mechanics

This paper presents a brief review of the recent advances in fracture mechanics at Northwestern University and Istanbul Technical University, prompted by the recent discovery of the gap test—a test that makes it easy and unambiguous to determine the effects of crack-parallel stresses on the mode-I fracture energy and, in consequence, on the nominal strength of structures of different sizes (aka, the size effect). The standard fracture specimens cannot reveal these effects since they have zero or negligible crack-parallel stresses. In addition, these effects cannot be reproduced by the standard, widely used, fracture models including the linear elastic fracture mechanics (LEFM), the cohesive crack model (CCM), as well as the popular computational models such as the extended finite element (XFEM) and the phase-field models (PFM). Therefore, it will be necessary to adopt fracture models that can reflect the tensorial damage behavior in the fracture process zone (FPZ), which is governed by at least two characteristic lengths, one for the FPZ length and one for the FPZ width. The modeling of elasto-plastic metals is even more complicated since the FPZ of micrometer-scale width is surrounded by a millimeter-scale plastic-hardening (yielding) zone. This role of the yielding zone has been understood well since the 1980s except for the scaling laws which are helpful for determining the effect of crack-parallel stresses more accurately. As a general conclusion, the line crack and phase field models cannot be used for practical problems with significant crack-parallel stress components (σxx,σzz,σxz). However, thanks to the finite width of its fracture front, the crack band model can be used, provided that its tensorial damage law is realistic. A new challenge for the nonlocal and gradient models is that they, too, will need to distinguish two independent material characteristic lengths, one for the direction of damage band and one transverse to it.

Automated vision-based inspection of drilled CFRP composites using multi-light imaging and deep learning

Inspection of drilled holes in aerospace Carbon Fiber Reinforced Polymers (CFRPs) is crucial to avoid failure of attachments and disintegration of aircraft structures. Vision-based systems can provide an efficient tool for rapid inspection of holes directly on production lines. However, automatic detection of damages in digital images is a challenging task due to the dark, textured, and semi-specular surfaces of CFRPs. This paper proposes a novel and fully autonomous system for accurate detection and segmentation of damages and cracks around drilled holes in CFRP composites. The proposed system comprises three modules: (1) An automated multi-light imaging end-effector is designed to sequentially illuminate the inspected hole from four different directions and capture images for each case. The four images are then fused to suppress the background and enhance the visibility of damages. (2) A series of image processing steps are proposed to automatically segment the hole profile, damage area, and crack lines in the fused images. The segmented images serve as labeled outputs (masks) in the following deep learning model. (3) A deep Fully Convolutional Network (FCN) with the U-Net architecture is designed and trained for pixel-wise semantic segmentation of hole images. Once trained, the U-Net model can reliably detect the hole profile, damages, and cracks directly from ‘raw’ multi-light images without any image processing required. Experimental tests show that the U-Net model can provide real-time and fully automated evaluation of the delamination factor with a maximum error of 5.4%.

Study on supporting time of tunnel lining in thin-layered rock mass

The thin-layered rock mass of Baokang tunnel has the characteristics of large deformation and failure of soft rock under the excavation unloading. More seriously, a serious question is that the lining cracking is prominent. The cause of the cracking can be traced to different failure modes of the surrounding rock mass. Specifically, the rock layer on left arch spandrel is prone to bending failure due to the action of tangential stress, while the right-side wall is prone to sliding failure due to the action of higher shear stress. Furthermore, the lining cracking may beyond the ultimate compressive capacity when the loosely collapsed rock mass acted on the lining. According to the transversely isotropic characteristics of layered rock mass, the failure approach index (FAI) was selected to evaluate the damage and failure of thin shale. Meanwhile, the result of the example shows that this index can effectively characterize the failure characteristics of the thin-layered rock mass. Hence, the FAI was used as an evaluation index of the loose failure of layered rock mass. In order to determine the lining support time, the stability of the lining under the action by the loose rock mass was analyzed by the numerical simulation. As a result, the distance between the lining and the face should not be bigger than 120m. According to the Feedback through onsite construction, the lining cracks didn’t appear under this supporting time, which ensured the stability of the lining structure. The research methods and ideas can provide reference for the similar tunnel lining construction in thin-layered rock mass.

Study on cracking behavior of tunnel linings with the diseases of void and lining insufficient thickness

Typical tunnel diseases, such as lining cracking, void behind the lining, and lining insufficient thickness, can commonly occur in tunnel structure, seriously threatening the safety state of tunnel operation. In this research, to investigate the relationship between these diseases, the cracking behavior of tunnel structure with typical combined diseases of void behind the lining and lining insufficient thickness were concentrated on using the cohesive zone model (CZM) method. At first, the zero-thickness cohesive elements were inserted between the lining solid elements globally to determine the possible cracking zone, guaranteeing the randomness of cracking. Subsequently, the characteristics of crack propagation of linings with typical combined tunnel diseases were explored detailed under the applied gradual loading. Finally, to quantitatively explore the development of lining cracks, the statistics of cracks (including the number of damaged cohesive elements and crack area) were conducted. The main results of this study indicated that the distribution of void and lining insufficient thickness influences the cracking behavior obviously, and the cracking degree shows a positive relationship with the applied gradual loading. Furthermore, as the gradual loading increases, the number of damaged cohesive elements presents a significant increasing trend, and the number of damaged cohesive elements also shows a positive relationship with the void range. In addition, the crack area also shows a positive relationship with the applied gradual loading and the void range.

Image-based crack recognition of tunnel lining using residual U-Net convolutional neural network

Concrete crack is a common disease of lining segments in tunnel projects, which will cause adverse risks without being repaired in time. Currently, various convolutional neural networks (CNNs) have been successfully applied in the computer vision field. An image-based crack recognition model of tunnel lining using Residual U-Net (ResU-Net) network is proposed. The residual learning units are added to the encoding path of the U-Net network to solve the problem of model degradation. Based on a highway tunnel project in western China, a dataset of lining crack is built. And through the size adjustment, annotation and binary processing, 2880 image samples with the same size of 448×448 is obtained. The dataset is divided into training set, validation set and test set with the ratio of 6:1:1. The quantitative results show that three evaluation metrics of pixel accuracy (PA), intersection over union (IoU) and Dice coefficient (Dice) are 98.67%, 56.45% and 68.09%, respectively, which is better than that of typical U-Net. It indicates that the ResU-Net model has good performance and robustness in the pixel level segmentation of tunnel lining cracks.

Study on cracking behaviors of shield tunnel segment with annular interfacial unevenness under jacking thrust force

As one of the major engineering disasters in tunnel structures, segment lining cracks have significant impacts on the carrying capacity and durability of shield tunnels. This study focused on the lining cracking problems that are induced by annular interfacial unevenness during construction; a three-dimensional finite element model of shield tunnel linings was established that uses particular gasket elements and considers the assembly tolerance between segments and dowel pads at the annular interface. Through the numerical simulation, the lining’s structural deformation and crack propagation in the presence of the annular joint’s unevenness were studied by adjusting the initial gap and the normal stiffness modulus of the dowel pad at the annular interface. The numerical results indicate that the cracks induced by the jacking thrust force are initiated in hang holes in the midspan of the segments and subsequently develop along the longitudinal direction. In addition, the critical thrust loads for crack occurrence and the crack length are directly related to the initial gap and the stiffness modulus of the dowel pads at the annular interface of the segments. Moreover, the higher the assembly tolerance and the dowel pad stiffness modulus, the more serious will be the longitudinal cracks. It is confirmed that the use of appropriate dowel pads can effectively control the initiation and development of longitudinal cracks and enhance the structure’s carrying capacity.

Volumetric strain behaviour and self-healing of large scale engineered cementitious composite and normal concrete panels under natural conditions

The application of engineered cementitious composite (ECC) in liquid containing structures (LCS) may help to improve the cracking performance of these structures. This study investigates the hydration temperature, shrinkage, cracking and self-healing behaviors of 10 m length ECC and normal concrete (NC) panels under real field conditions of volumetric strains. The restrained panels of NC and ECCs, with different compositions of fly ash (ECC/FF) and slag (ECC/SL), were designed to represent a segment of LCS and were cast and monitored on site for seven months under natural temperature changes of wet/dry and freeze/thaw cycles. A detailed microstructural analysis was completed on full depth drilled cores to explore the self-healing efficiency of different crack layers. At 28 days, only ECC/SL exceeded the ACI 224R limit for crack width of concretes to be used safely in LCS. However, at longer ages, unlike ECC/FF and ECC/SL panels which showed significant healing of their volumetric strain cracks, the NC panel experienced a sharp increase in crack widths up to seven months of monitoring. Different concentrations of CaCO3 and C-S-H/CH products were characterized at the top, core and bottom layers of crack lines, confirming higher self-healing performance of the volumetric strain cracking in ECC/FF compared to ECC/SL and NC segments.

A non-standard numerical method for finite element modelling of tensile cracks in quasi-brittle material

In this paper, a non-standard finite element (FE) method, coupled with a mathematical programming procedure, is presented to simulate initiation and propagation of in-plane tensile cracks in quasi-brittle material. Potential crack lines are defined and limited by the FE edges. The cracks are considered as localized plastic deformations imposed at the nodes along the potential crack paths. Crack opening is detected at each node by a limit value of tensile force normal to the crack direction. When the limit value is reached, a cohesive crack starts, following a linear softening branch. The mechanical model is such that no remeshing neither the introduction of interfaces is necessary to describe the discontinuity between elements, as usually required in standard FE approaches. The non-linear solution of the structural problem is obtained using a mathematical programming procedure based on the solution of a parametric linear complementarity problem (PLCP). The main advantage of the PLCP formulation is its ability to manage structural configurations in which instability and multiplicity of solutions are possible, providing one solution even at points characterized by a not-positive-semidefinite Hessian matrix. Simple numerical simulations are presented with the aim to test the method and the solution procedures.

Tunnel Lining Crack Recognition Based on Improved Multiscale Retinex and Sobel Edge Detection

China is gradually transitioning from the “tunnel construction era” to the “tunnel maintenance era,” and more and more operating tunnels need to be inspected for diseases. With the continuous development of computer vision, the automatic identification of tunnel lining cracks with computers has gradually been applied in engineering. On the basis of summarizing the weaknesses and strengths of previous studies, this paper first uses the improved multiscale Retinex algorithm to filter the collected tunnel crack images and introduces the eight-direction Sobel edge detection operator to extract the edges of the cracks. Perform mathematical morphological operations on the image after edge extraction, and use the principle of the smallest enclosing rectangle to remove the isolated points of the image. Finally, the performance of the algorithm is judged by the objective evaluation index of the image, the accuracy of crack recognition, and the running time of the algorithm. The image filtering algorithm proposed in this paper can better preserve the edges of the image while enhancing the image. The objective evaluation indexes of the image have been improved significantly, and the main body of the crack can be accurately identified. The overall crack recognition accuracy rate can reach 97.5%, which is higher than the existing tunnel lining crack recognition algorithm, and the average calculation time for each image is shorter. This algorithm has high research significance and engineering application value.

Water pressure evolution and structural failure characteristics of tunnel lining under hydrodynamic pressure

With the frequent occurrence of heavy rainfall, the lining cracking, leakage, and buckling collapse accidents of water-rich mountain tunnels are becoming increasingly prominent. A large amount of surface water rushing into the tunnel in a short time and exceeding the drainage capacity of the tunnel is an important reason for the occurrence of water pressure diseases. To ascertain the failure characteristics of the lining structure under the condition of surface rainfall recharge and tunnel drainage, we designed a seepage model test system. The evolution law of water pressure behind lining, vertical displacement of invert and failure characteristics of structure under water pressure were studied. On this basis, the influence of the optimized drainage tunnel structure on the water pressure of the lining was further studied. The results show that the water pressure of the lining invert cannot be effectively reduced through the drainage system when the conventional drainage scheme is adopted, and the invert deforms and gradually cracks and fails under the action of hydrodynamic pressure. The cracking sequence of the lining structure is the invert center, the sidewall foot, the vault, and the sidewall. The type of cracks is mainly longitudinal, supplemented by circumferential and oblique. When the optimized drainage scheme is adopted, the water pressure at the bottom of the invert and the uplift displacement of the structure are significantly reduced, ensuring the safety of the lining structure.

Sun-tanning with Deleuze and Guattari in greater Sydney, Australia

This paper is about relational becomings and opposing forces that may occur when white skin becomes tanned over the course of everyday life. In the Australian context of beach leisure culture and rising melanoma rates, the article draws on the only three participants with diverse ancestry from a larger qualitative research project conducted with 40 young men and women in Greater Sydney, New South Wales. I argue that Deleuze and Guattari’s assemblage thinking, specifically three related concepts of a lifeline have much to offer feminist geographers: molar lines (segmented lines), rupture lines (lines of flight) and molecular lines (crack lines). Here, I illustrate the potential of assemblage thinking to analyse the reciprocal relations between tanning, skin, gender, race and place. I illustrate how tanning sensations are comprised of contradictory forces. I argue that while participants do not escape the molar lines of gender and a Black-White racial dichotomy, there are molecular lines that temporarily disrupt these gendered and racialised regimes.

Properties of Mortars Mixed with Polystyrene and Hemp Fiber Wastes

When polystyrene (PS) and hemp fiber waste were mixed into the sand aggregate, some physical-mechanical properties of mortar changed. The PS and hemp fiber were tested as partial replacements for sand in mortar with three designated percentages of 2.5, 5.0 and 10.0% by mass. The properties of mortar with PS were found to be better than that of the mortar with hemp fiber. The water absorption of mortar with PS was comparable with the reference mortar but lower than that of mortar with hemp fiber. The compressive strength of the mortar with PS was higher than that with hemp fiber whereas the tensile strength of the mortar with 2.5% PS and hemp fiber was comparable and was higher than that of the reference mortar. The thermal conductivity of a wall plastered by mortar containing PS decreased as the PS content was increased, whereas the thermal conductivity of a wall plastered by mortar containing hemp fiber increased as the hemp fiber content was increased. Thick crack was detected in the reference wall while hair line crack occurred from the wall plastered with PS and hemp fiber mortars. The results indicated that 10.0% PS could be used as a partial replacement for sand in mortar with an improvement in some of the properties of the mortar.

Constitutive modelling of annealing behavior in through silicon vias-copper

The mechanical properties of electroplated copper (Cu) filled in through silicon vias (TSVs) play a key role in the thermo-mechanical reliability of TSV packages. Generally, it is necessary to anneal TSV-Cu after electroplating to stabilize its microstructure. Different annealing conditions could affect the microstructure and deformation behavior of TSV-Cu. Thermal and mechanical load during post-process and service life could often cause TSV-Cu reliability issues by its deformation, such as TSV-Cu pumping, interfacial delamination and back end of line (BEOL) cracking. To understand the deformation behavior of TSV-Cu, this article tries to obtain the constitutive equations of TSV-Cu under different annealing conditions. Nanoindentation tests and finite element method (FEM) inversion are used to establish a constitutive model of annealing behavior in TSV-Cu. The power law constitutive models are determined to describe the elastic and plastic behaviors. Strain rate and annealing soften effects are both found from the constitutive model. The microstructures of TSV-Cu are also characterized by electron backscatter diffraction (EBSD) to correlate with mechanical performance. Grain size increased with the increase of annealing temperature, and both hardness and yield strength follow the Hall-Petch relationship, which are meaningful for calculating the deformation of the TSV package and improving the thermomechanical reliability of the device.

Degradation and Failure of Flexible Low-Temperature Poly-Si TFTs Under Dynamic Stretch Stress

Degradation and failure behaviors of the flexible low-temperature poly-Si (LTPS) thin film transistors (TFTs) under repetitive stretch stress parallel to channel length (L) direction are investigated. A geometric effect is observed in degradation of the threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ), which depends on the channel width (W) and active area ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">WL</i> ), while has a weak correlation with L. Three failure modes of TFTs are identified from their I-V characteristics: damage in the gate insulator (GI), channel traps generation, and metal line cracks. Failure statistics show that the GI failure has a low failure rate and follows the exponential distribution, while the other two modes have high failure rates in the early stage of the stretch cycles, and their failure distributions follow the limited failure population (LFP) model.