Cracked Panel Research Articles

Surface crack effect on frequency and vibration mode switching of solar-powered aerospace structures

In the engineering design of modern wing panels and their optimal control system, the first step is to find and predict their dynamic characteristics. These characteristics are dependent on material properties, panel geometry, and boundary conditions. In addition, possible fracture existence, imperfections and environmental conditions may unpredictably change the frequency and modes shape of the panel and then the parameters of a control system. In the present paper, the effect of surface fracture depth and orientation on frequency and vibration mode switching of perovskite solar cells-based aircraft wing panels is investigated for the first time. The PSC (perovskite solar cell) panel is made of a polymer substrate reinforced with even-distributed graphene platelets (GPLs) and thin solar layers to enhance the overall electromechanical performance of the whole structure. Equations of motion of the panel are obtained by the Hamilton approach based on the properties of Reddy's third-order shear deformation theory and linear components of the Green-Lagrange strain tensor. The novel aspect is a line-spring model of surface crack by Cartmell et al. adapted to the model of the PSC panel under consideration. The discretization of the established equations of motion for the cracked panel is carried out by the element-free IMLS-Ritz method with mesh-free features. Validation of the obtained solutions is carried out by comparisons with results from previous studies for cracked laminated plates.First, material and geometric properties effect on vibration characteristics of the PSC structure was investigated. Next, partial surface crack depth and orientation angle are examined to show changes in frequency and vibration modes shape of the panel. It is shown, that there is a mode swapping between the second and third modes when transitioning from an intact panel to a cracked one. As the crack length increases, higher-order mode variations become more noticeable, potentially leading to their swapping or the excitation of new ones. Additionally, the findings demonstrate that the surface crack orientation angle significantly impacts the higher-order modes of the panel. When the orientation angle is 90°, the first six modes align with those of the intact plate. Mode shapes and frequency shifts are significant for crack orientation angles between 0° and 90°.

Low-cycle fatigue crack growth in brittle materials: Adaptive phase-field modeling with variable-node elements

This work presents an adaptive phase field framework for the simulation of crack nucleation and propagation in brittle materials subject to low-cycle loading. We introduce a fatigue history strain parameter within the phase-field framework to capture the fatigue effect. The resulting coupled differential equations are solved using a staggered iteration scheme. In order to improve the computational efficiency of the phase-field model, an adaptive refinement scheme is introduced. This scheme utilizes an artificial threshold that takes into consideration of both phase-field variables and cumulative fatigue history field variables to determine the elements to be refined. The handling of the hanging nodes resulting from mesh refinement is accomplished through the application of the variable-node element technique, offering a flexible and efficient mesh integration technique. We validate our proposed numerical scheme through five representative numerical examples: single-edge cracked specimen, compact tension specimen, double-edge cracked panel, plate with a hole and plate with multi-cracks and hole. The results demonstrate that the adaptive mesh refinement scheme significantly reduces computational costs without compromising the accuracy of the numerical predictions.

Uticaj prsline na nelinearno ponašanje ojačanog kompozitnog panela

Introduction/purpose: During their lifetime, ships and aircraft are subjected to severe service and aerodynamic loads that can cause structural damage and cracking. These cracks grow and propagate over time. Extending the life of a damaged structure is a very important area of research. In this context, the repair of composite panels is recommended to restore the performance of cracked structures. Methods: In order to minimize the concentration of stresses at the bottom of a crack, to stop and even to delay the propagation of this crack, this study seeks to propose a two-dimensional analysis by the software ANSYS to predict the effect of the propagation of a possible crack on the nonlinear behavior of cracked stiffened composite panels. Results: The results from this analysis will be a very good reference for improving performance and repairing cracked composite panels using stiffeners. Conclusion: It is recommended to provide patches for repairing cracked panels based on the modeling given in this study.

Ultimate strength prediction of cracked panels under extreme cyclic loads considering crack propagation

The objective of this study is to gain insights on the failure mechanism and behavior of cracked panels under cyclic loading. Numerical analyses were performed to investigate the ultimate strength of cracked panels. The prefabricated crack is assumed to be transverse and through-thickness, the relevant three types of crack location models are studied. Crack propagation arisen out of extreme cyclic loads is taken into consideration and the element erosion approach is adopted to simulate the process of crack growth. The influences of the amplitude of cyclic loads, the crack location, the panel thickness and the aspect ratio of panel on the ultimate strength of cracked panels under extreme cyclic loads are discussed in detail. Based on numerical results, the prediction formulae for dimensionless ultimate strength considering crack propagation are derived to estimate the ultimate strength of cracked panels under cyclic loads.

Optimisation of slab track design considering dynamic train–track interaction and environmental impact

Modern railway tracks for high-speed traffic are often built based on a slab track design. A major disadvantage of slab track compared to conventional ballasted track is that the environmental impact of the construction is higher due to the significant amount of concrete required. In this paper, the dimensions of the rectangular cross-sections and the types of concrete used in slab tracks are optimised with the objective to minimise greenhouse gas emissions, while considering the constraint that the design must pass the static dimensioning analysis described in the European standard 16432-2. The optimised track design is also analysed using a three-dimensional (3D) model of vertical dynamic vehicle–track interaction, where the rails are modelled as Rayleigh–Timoshenko beams and the concrete parts are represented by quadratic shell elements. Wheel–rail contact forces and the time-variant stress field of the concrete parts are calculated using a complex-valued modal superposition for the finite element model of the track. For the studied traffic scenario, it is concluded that the thickness of the panel can be reduced compared to the optimised design from the standard without the risk of crack initiation due to the dynamic vehicle load. In parallel, a model of reinforced concrete is developed to predict crack widths, the bending stiffness of a cracked panel section and to assess in which situations the amount of steel reinforcement can be reduced. To reduce the environmental impact even further, there is potential for an extended geometry optimisation by excluding much of the concrete between the rails.

Peridynamic Modelling of Propagation of Cracks in Photovoltaic Panels

Photovoltaics (PV) is a method of converting solar energy into direct current electricity using semiconducting materials that exhibit the photovoltaic effect. Cracking in PV panels can cause performance degradation in PV panels. In this study, a new computational methodology, peridynamics is utilised to investigate the cracking behaviour in PV panels. Peridynamics is based on integro-differential equations, and it is a very suitable technique to model crack initiation and propagation. Majority of PV panels are based on silicon solar cell technology. Therefore, polycrystalline material behaviour of silicon is explicitly considered in the model. The numerical framework can be used to support the design of high-performant, long-lasting and fracture-resistant PV panels. The results can also be used to produce practical guidelines aimed to facilitate the decision of PV module rejection due to cracking during production.

Analysis of Compressive Behaviour of Pristine and Cracked 5-Stringer Butt-Joint Panels Made from Carbon Fibre Reinforced Thermoplastic Polymer

The FE analysis of a panel made from carbon fibre reinforced thermoplastic polymer (CFRTP) loaded in compression is introduced. The panel contains five stringers with butt joint and demonstrates the alternative to CFRP panels made from fabrics by common laminate process. The pristine and cracked (initially delaminated) panels were investigated. The advanced detailed multi-layered model was generated by ABAQUS plug-in PbPModGen so that each composite layer was represented by a layer of finite elements. Cohesive elements (CZM) were applied to join the subparts of the panel. Buckling mode shapes were documented. The explicit nonlinear solver was used to study gradual buckling development for both, the simple and the detailed models. The effect of initial delamination between the central stringer and the skin was analysed. Local skin buckling in the delaminated area was found in addition. Compared to test results, the mode of the panel failure was captured with the lower load of 3% for the pristine and 9% for the cracked panel. The collapse occurred after local debonding of one stringer from the skin with its subsequent breakage and failure extension to other stringers. The presented work introduces buckling and post-buckling behaviour assessment and shows the effect of a crack on the compressive strength.

Investigation on repair of tension cracks in reinforced concrete panels

This research concentrates on repair of tension cracks in RC panels subjected to direct tensile loading and hydrostatic water pressure by incorporating high-performance materials including High-strength epoxy, Glass Fiber Reinforced Polymer (GFRP) laminate, Engineered Cementitious Composite (ECC) slag, and ECC fly ash. The findings are directly applicable to construction and repair of structures in which crack control and liquid tightness are critical such as liquid containing structures. The test setup simulates repairing internal surface of a cracked wall segment of a containment exposed to internal hydrostatic pressure. The study showed the applicability of ECC fly ash in repairing RC specimens with the ability to restore the structural strength along with improving the cracking and leakage behavior. GFRP exhibited high effectiveness in waterproofing and repair of damaged RC structures. Applicability of epoxy injection in local repair of cracked RC specimens was confirmed, while failure of epoxy resulted in substantial growth in crack width and leakage rate of the panel.

Effect of the Crack Tip Bifurcation on the Plasticity-Induced Fatigue Propagation in Metallic Materials.

This article deals with the influence of the crack path branching (at the micro level) on the plasticity-induced fatigue crack growth. With regard to this, a modeling by means of the finite element method was performed considering a cracked panel subjected to tension with different symmetric and asymmetric configurations of the bifurcated crack tip. The results show the appearance of a retardation effect in the growth rate of the bifurcated crack in relation to the growth rate of the fully straight crack in different cases studied, namely: (i) if the two branches of the bifurcation have different initial projected length, the propagation rate is greater at the crack tip corresponding to the long-branch than that of the short-branch, and the long-branch growth rate increases with the decrease of the initial branch angle and of the initial projected short-branch length and with the increase of the intensity of fatigue; (ii) if the two branches of the bifurcation have identical initial projected length, the retardation effect depends on the initial distance between the two bifurcated crack tips, the growth rate going up with the decrease of such a distance and with the increase of the fatigue intensity.

Design of An Integrated Solar Panel Monitoring and Cleaning System Based on Pixy Cmucam5

In recent years solar power has become the main source of clean energy in China. At the same time, the country has also introduced relevant policies to support it, and against this background, the solar photovoltaic industry has also flourished. However, solar photovoltaic power generation still has many problems, such as the huge amount of light energy and water loss caused by contamination of the solar panel surface and the high labour costs of dealing with the contamination, so it is necessary to carry out research on solar panel crack detection and cleaning.

Numerical investigation of composite patch repair of inclined cracked panel using XFEM

The life extension of the structure is an important area of research. Composite patch repair is widely used in restoring the strength of the cracked structures. Effective repair should offer repair efficiency as well as repair durability. The crack exists in the structure usually involves mixed-mode loading condition and therefore the study of the panel with inclined crack is significant. This article aims to investigate the performance of the inclined cracked panel bonded with composite patch. Numerical analysis of inclined cracked panel is carried out in ABAQUS. The J-integral and interfacial stresses are investigated which confirms repair efficiency and durability respectively. The orientation of the material in the composite influences the amount of reinforcement applied to the cracked panel and hence the effect of different material orientations is evaluated. The effect of patch stiffness on J-integral and interfacial stresses is also investigated. The results obtained indicate that the patch with adequate stiffness can contribute to diminish the J-integral and interfacial stresses to enhance the performance.

Modeling of interfacial crack propagation and kinking in sandwich panels

The paper presents an analytical model for the nucleation, propagation, and kinking of cracks in sandwich panels. The analytical approach adopts the variational principle of minimum of the total potential energy and it is based on cohesive interface modeling. The mathematical modeling considers two face sheets, a core layer, and an interfacial core-face sheet crack that can kink into the core and form a diagonal shear crack. This phenomenon, which has been observed in experiments, divides the core into two bodies. The core is therefore modeled using such two body approach. Three interfaces are introduced between the four components and appropriate interfacial laws are used to describe the interfacial phenomenon. The First-Order Shear Deformation Theory with geometrically nonlinear kinematic relations is adopted for the face sheets. The two core layers use linear geometrical relations and assume the high order polynomial displacement fields of the Extended High-Order Sandwich Panel Theory. Linear elastic laws are considered for the two face sheets and the core. The model is validated through a comparison with experimental observations of pre-cracked Double Cantilever Beam sandwich specimens that show a diversity of crack paths. The comparison and the quantitative investigation explore the capabilities and the limitations of the approach and shed light on the nucleation, debonding, and kinking phenomena in soft-core sandwich panels.

Buckling and bending properties of aluminium plate with multiple cracks

Purpose: In this paper, the bending strength and buckling stability of (AA 7075-T6) aluminium plate weakened by many transverse cracks, which located at different positions, subjected to concentrated loads applied at the ends were analysed. Design/methodology/approach: Numerical modelling and calculation by the finite element method (ANSYS Package), for the critical load of bending and compression panel were estimated. Findings: It found that the variation of the critical stress in bending and buckling is proportional to the crack conditions (no. of crack and location). In general, the critical load in bending and buckling decreases with increasing the crack number in structure. Research limitations/implications: For both bending and buckling, two transverse cracks on one face of plate is more stable than two transverse cracks on opposite faces. Practical implications: In addition, many experimental tests were carried out by using an INSTRON test machine to obtain the buckling critical loads, where the experimental results were compared with the ones of the finite element method. Furthermore, bending strength was calculated theoretically for the cracked panel. Originality/value: Comparison between the experimental and numerical (FE based model) data and between the theoretical and nu-merical (FE based model) data for buckling and bending strength respectively indicate the precise and the simplicity of the developed models to determine the critical loads in such cases.

Investigation of leakage and self-healing of direct tension cracks under sustained loading and high-water pressure

In this study, the leakage/self-healing of direct tension cracks of Normal Concrete (NC) and Engineered Cementitious Composite (ECC) panels have been investigated under the combined effect of sustained loading and high-water pressure. A test setup was designed and used to simulate the leakage in Liquid Containing Structures (LCS). The panels were subjected to direct tensile force in order to form full depth cracks through thickness. The water leakage test was then performed on the cracked panels and the water leakage through the cracks was studied under sustained loading with different water pressures. The leakage rate was recorded over time to study the short- and long-term self-healing of cracks. Furthermore, microstructural studies were completed on full depth drilled cores obtained from the self-healed sections of ECC and NC panels. The samples used for SEM-EDS analyses were taken from the top, middle and bottom portions of the healed cracks to investigate the potential influence of pressurized water on the self-healing products of different elevations of cracks. The results of this study confirm a greater self-sealing of leakage in loaded ECC panel and reveal a high effect of water pressure on the self-healing ability of concretes. Also, diverse concentrations of calcite and intermixed C-S-H/CH were characterized in various locations of healed cracks. Thus, unlike the normal water environment, the process of self-healing under high water pressure started from the middle portion of cracks and then propagated toward the lower and top parts.

Experimental and numerical studies for buckling and collapse behaviors of a cracked thin steel panel subjected to sequential tensile and compressive loading

The buckling and collapse behaviors of a cracked thin steel panel subjected to sequential tensile and compressive loading were investigated. An experimental apparatus was developed. Three different test specimens were employed, i.e., an intact panel and cracked panels with different crack lengths. The load-displacement curve and crack opening displacement (COD) were measured during the loading. The experimental results were examined via finite element (FE) computation. The results revealed that the developed experimental apparatus is quite suitable for investigating the buckling and collapse behaviors. Furthermore, the maximum tensile load, ultimate strength and local deformation around the crack were well simulated by the FE computation. The presence of the crack and length of the crack were strongly affected to the buckling and collapse behaviors.

Numerical investigation on the fracture driving force of laser welds and arc welds

The brittle fracture driving forces of laser beam welds (LBWs) and arc welds (AWs) are investigated and compared numerically with a center through-thickness cracked panel (CTCP) and a standard fracture toughness specimen (3-point bending specimen, 3PB). The effects of hard zone width (H) and strength mismatch ratio (Sr) were systematically studied at global strain (e∞) of 0.1% and 0.2%. It was found that the peak opening stress near the crack tip decreased with narrower H for LBW at e∞ = 0.2%, which can be ascribed to the better shielding effect provided by the softer base metal (BM) on hard zone welds. The peak normalized opening stress σyy/σY,WM was found nearly to be 3.0 for different Sr at e∞ = 0.1%, which decreased to 2.5 at e∞ = 0.2% due to more plastic deformation in the BM. The shielding effect ΔσW increased with higher Sr or narrower H. The effect of H and Sr on required CTOD fracture toughness in 3PB was also discussed basing on Weibull stress criterion. The required CTOD in 3PB of LBW can be decreased to be much lower than the AW with sufficiently narrow H. The harm effect of higher Sr on required toughness is less compared with the influence of lower H.

Integral Aircraft Wing Panels with Penetration Cracks: The Influence of Structural Parameters on the Stress Intensity Factor

The finite element model of integral wing panels with central penetration cracks under bending load was established, and the crack propagation process of the aircraft panel was simulated. The stress intensity factor (SIF) of the crack tip during crack propagation under varying conditions of crack length and panel structural parameters was determined. The effects of the panel structure parameters and crack size on the crack tip SIF were obtained. The regression analysis of the finite simulation element results has been performed and a regression model of SIF at the crack tip of the integral panel has been established, the determination coefficient of the regression model is 0.955.

Towards hybridization of composite patch in repair of cracked Aluminum panel

Purpose The maintenance of aircraft structure with lower cost is one of the prime concerns to regulatory authorities. The carbon fiber-reinforced polymer (CFRP) patches are widely used to repair the cracked structure. The demands and application of CFRP compel its price to increase in the near future. A distinct perspective of repairing the cracked aluminum panel with the hybrid composite patch is presented in this paper. The purpose of this paper is to propose an alternative patch material in the form of a hybrid composite patch which can provide economical repair solution. Design/methodology/approach The patch hybridization is performed by preparing the hybrid composite from tows of carbon fiber and glass fiber. Rule of hybrid mixture and modified Halpin–Tsai’s equation are used to evaluate the elastic constant. The stress intensity factor and interfacial stresses are determined using finite element analysis. The debonding initiation load is evaluated after testing under mode-I loading condition. Findings The hybrid composite patch has rendered the adequate performance for reduction of stress intensity in the cracked panel and control of interfacial stresses in the adhesive layer. The repair efficiency and repair durability of the composite patch repair was ensured by incorporation of the hybrid composite patch. Originality/value The studies involving patch hybridization for the application of composite patch repair are presently lacking. The influence of the patch stiffness, methodology to prepare the hybrid composite patch and effects of hybridization on the performance of composite patch repair is presented in this paper.

Local FRP-Reinforcement of Clay Hollow Block Panels under Shear Loading

The use of clay hollow blocks is common for new constructions in many parts of Europe. The results of 8 full-scale shear tests of block-masonry panels (dimensions 1.60x0.90x0.25 m) are reported in this paper. Non-defective and defective wall panels were tested in shear in the laboratory. Typical failure modes are investigated, not previously reported in the scientific literature. Test results show that the lateral load capacity of the panels is highly affected by construction defects. Furthermore, CFRPs were used in this research as local reinforcement (repair) in the area around the cracks previously opened in the masonry material. The lateral capacity for CFRP-repaired panels was restored to the original value of non-defective panels, indicating that the CFRP-repair of cracked panels is viable solution. An explanation for this phenomenon is suggested, which indicates that the high tensile strength of CFRPs can be effective in repairing cracked block-masonry. It is also argued that this large stress level of the CFRPs leads to a premature tensile CFRP crisis or a splitting failure of the blocks’ shells.

Mode I Stress Intensity Factor and T-Stress Solutions for Centre Cracked Orthotropic Plates

The main objective of this paper is the formulation of analytical expressions for the direct calculation of fracture parameters for the case of an orthotropic material with elastic behaviour. Numerical simulation by finite element method is performed to evaluate the singular and non-singular terms of William's series. Based on the obtained results, a fitting procedure is performed to propose an analytical formulation involving the geometric parameters of the plate and the crack in the approximate estimation of these parameters. The importance of the proposed analytical expressions is that they do not require a complex and time-consuming numerical analysis for the computation of the stress intensity factors and T-stresses for such an orthotropic cracked panel. A comparative study between the results obtained by the proposed equations and those obtained by finite element procedure has shown a good correlation.