Spiral Cracks Research Articles

Quasi-static and dynamic stab behavior and damage mechanisms of the spiral/laminated structure of CFRP

Stab resistance depends on the material’s strength and stiffness. Puncture energy is absorbed mainly through fracture and friction in the damaged area. To reduce stress concentrations and diffuse impact energy, this paper proposes a spiral CFRP inspired by spiral grass. Comparison of the puncture resistance of spiral CFRP and laminated CFRP by quasi-static and dynamic puncture. After separating the puncture process into longitudinal piercing and transverse cutting, it was found that spiral CFRP had excellent cutting resistance, with a maximum cutting force 44% higher than laminated CFRP. However, the detachment of the central structure leads to weaker perforation resistance of spiral CFRP than laminated CFRP. Laminated CFRP was found to undergo internal delamination damage after perforation by microscopic characterization and finite element analysis. Spiral CFRP has a helical yarn path and the interface distribution parallel to the impact direction, resulting in a greater susceptibility to delamination damage and rapid spiral crack propagation. The damaged area of spiral CFRP is up to 416% larger than that of laminated CFRP. The structural instability also resulted in a higher penetration depth for spiral CFRP than for laminated CFRP. The composite structure provides better puncture resistance than a single structure. Due to the combined advantages of the passivation of spiral CFRP and the structural stability of laminated CFRP, Sprial/laminated CFRP has the highest puncture resistance, with a maximum puncture load of 1,467 N, and is not penetrated at a puncture energy of 24 J. The spiral structure incorporating crack-inducing and transverse damage resistance could offer a promising approach to developing stab-resistant materials.

Experimental Investigation on Pure Torsion Behavior of Concrete Beams Reinforced with Glass Fiber-Reinforced Polymer Bars

The failure mechanism of torsional concrete beams with fiber-reinforced polymer (FRP) bars is essential for developing the design method. However, limited experimental research has been conducted on the torsion behavior of concrete beams with FRP bars. Therefore, the pure torsion test of four large-scale FRP-RC beams (2800 mm × 400 mm × 200 mm) was conducted to investigate the influence of the stirrup ratio (0, 0.49%, and 0.98%) and longitudinal reinforcement ratio (3.01%, 4.25%) on torsion behavior. The test results indicated that three typical failure patterns, including concrete cracking failure, stirrup rupturing failure, and concrete crushing failure, were observed in specimens without stirrups (stirrup ratio 0), partially over-reinforced specimens (stirrup ratio 0.49%), and over-reinforced specimens (stirrup ratio 0.98%), respectively. The tangent angle of spiral cracks at the midpoint of the long side of the cross-section was approximately 45° initially for all specimens. The torque–twist angle curves exhibited a linear and bilinear behavior for specimens without stirrups and specimens with stirrups, respectively. As the stirrup ratio increased from 0 to 0.98%, torsion capacity increased from 24.9 kN∙m to 27.8 kN∙m, increased by 12%, ultimate twist angle increased from 0.0018 rad/m to 0.0403 rad/m. As the longitudinal reinforcement ratio increased from 3.01% to 4.25%, the torsion capacity increased from 27.8 kN∙m to 28.3 kN∙m, and the ultimate twist angle decreased from 0.0403 rad/m to 0.0244 rad/m. Based on test results, the stirrup strain limit of 5200 με and spiral crack angle of 45° was suggested for torsion capacity calculation. In addition, based on the database of torsion tests, the performance of torsion capacity provisions was assessed.

Novel Approach in Fracture Characterization of Soft Adhesive Materials Using Spiral Cracking Patterns

A novel approach for the fracture characterization of soft adhesive materials using spiral cracking patterns is presented in this study. This research particularly focuses on hydrocarbon polymeric materials, such as asphalt binders. Ten different asphalt materials with distinct fracture characteristics were investigated. An innovative integrated experimental–computational framework coupling acoustic emissions (AE) approach in conjunction with a machine learning-based Digital Image Analysis (DIA) method was employed to precisely determine the crack geometry and characterize the material fracture behavior. Cylindrical-shaped samples (25 mm in diameter and 20 mm in height) bonded to a rigid substrate were employed as the testing specimens. A cooling rate of −1 °C/min was applied to produce the spiral cracks. Various image processing techniques and machine learning algorithms such as Convolutional Neural Networks (CNNs) and regression were utilized in the DIA to automatically analyze the spiral patterns. A new parameter, “Spiral Cracking Energy (ESpiral)”, was introduced to assess the fracture performance of soft adhesives. The compact tension (CT) test was conducted at −20 °C with a loading rate of 0.2 mm/min to determine the material’s fracture energy (Gf). The embrittlement temperature (TEMB) of the material was measured by performing an AE test. This study explored the relationship between the spiral tightness parameter (“b”), ESpiral, Gf, and TEMB of the material. The findings of this study showed a strong positive correlation between the ESpiral and fracture energies of the asphalt materials. Furthermore, the results indicated that both the spiral tightness parameter (“b”) and the embrittlement temperature (TEMB) were negatively correlated with the ESpiral and Gf parameters.

Structure and thermal properties of cellulose nanofibrils extracted from alkali–ultrasound treated windmill palm fibers

Windmill palm, a tree species that is native to China, has gained attention with regard to the production of substantial amounts of biomass fibers via yearly pruning. This study investigates the structure and thermal properties of cellulose nanofibrils (CNFs) obtained from windmill palm biomass, with the goal of promoting the usage of these CNFs. Alkali–ultrasound treatments are employed herein to prepare samples of the CNFs. The micromorphology of the prepared samples is observed using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Furthermore, X-ray diffraction analysis is used to examine the aggregated structure of the samples, and thermogravimetric analysis is used to investigate their thermal properties. Results indicate that during alkali hydrolysis when obtaining CNFs, the fiber cell wall exhibits distinct spiral cracking. The diameter of the obtained nanocellulose is <90 nm. The removal of lignin and hemicellulose materials from the fiber cell enhances the crystallinity of CNFs to as high as 60 %, surpassing that of windmill palm single fibers. The thermal decomposition temperatures of the CNFs are found to be 469 °C and 246 °C for the crystalline and amorphous regions, respectively.

Use of spiral cracking patterns in fracture characterization of asphalt materials

A new approach for fracture characterization of asphalt materials through use of spiral cracking patterns is presented. Five different asphalt materials each at three different oxidative-aging levels, were utilized in this work. An efficient image processing framework using Convolutional Neural Networks (CNN) was implemented to analyze spiral cracking images. Results showed that spiral tightness parameter was sensitive to fracture energy, performance grade (PG), and oxidative aging level of asphalt binders. Machine learning approaches such as XGBoost and Elastic-Net regularized regression were employed to develop prediction models to estimate fracture in asphalt materials.

Predicting the head leakage behaviour of cracks in pipe elbows

In this study, finite element analysis (SAP2000 program) was used to investigate the relationship between the pressure and leakage area in 90° pipe elbows with longitudinal, spiral, and circumferential cracks. The results show that leakage areas expand linearly as the internal pressure increases and its inclination is called the pressure–area slope (m). A sensitivity study was conducted to recognize the influence of different parameters (inside diameter, wall thickness, modulus of elasticity, longitudinal stress, Poisson’s ratio, and finally crack orientation) on both m and leakage exponent (N). The results reveal that the elasticity modulus has the dominant impact on m, followed by elbow wall thickness, and then elbow inside-diameter. The Poisson’s ratio and the longitudinal stress have an insignificant influence on m. Moreover, the slope m varies more in the longitudinal and spiral cracks than the circumferential cracks. The amount of leakage through the different cracks is a function of the internal pressure raised to an exponent ranging from 0.5 to 1.01. An attempt was made to find empirical equations to express the pressure–area slope as a function of elbow properties and crack orientation. The study’s findings were checked against numerical and experimental results and good correlations were obtained.

Use of Spiral Cracking Patterns in Fracture Characterization of Soft Adhesive Materials

Use of Spiral Cracking Patterns in Fracture Characterization of Soft Adhesive Materials

Corrosion behaviors of basalt fiber exposed to the acids

In this work, Taguchi method was employed to elaborate the effects of temperature, concentration and immersion time of typical acids (HCl, H2SO4, HNO3) on the morphology and tensile strength of basalt fiber (BF). The results showed that the corrosion behavior of BF was controlled by the ion-exchange process with presence of H+ ions, and irregular and spiral cracks were formed during this process, which led to the severe degradation on the tensile strength of fiber. Besides the governing role of H+ concentration in acids, SO42- also aggravated the corrosion in sulfuric acid with precipitant of CaSO4. The reasons behind the acid-induced low-energy crack opening paths were given to illustrate the formation of spiral cracks on fiber surface in acids. The ubiquitous axial defects were revealed on fiber surface, and comparative results confirmed that such defects originated from the scratching between the filament and bushing during the fiber spinning process.

Drying silica-nanofluid droplets

Exsiccation of suspension droplets generates characteristic ring-like stains. The homogeneity of such coffee rings is disturbed by subsequent cracking. Placing silica droplets on copper and stainless steel substrates, the ensuing drying and cracking chronology is investigated. The formation of the coffee ring and its cracking are visualised through microscopic imaging and videotaping. Based on the cracking chronology, three crack generations are identified. The evolution of the 1st crack generation is studied in detail. Two fracture types – logarithmic spiral and straight radially oriented – characterise these initial cracks. While the first type is due to deposition delamination, the straight cracks are induced by the interplay of capillary pressure and shear stress between coating and substrate. Most noteworthy is our finding that the cracking speed of the straight cracks is one order of magnitude larger than that of the spiral cracks. The pattern of the 1st generation cracks defines the final crack network. Our findings provide a comprehensive understanding of the crack pattern formation following the desiccation of silica droplets. This study offers details on nanofluid exsiccation on metal substrates, thereby opening routes for depositing nanoparticles on heated and non-heated surfaces for various engineering applications.

CALCULATION MODEL OF A COMPLEX-STRESSED REINFORCED CONCRETE ELEMENT UNDER TORSION WITH BENDING

The article presents the methodology and principles of creating calculation models for reinforced concrete structures operating in conditions of complex resistance. A block calculation model of reinforced concrete bar structures in torsion with bending is presented. This model consists of a support block formed by a spatial crack and a compressed zone of concrete closed on it and a second block formed by a vertical section running perpendicular to the longitudinal axis of a reinforced concrete element along the edge of the compressed zone closing the spatial spiral. Cases are considered when the torque effec has the greatest influenceon the stress-strain state of structures. In this case, the following forces are taken into account as the calculated forces in the spatial section: normal and tangential forces in the concrete of the compressed zone; components of axial and shear forces in the reinforcement crossed by a spatial crack. A feature of the proposed calculation model is that it considers independently of each other the strength of an element in spatial sections passing along a spatial crack, and the strength of an element between spatial cracks. The spatial section is formed by a crack located on three sides of the element and a compressed zone located on the fourth side and closing the ends of the spiral crack. In this case, the compressed zone, depending on the ratio of the bending and torque moments, can be located along the horizontal and vertical (lateral) edges of the element. The governing equations are written in the form of static equations for the adopted calculation cross-sections and a closed-loop system that unites them, written as a function of many variables with Lagrange multipliers λi. On the basis of the constructed function for all the variables included in it, an additional non-decaying system of equations has been compiled, from which follows a dependence that allows finding the projecton of a dangerous spatial crack.

On radial, circumferential, and spiral cracks in fractured glass plates

AbstractThis is a fractographic case study of a mechanically loaded glass plate that formed a remarkable spiral crack when the plate fractured. Common radial and circumferential cracking in disks and plates in general are first reviewed. The exceptional spiral crack is then analyzed. The origin of failure was an unusual flaw on the nominal compression side of the plate. The complex spiral fracture pattern has been observed in other large plate glass fractures that break under blunt impact conditions. Spiral cracks can form and propagate from flaws on the front side of a flexed plate that is rigidly supported at its rim or, alternatively, is supported from underneath and has a large overhang.

What happens to glass fiber under extreme chemical conditions?

In this study, the properties of E-glass fiber (GF) (0.5 g) exposed to sulfuric acid (100 mL, cH+=0.1 mol/L) and potassium hydroxide (100 mL, cOH−=0.1 mol/L) solutions were studied. The results showed that after acid treatment, the GF was damaged with decreased tensile strength, and spiral cracks developed on the fiber surface. Acid corrosion of the GF was mainly attributed to the depletion of metal ions in the GF, and the ion-depletion-depth model was proposed to explain the mechanism. In the alkali solution, the SiOSi bonds in the network structure of the GF were degraded by the OH− ions, resulting in the destruction of the glass network. It formed a corrosion layer with sheet-like nanostructures on the fiber surface, which prevented further attack of alkali ions on the fiber. Comparative results of the tensile strength of the treated GF confirmed that the filament was more susceptible to acid attack than alkali attack.

Hydraulic Burst Test of X52 Pipes With Defects or Nozzle Repair Structure

Abstract Hydrostatic blasting test can be used to verify the bearing capacity of the pipeline in service. Spiral weld cracks and dents are common defects of pipes, and nozzle repair is a common repair method of perforated pipes. In order to determine the carrying capacity of the X52 pipeline with the above defects and the repaired structure, the corresponding pipe specimens were tested by hydraulic experiment, the yield pressure and burst pressure were recorded for each case. The axial and circumferential strains of the defect and repaired structure were measured in detail, the wall thickness and perimeter of the specimen before and after the experiment were measured, and the failure mechanism was analyzed. According to the relative safety factor in the standard, the bearing capacity of the pipeline was determined.

A novel method to determine the mixed mode (I/III) dynamic fracture initiation toughness of materials

A novel hybrid experimental-numerical approach is proposed to determine the mixed-mode (I/III) dynamic fracture initiation toughness of engineering materials. To demonstrate the methodology, cylindrical aluminum alloy specimens with V-notch spiral cracks on the surface at spiral inclined angles of $${\beta _{sp}=0}^{\circ }, {11.25}^{\circ }, {22.5}^{\circ }, {33.75}^{\circ }$$ and $${45}^{\circ }$$ are subjected to dynamic torsion load using a torsional Hopkinson bar apparatus. The torque applied at the onset of fracture is measured through strain gages attached to the incident and transmitter bars. Stereo digital image correlation (StereoDIC) is performed to measure the full field deformation and crack mouth opening displacement (CMOD) as a function of loading time. Results are used to estimate the crack initiation time. The dynamic stress intensity factors are extracted numerically based on the dynamic interaction integral method using ABAQUS. The mode-I $$ {(K}_{Id})$$, mode-III $$(K_{IIId})$$, and mixed-Mode ($$K_{(I/III)d})$$ dynamic initiation toughness data as a function of spiral angles are presented and discussed.

Study of the character and causes of destruction of the cardan shaft of the propeller engine

The results of studying operational destruction of a high-loaded cardan shaft of the propeller engine made of steel 38KhN3MFA are presented to elucidate the cause of damage and develop a set of recommendations and measures aimed at elimination of adverse factors. Methods of scanning electron and optical microscopy, as well as X-ray spectral microanalysis are used to determine the mechanical properties, chemical composition, microstructure, and fracture pattern of cardan shaft fragments. It is shown that the mechanical properties and chemical composition of the material correspond to the requirements of the regulatory documentation, defects of metallurgical origin both in the shaft metal and in the fractures are absent. The microstructure of the studied shaft fragments is tempered martensite. Fractographic analysis revealed that the destruction of cardan shaft occurred by a static mechanism. The fracture surface is coated with corrosion products. The revealed cracks developed by the mechanism of corrosion cracking due to violation of the protective coating on the shaft. The results of the study showed that the destruction of the cardan shaft of a propeller engine made of steel 38Kh3MFA occurred due to formation and development of spiral cracks by the mechanism of stress corrosion cracking under loads below the yield point of steel. The reason for «neck» formation upon destruction of the shaft fragment is attributed to the yield point of steel attained during operation. Regular preventive inspections are recommended to assess the safety of the protective coating on the shaft surface to exclude formation and development of corrosion cracks.

Geometry factors for Mode I stress intensity factor of a cylindrical specimen with spiral crack subjected to torsion

A geometry factor is proposed for extracting the Mode I stress intensity factor from experimental data obtained during torsional loading of solid and tubular cylindrical specimens with a spiral crack on the surface. Using torque at fracture and specimens geometry as an input, the stress intensity factor at the corresponding fracture load was determined using a finite element analysis based on interaction integral method. The computed Mode-I stress intensity factor and the measured fracture load are used to quantify the geometry factor for different depths of spiral crack in cylindrical specimens following Benthem’s circumferential crack solution approach. The proposed model was validated by testing a polycarbonate specimen and compared it with a conventional three-point bending method. The difference between results from the proposed formula and the standard method was about 1.7% and 4.1% for solid and tubular specimens respectively. Furthermore, the fracture toughness value of different materials in the open literature was compared to the results recalculated by using the proposed formula. The result is in good agreement with different materials considered with a maximum difference of less than 6%.

Mode-I dynamic fracture initiation toughness using torsion load

An experimental and numerical approach is proposed to determine the dynamic fracture initiation toughness of materials from a cylindrical specimen with spiral surface crack subjected to dynamic torsional load using a torsional Hopkinson bar apparatus. The torsion load creates predominantly tensile stress perpendicular to the spiral crack of the specimen, resulting in nominally Mode I conditions. The torque applied to the specimen is measured by strain gages attached to the bar and the time at which the crack propagation initiated is measured using stereo imaging and stereo digital image correlation. Using the measured torque and the time of fracture as input, a commercial FE package, ABAQUS, is utilized to analyze the spiral crack and numerically extract the dynamic fracture parameters. A 3D format of the dynamic interaction integral method is utilized to calculate the three components of the applied dynamic stress intensity factors. The result demonstrates that the spiral crack-torsional loading configuration indeed generates nominally Mode I conditions and can be used to measure the dynamic fracture initiation toughness. To demonstrate the proposed method, three aluminum alloys; Al 7050-T6, Al 2024-T3, and Al 6061-T6, were experimentally studied. The results are consistent, repeatable and in good agreement with literature data.

Failure analysis of a cracked Q125 casing for ultra-deep wells at the Tarim Oilfield

Abstract In this paper, the reasons for cracking in the longitudinal and spiral of Q125 casing in ultra-deep wells (UDWs) at the Tarim Oilfield were investigated for the first time ever. Up to know an evaluation of Q125 casing materials of UDWs were were limited to comparisons with WSP-2T and P110 via performance tests. In addition, an applicability evaluation of UDWs was carried out using MPC software and theoretical calculations. The results show that mechanical damage and stress corrosion cracking are the principal causes for longitudinal cracking. Spiral cracking can be the result of the manufacturing process. It should be added that the material out of which Q125 casing is produced manifests high strength, low toughness and great sensitivity to cracks, stress corrosion and low allowable limit crack size (ALCS) when compared with WSP-2T and P110. Owing to the complicated field environment of UDWs at the Tarim Oilfield, the causes of cracking failure have been analyzed, with the result that WSP-2T casing of a similar strength to Q125 casing ought to be selected in UDWs rather than Q125 casing with high strength and low toughness, which is significant for the development of UDWs at the Tarim Oilfield.

Evolution of wrinkles with spiral crack on stiff film/compliant substrate under controllable micro-probe loading

Global wrinkling can be widely observed in nature and engineering materials, however, the dynamic evolution of localized wrinkles is seldom observed in experiments. In this paper, a controllable micro-probe is applied to an ultrathin Au film deposited onto a thick PDMS substrate to demonstrate the co-evolution of the localized wrinkles and crack. The experiment shows that the film subjected to the increasing indentation will produce two stress relief mechanisms: the tensile stress is relieved by the formation of spiral crack and the compressive stress is relieved by the formation of radial wrinkles. The crack forms near the edge of the probe tip and then propagates along right- or left-handed spiral path. Meanwhile, the high compressive stress is generated and contained in a narrow strip between consecutive passes of the spiral crack, which causes the propagation of the crack to be always accompanied by wrinkles. As the indentation increases, circular crack tends to be formed in the film and the crack propagation is ceased. The localized wrinkling and cracking patterns may have potential applications in some fields.

Spiral cracking pattern in asphalt materials

The present work for the first time reports observations and modeling to characterize three-dimensional spiral-shaped fracture patterns in a bi-axially stressed layer of asphalt material bonded to an aluminum substrate. Five different asphalt materials with different fracture characteristics are investigated. A logarithmic spiral model was found to mathematically represent the 3D helix-shaped cracks observed. A spiral tightness parameter is proposed for the characterization of spiral fracture patterns in asphalt. Results of acoustic emission and compact tension tests are also presented and employed in the evaluation of observed spiral cracks. The shape of spirals are found to be influenced by the fracture properties of the asphalt materials tested and appear to be independent of the thickness and shape of the test sample. The embrittlement temperature and fracture energy of tested asphalt materials were found to correspond to the characteristic parameters of spiral cracks.