Effect Of Hole Shape Research Articles

Phase field modeling for composite material failure

AbstractA computational framework of anisotropic phase field model is used to investigate the effects of effective critical energy release rate, interface property, and hole shape on the failure of composite material in this paper. This model is implemented in ABAQUS using a user‐defined element (UEL). First of all, the model is validated through a benchmark model. Second, the effective critical energy release rate is introduced, which can improve the accuracy of the simulation result. Then, the influence of strong and weak interfaces on the failure of composite material is studied. It can be found that the interface properties can change the evolution mode of crack and the final load–displacement response. Finally, the effect of hole shapes on the failure of the composite material is also explored, which shows that the bearing capacity of model can be improved by changing the shape of the hole.

Numerical simulation on the dynamic mechanical response and fracture mechanism of rocks containing a single hole

Caverns and tunnels are constantly exposed to dynamic loads, posing a potentially significant threat to the safety of rock structures. To facilitate the understanding of dynamic fracture around openings, a series of discrete element models were established to numerically examine the effect of hole shape on dynamic mechanical properties and crack evolution. The results indicate that the existence of a hole greatly reduces dynamic strength, and the reduction is closely related to hole shape. The strain variation of pre-holed specimens is more complicated and even larger than the value of intact specimens. Although crack initiation differs for varying hole shapes, the entire structural collapse of specimens is controlled by macro shear cracks along the diagonal direction of the specimen, which are effectively identified by velocity trend arrows and contact force distribution. Finally, comparative analysis between failure pattern of pre-holed specimens under static and dynamic loads were conducted.

Effects of hole shape on mechanical behavior and fracturing mechanism of rock: Implications for instability of underground openings

Rock failure commonly initiates near the wall of openings with various geometries in underground excavation. In this study, to elucidate the hole-shape influences on the mechanical response and fracturing behavior on rock sample subjected to uniaxial compression, a thorough experimental–numerical-theoretical investigation is conducted on the intact and pre-holed rock samples with different hole shapes, including circular, elliptical, rectangular, and inverted-U shapes. Digital image correlation technology is employed to monitor the crack initiation and development around the hole during the loading process. The results show that the presence of different hole shapes leads to varying degrees of mechanical property deterioration in rock samples. The load capacity and stiffness of the tested samples follow the same order: intact sample > circular-holed sample > elliptical-holed sample > inverted-U holed sample > square-holed sample. Irrespective of the hole shape, the primary tensile crack initiates at the top and bottom of the hole, but its development is trapped. The growth and coalescence of shear cracks near the sidewalls eventually give rise to the sample failure. Stress analysis around the holes reveals a positive dependence of the reduction in load capacity on the maximum compressive stress concentration which is controlled by the shape of the hole. This indicates that the amplification of compressive stress induced by the hole governs the rock collapse. These findings offer valuable insights for the design and construction of underground engineering projects.

Effects of hole shape and bottom gap on the flow characteristics behind butterfly porous fence and its application in dust diffusion control in large open-air piles.

In view of the possible dust pollution of atmospheric caused by large open-air piles, a scheme of using butterfly porous fences is proposed. Based on the actual cause of large open-air piles, this study makes an in-depth study on the wind shielding effect of butterfly porous fences. The effects of hole shape and bottom gap on the flow characteristics are investigated behind the butterfly porous fence with the porosity of 0.273 through the combined methods of computational fluid dynamics and validating PIV experiments. The streamlines distribution and X-velocity behind the porous fence of numerical simulation are in good agreement with the experimental results and based on the research group's previous work, the numerical model is feasible. The concept of the wind reduction ratio is proposed to quantitatively evaluate the wind shielding effect of the porous fence. The results show that the butterfly porous fence with circular holes provided the best shelter effect with the wind reduction ratio of 78.34%, and the optimal bottom gap ratio is about 0.075 with the highest wind reduction ratio of 80.1%. When a butterfly porous fence is applied on site, the diffusion range of dust in open-air piles is significantly reduced compared with that without a fence. In conclusion, the circular holes with the bottom gap ratio of 0.075 are suitable for the butterfly porous fence in practical applications and provide a solution for wind-induced control in large open-air piles.

Performance analysis of multi hole directional coupler for different hole profiles

The most critical and efficient circuits in guide wave single-mode systems are directional couplers. For Radio Frequency (RF) system designers, the directional coupler is a useful measurement unit. It offers not only an amplitude measured image of RF power levels but also identifies forward and reflected signal components to better characterize loads. They have been used in various telecommunications instruments, such as splitters, wavelength-dividing multiplexers, optical switches, etc. The paper streamlines the designing process of the waveguide coupler and its performance thereafter. The effects of hole shape and count for waveguide directional couplers are further investigated and compared in this study. The directional coupler with elliptical-shaped holes has been found to be more effective than its circular-holed counterpart. Also, compared to a coupler with circular holes, an elliptical hole directional coupler looks to be able to achieve high coupling with a reduced number of holes.

Numerical evaluation of macroscopic fatigue criterion of anisotropic materials using computational homogenization and conic programming

In this paper, an efficient computational approach, that combines the computational homogenization method with conic programming, is proposed to evaluate the macroscopic fatigue domain of anisotropic heterogeneous materials under variable repeated loads. The computational homogenization method is extended for use in the framework of kinematic shakedown analysis of micro-structures under macro-stress control, allowing the direct evaluation of the macroscopic fatigue domains. The discrete optimization problem is cast as conic programming and solved by using highly efficient solvers, demonstrating that the conic algorithm performs well for kinematic shakedown analysis involving a huge number of incompatible strain rate variables arising at each vertex of the convex load domain. The effects of hole shapes, porosity, plastic behaviors of metal matrices and hole distribution on the overall fatigue domains of micro-structures with regular and random patterns are studied. Numerical investigation shows that the Poisson coefficient does not effect on the macroscopic fatigue criterion in 2D analysis, at least for the problems investigated.

Effect of Hollow Shape on the Behavior of Reinforced Self-Compacting Concrete Slender Column Under Eccentric Loading

Results of testing reinforced self-compacted concrete slender columns having longitudinal holes concealing PVC pipe in their cross sections under axial compression load and uniaxial bending are presented in this paper. The effect of hollow shape on the performance of slender columns having 200x200mm quadratic cross section and 1300mm long under concentric and eccentric loads was investigated. Three different shapes of central hole: circular, square, and lozenge pattern in addition to the different load eccentricity values were considered to investigate the axial loading resistance and cracking load, lateral and longitudinal deflections of the columns. Test results have showed that altering the hollow shape inside the area of column cross section does not show a great influence on the column behavior unless the hollow ratio changed. The effect of hole shape or the hollow ratio on loading capacity is insignificant but the existence of a hole embedded longitudinally in the column significantly decreases its ultimate capacity. The effect of hollow shape or hollow ratio on a slender columns behavior subjected to eccentric loading with small ratio of load eccentricity to total column thickness (e/h=.33) was more than that of large eccentricity (e/h=1.0). Accordingly, the decrease in loading column capacity of columns was (5.0%, 2.5%, and 6.6%) compared to (3.2%, 2.2%, and 4.7%) for the same hole shapes respectively.

Turbine platform phantom cooling from airfoil film coolant, with purge flow

Phantom cooling is a new cooling term used in gas turbine cooling designs. It refers to all the second-order or unintentional cooling by various cooling discharges, including leakage, in the turbine passage. In this paper, numerical simulations of phantom cooling on platform surfaces from blade film-cooling injection are performed in a blade linear cascade model. The effects of hole shape and compound angle for the blade pressure and suction side holes on blade platform phantom cooling are studied with various coolant-to-mainstream mass flow ratios (MFRs) from 2.0% to 4.0%. Purge flow cooling from a 45 deg upstream slot is added to the analysis to investigate the combined cooling performance of phantom cooling and purge flow cooling. Results show that phantom cooling from the blade surface coolant films noticeably helps cooling of the platform, particularly at the junction between the blade pressure surface and the platform, which is usually difficult to cool. Increasing MFR is found to significantly improve phantom cooling performance. Adding compound angle injection to the blade cooling design enhances phantom cooling effectiveness, but shaping the hole exit is detrimental. Generally, a combined cooling scheme with upstream purge flow and phantom cooling from blade surface injection could sufficiently protect the entire platform surface without additional platform discrete hole film cooling. The effectiveness of the combined cooling effect cannot be found by a simple superposition of the two cooling sources because of the interactions between the coolant and secondary flows. It is recommended that accounting for phantom cooling could not only improve cooling design but also save cooling air.

Flat plate film cooling with linear and curved round-to-diffusion shaped slots using PSP measurement technique

This paper experimentally examines the effect of hole shape and coolant trajectory on film cooling effectiveness by using PSP measurement technique. Three different density ratios DR = 1, DR = 1.5, and DR = 2 were tested with five blowing ratios ranging from M = 0.5–1.5 with an increment of 0.25. Three different hole geometries (round to slot, round to annulus, and round to annulus2) were used with linear and projectile trajectories. Results obtained agreed with the general trend of shaped holes. In terms of hole shape, the slot-shaped hole resulted in better performance as compared to annulus shaped holes. Particularly, the slot-shaped hole with projectile trajectory results in 30–35% increase in effectiveness as compared to its linear trajectory slot-shaped counterpart. This design is found to have lowest discharge coefficient, but it works best at DR = 2. A correlation was also developed for single row different exit shaped holes helping the designers to calculate the spanwise effectiveness at different conditions.

Multi-objective crashworthiness optimization of square and octagonal bitubal structures including different hole shapes

This paper investigates the effects of hole shapes and dimensions on crashworthiness performance of the square and octagonal bitubal structures under impact loading. Several holes with three different shapes including rectangle, hexagon and ellipse are considered on the walls of the square and octagonal structures. For these structures, crashworthiness indicators SEA and PCF are numerically obtained using finite element code LS-DYNA. Based on the results, a significant improvement on the crashworthiness capacity is achieved by employing the technique of creating holes on the walls of structures; such that the hexagonal holes created on the square and octagonal bitubal structures improve the crashworthiness capacity by 60% and 42%, respectively in comparison to the corresponding conventional structures. Interestingly, all the holed structures show less PCF compared to those without hole. In the next phase, the hole dimensions are optimized using NSGA-II (non-dominated sorting genetic algorithm) and ANNs (artificial neural networks) methods to find the optimal structures. The SAW (simple additive weight) method is then implemented on the optimal structures, and the square and octagonal structures having the hexagonal holes are finally found as the best and superior energy absorbing devices. The effect of oblique loading on crushing behavior of the holed structures is also considered. According to the results, the holes created on the structure walls improve the crashworthiness capacity of structures under oblique loading, as well.

The Effect of Hole Shape of Bolted Joint with Aluminum for Slip Coefficient

The Effect of Hole Shape of Bolted Joint with Aluminum for Slip Coefficient

Experimental and numerical study of double-through plate connections to CFST column

This paper proposes an innovative connection known as double-through plate connection, in which two plates pass through a slotted square column with the concrete infill. The type of connection can be used to connect the steel hollow structural section (HSS) beam to the concrete-filled steel tube (CFST) column. Three specimens were tested under cyclic loading. The failure modes, hysteretic performance, stiffness, strength, ductility and classification of the joints were evaluated. The results revealed that the type of connection exhibited similar behaviors with single plate connection. The characteristics of the connection effectively reduced the stress level on the column flange and improved stress distribution. Then a nonlinear finite element (FE) model was developed and verified by the experimental results in terms of moment-rotation relationship and failure mode. The parametric analyses were utilized to explore the effect of hole shape and bolt pretension force on the connection performance. In addition, bolt slippage and load transfer mechanism in the joint region were also discussed.

Mosaics of topological defects in micropatterned liquid crystal textures.

Topological defects in the orientational order that appear in thin slabs of a nematic liquid crystal, as seen in the standard schlieren texture, behave as a random quasi-two-dimensional system with strong optical birefringence. We present an approach to creating and controlling the defects using air pillars, trapped by micropatterned holes in the silicon substrate. The defects are stabilized and positioned by the arrayed air pillars into regular two-dimensional lattices. We explore the effects of hole shape, lattice symmetry, and surface treatment on the resulting lattices of defects and explain their arrangements by application of topological rules. Last, we show the formation of detailed kaleidoscopic textures after the system is cooled down across the nematic-smectic A phase transition, frustrating the defects and surrounding structures with the equal-layer spacing condition of the smectic phase.

Effects of hole shape on impingement jet array heat transfer with small-scale, target surface triangle roughness

Considered is the addition of special surface roughness patterns to impingement target surfaces to improve the effectiveness and surface heat transfer augmentation levels of impingement cooling. Three different impingement hole shapes are employed within a jet array: circle, racetrack, and triangle. These are designed so that all three hole shapes have the same hydraulic diameter. Different sizes, different shapes, and different distributions of surface roughness elements are utilized, including arrays of small triangle roughness, with different roughness heights, employed with and without the addition of large pin roughness elements. Data are presented for impingement jet Reynolds numbers of 900, 1500, 5000, and 11,000. Overall, the racetrack hole configuration generally provides approximately the same heat transfer augmentation as the circle hole configuration, with slightly better performance, under some conditions. The triangle hole configuration provides lower heat transfer augmentation, compared to both the circle hole and racetrack hole configurations. The addition of small triangle roughness to the target plates shows an increase in heat transfer augmentation, compared to the baseline target plate, for both the circle and racetrack hole configurations. For the triangle hole configuration, the addition of small triangle roughness generally shows negligible or negative improvement, compared to the baseline target plate. Also illustrated is significantly different Reynolds number dependence for impingement cooling, as hole shape changes from circle to racetrack, and triangle.

Influence of hole shape on sound absorption of underwater anechoic layers

A theoretical model is established to evaluate the sound absorption performance of underwater anechoic layers containing periodically distributed axial holes. Based on the concept for homogenized equivalent layer and on the theory of wave propagation in viscoelastic cylindrical tubes, the transfer function method is used to obtain the absorption coefficient of the anechoic layer adhered on the rigid plate. Three different types of axial holes are considered, the cylindrical, the conical and the horn shaped one. Results obtained with full finite element simulations are used to validate the model predictions. For each hole type, the vibration characteristics of the anechoic layer as well as the propagation of longitudinal and transverse waves in the layer are analyzed in detail to explore the physical mechanisms underlying its absorption performance. Furthermore, a three-dimensional finite element model for oblique incidence is developed to study the effect of hole shape at different incidence angles. The results show that two new absorption peaks appear since the oblique incidence excites two horizontal modes. Among the three hole types, the horn one achieves the best absorption performance at relatively low frequencies both in normal incidence and in oblique incidence.

Effects of structure parameters on high-order diffraction suppression of quasi-periodic gratings

We introduce the design and implementation of quasi-periodic gratings for high-order diffraction suppression. The effects of hole shape (circle, rectangle, diamond, and hexagon) and location distribution on the diffraction properties are investigated. We theoretically and experimentally demonstrate that the quasi-triangle array with hexagonal holes is highly advantageous for suppressing high-order diffractions. Additionally, the quasi-periodic location distribution also helps to suppress high-order diffraction. Remarkably, the analytical results show that the 1st, 2nd, 3rd, 4th, 5th, and 6th order diffractions can be completely suppressed for the special structure parameters of the quasi-periodic gratings, and the 7th order diffraction intensity is as low as 2.2×10−5 of the 1st order. The experimental results show there exist only 0th and ±1st order diffraction peaks along the ξ axis, which qualitatively agree with the theoretical and numerical predictions. Compared with the traditional 1∶1 grating, the quasi-triangle array with hexagonal holes can effectively suppress high-order diffractions. We except the quasi-periodic gratings may find significant applications in high-accuracy wide spectral measurement ranging from the far infrared to the x-ray regions.

Numerical investigation of particle deposition on converging slot-hole film-cooled wall

Numerical research on the dilute particles movement and deposition characteristics in the vicinity of converging slot-hole(console) was carried out, and the effect of hole shape on the particle deposition characteristics was investigated. The EI-Batsh deposition model was used to predict the particle deposition characteristics. The results show that the console hole has an obvious advantage in reducing particle deposition in comparison with cylindrical hole, especially under higher blowing ratio. The coolant jet from console holes can cover the wall well. Furthermore, the rotation direction of vortices near console hole is contrary to that near cylindrical hole. For console holes, particle deposition mainly takes place in the upstream area of the holes.

Impingement Heat Transfer on a Cylindrical, Concave Surface With Varying Jet Geometries

Jet impingement is often employed within the leading edge of turbine airfoils to combat the heat loads incurred within this region. This experimental investigation employs a transient liquid crystal technique to obtain detailed Nusselt number distributions on a concave, cylindrical surface that models the leading edge of a turbine airfoil. The effect of hole shape and differing hole inlet and exit conditions are investigated. Two hole shapes are studied: cylindrical and racetrack-shaped holes; for each hole shape, the hydraulic diameter and mass flow rate into the array of jets is conserved. As a result, the jet's Reynolds number varies between the two jet arrays. Reynolds numbers of 13,600, 27,200, and 40,700 are investigated for the cylindrical holes, and Reynolds numbers of 11,500, 23,000, and 34,600 are investigated for the racetrack holes. Three inlet and exit conditions are investigated for each hole shape: a square edged, a partially filleted, and a fully filleted hole. The ratio of the fillet radius to hole hydraulic diameter is set at 0.25 and 0.667 for the partially and fully filleted holes, respectively, while all other geometrical features remain constant. Results show the Nusselt number is directly related to the Reynolds number for both cylindrical and racetrack-shaped holes. The racetrack holes are shown to provide enhanced heat transfer compared to the cylindrical holes. The degree of filleting at the inlet and outlet of the holes affects whether the heat transfer on the leading edge model is further enhanced or degraded.

Mechanism of Hydrojoining and Approach to Increase Torsion Strength of Assembled Camshafts

Assembled hollow camshaft can be manufactured through hydrojoining process which has the advantages including joining multiple elements onto a tube in once loading, high joining strength, efficiency, and precision. The method of improving joining strength by using cams with noncircular hole was presented. Through numerical simulation and experiment, plastic deformation law of hydrojoining process was studied. The displacement of cam and tube, and the profile dimension change of cam during hydrojoining were obtained. The effect of hole shape of cams on joining strength was analyzed. The assembled hollow camshafts with casting iron cams used for a car engine and those with quenched steel cams for a truck engine were successfully manufactured using hydrojoining technology.

The Effect of Opening on Elastic Buckling of Plates Subjected to Unidirectional Compression Load

This paper has investigated the effect of hole shape, hole size and hole position on elastic buckling of square perforated plates by using the finite element method. According to the effect law of these three geometric factors on buckling bearing capacity, buckling coefficient was obtained by data fitting. The results show that: The plate with circular perforation has the greatest buckling bearing capacity of the three perforation shape plate; When the center perforations have the same area, the relationship between buckling coefficient and perforation size is exponential for the plate with circular hole or square hole, the relationship between buckling coefficient and perforation size is biquadratic for the plate with triangular hole and the greater the perforation size is, the less the buckling bearing capacity will be; For the plate with uniform circular perforation size, The relationship of buckling coefficient and the spacing between perforation center and structure center is quadratic and the greater the spacing is, the less the buckling bearing capacity will be. The results in this paper provide reference for perforation design of plate.