Large Thickness Ratio Research Articles

Dynamic modeling and vibration suppression evaluation of composite honeycomb hemispherical shell with functional gradient protective coating

The vibration reduction performance of composite honeycomb hemispherical shells (CHHSs) coated with functional gradient protection coating (FGPC) are investigated in this work. Using the first-order shear deformation theory and the power-law distribution rule, the virtual spring technique, the regional decomposition method, and the Newmark-Beta approach, etc., a dynamic model of the FGPCCHHSs under base excitation is formulated to solve the inherent characteristics and displacement responses in time and frequency domains. After a set of convergence analyses are completed to ascertain an appropriate segment number and the stiffness values of virtual springs employed in the predictive model, the forecasted vibration parameters are verified using the literature and experimental results that are performed on uncoated and coated shells. The maximal natural frequency errors of the current model compared to the experimental results are 3.8% and 4.8%, and the displacement response errors under different excitation amplitudes are less than 10.3% and 12.7%, respectively, which demonstrate the correctness of such a model. Finally, the impact of key structural and material parameters on the vibration behaviors of the FPGCCHHSs is evaluated. To improve their vibration suppression capability, it is recommended to choose a high gradient index of coating material and a large thickness ratio of the FGPC to the overall shell with a reasonable moduli ratio of Material A to Material B of the FGPC to improve vibration reduction capability. This study offers a practical model tool and several important design recommendations for vibration prediction and dynamic attenuation of honeycomb sandwich hemispherical shell structures in aerospace engineering.

Investigation on laminated steel slit shear walls with low yield steel

To improve the energy dissipation capacity of steel slit shear walls made of thin plates and mitigate the adverse effects from the large out-of-plane deformation and potential local buckling failure, a novel laminated steel slit (LSS) shear wall assembled from two single-layer steel slit (SSS) shear walls is proposed in this study. First, the theoretical analysis method for predicting the shear strength and stiffness of the LSS shear walls is proposed. To validate the theoretical method as well as investigate the hysteretic performance of the LSS shear walls, two specimens made from different materials, common carbon steel and low yield steel, are designed and tested experimentally under quasi-static cyclic loading. Refined finite element models are developed to simulate the hysteretic behaviors of the LSS shear walls, which show good agreement with the test results. Further, the performance differences between the LSS shear walls and SSS shear walls are analyzed using the validated numerical simulation approach. The strength and stiffness of the LSS shear walls are greater than the summation of the individual SSS shear walls, attributed to the interaction between the different layers in the LSS shear walls. The energy dissipation efficiency of the LSS shear walls is improved and the stiffness degradation is effectively delayed, thanks to the incorporation of the low yield steel material. Finally, to evaluate the effects of the contributing factors on the seismic performance of the LSS shear walls, a series of parametric analyses are performed. Parametric analysis results show that the use of the low yield steel helps to improve the ductility and energy dissipation capacity of the LSS shear walls and delay the stiffness degradation. A large link width ratio, small link length ratio and large link thickness ratio can all contribute to a large strength, stiffness and absolute energy dissipation of the LSS shear walls, but the former two at the same time deteriorate the stiffness degradation.

Rolling force model of V-shaped variable thickness rolling based on energy approach

V-shaped Variable Thickness Rolling (V-VTR) serves as a specialized cold rolling method for manufacturing rolled profiled strips, particularly useful for quickly preparing rolled profiled strips with large thickness ratios. In the process of variable thickness rolling, metal predominantly flows in the lateral direction. However, there is a scarcity of theoretical models for calculating the rolling force of variable thickness rolling, leading to a void in theoretical guidance for both device design and product thickness control. To fill this gap, we introduce a novel mathematical model specifically designed to calculate the rolling force, considering the lateral flow of the metal. Initially, the deformation pattern is investigated and subsequently modeled. Then, the models for kinematically permissible velocity and strain fields are developed, and their validity is confirmed through both experimental data and simulation analysis. Incorporating factors like strain energy and frictional work, a formula for rolling force of variable thickness rolling is derived based on the upper bound theory. The efficacy of this newly proposed rolling force model is confirmed through experimental testing, which indicates that the formula offers a high degree of accuracy.

Hot-rolling process and properties of large thickness ratio Al/Mg/Al laminates

Large thickness ratio Al/Mg/Al laminates with the initial thickness ratio (ITR, the ratio of initial thickness of a single Mg layer to initial thickness of a single Al layer) ranging from 5 to 40 were prepared by hot rolling. The effects of ITR on the stress and strain fields, microstructure evolution and properties of Al/Mg/Al laminates were investigated by means of simulations and experiments. The results show that with increasing ITR, the ultimate tensile strength and yield strength of the laminates increase, while the interfacial bonding strength and elongation increase first and then decrease, and reach their maximum values of 12.3 N/mm (peel strength) and 23.32%, respectively, when the ITR is 20. At this time, the laminates have the best comprehensive mechanical properties, the deformation coordination ability between component metals is the best, and the texture on the Al side changes to shear texture. After the ITR reaches 40, the bonding performance of the laminates decreases, and the performance of the magnesium alloy is dominant.

Effect of annealing parameters on the interfacial structures and mechanical properties of Al/Mg/Al laminates with large thickness ratio

Herein, the large thickness ratio Al/Mg/Al laminates with the initial thickness ratio (ITR, initial thickness of a single Mg layer/initial thickness of a single Al layer) of 20 were prepared adopting hot roll bonding method successfully. The microstructure, mechanical properties of the laminates and the intermetallic compound (IMC) layers growth kinetics were discussed as a function of annealing time and temperature. The results show that when annealing at 200 °C for more than 1 h, an IMC layer will be formed at the interface consisting of Al3Mg2 phase and Al12Mg17 phase. Comparing the IMC layer components growth rate, Al3Mg2 phase is faster. When annealed at 250 °C for more than 1 h and at higher temperature, the thickness of Al3Mg2 phase is thicker than that of Al12Mg17 phase. The main growth control mechanism of IMC layer is lattice diffusion. The increasing annealing temperature and the lengthening annealing time will lead to the ultimate tensile strength of the laminates show a decreasing trend, so well as the yield strength. However, the maximum elongation value (24.69 %) appears when annealing at 200 °C for 4 h. The existence of IMC layers which are hard and brittle will give rise to the interface delamination and the increase of the residual stress.

Layer structure-based grain refinement mechanism and its effect on the mechanical behavior of Ti/Al laminated metal composites

In this study, the effect of layer structure on the mechanical behavior of Ti/Al laminated metal composites (LMCs) was explored, focusing on the occurrence of an additional strengthening mechanism introduced by heterogeneous microstructures between constituent layers. Experimental results showed that the change in layer structure parameters and rolling conditions had a significant effect on the microstructure of the Al layer, and the difference in shear strain scale near the interface led to the formation of a grain refinement zone (GRZ) with various microstructural characteristics during dynamic recrystallization. In addition, the recrystallized distribution and texture evolution (i.e., the increasing recrystallized fraction and the intensifying shear texture r-Cube {001} 〈110〉) revealed that the deformation storage energy as the driving force of recrystallization played an important role in the difference in the heterogeneous degree formed in various Ti/Al LMCs. On the other hand, the strength deviation between the experimental strength and the theoretical strength predicted by the rule of mixture can be detected in all LMCs with different thickness ratios after hot rolling, resulting from the pile-up of geometrically necessary dislocations (GNDs) caused by the synergetic deformation induced by mechanical incompatibility between Ti and Al layers during plastic deformation. With a change in the layer structure parameter, a considerable strength deviation in the Ti/Al LMC with a large thickness ratio indicated that the high mechanical incompatibility between the constituent layers was conducive to the enhancement of additional strengthening behavior.

Vibro-impact response of FRP sandwich plates with a foam core reinforced by chopped fiber rods

In the present study, both the impact and vibration response characteristics of fiber reinforced polymer (FRP) sandwich plates (FRPSPs) with a foam core (FC) reinforced by chopped fiber rods (CFRs) are investigated. Initially, a dynamic model is proposed to predict the vibro-impact characteristics of the FC-CFRs-FRPSP structures. Here, by considering the influence of the dispersion pattern of chopped fiber rods, the equivalent material parameters of this complex core are redefined. Also, by employing the modified mid-plane displacement equation based on the principle of virtual work at the impact point, together with the progressive quasi-static approach and Reddy's high-order shear deformation principle, the key parameters such as impact contact force and displacement related to each failure event are obtained. In addition, with consideration of the impact damage, the natural frequencies and vibration responses are solved by using the energy principle, the proportional damping method, and the Duhamel integral technique. Finally, a number of the FC-FRPSP specimens with and without reinforcement of CFRs are fabricated and tested under different impact energies for verifying the present model. Also, the influences of critical geometric and material parameters on the vibro-impact response of the FC-CFRs-FRPSP structures are discussed. It has been found that the FC-CFRs-FRPSP specimens have a smaller vibro-impact response compared to the specimens without CFRs. For example, when impact energy of 10 J is applied, the impact peak force increases by 19.1%, the impact displacement reduces by 26.6%, and the maximum time-domain vibration response reduces by 5.8%. To reduce the vibro-impact response of such structures, it is recommended to adopt a large thickness ratio of the CFR reinforced foam core to the overall sandwich plate as well as volume fraction of CFRs to the foam core with a uniform dispersion pattern.

Modulation effect on mechanical properties of nanolayered MoN/MoSiN coatings

The combination of molybdenum nitride, MoN, and molybdenum silicon nitride, MoSiN, to be a naolayered MoN/MoSiN film was developed by the reactive radio frequency, r.f., magnetron sputtering system. The MoN and MoSiN building layers were designed and fabricated with a crystalline and an amorphous/nanocrystalline feature, respectively. The effect of thickness modulation of the c-MoN and a-MoSiN layers on microstructure and mechanical properties of the MoN/MoSiN coatings were investigated. With a fixed 50.0 nm crystallines MoN building layer, the amorphous/nanocrystalline MoSiN building layer with a designed thickness of 25.0 nm would suppress the continuous growth of crystalline phases. For mechanical characterization, the change in modulation did not lead to significant influence on hardness and Young's modulus. When a large thickness ratio of c-MoN/a-MoSiN was applied, phenomenal increase in scratch and wear resistance was observed due to higher volumetric ratio of hard crystalline MoN layer and discontinuity of crystalline phase growth through building layers in the nanolayered MoN/MoSiN coatings.

Experimental damage tolerance evaluation of thick fabric carbon/epoxy laminates under low-velocity and high-velocity impact and compression-after-impact

Impact experiments of thick fabric carbon/epoxy laminate specimens, with small thickness ratio, are conducted at distinct energy levels and thicknesses to characterise the damage process. These specimens and loading conditions are representative of a new generation of critical structural components in aviation, such as wing spars, landing gear beams and fittings, that are increasingly being made entirely from composites. The tests address the need to better understand the damage process for specimens with a small thickness ratio since existing experimental impact data for large thickness ratio (thin laminates) may not be directly applicable. Two energy levels, two different fabric layups and two impact methods (drop-weight and gas-cannon) were used. Data from high-speed cameras were processed in a novel way, providing the force during impact. C-scans and micrographs were used to characterise damage. The results show that specimens with a thickness ratio of 5 (20 mm thick) experience more bending compared to specimens with a ratio 2.5 (40 mm thick). For gas-cannon impacts, this results in a higher delaminated area. The drop-weight impacts show almost no differences in damage size for the thickness range analysed. The influence of layup on the global impact response is negligible, but locally it can result in significant variations in dent depth. The dent depth scales linearly with the impact energy and the delaminated area linearly with the impact velocity. There is no clear correlation between the compression-after-impact failure mechanisms and the residual strength. Impact damage, at the current energy levels, showed a minimal reduction of residual strength.

Design and experiment of V-shaped variable thickness rolling for rolled profiled strips

A novel processing method called V-shaped variable thickness rolling (V-VTR), has proposed to produce rolled profiled strips (RPS) by combining numerical simulation with experiment. Purpose to find a design method for accurately calculating roll parameters, and produce RPS with large thickness ratio. The V-VTR is short-term process includes preforming, decreasing, flattening and final passes. The critical minimum angle of roll and its calculation formula are proposed to ensure that metal only flow in TD, and the correctness of this method is proved by simulation and experiment. The metal flow and stress–strain state of angle below and above the critical minimum angle are discussed. Finally, target RPS with thickness ratio of 2:1 is successfully produced for the first time.

Enhancing co-deformation ability of nanograined Ni-W layers in the Ni/Ni-W laminated composites

Tensile properties and plastic deformation behavior of the Ni/Ni-W laminated composites with different thickness ratios of the Ni layer to the Ni-W layer were investigated systematically. Experimental results reveal that the strength/ductility synergy of Ni/Ni-W laminated composites with a large thickness ratio is improved compared with that of monolithic Ni, which is attributed to the enhanced co-deformation ability of the nanograined Ni-W layers with decreasing the Ni-W layer thickness. Ni-W layers with small original layer thickness achieve continuous thinning through the stable grain boundary sliding under the interface constraint. Furthermore, there is an evident transition of the fracture behavior from the co-existence of channel cracks and micro shear bands to micro shear bands for the Ni-W layers with decreasing the Ni-W layer thickness. Finite element simulations show that the decrease of the Ni-W layer thickness leads to the decrease in the sensitivity of the composites to defects, which is corresponding to the reduced stress concentration degree at the crack tip. Based on the energy criterion, the plastic deformation map controlled by the length scale and the flow stress for the Ni-W layers was evaluated. The finding may provide a potential strategy for the design and development of high-performance materials for high-temperature microelectromechanical systems.

Buckling Test of Composite Cylindrical Shells with Large Radius Thickness Ratio

A buckling test of composite cylindrical shells with a radius–thickness ratio (r/t) = 893 under axial compression was conducted to investigate the effects of the radius–thickness ratio (r/t). It is known that the buckling load of cylinders shows large differences and scatter between theory and experiment. The ratio of the experimental buckling load and theoretical buckling load is called the knockdown factor (KDF). Many investigations have been conducted to find the cause of the degradation and scatter in the KDF, but as yet, no cause has been found. In 1968, NASA’s buckling design criterion, NASA SP-8007, gave an empirical KDF curve that decreased with the increasing r/t (up to 2000) for metal cylinders. The same curve has been applied to composite cylinders. Recently, Takano derived a flat lower-bound KDF in terms of A- and B-basis values (99% and 90% probability with a 95% confidence level) through a statistical analysis of experimental buckling loads. The result, however, based on experimental results up to r/t = 500 and, thus, the dependency on a large range of r/t, is not clear. Thus, the authors focused on a larger range of r/t. Cylindrical shells made from carbon fiber-reinforced plastic (CFRP) were tested. The nominal radius, thickness, and length were r = 100.118 mm, t = 0.118 mm, and L = 200 mm and, thus, the r/t = 848 and length-to-radius ratio (L/r) = 2.0. Shape imperfections were also measured by using in-house laser displacement equipment. The buckling load was slightly affected by the r/t, but the reduction in the KDF was insignificant.

The impact of macro/microstructure features on the mechanical properties of refill friction stir spot–welded joints of AA2219 alloy with a large thickness ratio

AA2219 aluminium alloy plates of large thickness ratios were successfully produced by refill friction stir spot welding (RFSSW) method. In addition to common defects, such as holes and hook, insufficient refill and weak bonding also appeared in the joints with large thickness ratios. Besides, the stir zone of the typical RFSSWed joint exhibited refined and equiaxed grains because of the dynamic recrystallization, while the elongated grains with a large proportion of the low angle grain boundaries were the main microstructure features in the thermomechanically affected zone due to insufficient heat input and deformation. Moreover, in all cases of large thickness ratio, the micro-hardness distribution of the joints presented an M-shaped profile. The maximum tensile-shear strength reached 7.2 kN, corresponding to the rotation speed of 2000 rpm, welding time of 3.6 s and plunge depth of 2.2 mm, which displayed a close correlation with the defect morphology, such as the weak bonding length and hook height. Also, two types of fracture modes were observed in the tensile-shear specimens, plug fracture mode and mixed fracture mode.

Design and bearing capacity analysis of cold-formed thin-walled steel-timber composite members

Cold-formed thin-walled steel has light weight, large width thickness ratio, good economy and seismic performance. It is easy to realize standardization of design, and is very suitable for the development of prefabricated buildings. Due to the large width thickness ratio of cold-formed thin-walled steel , the steel plate is prone to local buckling when it is compressed, which will reduce the ductility and bearing capacity of the structure, which also leads to the limitation of the use of cold-formed thin-walled steel structure system in medium and high-rise buildings. In this paper, a kind of cold-formed thin-walled steel-timber composite members is designed. The section steel and the board are closely linked by bolts to work together. The thickness of the board and the spacing of the bolts are designed respectively, so as to provide reference for engineering design.

Application of binary compound water control technology in the development of horizontal wells in offshore oil fields

Offshore A oil field is a typical bottom water reservoir with thin thickness of oil layer and large thickness ratio of water layer and oil layer. Due to its strong bottom water energy, serious non-homogenous and the impact of the bottom ridge, most of the horizontal well production segment is seriously water out.Based on interaction relationship between horizontal segment trajectory and oil and-water interface, the distribution and contrast of permeability along horizontal segment and the comprehensive analysis of production performance, this paper combines the characteristics of the residual oil distribution of typical wells and the mechanism of dual compound oil addition, and from the perspective of combining theory with the field creatively put forward the dual composite water control mode of first injecting gel segment plug and then injecting foam. then completed the design of dual compound water control mode and dosage of the typical well. After processing water control measures, the production data shows that the water content decreased significantly after opening the well, from 95.1% before water control to 80%, which was 15% lower. Also the oil production rate has a significant increase from 2.3t/d before water control to maximum to 9t/d after implementing control measures and cumulative oil increase is 550t with effective period of 135 days. The effect of oil and precipitation is obvious.

Microstructure and mechanical properties of thin varying thickness strips with different transition zones produced by micro flexible rolling

In order to better understand transition zones with a variety of structural features that affect thin varying thickness strips, 6061 aluminium alloy thin strips were flexibly rolled into different thickness ratios and transition zone lengths, using an innovative micro rolling mill. The microstructure and mechanical properties of the thin varying thickness strips produced by micro flexible rolling were systematically investigated and the mechanisms were analysed. The results indicate that a thin varying thickness strip with either a larger thickness ratio or a shorter transition zone length will present a relatively high slope of the transition zone during micro flexible rolling. After tensile tests, a thin varying thickness strip with the highest thickness ratio achieved the largest yield strength and ultimate tensile strength. In comparison, transition zone length can have a greater influence on the strain of the transition zone than on the thickness ratio because of the variation in β. The measured hardness is greater in the thinner zone than in the thicker zone. Values in the thinner zone are about 7%–21% greater than those in the thicker zone for strips with different thickness ratios due to the increased strain level which causes different degrees of work hardening.

Reducing tonal sound from a cascade of flat plates by varying the thickness ratio of neighboring plates

To mitigate the tonal noise from air flow around a cascade of flat plates, such as the grills in front of automobile engines, the thickness ratio of neighboring plates was varied in numerical simulations. Direct aeroacoustic simulations were based on compressible Navier-Stokes equations. For the baseline case with all plates at the thickness ratio of 1.0, the tonal sound is radiated because of the acoustic resonance occurring between the plates. In a controlled flow with plates alternating between large and small thicknesses, the width of the wake behind each plate varies between the neighboring plates. This indicates that the flow around the cascade of flat plates becomes biased. Simulated sound-pressure spectra show that the intensity of tonal sound at the fundamental frequency is reduced by the large thickness ratio between neighboring plates. Also, a secondary intensity peak appears at a frequency higher than the fundamental frequency. This peak appears because vortex shedding occurs at this higher frequency in the wakes behind the thin plates, whereas it occurs at the fundamental frequency in the wakes behind the thick plates. To elucidate the flow and sound related to the tonal sound at the fundamental frequency, the flow fields were phase-averaged with reference to the vortex shedding from the thick plates. With all plates of the same size, two-dimensional large-scale vortices are formed in the wakes of all the plates. Moreover, vortex shedding occurs in the anti-phase mode between the neighboring plates, which reinforces acoustic resonance. Meanwhile, for controlled flow with the plates of alternating thickness, the vortices lose their structure and spread into finer-scale vortices. The synchronization of vortex shedding between the neighboring plates is suppressed, which weakens the tonal sound from acoustic resonance.

Optimizing fatigue performance of nacre-mimetic PE/TiO2 nanolayered composites by tailoring thickness ratio

Abstract

Effect of the grid geometry on the convective heat transfer of impinging jets

Passive methods are recognized as one of the most efficient means to achieve high heat and mass transfer in impinging jets. In a recent study, Cafiero et al. (2014) demonstrated the effectiveness of square fractal grids (SFGs, obtained repeating the same square pattern at increasingly smaller scales) in terms of heat transfer enhancement when locating the grid in correspondence of the nozzle exit section. Indeed, the capability of producing turbulence at multiple scales and the possibility of tuning the peak in the turbulence intensity profile as a function of the grid geometric parameters are both extremely appealing for heat transfer enhancement purposes. In this study, the effect of the grid geometry on the convective heat transfer rate of impinging jets is assessed and discussed. Three main effects are taken into account: the grid thickness ratio (obtained by varying the thickness of the first iteration of the SFG), the effect of the secondary grid iterations and the choice of the initial pattern. It is demonstrated how a larger thickness ratio, which in the present case corresponds to an anticipated location of the peak in the turbulence intensity profile, is beneficial to get a spotted high convective heat transfer rate at short nozzle to plate distances. Either the use of a single square grid, or the choice of a different initial pattern (for example a circular fractal grid) is instead indicated when it is desirable a uniform distribution of the convective heat transfer rate.

Influences of thickness ratios of flange and skin of composite T-joints on the reinforcement effect of Z-pin

Abstract Experiments along with the finite element model were used to analyze the influences of thickness ratio of flange and skin (hereinafter referred to as thickness ratio) of T-joint on the reinforcing effect of Z-pin. Results showed that the thickness ratio significantly influences the reinforcement effect of Z-pin. Whether or not Z-pin should be applied to a specific T-joint can be decided by the thickness ratio. For T-joints with large thickness ratios (larger than 0.32 for the studied T-joint), the application of Z-pin is an effective way to increase the carrying capacities of the T-joints, while for T-joints with small thickness ratios (smaller than 0.32 for the studied T-joint), the reinforcing effect of Z-pin is not obvious. Besides, the corresponding load value under large displacement in the load-displacement curves of T-joints with different thickness ratios are similar.