Face Plate Research Articles

Ballistic resistance and energy absorption of honeycomb structures filled with reactive powder concrete prisms

Two kinds of innovative re-entrant and hexagonal cell honeycomb sandwich structures filled with reactive powder concrete were proposed, and the ballistic resistance and energy absorption of the sandwich structures were investigated by numerical simulations. The deformation and failure modes of the different structures were analyzed and evaluated in detail. The honeycomb sandwich structures filled with reactive powder concrete prisms improved the capacity of ballistic resistance and energy absorption significantly, compared to the normal reactive powder concrete plates and sandwich structures without reactive powder concrete prisms. The analysis shows that the auxetic re-entrant cell honeycomb sandwich structures have a better ballistic performance than the hexagonal cell honeycomb sandwich structures. The sandwich structures were subjected to impact by three kinds of projectiles: flat, hemispherical and conical nosed. The ballistic limit of the flat nosed projectile is the highest, while the impact performance of the conical and hemispherical nosed projectiles is obviously different from the flat nosed projectile, especially in a relative high velocity range. The sharper nose leads to a higher value of exit velocity and mass loss. In addition, effects of different design parameters on ballistic resistance were also studied by changing the thickness of honeycomb cell and face plates. Results indicate that the thickness of honeycomb walls and face plates have significant effect on the ballistic resistance and energy absorption in a relative low velocity range, while there are no big differences when the initial impact velocity exceeds 400 m/s.

Effects of nails and facing plates on seismic slope response and failure

A rock bolt with a facing plate is one of the soil nailing methods against relatively shallow sliding failure, which can be applied to natural slopes without cutting trees. In this research, dynamic centrifuge model tests were conducted to study the reinforcement mechanism of the nailing with individual facing plates and the effects of facing plate width, bolt spacing and bolt inclination angle on the seismic stability of reinforced slope. From the test results, it was confirmed that the facing plate resistance works well against the seismic load, which suppresses the slope deformation during shaking, and the mobilised resistance increases with increasing plate size. Plate bearing failure and local surface failure are critical failure mechanisms. The bearing failure could occur for small plates, while for relatively large plates, the local failure causes reduction of plate resistance and triggers large deformation and slip failure of the slope. These failures could be controlled by slope acceleration and uncovered width. Downward inclined installation of the nailing from the normal to the slope surface can effectively prevent the movement and secure the slope stability with less mobilised resistance.

Elastic constants for adhesively bonded corrugated core sandwich panels

In this paper, the adhesively bonded corrugated core sandwich panel is introduced and its elastic properties are discussed. Due to the relative displacement and rotation between face and core plates in adhesive joints caused by adhesive layer distortion, traditional elastic constants with considering both face and core plates to be fastened to each other are no longer fit for adhesively bonded sandwich panels. Therefore, its elastic constants with effect of adhesive layer distortion have been derived and presented in this paper. By submitting these elastic constants into closed-form solution, the response of simply supported sandwich panel under uniform load with small deflection is calculated which agrees well with 3D FEM analysis. Lastly, with the elastic constants, the effects of adhesive layer thickness and its elastic modules on both transverse shear stiffnesses with different shapes and dimensions are further studied and discussed.

A novel and simple HSDT for thermal buckling response of functionally graded sandwich plates

A new higher shear deformation theory (HSDT) is presented for the thermal buckling behavior of functionally graded (FG) sandwich plates. It uses only four unknowns, which is even less than the first shear deformation theory (FSDT) and the conventional HSDTs. The theory considers a hyperbolic variation of transverse shear stress, respects the traction free boundary conditions and contrary to the conventional HSDTs, the present one presents a new displacement field which includes undetermined integral terms. Material characteristics and thermal expansion coefficient of the sandwich plate faces are considered to be graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are supposed as uniform, linear and non-linear temperature rises within the thickness direction. An energy based variational principle is used to derive the governing equations as an eigenvalue problem. The validation of the present work is carried out with the available results in the literature. Numerical results are presented to demonstrate the influences of variations of volume fraction index, length-thickness ratio, loading type and functionally graded layers thickness on nondimensional thermal buckling loads.

Push-out test on the one end welded corrugated-strip connectors in steel-concrete-steel sandwich structure

Current form of Corrugated-strip connectors are not popular due to the fact that the two ends of this form need to be welded to steel face plates. To overcome this difficulty, a new system is proposed in this work. In this system, bi-directional corrugated-strip connectors are used in pairs, and only one of their ends is welded to the steel face plates on each side. The other end is embedded in the concrete core. To assemble the system, common welding devices are required, and welding process can be performed in the construction sites. By performing the Push-out test under static loading, the authors experimentally assess the effects of geometric parameters on ductility, failure modes and the ultimate shear strength of the aforesaid connectors. For this purpose, sixteen experimental samples are prepared and investigated. For fifteen of these samples, one end of the shear connectors is welded to steel face plates, and the other end is embedded in the concrete. Another experimental sample is prepared in which both ends are welded to the steel face plates. According to the achieved results, several relations are proposed for predicting the ultimate shear strength and load vs. interlayer slip (load-slip) behavior of corrugated-strip connectors. Moreover, these formulas are compared with those of the well-known codes and standards. Accordingly, it is concluded that the authors' relations are more reliable.

Linear stability assessment of a cryogenic rocket engine

The linear high frequency stability of DLR’s cryogenic H2/O2 BKD test chamber is assessed using a hybrid computational fluid dynamic/computational aeroacoustic methodology, which is based on single flame simulations for the generation of an adequate mean flow and for the calibration of feedback models as well as on frequency space transformed linearized Euler equations. The application of a realistic mean flow field including combustion explains the spatial separation of transverse modes into a near face plate mode, which is found linearly unstable under certain operation conditions for the first transverse and a rear part mode. The axial mode shape length as well as eigenfrequencies is affected by propellant injection specifications and, in consequence, decisively influence pressure and transverse velocity sensitive dynamic flame response. The stability assessment procedure is finally applied to four operation conditions and the linear stability is predicted for the first transverse mode.

Transverse shear stiffness of corrugated core steel sandwich panels with dual weld lines

Advances in the field of laser welding have recently enabled the commercial production of all-steel sandwich panels with a continuous and robust connection between the core and the face plates, even for plate thicknesses over 10mm. This allows for the application of the high-performance steel sandwich panel in several fields, such as civil structures. In this paper, an analytical model is presented to determine the transverse shear stiffness of corrugated core steel sandwich panels with dual weld lines. The derivation is based on the direct stiffness method (DSM). At the welded connection between the core and the faces, a rotational spring is included in the structural model, as the idealised rigid connection is unable to properly capture the mechanical interaction between the constituent plates. Both bending and shear deformation in the cross-sectional constituent members is taken into account. The model is shown to have high precision in terms of predicting the transverse shear stiffness when compared with numerical analyses. Furthermore, high precision is also shown when it comes to predicting normal stresses in the constituent members of the panel with respect to shear action. In a case study included in this paper, the impact of having two weld lines compared with a single weld was studied, together with the effect of the distance between the welds. The results show a large impact with respect to shear stiffness and stresses in the constituent plates. This paper focuses on laser-welded corrugated core steel sandwich panels, but the presented model can also be used for analyses of general continuous core shapes and other isotropic materials.

Centrifuge modelling of rock bolts with facing plates

In this study, a series of centrifuge model tests were carried out to study the mechanical behaviour of the slope reinforced by a soil nailing method using rock bolts with prestressed facing plates. A centrifuge model testing system was developed, in which the preloading process of rock bolts with a facing plate in a model slope can be simulated by hoisting jacks, and pseudo-static seismic force can also be imposed on the slope by a tilting table. Simplified tests of the reinforced slope were performed with various preloading forces. The displacements of the facing plates and the slope surface, and the facing stresses were measured during both the preloading process and the tilting table tests. It was found that the reinforcement of slopes by the rock bolts with facing plates could effectively prevent deformation and failure. The larger the prestress is, the smaller the slope deformation. However, the effect of prestress increment on slope stability became smaller as the prestress increased, especially after large deformations. The deformation of the slope was deeper and wider for the reinforcement with smaller prestress, while for those with larger prestress it becomes shallower in limited local areas.

In situ synchrotron X-ray diffraction study of hydrides in Zircaloy-4 during thermomechanical cycling

The d-spacing evolution of both in-plane and out-of-plane hydrides has been studied using in situ synchrotron radiation X-ray diffraction during thermo-mechanical cycling of cold-worked stress-relieved Zircaloy-4. The structure of the hydride precipitates is such that the δ{111} d-spacing of the planes aligned with the hydride platelet face is greater than the d-spacing of the 111 planes aligned with the platelet edges. Upon heating from room temperature, the δ{111} planes aligned with hydride plate edges exhibit bi-linear thermally-induced expansion. In contrast, the d-spacing of the (111) plane aligned with the hydride plate face initially contracts upon heating. These experimental results can be understood in terms of a reversal of stress state associated with precipitating or dissolving hydride platelets within the α-zirconium matrix.

Suppression of initial failure at tapered end-closure sandwich panel joint by taper angle change

To examine the configuration of CFRP face plates/foamed plastic core sandwich panel joints, a tapered end-closure-type joint is selected and studied. In this type of joint, the sandwich panel is tapered to form a solid laminate comprising two face plates near the joint, and the two panels to be joined are mechanically fastened at the solid laminate with a splice plate. This type of joint may be suitable for aircraft panels because a flat surface can be obtained at the joint, which is advantageous from an aerodynamic viewpoint. However, in a previous study on such a joint, it was found that a delamination crack initiated from the tapered core end and propagated through the interface between the two face plates as an initial failure mode at a much lower tensile load than the final failure load in a tensile strength test. In this study, the angle of the tapered panel was focused on and the effect of changing the taper angle on suppressing the initial failure was investigated through experiments and numerical analysis. It was found that a smaller taper angle is more effective for suppressing the initial failure.

Ballistic performance of honeycomb sandwich structures reinforced by functionally graded face plates

This study investigates damage mechanisms and deformation of honeycomb sandwich structures reinforced by functionally graded face plates under ballistic impact. The honeycomb sandwich structure consists of two identical functionally graded face sheets, having different material compositions through the thickness, and an aluminum honeycomb core. The functionally graded face sheets consist of ceramic (SiC) and aluminum (Al 6061) phases. The through-thickness mechanical properties of face sheets are assumed to vary according to a power-law. The locally effective material properties are evaluated using the Mori–Tanaka scheme. The effect of material composition of functionally graded face sheets on the ballistic performance of honeycomb sandwich structures was investigated using the finite element method and the penetration and perforation threshold energy values on ballistic performance and ballistic limit of the sandwich structures are determined. The contribution of the honeycomb core on the ballistic performance of the sandwich structure was evaluated by comparing with spaced plates (without honeycomb core) in terms of the residual velocity, kinetic energy, and damage area.

Analysis and Comparison of Total Deformation of Welded Plates in Tensile and Fatigue Tests using ANSYS

In this paper tensile testing and fatigue testing had been concluded which is analyses in Ansys workbench at same condition and load. These testing are completed on two plates; which are welded by applying filler material between the three corners of the plate which is going to be weld on the face of other face of material. In this paper material of the plates are frequently changed to determine the various results for respective materials. When these plates are analyzed under same condition then minimum deformation was checked for various materials like: Aluminum, Copper alloy, Stainless steel and structural steel. All these analysis are completed by applying 1000N force on the one face of plates.

Damage behavior of honeycomb sandwich structure under low-energy impact

Honeycomb sandwich structure is widely used in aircrafts and ships to absorb impact energy. Damage caused by low-energy impact is difficult to investigate, but will significantly reduce the strength of the sandwich structure. This paper presented a systematical experimental study on the damage behavior of honeycomb sandwich structure under different configurations. Drop weight tests were carried out to investigate the effect of impact energy, core material and face plate structure on the dynamic response of sandwich plate. Delamination regions were obtained through ultrasonic scanning. Conclusions were made that the damage behavior of the face plate was similar with composite laminates while the energy absorption capacity was related to the parameters of the honeycomb core and the mismatch angle of the face plate.

A numerical modelling study of longwall face stability in mining thick coal seams in China

Longwall face failures remain a major ground control and safety hazard in Chinese coal mines. This paper develops a better scientific understanding of stress and displacement distribution in the face area through 2-D finite element modelling of a typical longwall face in China. The results show: 1) most of the yielding occurs in the upper part of the face; 2) most vertical displacement occurs near the upper part of the coal face, while most horizontal displacement occurs around the centre part; 3) most face falls should, therefore, occur in the upper part of the coal face; 4) face stability is most affected by the load carrying characteristics of caved gob; 5) increased loading capacity of shields has limited effect on the stress distribution ahead of the face; 6) currently used face plate pressure distribution does not have a major effect on the redistribution of stress in the face area.

A numerical modelling study of longwall face stability in mining thick coal seams in China

Longwall face failures remain a major ground control and safety hazard in Chinese coal mines. This paper develops a better scientific understanding of stress and displacement distribution in the face area through 2-D finite element modelling of a typical longwall face in China. The results show: 1) most of the yielding occurs in the upper part of the face; 2) most vertical displacement occurs near the upper part of the coal face, while most horizontal displacement occurs around the centre part; 3) most face falls should, therefore, occur in the upper part of the coal face; 4) face stability is most affected by the load carrying characteristics of caved gob; 5) increased loading capacity of shields has limited effect on the stress distribution ahead of the face; 6) currently used face plate pressure distribution does not have a major effect on the redistribution of stress in the face area.

A new and simple HSDT for thermal stability analysis of FG sandwich plates

The novelty of this work is the use of a new displacement field that includes undetermined integral terms for analyzing thermal buckling response of functionally graded (FG) sandwich plates. The proposed kinematic uses only four variables, which is even less than the first shear deformation theory (FSDT) and the conventional higher shear deformation theories (HSDTs). The theory considers a trigonometric variation of transverse shear stress and verifies the traction free boundary conditions without employing the shear correction factors. Material properties of the sandwich plate faces are considered to be graded in the thickness direction according to a simple power-law variation in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are assumed as uniform, linear and non-linear temperature rises within the thickness direction. An energy based variational principle is employed to derive the governing equations as an eigenvalue problem. The validation of the present work is checked by comparing the obtained results the available ones in the literature. The influences of aspect and thickness ratios, material index, loading type, and sandwich plate type on the critical buckling are all discussed.

A simple analytical approach for thermal buckling of thick functionally graded sandwich plates

This study aimed to presents a simple analytical approach to investigate the thermal buckling behavior of thick functionally graded sandwich by employing both the sinusoidal shear deformation theory and stress function. The material properties of the sandwich plate faces are continuously varied within the plate thickness according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are considered as uniform, linear and non-linear temperature rises across the thickness direction. Numerical examples are presented to prove the effect of power law index, loading type and functionally graded layers thickness on the thermal buckling response of thick functionally graded sandwich.

Steel-concrete-steel sandwich composite structures-recent innovations

Steel-concrete-steel (SCS) sandwich structures consisting of two steel face plates infilled with lightweight cement composite material has been developed. This paper reviews the recent innovations of SCS sandwich structures subject to blast, impact, fatigue, and static loads. Novel J-hook connectors, high strength steel plates and new lightweight cement composite materials have been considered for the development of the SCS sandwich products to improve their strength-to-weight performance. Extensive tests have been conducted to investigate the effectiveness of J-hook connectors to achieve better composite action to resist flexural, shear, impact, blast and fatigue loads. Flat and curved SCS sandwich plates under patch loading are also investigated. The experimental results are essential to understand the structural behaviour of the SCS sandwich structures and to provide data for the development of analytical models for design implementation. Design equations have been proposed to predict the shear and tensile resistances of J-hook connectors and to determine the flexural, shear, impact, blast and fatigue resistances of SCS sandwich beam. The punching shear resistance of sandwich shells and compression resistance of sandwich walls are also investigated. The accuracy of the design equations are validated by the test data and finite element analysis results.

Disintegration process and performance of a coaxial porous injector

In order to understand the breakup performance of coaxial porous injectors, the sprays of coaxial porous injectors with two different porous material cylinder lengths were compared with those of conventional shear coaxial injectors. To allow comparison, the wall injection lengths were designed to be equivalent to the value of the recess depth. Cold flow sprays were visualized using back-lit photography methods and analyzed quantitatively with a laser diffraction apparatus, in order to study the effects of the momentum flux ratio and Weber number on the breakup for each type of injector. In case of the shear coaxial injector, the large liquid core was observed in low air mass flow rate condition. However, the destabilization of the liquid jet from the coaxial porous injector is almost complete within the inner region, near the injector face plate. Additionally, better breakup performance in low gas flow rate condition was obtained when the porous cylinder length decreased, while the shear coaxial injectors showed better breakup efficiency when the recess length increased. In conclusion, the different breakup process caused by the radial momentum in the inner region of the porous injector disintegrated the liquid core.

Responses of curved steel-concrete-steel sandwich shells subjected to blast loading

The blast response behaviors of curved Steel-Concrete-Steel (SCS) sandwich shells were investigated using nonlinear finite element method. The accuracy of the numerical model was verified against the available field blast test results. The numerical results showed that shear connectors played a vital role in bonding the face plates and concrete core and therefore improving the blast resistant capacity of curved SCS sandwich shell. In addition, different failure modes for the curved SCS sandwich shell under close- and far-field blast loading were observed, i.e., separation of rear plate from concrete core and buckling of face plates for the shell under close- and far-field blast loading, respectively. The effects of rise height (or rise to span ratio) and rear to front plate thickness ratio on the blast responses of curved SCS sandwich shells were also studied. Numerical results showed that the damage of curved SCS sandwich shell could be reduced by increasing rise height and rear to front plate thickness ratio. Moreover, the energy absorption efficiency of concrete core also showed increase with increasing rear to front plate thickness ratio.