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The nonlinear mechanical responses of tetrachiral honeycombs under large deformation are theoretically analyzed by employing elliptic integrals, and the results are verified by numerical simulations. The nonlinear relationships between normal stress, shear stress, Poisson's ratio and the strain are derived for the tetrachiral honeycombs. It is found that the Poison's ratio of the tetrachiral honeycombs under large deformation is totally different from that under small deformation. The Poisson's ratio can achieve to a large magnitude of 0.8 in the former case, while remains 0 in the latter case. Moreover, the tetrachiral honeycombs exhibit positive Poison's ratio under large tensile-deformation, whilst showing negative Poisson's ratio under large compression-deformation. The magnitude of Poisson's ratio depends on both the honeycomb's deformation and the ligament relative length, while it is insensitive to the ligament thickness. Besides, the coupling effect between tensile (or compression) and shear is observed for the tetrachiral honeycombs. In other words, shear deformation appears within the honeycomb under uniaxial loading. The coupling effect depends on both the honeycomb's deformation and the geometric parameters of the cell structure. And the quantitative relationships among them are derived. This special coupling effect of tetrachiral honeycombs provides a new idea for designing more metamaterials.

The temperature and strain rate-dependent compressive behaviour of ice-1h was investigated through molecular dynamics simulations. The ice strength increased in response to a decrease in the initial temperature and an increase in the strain rate. Various deformation mechanisms depended on the ice’s initial temperature. Solid-liquid phase transformation was more likely to at a relatively high temperature. However, solid-solid phase transformation and dislocation-like glide were observed at relatively low temperatures. Experimental observations on the strength versus strain rate relationship of ice could be interpreted based on a prior study by Wu and Prakash [1].

Residual stresses play a crucial role in both light-electricity conversion performances and the lifespan of photovoltaic (PV) cells. In this paper, the residual stress of triple junction cells (i.e. GaInP/GaInAs/Ge) induced by laser-driven massive micro-particle impact is analyzed with a novel method based on backscattering Raman spectroscopy. The impact process, which induces damage to the PV cells and brings the residual stress, is also investigated by optical microscopy (OM) and Scanning Electron Microscopy (SEM). The results show that the PV cells would exhibit various damage patterns. At the same time, strong residual stresses up to hundreds of MPa introduced in the damaged PV cells after impact have been analysis, providing an effective perspective to better understand the damage behavior and residual stress features of PV cells during their service life.

The dynamic compressive behaviour of sandwich panels with shear thickening fluid (STF) filled pyramidal lattice truss cores at high strain rates is studied and compared with that of pure STF as well as the sandwich panels with empty and water filled pyramidal lattice truss cores by modified split Hopkinson pressure bar (SHPB) apparatus. The dynamic compressive strengths of the sandwich panels while filled with STF increase significantly when compared to the strengths of the sandwich panels with empty pyramidal lattice truss cores. It is interesting to note that the sandwich panel with the STF filled pyramidal lattice truss core shows “1 + 1 >> 2” dynamic energy absorption behaviour. The excellent energy absorption behaviour of the sandwich panel with STF filled truss core is interpreted by the transformation of deformation modes of core beams from non-symmetry to symmetry after filled with the STF through strong interaction between the buckling behaviour of pyramidal lattice truss core and the shear thickening behaviour of the filled STF material.

Billiards is one of the most fashionable indoor sports around the world. The choice of billiard cues is important for players to win a game. Up to now, the evaluation on the performance of billiard cue almost merely depends on the experience of the famous players, which is subjective and controversial. Aiming at both the objective evaluation and the testing method on the performance of billiard cue, a set of experimental device was designed to measure the dynamic behaviors of both the cue and the ball. Based on theoretical considerations, a force-transferring coefficient is proposed to quantitatively and objectively evaluate the performance of a cue in the efficiency of hitting balls. Both experiments and numerical simulations indicate that those cues with moderate stiffness exhibit the most advantageous force-transferring performance, better than the softer and the harder cues. Moreover, further numerical simulation results indicate that the force-transferring performance of the cue can be enhanced by reducing the anisotropy of the shaft material. For the spinning-ball skills, the rotational velocity of the ball is derived and can be calculated from the ball's translational velocity measured by the device. Experiments showed that a softer tip could make a larger rotating velocity of the ball compared to the harder tip. It is expected that the present work will facilitate the objective and quantitative characterization of the performance of billiard cues, so as to assist players in evaluating and selecting billiard cues. It also offers a technical suggestion for selecting proper row material of cues in order to improve cues’ performance.

Vibration of flange joints and force transmission characteristics of connection interfaces are important due to concerns over the structural strength and signal identification in engineering structures such as missiles and rockets. However, nonlinear factors such as clearance, damping and discontinuous interfaces make it difficult to predict the responses under specific excitations such as shock impacts. This paper proposed a typical configuration of a bolted flange joint and investigated the response of vibration and dissipation of the joint under a series of impact loadings. The amplitude of excitation was 120 MPa, and the duration of the loading ranged from 20 μs to 200 μs. The excitations of high amplitude and frequency lead to a vibrational response coupled to a shock response of the joints. The connecting interfaces contributed to the distortion of the shockwave and changed its frequency, which can be characterized by the factor α. Those interfaces were also sources of energy dissipation, and their effect decreased as the frequency of excitation decreased. This methodology is helpful for predicting the local behavior of joints in a complex engineering structure under extreme conditions.

The shock behaviour of NiTi shape memory alloy is investigated by using molecular dynamics simulation. The nano-pillar samples of the alloy are subjected to the impact of a piston with a velocity of 350 m/s at initial environment temperatures of 325 and 500 K. At 325 K, we observe two different pathways of the formation of BCO phase, the gradient twins, and the detwinning phenomena, strongly depending on the local stress and the deformation state. As the initial temperature increases to 500 K, the plasticity is dominated by the dislocation movements rather than the twinning at 325 K. The phase transformation and plasticity result in stress attenuation when the stress wave propagates through the nano-pillar. Furthermore, it is interesting to note that multiple stress peaks occur due to the formation of local complex atomic structures with various wave speeds, leading to the catch up and overlap of the stress waves.

In the present research the dynamic energy absorption behavior of lattice material filled with shear thickening fluid (STF) is studied by the modified split Hopkinson pressure bar (SHPB) apparatus. The nominal engineering stresses versus strain curves are measured to analyze the dynamic energy absorption behavior of the combined material. The dynamic behavior of lattice material is also measured as a comparison. The results show the dynamic strength of the lattice material is about 3 MPa, which is a little higher than the static strength of about 2.3 MPa because of the inertial effect during impact. However, when filled with STF, the combined material shows extraordinary energy absorption behavior when compared to the empty lattice material. The stress of the lattice material filled with STF increase almost linearly to about 9 MPa and then increases slowly with the increase of strain. The excellent energy absorption behavior of the lattice material filled with STF could be explained by the interaction between the lattice cores and the STF during compression. For the lattice material, while some of cores buckling, it will lose the load capacity. While filled with STF, if the initial buckling of some of the lattice cores happens during impact, the strong lateral drag force is generated by the ambient STF due to the fast lateral velocities of the cores, leading to the great increase of its dynamic energy absorption behavior.

Experimental and numerical simulations were undertaken to estimate the effects of imperfect conditions on stress waves in split Hopkinson pressure bar (SHPB) experiments.ThephotonicDopplervelocimetry(PDV)mea- surement results show that the rise and fall times of an incident wave increases with an increasing inclination angle; also,thefluctuationsoftheincidentwavedisappeargradually with the increase of inclination angle. The following charac- teristics for various defects in the SHPB were obtained by numerical simulation: (1) the influence of a curved bar was negligible; (2) misalignment modestly affects the fluctuation characteristics, and bending waves were generated at this condition; (3) inclination and indentation of the impact end- surface had a great impact on the incident waves, and both of themincreasetherisetimeoftheincidentwavebyincreasing the degree of defects. In view of the results, misalignment, inclination, and indentation in SHPB experiments should be minimized.

Molecular dynamics simulation was conducted to investigate the phase transformation behaviour of nickel-titanium (NiTi, 50%-50% at.%) nanopillar under uniaxial compression at loading rates varying from 3.30x10(7) to 3.30x10(9)s(-1) and at temperatures varying from 325 to 600K. The phase transformation of NiTi was observed to be sensitive to loading rates and temperatures. The phase transformation stress of B2 -> B19 increased with increasing temperature while it was insensitive to loading rate. The phase transformation stress of B19 -> B19 '-> BCO increased with increasing strain rate and decreasing temperature. In addition, reverse phase transformation was observed during compression due to the interaction between the phase transformation of B19 -> B19 '-> BCO and the deformation twinning/dislocation slide-induced plasticity of the BCO phase, leading to different residual crystal structures after loading. Moreover, a diagram for the phase transformation behaviour of NiTi in the simulated ranges of strain rate and temperature was obtained, from which the contrary experimental observations on the phase transformation behaviour of NiTi from the studies of Nemat-Nasser et al. (Mech. Mater. 37 (2005) p.287) and Liao et al. (J. Appl. Phys. 112 (2012) p.033515) at various strain rates could be well explained.

La doping effects on intergrowth Bi 2 WO 6 -Bi 3 TiNbO 9 ferroelectric ceramics were studied by X-ray diffraction, electron probe microanalysis and dielectric spectroscopy. It was found that the La 3+ distribution, ferroelectric phase transition and dielectric relaxation behavior are apparently affected by La doping. With increasing La 3+ content, the site of dopant ion varies, the grain growth of Bi 5 TiNbWO 15 is restrained, the Curie temperature is reduced and broadened. Furthermore, two dielectric relaxation loss peaks were observed both in temperature and frequency spectra. The calculated relaxation parameters revealed the oxygen vacancy related to the relaxation process.

AFM experiments and molecular dynamics simulation of rectangular graphdiyne films are performed in this paper. The force-deflection curves are obtained, and the elastic modulus is calculated as 218.5 GPa and 482.615 GPa, respectively. The simulated maximum stress and pre-tension of graphdiyne film are 33.088 GPa and 0.551 GPa, respectively. It is observed that the graphdiyne film fractured in the central point once the indentation depth over the critical depth. Also, the obviously elastic behaviour has found during the loading-unloading-reloading process. The deformation mechanisms and fractured behaviour of the graphdiyne film are discussed in detail during the loading process. Moreover, the effects of various factors including loading speed and indenter radii of the graphdiyne film by the MD simulation are discussed.

The electron acoustic images of domain structure BaTiO3 single crystal under the applied electric field have been observed with Scanning Electron Acoustic Microscope (SEAM). By increasing applied electric field, the growth and merging of domains were revealed. The successive images of domain movement in real time demonstrated the promising potential application of SEAM in the dynamic study of ferroelectric domains. The influence of the applied electric field on the incident electron beam was also discussed in this paper.

The domain structure of ferroelectric BaTiO3 ceramics were directly observed with Scanning electron acoustic microscope (SEAM) made in our lab. The relationships of domain structures with surface grains in BaTiO3 ceramics were revealed with electron acoustic imaging. The generation of the electron acoustic signal and imaging mechanism of ferroelectric domain was analyzed. The electron acoustic imaging of BaTiO3 Crystal and semiconducting BaTiO3 ceramics were also shown for deducing electron acoustic imaging mechanism of ferroelectric domain.

A scanning acoustic microscope (SAM) and a scanning electron acoustic microscope (SEAM) have been used to study domain structures in ferroelectric BaTiO3, Bi4Ti3O12 and ferroelastic NdP5O14 single crystals. In SAM, domain walls act as scattering boundaries for leaky surface acoustic waves and thus sources of image contrast; While in SEAM, different signal generation and image contrast mechanisms may arise, mainly thermal elastic and piezoelectric effects. Further insight into the properties of domains was approached by discussing and comparing the image contrasts involved in both techniques.

The scanning electron-acoustic imaging technique has been used in the characterization of the residual stress field distributions existing in the subsurface in aluminum disks and 20 vol % SiC ( w)/ZrSiO4 multiphase ceramics left by Vicker’s indentation. The experimental results reveal that the distribution areas are the plastic-elastic interchange zones. The electron-acoustic signal generation mechanism in the samples are discussed.

Scanning electron acoustic microscopy (SEAM) has been used in the observation of ferroelectric domain configurations in barium titanate single crystals. The contribution to the image contrasts is related to signal generation through a piezoelectric coupling mechanism. The results prove that SEAM really has the ability to show not only the surface shape and domain structures but also the subsurface domain structures. Furthermore, SEAM is a convenient, fast and nondestructive way of observing the ferroelectric domains compared with other methods.

The dynamic response of the 57 vol./vol. % dense spherical silica particle-polyethylene glycol suspension at high pressure was investigated through short pulsed laser induced shock experiments. The measured back free surface velocities by a photonic Doppler velocimetry showed that the shock and the particle velocities decreased while the shock wave transmitted in the shear thickening fluid (STF), from which an equation of state for the STF was obtained. In addition, the peak stress decreased and the absorbed energy increased rapidly with increasing the thickness for a thin layer of the STF, which should be attributed to the impact-jammed behavior through compression of particle matrix, the deformation or crack of the hard-sphere particles, and the volume compression of the particles and the polyethylene glycol.

This work was supported by the Ministry of Science and Technology of China through 973-Project No. 2002CB613307, the National Natural Science Foundation of China No. 50572113, and the Innovation Project of Shanghai Institute of Ceramics No. SCX200409.

This work was supported by the Ministry of Science and Technology of China through 973-Project No. 2002CB613307 and the National Natural Science Foundation of China No. 50572113.

This work was supported by the Ministry of Science and Technology of China through 973-Project No. 2002CB613307, the National Natural Science Foundation of China No. 50572113, and Shanghai Commission of Science and Technology No. 05JC14079.

Dielectric, impedance, and electric modulus spectroscopies were employed to study the dielectric anomalies in Bi 5 Ti 1.5 W 1.5 O 15 ceramics. It was found that the ferroelectric transition temperature is at 986 K. Besides, two relaxation processes attributed to bulk and grain boundary effects were observed both in the dielectric and impedance spectra. However, only one relaxation process corresponding to the bulk response was observed in the electric modulus spectra. The relaxation parameters were deduced. It was found that the bulk response of the material was of localized relaxation process at low temperatures, and long-range conductivity only emerged at high temperatures. Finally, the relaxation species and dynamics of the bulk response were discussed.

This work was supported by the Ministry of Science and Technology of China through 973-Project under Grant No. 2002CB613307.

This work was supported by the Ministry of Science and Technology of China through 973-Project under Grant No. 2002CB613307.