With the rapid development and wide applications of nano-science and nano-technology, there is an urgent need for nanoscale quantitative mechanical property measurementsasic physical concepts and principles for both quantitative elastic and viscoelastic property measurements are discussed in details. The two theoretical mechanical models for quantification process are recapitulated, which are the cantilever vibration model and the contact mechanics model between the tip and the sample. Next, the fixed frequency excitation mode for qualitative imaging and the resonance tracking mode for quantitative imaging of AFAM are explained. Then, the development of AFAM method is reviewed, including the development of basic quantitative measurement theory, the study on the accuracy and sensitivity of AFAM, the development of new measurement modes, and the new hardware and software upgrades, etc. The advances in the applications of AFAM method to nanomechanical measurement and characterization are given afterwards. The wide applications of AFAM mainly involve the nanomechanical characterization of fiber reinforced composites and their interfaces, the microstructure characterization of smart materials due to mechanical heterogeneity at the microscale, the nanomechanical measurements of bio-materials as well as their interfaces, and the characterization of nanomaterials and thin film systems (e.g., nanocrystalline materials, nanowires, subsurface imaging, etc.). The summary and prospect are finally given to show the problems and future work of AFAM. This review provides a general description of the state of the art, and aims to make researchers achieve a better understanding on the implementation of their own AFAM measurements and extend the applications of AFAM to the nanoscale mechanical characterization of various natural and artificial materials. and characterization. Combining acoustics and atomic force microscopy together, the atomic force acoustic microscopy (AFAM) provides a promising technique for quantitative, high resolution and non-destructive mechanical property characterization of materials on a nanoscale. This paper focuses on the research progress in the AFAM measurement method and its wide applications in various fields. First, the b

As a kind of thermoplastic materials, nylon-type polymers have been widely used in automotive, electronics, micro-electronics areas due to their excellent mechanical properties. However, such polymers are apt to absorb moisture from ambient air, leading to expansions in volume and variations in mechanical properties. Therefore, it is of great importance to investigate the effect of hygroscopicity on the cyclic deformation of nylon-type polymers, which are often subjected to certain types of cyclic loading in their engineering applications. In this work, the uniaxial ratchetting behaviors of nylon-type polymers (typically for nylon-6, i.e. the PA6 polymer) are investigated by performing a series of uniaxial stress-controlled cyclic tests at different relative hygroscopicities (e.g. 0, 1.0% and 2.12%) to evaluate the effect of relative hygroscopicity on uniaxial ratchetting. Tests are also conducted with different durations of peak stress hold time (e.g. 0 s, 5 s and 10 s) to address the time-dependent ratchetting of nylon-type polymers. After the ratchetting tests, the specimens are held for a certain period of time at zero stress to investigate the strain recovery denoted by the ratio of the viscoelastic stain to the total stain of the polymer. The obtained results show that significant ratchetting occurs in the uniaxial asymmetrical stress-controlled cyclic tests of the nylon-6 polymer; and the ratchetting strain of solid-state nylon-type polymer consists of the recoverable viscoelastic and irrecoverable viscoplastic parts. It is also shown that the ratchetting is time-dependent; and the ratchetting strain increases remarkably with the increase of peak stress hold time. More importantly, the ratchetting of nylon-type polymer shows obvious dependence on the relative hygroscopicity; and the ratchetting becomes more remarkable and the irrecoverable viscoplastic strain increases as the relative hygroscopicity increases. These conclusions provide guidance for the applications of nylon-type polymer materials in engineering, and are very important to the construction of corresponding cyclic constitutive models describing the hygroscopicity- and time-dependent ratchetting of nylon-type polymers.

The study on partitioning of energy in hypervelocity impact is theoretically significant to resolving problems involving high kinetic energy impact, developing missile intercept technology, analyzing collided spacecraft, and evaluating collision damages. Based on the previous research on partitioning of energy in hypervelocity impact, the kinetic energy of projectile in hypervelocity impact on thick target was divided into four parts, i.e. the deformation energy, the increase in internal energy of target board due to stress wave propagation, the splashing energy of debris，and the electromagnetic radiant energy. Through a combination of theoretical derivation, experiments and numerical simulation, the partitioning of energy in the direct impact of projectile at the velocity of 2.61 km/s on the 2A12 aluminum target was quantitatively calculated. The results of numerical simulation on crater morphology, size and radiant temperature were basically consistent with those of experiments and theoretical derivation. The research results provide useful knowledge in solving the problems of moving vehicle collisions and bird strikes.

In this study, based on the anisotropic modified couple stress theory, a free vibration model of composite laminated Reddy plate containing only one internal material length scale parameter was developed. The presented model predicted the frequency of free vibration of composite laminated plate in micro scale more accurately than the Kirchhoff model in published literature. The Hamilton's principle was employed to derive the governing equations of motion and the boundary conditions. A simply supported square plate was taken as an illustrative example, the problem of which was solved analytically. Influence of the length scale parameter on natural frequency of material was analyzed, and differences between the results obtained using the Kirchhoff, Mindlin and Reddy plate theories were discussed. Numerical results showed that the presented model was capable of capturing the scale effects. The natural frequencies were always shown to be overestimated by the Kirchhoff theory, especially in thick plate cases, when comparing with the more accurate results obtained using the Mindlin or Reddy theory.