This study of the dynamic compressive strength properties of metal foams is in two parts. Part I presents data from an extensive experimental study of closed-cell Hydro/Cymat aluminium foam, which elucidates a number of key issues and phenomena. Part II focuses on modelling issues. The dynamic compressive response of the foam was investigated using a direct-impact technique for a range of velocities from 10 to 210 ms - 1 . Elastic wave dispersion and attenuation in the pressure bar was corrected using a deconvolution technique. A new method of locating the point of densification in the nominal stress–strain curves of the foam is proposed, which provides a consistent framework for the definition of the plateau stress and the densification strain, both essential parameters of the ‘shock’ model in Part II. Data for the uniaxial, plastic collapse and plateau stresses are presented for two different average cell sizes of approximately 4 and 14 mm. They show that the plastic collapse strength of the foam changes significantly with compression rate. This phenomenon is discussed, and the distinctive roles of microinertia and ‘shock’ formation are described. The effects of compression rates on the initiation, development and distribution of cell crushing are also examined. Tests were carried out to examine the effects of density gradient and specimen gauge length at different rates of compression and the results are discussed. The origin of the conflicting conclusions in the literature on the correlation between nominal strain rate ɛ ˙ (ratio of the impact velocity V i to the initial gauge length l o of the specimen) and the dynamic strength of aluminium alloy foams is identified and explained.

Dynamic compressive strength properties of aluminium foams. Part I—experimental data and observations

Group velocity and characteristic wave curves of Lamb waves in composites: Modeling and experiments

Sensors and Actuators A: Physical

http://www2.dec.fct.unl.pt/projectos/SMA_2008/Bib/HG06.pdf

Smart structure dynamics

Wavelet analysis of plate wave propagation in composite laminates

A new approach is presented for investigating the dispersive character of structural waves. The wavelet transform is applied to the time-frequency analysis of dispersive waves. The flexural wave induced in a beam by lateral impact is considered. It is shown that the wavelet transform using the Gabor wavelet effectively decomposes the strain response into its time-frequency components. In addition, the peaks of the time-frequency distribution indicate the arrival times of waves. By utilizing this fact, the dispersion relation of the group velocity can be accurately identified for a wide range of frequencies.

Time Frequency Analysis of Dispersive Waves by Means of Wavelet Transform

Review of inverse analysis for indirect measurement of impact force

The wavelet transform (WT) is applied to the time-frequency analysis of flexural waves in beams. The WT with the Gabor wavelet decomposes a dispersive wave into each frequency component in the time domain, which enables one to determine the traveling time of a wave along the beam at each frequency. By utilizing this fact, a method is developed to identify the dispersion relation and impact site of beams.

Experimental wavelet analysis of flexural waves in beams

The effects of temperature and crystal orientations on fatigue crack propagation in a single crystal Ni-base superalloy were experimentally investigated at room temperature, 450 °C and 700 °C. Four types of C(T) specimens with different combinations of crystal orientations in loading and crack propagation directions were extracted from a partially modified CMSX-4, and fatigue crack propagation tests were conducted at room temperature, 450 °C and 700 °C. The experiments showed that the crack propagated in shearing mode at room temperature, while the cracking mode transitioned from the opening to shearing mode at 450 °C and 700 °C. ΔKI values at the transition depended on the testing temperature. These phenomena were attributed to the distinctive temperature dependence of the strength of the γ and γ’ phases. The effect of crystal orientation on the cracking mode transition behavior was interpreted by the trend in the crack propagation rate of the shearing cracking at room temperature. This implied that the driving force of the shearing mode cracking has a significant effect on the cracking mode transition. Finally, crack propagation rates of the opening mode cracking at 450 °C and 700 °C were analyzed. It was revealed that difference of crack propagation rates between the two temperatures varied with the orientation in the loading direction of the specimen. This was attributed to difference in arrangement of γ/γ’ microstructure respect to the loading and crack propagation direction.

Hirotsugu Inoue

Papers

Time Frequency Analysis of Dispersive Waves by Means of Wavelet Transform

Review of inverse analysis for indirect measurement of impact force

Experimental wavelet analysis of flexural waves in beams

Temperature dependent fatigue crack propagation in a single crystal Ni-base superalloy affected by primary and secondary orientations

Crystal plasticity assessment of crystallographic Stage I crack propagation in a Ni-based single crystal superalloy