Analysis of delamination fatigue growth for delaminated piezoelectric elasto-plastic laminated beams under hygrothermal conditions

A nonlinear analysis model of fatigue delamination growth for piezoelectric elasto-plastic laminated beams under hygrothermal conditions is presented. Based on the incremental elasto-plastic constitutive equations, the incremental nonlinear governing equations of the piezoelectric elasto-plastic laminated beams with delamination are derived when taking into account the hygrothermal environments, transverse shear deformation, geometrical nonlinearity and piezoelectric effect. According to the elasto-plastic fracture dynamics and J-integral theory, the energy-release-rate along the delamination is obtained. Then, applying the Paris law, the delamination growth rate is obtained and the delamination growth lengths along the delamination fronts under cyclic loads are finally determined by using the cyclic skip method. The equations are solved by the finite difference method and iterative method as a whole. Effects of voltages, variation of temperature and humidity, delamination length and depth on the energy-release-rate and delamination growth length for the piezoelectric elasto-plastic laminated beams are discussed in numerical examples.     

Characterization of the permeability of a high performance composite coating to cathodic protection and its implications on pipeline integrity

In this work, the permeability of a high performance composite coating (HPCC) and its component layers, fusion bonded epoxy (FBE) and medium-density polyethylene (MDPE), to cathodic protection (CP) was investigated by various electrochemical measurements. Results demonstrate that the permeability of the coatings to water is ranked as FBE > MDPE > HPCC. Compared to FBE, MDPE, as a highly non-polar coating, plays a key role in protecting the HPCC from the water permeation. HPCC is impermeable to CP, and shows a pure capacitive behavior, with ultra-high low-frequency impedance at the order of 10¹⁰ Ω cm² during the test period. Both FBE and MDPE coatings are permeable to CP, which will make up the degradation of the coatings due to the water-uptaking. Therefore, under an appropriate CP application, the two coatings are capable of maintaining the pipeline integrity. HPCC provides an excellent alternative to maintain the pipeline integrity in the soil environment.     

OPTICAL SPECTRA OF LOW-DIMENSIONAL SEMICONDUCTORS

IntroductionThedevelopmentoflow dimensionalsemiconductormaterialshasbeenextensive[1].Toalargeextent,themodernmicroelectronicsindustryisstilllargelybasedontheconventionaldevicecomponents (withareduceddis cretedevicedimensionfollowingMoore′slaw) ,whereasth…     

Microstructure and mechanical properties of Mg-Al-Zn alloy under a low-voltage pulsed magnetic field

Effect of a low-voltage pulsed magnetic field on the solidified microstructure and mechanical properties of Mg-Al-Zn alloy has been investigated. When the low-voltage pulsed magnetic field is applied during solidification, the as-cast microstructure is significantly refined and α-Mg is modified from developed dendrite to fine rosette. This morphology modification is caused by the accumulation of Joule heat on the dendrite tip. The yield strength is improved with the application of the low-voltage pulsed magnetic field under normal casting and semi-continuous casting conditions. The ultimate tensile strength is decreased slightly under normal casting condition due to the occurrence of plenty of shrinkage under the low-voltage pulsed magnetic field. The shrinkages are removed and the yield strength and ultimate tensile strength are increased under semi-continuous casting condition with low-voltage pulsed magnetic field.     

A molar mass induced transition in the yielding properties of linear polyethylene

The mechanism of tensile deformation in a semi-crystalline polymer like PE changes at four critical points which can be associated with (A) the onset of single slip-processes, (B) a turnover into a collective activity of slips, (C) the beginning of a disaggregation of the crystal blocks, followed by fibril formation, and (D) the onset of chain disentangling. Studies of the deformation behavior of series of LPEs with increasing molar mass show an abrupt rise of the critical strains ε_H(C) and ε_H(D) at a molar mass of M_t≈(1 5-2)×10⁵ g mol⁻¹. As indicated by dynamic mechanical tests the rise originates from a change in the mobility and compliance of the amorphous regions, which are melt-like for M_w>M_t, but reduced for M_w<M_t. As a consequence, both, crystal block disaggregation and chain disentangling, set in at lower strains.