A self-adaptive cohesive zone model for interfacial delamination

Interfacial failure in the form of delamination, often results in malfunction or failure of laminated structures. Different numerical approaches have been proposed for the simulation of this process. Due to the appealing feature of predicting both the delamination onset and its growth, cohesive zone models have been widely used to simulate delamination as a result of a gradual degradation of the adhesion between two materials when they become separated. Application of cohesive zone models for the modelling of delamination in brittle interfaces in a quasi-static finite element framework suffers froman intrinsic discretization sensitivity. A large number of interface elements are needed for the discretization of the process zone of a cohesive crack. Otherwise, a sudden release of energy in large cohesive zone elements results in a sequence of snap-through or snap-back points to appear in the global load-displacement response of the system which compromises the numerical efficiency. While computationally expensive path-following techniques can be used to follow the oscillatory path, the efficiency and robustness of brittle cohesive zone models can be significantly increased by reducing the oscillations observed in the global load-displacement behaviour without a further mesh refinement. In line with this purpose, the separation approximation in the process zone is enriched with an adaptive hierarchical extension. The linear separation approximation throughout the cohesive zone element is enriched with a bi-linear function, where the enrichment peak position and the magnitude of the enrichment are regarded as additional degrees of freedom obtained by minimization of the total potential of the global system. The mobility of the peak of the enrichment function within individual cohesive zone elements locally adapts the discretization to the physics governing the problem. Important numerical aspects of the proposed enrichment strategy such as its mobility and uniqueness have been thoroughly investigated while its limitations are addressed. The efficiency and robustness of the enrichment are shown through numerical examples which prove the general applicability of the methodology. In fact, application of the elaborated enrichment eliminates the need for a further mesh refinement while keeping the standard Newton-Raphson approach applicable in the case of a relatively coarse mesh which saves considerable computational costs. Extension of the proposed enrichment scheme to delamination in a threedimensional finite element framework has been carried out as well. Planar interix face elements have been enriched along all edges by bi-linear functions with mobile peaks. The effect of the proposed methodology on reducing discretization-induced oscillations is quantitatively evaluated. To deal with planar crack growth where the crack front is oblique with respect to element edges, a non-hierarchical enrichment strategy is also developed and its performance is compared with its hierarchical counterpart. The self-adaptive finite element formulation is extended to a framework suitable for large deformations and is applied to interfaces in microelectronics under realistic mixed-mode loading conditions. In particular, the material/interface systems used in miniaturized mixed-mode bending tests, which are conducted for a wide range of mode angles, are modelled to make a direct comparison with experimental results. The interface constitutive lawthat is used takes the dependence of fracture toughness on mode-mixity into account. Thereby, the enhanced cohesive zone model can be used for the simulation of the behaviour of brittle interfaces in an accurate, effective, and efficient manner

A Study on anisotropy of cosmic ray distribution with a small array of water-cherenkov detectors

The study of the anisotropy of the arrival directions is an essential tool to investigate the origin and propagation of cosmic rays primaries. A simple way of recording many cosmic rays is to record coincidences between a number of detectors. We have monitored multi-TeV cosmic rays by a small array of water cherenkov detectors in Tehran(35 43 N, 51 20 E, 1200m a.s.l). More than 1.1*10^6 extensive air shower events were recorded. In addition to the Compton- Getting effect due to the motion of the earth in the Galaxy, an anisotropy has been observed which is due to a unidirectional anisotropy of cosmic ray flow along the Galactic arms.Comment: 16 pages 9 figs and one tabl

Estimation of N-acetyltransferase 2 haplotypes

N-Acetyltransferase 2 (NAT2) genotyping may result in a considerable percentage in several ambiguous allele combinations. PHASE 2.1 is a statistical program which is designed to estimate the probability of different allele combinations. We have investigated haplotypes of 2088 subjects genotyped for NAT2 according to standard PCR/RFLP methods. In 856 out of 2088 cases the genotype was clearly defined by PCR/RFLP only. In many of the remaining cases the program clearly defined the most probable allele combination: In the case of *5A/*6C, *5B/*6A the probability for *5B/*6A is 99% whereas the alternative allele combination *5A/*6C can be neglected. Other combinations cannot be allocated with a comparable high probability. For example the allele combination *5A/*5C, *5B/*5D provides for *5A/*5C a probability of 69% whereas the estimation for *5B/*5D allele is only 31%. In the two most often observed constellations in our data [(*12A/*5B, *12C/*5C); (*12A/*6A, *12B/*6B, *4/*6C)] the probability of allele combination was ascertained as follows: *12A/*5B, 98%; *12C/*5C, 1.4% and *12A/*6A, 82%; *4/*6C, 17%; *12B/*6B, 0%. The estimation of the NAT2 haplotype is important because the assignment of the NAT2 alleles *12A, *12B or *13 as a rapid or slow genotype has been discussed controversially. Otherwise the classification of alleles in subjects which are not showing a clearly allocation can result in a rapid or slow acetylation state. This assignment has an important role in survey of bladder cancer cases in the scope of occupational exposure with aromatic amines. --PHASE 2.1,NAT2 genotyping,single nucleotide polymorphism

An enriched cohesive zone model for delamination in brittle interfaces

Application of standard cohesive zone models in a finite element framework to simulate delamination in brittle interfaces may trigger non-smooth load-displacement responses that lead to the failure of iterative solution procedures. This non-smoothness is an artifact of the discretization; and hence it can be avoided by sufficiently refining the mesh leading to unacceptably high computational costs and a low efficiency and robustness. In this paper, a process-driven hierarchical extension is proposed to enrich the separation approximation in the process zone of a cohesive crack. Some numerical examples show that instead of mesh refinement, a more efficient enriched formulation can be used to prevent a non-smooth solution

Optimal conditions for the biological removal of ammonia from wastewater of a petrochemical plant using the response surface methodology

High concentrations of nitrogen compounds, such as ammonia observed in the petrochemical industry, are the major environmental pollutants. Therefore, effective and inexpensive methods are needed for its treatment. Biological treatment of various pollutants is a low cost and biocompatible replacement for current physico-chemical systems. The use of aquatic plants is an effective way to absorb the nutrient pollutants. In this study, the optimal operating conditions in the biological removal of ammonia from the urea-ammonia wastewater of Kermanshah Petrochemical Company by Lemna gibba were determined using the response surface methodology. Lemna gibba was collected from the ponds around Kermanshah and maintained in a nutrient medium. Effect of the main operational variables such as ammonia concentration, residence time and Lemna gibba to surface ratio on optimal conditions of ammonia removal from wastewater has been analyzed using  the Box-Behnken model design of experiments. Model numerical optimization was performed to achieve the maximum amount of ammonia removal from wastewater. The ammonia removal percentage varied from 13% to 88%, but the maximum amount of ammonia removal was determined at ammonia concentration of 5 ppm and Lemna gibba residence time of 11 days in wastewater based on the quadratic model. Lemna gibba to surface ratio of 2:5 was measured at 96.449%. After optimization, validation of ammonia removal was performed under optimum conditions and measured at 92.07%. Based on the experimental design and the predicted under model conditions, the maximum amounts of ammonia removal percentage in the experiments were 82.84% and 88.33% respectively, indicating the high accuracy of the model to determine the optimum conditions for the ammonia removal from wastewater