Simple modeling for stiffness evaluation of bolted joints using interfacial element

This study has developed a novel finite element named interfacial element which simulates the contact between microscale asperities at contact surfaces of bolted joints. In this element, the contact is assumed to be the Hertzian contact of elastic asperities whose peak heights obey the Gaussian distribution. Based on this assumption, the stiffness of the interfacial element is derived from the compressive stress and the surface texture of the interfaces. On the other hand, it is necessary for large-scale simulations that target the entire vehicle body to reduce the number of nodes and elements in the finite element models. This study has further proposed simple modeling for stiffness evaluation of bolted joints using the interfacial element. Finite element simulations by simplified models in which heads, axes and holes of bolts were ignored were conducted and compared with detailed models and hammering tests. The results revealed that the mean value of the natural frequency of the simplified models had good agreement with that of the detailed models and the hammering tests though the calculation accuracy of the simplified models were lower than the detailed models. The bolt heads and the nuts could be ignored by increasing the density of the bolt axes to be equal to the total weight

Interfacial Element for Finite Element Modal Analysis of Bolted Joints

Multi-material structures are going to be a main scheme to construct automobiles. For the construction of multi-material structures, techniques to join dissimilar materials are required. The major joining techniques are classified into welding, adhesion and mechanical fastening such as bolted joints and riveting. Especially, bolted joints enable joining of metallic materials (steel and aluminium alloy, etc.) and non-metallic materials (CFRP, etc.) with high joint strength. However, the total stiffness of structures with bolted joints is relatively low because interfaces in bolted joints just contact each other, and its interfacial stiffness is lower than elastic modulus of base materials. Moreover, interfacial stiffness of bolted joints depends on clamping force of bolt and nut. This study has proposed an interfacial element for finite element modal analysis of bolted joints. The interfacial element simulates interfacial stiffness of bolted joints. Contact of interfaces is assumed to be the Hertzian contact of elastic asperities whose peak heights obey the Gaussian distribution. Based on this assumption, the stiffness of the interfacial element is derived from the compressive stress and the surface texture of the interfaces. By using the finite element model with the interfacial element, the modal analysis computes the natural frequency and the vibration mode. Finite element simulations and hammering tests have been conducted with several bolted joints. In general, the natural frequency of the bolted joints in the hammering tests increases with the increase in the clamping force, but it is lower than the calculation results in which the stiffness reduction of the jointed interfaces is ignored. The calculation results by using the proposed interfacial element agree with the hammering tests. Therefore, the proposed interfacial element contributes to improvement of modal analysis of bolted joints by mathematically modelling stiffness reduction of jointed interfaces based on tribology

On the Approximation in the Hermitian Treatment of Dyson Boson Expansion Theory

We discuss about the Hermitian treatment of Dyson-type boson expansion theory. We show that the basic assumption of the conventional treatment does not hold in general and the method is only approximately valid. We also show that the approximation is the same order as that of truncation of the expansion usually done in the Hermitian type boson expansion theory.Comment: 18 page, no figur

Complete genomic DNA sequence of the east asian spotted fever disease agent rickettsia japonica

Rickettsia japonica is an obligate intracellular alphaproteobacteria that causes tick-borne Japanese spotted fever, which has spread throughout East Asia. We determined the complete genomic DNA sequence of R. japonica type strain YH (VR-1363), which consists of 1,283,087 base pairs (bp) and 971 protein-coding genes. Comparison of the genomic DNA sequence of R. japonica with other rickettsiae in the public databases showed that 2 regions (4,323 and 216 bp) were conserved in a very narrow range of Rickettsia species, and the shorter one was inserted in, and disrupted, a preexisting open reading frame (ORF). While it is unknown how the DNA sequences were acquired in R. japonica genomes, it may be a useful signature for the diagnosis of Rickettsia species. Instead of the species-specific inserted DNA sequences, rickettsial genomes contain Rickettsia-specific palindromic elements (RPEs), which are also capable of locating in preexisting ORFs. Precise alignments of protein and DNA sequences involving RPEs showed that when a gene contains an inserted DNA sequence, each rickettsial ortholog carried an inserted DNA sequence at the same locus. The sequence, ATGAC, was shown to be highly frequent and thus characteristic in certain RPEs (RPE-4, RPE-6, and RPE-7). This finding implies that RPE-4, RPE-6, and RPE-7 were derived from a common inserted DNA sequence

Diagnostic Assay for Rickettsia japonica

We developed a specific and rapid detection system for Rickettsia japonica and R. heilongjiangensis, the causative agents of spotted fever, using a TaqMan minor groove binder probe for a particular open reading frame (ORF) identified by the R. japonica genome project. The target ORF was present only in R. japonica–related strains