Impact of mode shapes on experimental loss factor estimation in automotive joints

This paper presents the experimental work carried out on single-lap joints fastened together with bolts and nuts to investigate the contribution of mode shapes, and the effect that bolt sizes has in dissipating energy in built-up structures. Five different bolt sizes are chosen to assemble five single-bolted single-lap joints using aluminum plates. An analogous monolithic solid piece carved from the same aluminum material is used to determine the material damping and compare it against the damping from bolted joints. The dynamic response of all structures is captured under free-free boundary conditions, and the common modes are analyzed to understand the contribution and primary source of damping in the same range of the sampling frequency. This investigation has revealed that the source of damping in the joints is heavily linked to the mode shapes of the structure and structural damping (also referred to as material damping) contributes more during specific mode shapes compared to the joint damping itself. The findings allow a more accurate implementation of energy loss in automotive structures which contain bolted joints, allowing an implementation of both material and joint loss factor, respectively

Modal analysis of a single-lap joint under dynamic loading

A well-known source of energy dissipation of mechanical vibration in built-up structures is the frictional forces arising from the relative motion of two mating surfaces, internal material damping and induced pumping in air gaps. Dissipation of mechanical vibration energy at contact interfaces in built-up structures is commonly referred to as interface damping in the research literature. Out of all the energy dissipation methods mentioned earlier, the most significant and immensely powerful source of vibration damping in mechanical structures is the contact interface damping. Investigation of damping associated with bolted joints in dynamic built-up structures is presented in this paper. Bolted single-lap joints are chosen for performing experimental investigation and subjected to different dynamic loadings and tightening torques to study the effects these conditions have on interface damping. A wide range of bolt torques are considered for this investigation to analyse the impact of contact interface damping on built-up structures. Modal parameter extraction methods are used to estimate the damping in selected modes and compare the ability of the methods in estimating the loss factor

Additional file 1: of The feasibility and RE-AIM evaluation of the TAME health pilot study

Five A’s Counseling Script. (DOCX 27 kb

Summary of the microorganisms isolated in 162 cases from 368 patient intervertebral disc specimens by anaerobic culture.

<p>Summary of the microorganisms isolated in 162 cases from 368 patient intervertebral disc specimens by anaerobic culture.</p

Distribution of <i>P</i>. <i>acnes</i> colony counts in culture-positive disc tissue specimens.

<p>Distribution of <i>P</i>. <i>acnes</i> colony counts in culture-positive disc tissue specimens.</p

<i>Propionibacterium acnes</i> biofilm is present in intervertebral discs of patients undergoing microdiscectomy

<div><p>Background</p><p>In previous studies, <i>Propionibacterium acnes</i> was cultured from intervertebral disc tissue of ~25% of patients undergoing microdiscectomy, suggesting a possible link between chronic bacterial infection and disc degeneration. However, given the prominence of <i>P</i>. <i>acnes</i> as a skin commensal, such analyses often struggled to exclude the alternate possibility that these organisms represent perioperative microbiologic contamination. This investigation seeks to validate <i>P</i>. <i>acnes</i> prevalence in resected disc cultures, while providing microscopic evidence of <i>P</i>. <i>acnes</i> biofilm in the intervertebral discs.</p><p>Methods</p><p>Specimens from 368 patients undergoing microdiscectomy for disc herniation were divided into several fragments, one being homogenized, subjected to quantitative anaerobic culture, and assessed for bacterial growth, and a second fragment frozen for additional analyses. Colonies were identified by MALDI-TOF mass spectrometry and <i>P</i>. <i>acnes</i> phylotyping was conducted by multiplex PCR. For a sub-set of specimens, bacteria localization within the disc was assessed by microscopy using confocal laser scanning and FISH.</p><p>Results</p><p>Bacteria were cultured from 162 discs (44%), including 119 cases (32.3%) with <i>P</i>. <i>acnes</i>. In 89 cases, <i>P</i>. <i>acnes</i> was cultured exclusively; in 30 cases, it was isolated in combination with other bacteria (primarily coagulase-negative <i>Staphylococcus spp</i>.) Among positive specimens, the median <i>P</i>. <i>acnes</i> bacterial burden was 350 CFU/g (12 - ~20,000 CFU/g). Thirty-eight <i>P</i>. <i>acnes</i> isolates were subjected to molecular sub-typing, identifying 4 of 6 defined phylogroups: IA₁, IB, IC, and II. Eight culture-positive specimens were evaluated by fluorescence microscopy and revealed <i>P</i>. <i>acnes in situ</i>. Notably, these bacteria demonstrated a biofilm distribution within the disc matrix. <i>P</i>. <i>acnes</i> bacteria were more prevalent in males than females (39% vs. 23%, p = 0.0013).</p><p>Conclusions</p><p>This study confirms that <i>P</i>. <i>acnes</i> is prevalent in herniated disc tissue. Moreover, it provides the first visual evidence of <i>P</i>. <i>acnes</i> biofilms within such specimens, consistent with infection rather than microbiologic contamination.</p></div

Visualization of bacterial biofilm in the disc tissue by CSLM and confirmation of <i>P</i>. <i>acnes</i> by FISH.

<p>A. Three dimensional reconstructed CSLM image of biofilm bacteria stained with a DNA stain (SYTO9, green) in a disc tissue sample (#4, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174518#pone.0174518.t002" target="_blank">Table 2</a>). B-C. The presence of <i>P. acnes</i> biofilms in this sample verified using FISH. Epifluorescence micrographs of a biofilm cluster showing red fluorescence from the CY5-labeled EUB338 general eubacterial probe (B) and green fluorescence from the CY3-labled <i>P. acnes</i>-specific probe (C). Co-localization of the red and green fluorescence indicates that all of the bacteria in this biofilm were <i>P. acnes</i>.</p

Characteristics of the disc samples evaluated by microscopic methods.

<p>Characteristics of the disc samples evaluated by microscopic methods.</p

Visualization of <i>P</i>. <i>acnes</i> biofilm in the disc tissue by use of FISH.

<p>A. This color-combined image shows the “pocket” of green fluorescent <i>P. acnes</i> cells (biofilm) near the center right of the image (disc tissue sample #8, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174518#pone.0174518.t002" target="_blank">Table 2</a>). The presence of <i>P. acnes</i> biofilms in this sample was verified using FISH. B-C. Red fluorescence is the general eubacterial probe (B) and green is the <i>P. acnes</i> probe (C). The B/C image is a zoom of A showing fluorescence from the red and green channels separately. Almost all of the cells in A are emitting both red and green fluorescence indicating that they are <i>P. acnes</i>.</p