Design of compliant mechanisms for attenuation of unidirectional vibrations in rotational systems

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (leaves 146-148).The purpose of this research was to generate the knowledge required to design compliant mechanisms that (1) attenuate undesired small-motion angular vibrations in rotational power transmission systems and (2) preserve the desired transmission of large-motion torque/angle inputs. This thesis investigates the design of vibration attenuating compliant mechanisms that are directly integrated into the load path of rotational systems. These devices enable designers to attenuate the amplitude of undesirable vibrations while simultaneously optimizing the transmission of torque inputs. The design, modeling, fabrication and experimental validation of two Compliant Vibration Attenuator (CVA) concepts will be presented. The first device, the Small Amplitude Vibration Isolator (SAVI), is a non-linear compliant device that isolates a resonating or non-resonating rotational system from vibrations by acting as a mechanical lowpass filter. The second device, the Damping Vibration Link (DVL) utilizes compliance and damping to attenuate undesired vibrations due to resonance. A linear lumped parameter model was created in Matlab® to simulate the static and dynamic characteristics of rotational power transmission systems. This model enables one to determine the dynamic characteristics of a system for a given set of inputs, thereby making it possible to (1) understand the requirements for the CVA and (2) ascertain the effect of the CVA on the system. Finite-element simulations were conducted to verify an empirical, parametric model that describes the performance of a SAVI as a function of its stiffness parameters.(cont.) Proof-of-concept prototypes were tested to verify performance predictions and to determine the practical issues related to implementation. The thesis concludes with a case study which demonstrates the effectiveness of a SAVI when integrated into the steering system of a light-duty pickup truck. The SAVI was shown to offer a 60% reduction in vibration amplitude by trading off 7 ms of delay in steering wheel-vehicle response.by Spencer E. Szczesny.S.M

Mechanically Induced Chromatin Condensation Requires Cellular Contractility in Mesenchymal Stem Cells

This work was supported by the National Institutes of Health (R01 AR056624, R01 EB02425, T32 AR007132, and P30 AR050950). Additional support was provided by a Montague Research Award from the Perelman School of Medicine and a University of Pennsylvania University Research Foundation Award

CMS physics technical design report : Addendum on high density QCD with heavy ions

Peer reviewe

DTAF dye concentrations commonly used to measure microscale deformations in biological tissues alter tissue mechanics.

Identification of the deformation mechanisms and specific components underlying the mechanical function of biological tissues requires mechanical testing at multiple levels within the tissue hierarchical structure. Dichlorotriazinylaminofluorescein (DTAF) is a fluorescent dye that is used to visualize microscale deformations of the extracellular matrix in soft collagenous tissues. However, the DTAF concentrations commonly employed in previous multiscale experiments (≥2000 µg/ml) may alter tissue mechanics. The objective of this study was to determine whether DTAF affects tendon fascicle mechanics and if a concentration threshold exists below which any observed effects are negligible. This information is valuable for guiding the continued use of this fluorescent dye in future experiments and for interpreting the results of previous work. Incremental strain testing demonstrated that high DTAF concentrations (≥100 µg/ml) increase the quasi-static modulus and yield strength of rat tail tendon fascicles while reducing their viscoelastic behavior. Subsequent multiscale testing and modeling suggests that these effects are due to a stiffening of the collagen fibrils and strengthening of the interfibrillar matrix. Despite these changes in tissue behavior, the fundamental deformation mechanisms underlying fascicle mechanics appear to remain intact, which suggests that conclusions from previous multiscale investigations of strain transfer are still valid. The effects of lower DTAF concentrations (≤10 µg/ml) on tendon mechanics were substantially smaller and potentially negligible; nevertheless, no concentration was found that did not at least slightly alter the tissue behavior. Therefore, future studies should either reduce DTAF concentrations as much as possible or use other dyes/techniques for measuring microscale deformations

Explanation for how effects of DTAF may be masked during constant strain rate testing.

<p>Although the non-stained fascicles have a lower quasi-static modulus, they have a greater viscous response than the stained samples. Therefore, the non-stained samples stiffen more in response to the higher strain rate during the constant strain rate testing, possibly causing the stress-strain curves to overlap.</p

DTAF synthesis and structure.

<p>DTAF is synthesized by conjugating aminofluorescein with cyanuric chloride. Extracellular matrix proteins can then be fluorescently labeled through the reaction between the remaining chloro groups (highlighted in red) attached to the triazine ring and free amine groups on the protein.</p

Results of multiscale testing and modeling.

<p>Multiscale testing demonstrates that higher concentrations of DTAF (A) decrease interfibrillar sliding and (B) increase fibril strains. However, the relationship between both of these microscale deformations and the macroscale tissue strains are similar between the two DTAF concentrations. Additionally, a shear lag model incorporating a perfectly plastic interfibrillar shear stress was successful in (C) fitting the macroscale fascicle mechanics (R² = 0.997) and (D) predicting the microscale fibril strains (R² = 0.68) of tendon fascicles stained at 10 µg/ml. These results are similar to the model performance for samples stained at 2000 µg/ml <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099588#pone.0099588-Szczesny1" target="_blank">[22]</a>. Therefore, these data suggest that while DTAF alters fascicle multiscale mechanics it doesn' change the physical mechanisms underlying fascicle behavior.</p

Macroscale mechanical properties as a function of DTAF concentration and applied grip-to-grip strain level.

<p>(A) Samples stained at high concentrations (>10 µg/ml) maintain large positive quasi-static moduli at greater applied grip-to-grip strains, suggesting that DTAF increases the tissue yield strain. (B) Staining also reduced the amount of stress relaxation throughout testing, with greater effects observed with increasing DTAF concentration. Note: The Non-Stained group contains all the paired non-stained control samples (n = 16). (C,D) Paired differences between stained samples and non-stained controls confirm that high DTAF concentrations produce (C) large increases in quasi-static modulus and (D) decreases in stress relaxation at all applied grip-to-grip strain levels. Lower DTAF concentrations (≤10 µg/ml) exhibited relatively small effects at 6-8% grip-to-grip stains. *p<0.05, ^#p<0.10.</p

Fascicle macroscale response.

<p>Plots of the average stress-strain response to incremental loading for samples stained at (A) 2.5, (B) 10, (C) 100, and (D) 2000 µg/ml along with their paired non-stained controls.</p