Muhammad Ekhlasur Rahman

Wire rope isolators for vibration isolation of equipment and structures - A review

Vibrations and shocks are studied using various techniques and analyzed to predict their detrimental effect on the equipment and structures. In cases, where the effects of vibration become unacceptable, it may cause structural damage and affect the operation of the equipment. Hence, adding a discrete system to isolate the vibration from source becomes necessary. The Wire Rope Isolator (WRI) can be used to effectively isolate the system from disturbing vibrations. The WRI is a type of passive isolator that exhibits nonlinear behavior. It consists of stranded wire rope held between two metal retainer bars and the metal wire rope is made up of individual wire strands that are in frictional contact with each other, hence, it is a kind of friction-type isolator. This paper compiles the research work on wire rope isolators. This paper presents the research work under two categories, namely monotonic and cyclic loading behaviors of WRI. The review also discusses the different terminologies associated with vibration isolation system and highlights the comparison between various isolation systems.

A Study on Hardened State Properties of SCC using Fly Ash and Blended Fine Aggregate

The aim of this research is to investigate hardened state properties of Self Compacting Concrete (SCC) containing low calcium based fly ash. The mixtures were prepared using various proportions of Class F fly ash ranging from 0% to 30% cement replacement. Water to powder ratio is 0.38 – 0.39 and powder content was kept constant at 540 kg/m3. Properties investigated were strength properties (compressive strength and splitting tensile strength), and durability properties (complete immersion water absorption, apparent volume of permeable voids (AVPV), sorptivity, and RCIPT tests. These tests were done at various days. Results showed that fly ash replacement of up to 30% gave acceptable strength and durability properties for medium strength SCC.

Static lateral stiffness of wire rope isolators

ABSTRACT This paper presents an analytical model for the static lateral stiffness of Wire Rope Isolators (WRI). The wire rope isolator, which is a passive isolation device, has been widely adopted as a shock and vibration isolation for many types of equipment and lightweight structures. The major advantage of the WRI is its ability to provide isolation in all three planes and in any orientation. The WRI in the lateral roll mode, is required to possess the required lateral stiffness to support and isolate the equipment effectively. The static lateral stiffness of WRI depends mainly on the geometrical characteristics and wire rope properties. The model developed in this paper is validated experimentally using a series of monotonic loading tests. The flexural rigidity of the wire ropes, which is required in the model, was determined from the transverse bending test on several wire rope cables. It was observed that the lateral stiffness is significantly influenced by the wire rope diameter and height of the isolator. The proposed analytical model can be used for the evaluation of lateral stiffness and in the preliminary design of the WRI.

Performance of Solder Bond on Thermal Mismatch Stresses in Electronic Packaging Assembly

Thermo-mechanical stresses have been considered one of the major concerns in electronic Packaging assembly structural failure. The interfacial stresses are often caused by the thermal mismatch stresses induced by the coefficient of thermal expansion (CTE) difference between materials, typically during the high temperature change in the bonding process. This research work examined the effect of bond layer on thermal mismatch interfacial stresses in a bi-layered assembly. The paper verified the existing thermal mismatch solder bonded bi-layered analytical model using finite element method (FEM) simulation. The parametric studies were carried out on the effect of change of bond layer properties in order to provide useful references for interfacial stress evaluation and the electronic packaging assembly design. These parameters included CTE, temperature, thickness, and stiffness (compliant and stiff bond) of the bond layer. The recent development on lead free bonding material was being reviewed and found to have enormous potential and key role to address the future electronic packaging assembly reliability.

Experimental study on vertical static stiffnesses of polycal wire rope isolators

Wire rope isolator is one of the most effective isolation system that can be used to attenuate the vibration disturbances and shocks during the operation of machineries. This paper presents the results of investigation on static elastic stiffnesses (both in tension and in compression) of Polycal Wire Rope Isolator (PWRI) under quasi-static monotonic loading conditions. It also studied effect of variations in height and width of PWRI on its static stiffnesses. Suitable experimental setup was designed and manufactured to meet the test conditions. The results show that their elastic stiffnesses for both tension and compression loading conditions are highly influenced by their geometric dimensions. It is found that their compressive stiffness reduced by 55% for an increment of 20% in their height to width ratio. Therefore, the stiffness of PWRI can be fine-tuned by controlling their dimensions according to the requirements of the application.

Bi-Layered Model of Interfacial Thermal Stresses with the Effect of Different Temperatures in the Layers

An interfacial shearing and peeling stress model is proposed to account for different uniform temperatures and thickness wise linear temperature gradients in the layers. This upgraded model can be viewed as a more generic form to determine interfacial stresses under different temperature conditions in a bi-layered assembly. The selected shearing and peeling stress results are presented for the case of die and die attach as commonly seen in electronic packaging. The obtained results can be useful in interfacial stress evaluations and physical design of bi-material assemblies, which are used in microelectronics and photonic applications.

Hybrid Composite Using Natural Filler and Multi-Walled Carbon Nanotubes (MWCNTs)

This paper presents an experimental study on the development of hybrid composites comprising of multi-walled carbon nanotubes (MWCNTs) and natural filler (oil palm shell (OPS) powder) within unsaturated polyester (UP) matrix. The results revealed that the dispersion of pristine MWCNTs in the polymer matrix was strongly enhanced through use of the solvent mixing method assisted by ultrasonication. Four different solvents were investigated, namely, ethanol, methanol, styrene and acetone. The best compatibility with minimum side effects on the curing of the polyester resin was exhibited by the styrene solvent and this produced the maximum tensile and flexural properties of the resulting nanocomposites. A relatively small amount of pristine MWCNTs well dispersed within the natural filler polyester composite was found to be capable of improving mechanical properties of hybrid composite. However, increasing the MWCNT amount resulted in increased void content within the matrix due to an associated rapid increase in viscosity of the mixture during processing. Due to this phenomenon, the maximum tensile and flexural strengths of the hybrid composites were achieved at MWCNT contents of 0.2 to 0.4 phr and then declined for higher MWCNT amounts. The flexural modulus also experienced its peak at 0.4 phr MWCNT content whereas the tensile modulus exhibited a general decrease with increasing MWCNT content. Thermal stability analysis using TGA under an oxidative atmosphere showed that adding MWCNTs shifted the endset degradation temperature of the hybrid composite to a higher temperature.

Practical Soil-Shallow Foundation Model for Nonlinear Structural Analysis

Soil-shallow foundation interaction models that are incorporated into most structural analysis programs generally lack accuracy and efficiency or neglect some aspects of foundation behavior. For instance, soil-shallow foundation systems have been observed to show both small and large loops under increasing amplitude load reversals. This paper presents a practical macroelement model for soil-shallow foundation system and its stability under simultaneous horizontal and vertical loads. The model comprises three spring elements: nonlinear horizontal, nonlinear rotational, and linear vertical springs. The proposed macroelement model was verified using experimental test results from large-scale model foundations subjected to small and large cyclic loading cases.

Elliptical Leaf Spring Shock and Vibration Mounts with Enhanced Damping and Energy Dissipation Capabilities Using Lead Spring

We present an enhancement to the existing elliptical leaf spring (ELS) for improved damping and energy dissipation capabilities. The ELS consists of a high tensile stainless steel elliptical leaf spring with polymer or rubber compound. This device is conceived as a shock and vibration isolator for equipment and lightweight structures. The enhancement to the ELS consists of a lead spring plugged vertically between the leaves (referred to as lead-rubber elliptical leaf spring (LRELS)). The lead is shown to produce hysteretic damping under plastic deformations. The LRELS isolator is shown to exhibit nonlinear hysteretic behavior. In both horizontal directions, the LRELS showed symmetrical rate independent behavior but undergoes stiffening behavior under large displacements. However, in the vertical direction, the LRELS behavior is asymmetric, exhibiting softening behavior in compression and stiffening behavior in tension. Mathematical models based on the Bouc-Wen model, describing the hysteretic behavior of the proposed isolator, are developed and numerically calibrated using a series of finite element analyses. The LRELS is found to be effective in the in-plane and vertical directions. The improved damping and energy dissipation of the LRELS is provided from the hysteretic damping of the lead spring.

Compressive Stiffness of Elliptical Leaf Spring Antivibration Mounts

This paper presents an analytical solution to the in- plane compressive stiffness of elliptical leaf spring anti-vibration mounts (ELS). The accuracy of the proposed solution has been verified with the finite element analysis of the ELS 3D solid model. Parametric analysis conducted to study the effects of transverse shearing, ELS geometry, and compound material properties on the stiffness showed that the transverse shearing has negligible effect and led to the development of useful equations that simplify the determination of the spring stiffness. In addition, it was demonstrated that the stiffness is more sensitive to the outer radius as compared to other design parameters. The authors showed that the spring stiffness increases with the increase in width and thickness of the composite spring but decreases with the increase in inner radius. However, the spring stiffnesses were more sensitive to the change in spring radius than the thickness.