|M.Sc Student||Katalan Dror|
|Subject||Coupled Compression-Shear Behavior of Rubber Joint|
|Department||Department of Mechanical Engineering||Supervisor||Professor Emeritus Eli Altus|
|Full Thesis text|
Elastomeric bearings (EBS) are structural elements made from laminated alternating rubber- metal plates and are used in Thrust vector control (TVC) rocket engines as a joint between the rocket and the engine and as shock isolators in bridges and high rise buildings.
EBS for TVC engines work under coupled compression-shear loading. Compression occurred as a result of the thrust and shear as a result of maneuvering movements. The important feature of the element is the shear modulus after compression is applied. Experiments on full scale multi layers systems show a reduction of this modulus with increasing compression.
The aim of this research is to study experimentally the mechanical behavior of a single layer rubber joint under combined Compression-Shear loading for which a novel experimental setup was designed and tested. Data of multiple shear cycles were obtained. Each cycle was imposed on a different increasing pressure loading, where the pressure was maintained constant during each cycle. Testing results show the characterized shear stress strain curve of each compression loading and allow monitoring the shear modulus variation with compression increase. Literature survey which covered 20 well known rubber models have not considered thoroughly the above coupled effects, or hysteresis behavior.
Single layer rubber joint differs from a typical EBS. Its shear modulus increases with compression. The reason stems from instability effects which are more pronounced in the multilayer case. The above phenomenon was validated by Finite Element analysis using Mooney-Rivlin constitutive model.
More generalized model (Ogden) was able to follow each type of loading separately (compression or shear) but lacked the ability to predict the coupled effect. Part of this drawback could come from the simplified assumption of a uniform displacement field taken in this study.
The main characteristics of the rubber joint behaviour that were found are: The shear modulus is unchanged up to a certain compression level and then increases linearly. The typical shear stress strain curve includes hysteresis response behaves similarly to the shear modulus. The shear response of the rubber joint is insensitive to loading direction.
The correlation between hysteresis and shear modulus suggests a micro-mechanical friction type of model. Heuristic development of friction based model is proposed. The development suggests mechanism that follows most characteristics of the shear stress strain response observed in this research. This model may assist in predicting the coupled shear modulus effect.