When exposed to mechanical environments such as shock and vibration, electrical connections may experience increased levels of contact resistance associated with the physical characteristics of the electrical interface. A phenomenon known as electrical chatter occurs when these vibrations are large enough to interrupt the electric signals. It is critical to understand the root causes behind these events because electrical chatter may result in unexpected performance or failure of the system. The root causes span a variety of fields, such as structural dynamics, contact mechanics, and tribology. Therefore, a wide range of analyses are required to fully explore the physical phenomenon. This paper intends to provide a better understanding of the relationship between structural dynamics and electrical chatter events. Specifically, electrical contact assembly composed of a cylindrical pin and bifurcated structure were studied using high fidelity simulations. Structural dynamic simulations will be performed with both linear and nonlinear reduced-order models (ROM) to replicate the relevant structural dynamics. Subsequent multi-physics simulations will be discussed to relate the contact mechanics associated with the dynamic interactions between the pin and receptacle to the chatter. Each simulation method was parametrized by data from a variety of dynamic experiments. Both structural dynamics and electrical continuity were observed in both the simulation and experimental approaches, so that the relationship between the two can be established.
Electrical switches are often subjected to shock and vibration environments, which can result in sudden increases in the switch's electrical resistance, referred to as 'chatter'. This paper describes experimental and numerical efforts to investigate the mechanism that causes chatter in a contact pair formed between a cylindrical pin and a bifurcated receptacle. First, the contact pair was instrumented with shakers, accelerometers, laser doppler vibrometers, a high speed camera, and a 'chatter tester' that detects fluctuations in the contact's electrical resistance. Chatter tests were performed over a range of excitation amplitudes and frequencies, and high speed video from the tests suggested that 'bouncing' (i.e. loss of contact) was the primary physical mechanism causing chatter. Structural dynamics models were then developed of the pin, receptacle, and contact pair, and corresponding modal experiments were performed for comparison and model validation. Finally, a high-fidelity solid mechanics model of the contact pair was developed to study the bouncing physics observed in the high speed videos. Chatter event statistics (e.g. mean chatter event duration) were used to compare the chatter behavior recorded during testing to the behavior simulated in the high-fidelity model, and this comparison suggested that the same bouncing mechanism is the cause of chatter in both scenarios.
Numerically modeling chatter behavior of small electrical components embedded within larger components is challenging. Reduced order models (ROMs) have been developed to assess these components’ chatter behavior in vibration and shock environments. These ROMs require experimental validation to instill confidence that these components meet their performance requirements. While achieving conservative results, experimental validation is required, especially considering that the ROMs neglect the viscous damping effects of the fluid that surrounds these particular components within their system. Dynamic ring-down data of the electrical receptacles in air will be explored and will be assessed as to whether that data provides a validation data set for this ROM. Additional data will be examined in which dynamic ring-down data was taken on the receptacle while submerged in an oil, resulting in a unique experimental setup that should prove as a proof of concept for this type of testing on small components in unique environments.
Classical structural analysis techniques have proven time and time again to be remarkably accurate for systems consisting of a single, continuous piece of material. Unfortunately, nearly all real engineering structures are assembled from multiple parts, joined by bolts, rivets, or other fasteners, and these joints introduce nonlinearities and uncertainties into systems’ structural stiffness and damping. Nonlinear damping due to jointed connections in particular is critical to limiting the resonant response of a structure, yet it remains poorly understood. This work seeks to understand the degree to which joint properties are dependent on the rest of the structure. The testable hypothesis is that the boundary conditions and the far-field structure itself (i.e. distribution of the stiffness and mass) change the way in which the interface is loaded, thus altering the perceived or deduced nonlinear properties of the mechanical joint. This hypothesis is investigated using experimental impact hammer testing methods in order to understand the extent to which alteration in the boundary conditions and far-field structure change the interface properties as well as the underlying mechanics during loading. Numerical tools are also employed to investigate and complement the experimental results, focusing on two fronts: replicating the experimental results with discrete joint models, and investigating joint loading for different modes using numerical modal analysis.
Currently there are limitations in computing chatter behavior of small electrical contacts embedded in components using finite element models. Reduced order models (ROM) have been developed of such electrical contact sub-assemblies to assess the chatter behavior of the contacts during vibration and shock environments. The current ROM method requires experimental validation. This ROM also neglects the frequency and damping effects of the viscous fluid that typically surrounds such sub-assemblies. Dynamic ring-down testing of the electrical contacts in air will be performed and will provide a validation data set for the current ROM. Additionally, dynamic ring-down testing of the electrical contact will be performed in fluids of varying viscosities that will help characterize the effect of the fluid on the contact for an improved ROM.