Damping and cushioning characteristics of Polyjet 3D printed photopolymer with Kelvin model

This study extends previous research on the measurement of a 3D printed photopolymer’s quasi-static cushion properties, to include cushion and damping properties due to impact loading. In order to develop analytical packaging models of 3D printed materials, it is essential to know how energy induced by shipping and handling is dissipated through damping. Compared to the cushion curve, investigating how damping influences packaging design is relatively unfamiliar to the packaging practitioner. This study uses experimentally derived hysteresis loops, from platen impact and quasi-static compression tests, to estimate specific damping capacities for 3D printed photopolymer. This study found that the “sticky” rubber like 3D printed photopolymers, based on a repeating pattern of Kelvin cells, were able to dissipate close to 100% of the input energy in platen impact tests and still return to their original dimensions after impact. In addition, this study shows that the specific damping capacity of the 3D printed structure increases significantly with strain rate.

Detection of Friction Stir Welding Defects of AA1060 Aluminum Alloy Using Specific Damping Capacity

The demand for nondestructive testing has increased, especially in welding testing. In the current study, AA1060 aluminum plates were jointed using the friction stir welding (FSW) process. The fabricated joints were subjected to free vibration impact testing in order to investigate the dynamic properties of the welded joint. Damping capacity and dynamic modulus were used in the new prediction method to detect FSW defects. The data acquired were processed and analyzed using a dynamic pulse analyzer lab shop and ME’Scope’s post-processing software, respectively. A finite element analysis using ANSYS software was conducted on different types of designed defects to predict the natural frequency. The results revealed that defective welded joints significantly affect the specific damping capacity. As the damping ratio increased, so did the indication of opportunities to increase the presence of defects. The finite element simulation model was consistent with experimental work. It was therefore revealed that natural frequency was insufficient to predict smaller defects.

Analytical model for flexural damping responses of CFRP cantilever beams in the low-frequency vibration

In this paper, an analytical model for the flexural vibration damping of Carbon Fiber Reinforced Plastics (CFRP) cantilever beams was proposed, which is based on the Lamination Theory and Euler–Bernoulli Beam Theory. By using a finite element analysis and an analytical model, four sets of specific damping capacity with different pavement schemes were predicted, and flexural vibration test and damping analysis were carried out. Comparing the analytical model, finite element analysis, and test results, it could be found that the analytical model had relatively good accuracy in predicting the first-order natural frequency and specific damping capacity of the bending vibration of CFRP beams. The maximum error of the first-order natural frequency between the analysis result and the experimental result was 7.05%; the maximum specific damping capacity error was only 5.65%. Comparing the finite element analysis method and the experiment results, the maximum error of the first-order natural frequency was 7.8%, the error of the specific damping capacity was bigger, and the [±30°]5S specimen was as high as 18.7%. However, there was a significant error when the analytical model was used to predict the second-order natural frequency and the specific damping capacity of CFRP beam’s flexural vibration.

Identification of Material Damping of a Carbon Composite Bar and Study of Its Effect on Attenuation of Its Transient Lateral Vibrations

Reduction of noise and vibrations is one of the major requirements put on operation of modern machines. It can be achieved by application of new materials. The ability to utilize them properly requires learning more about their mechanical properties. Vibration attenuation depends on material damping as an important factor. This paper presents the results of research in a carbon composite material focusing on its internal damping, on the measurement of the damping coefficients and on its implementation into mathematical models. The obtained results were used for investigation of suppressing lateral vibrations of a long homogeneous carbon composite bar oscillating in the resonance area. During the transient period and due to nonlinear effects, the harmonic time-varying loading excites the bar response consisting of a number of harmonic components. The specific damping capacity referred to several oscillation frequencies determined by measurement. The results were evaluated from the point of view of two simple damping theories — viscous and hysteretic. The experiments showed that internal damping of the investigated material could be considered as frequency independent. Therefore, in order to carry out simulations, the bar was represented in the computational model by an Euler beam constituted of Maxwell–Weichert theoretical material. A suitable setting of material constants enabled reaching a constant value of the damping parameters in the required frequency range. The investigated bar vibration is governed by the motion equation in which the internal damping forces depend not only on instantaneous magnitudes of the system’s kinematic parameters but also on their past history. Solution of the equations of motion was performed after its transformation into the state space in the time domain. Results of the computational simulations showed that material damping significantly reduced amplitude of the bar vibrations in the resonance area. The producers of composite materials usually provide material parameters allowing to solve various stationary problems (density, modulus of elasticity, yielding point, strength, etc.), but there is only little or almost no information concerning the data needed for carrying out dynamical or other time-dependent analyses such as internal damping coefficients, fatigue limit, etc. Therefore, determination of the hysteretic character of material damping of the investigated carbon composite material, measurement of its specific damping capacity and implementation of the frequency-independent damping into the computational model are the principal contributions of this article.

An experimental study of a multi-particle impact damper

In this article, an experimental study of a vertical particle impact damper under free excitation is investigated. Specific impact damping is determined for a primary structure (clamped-free beam) with an enclosure attached to its free end and containing a lead particle. The influence of some system parameters such as clearance and intensity of excitation are investigated. An analytical model based on the concept of an equivalent system with impacting mass is presented and used to compute the specific impact damping. Driven by the experimental observation, it has been shown that a high value of specific damping capacity was reached with a particle impact damper. The obtained results prove the efficiency of this process for achieving high structural damping.

Internal Friction of Fe-Mn-Si-Based Shape Memory Alloys Containing Nb and C and Their Application as a Seismic Damping Material

The damping behavior of an Fe-28Mn-6Si-5Cr-0.5NbC (mass%) shape memory alloy was measured by low cycle fatigue tests during tension-compression loadings. A remarkable damping capacity was observed above the strain amplitude of 0.1%, and the specific damping capacity (SDC) parameter reached saturation at ~ 80% above 0.4%. The reversible motion of the γ/ε interfaces is considered to dominate the cyclic deformation behavior, while the work hardening during tension-compression loading is negligible. These characteristics are favorable for seismic damping devices that protect civil structures from earthquakes.

Specific Properties of Industrial High-Damping Fe-Al Steels

It is shown that industrial high damping steels based on the Fe-Al metallic system are characterized by a very high level of internal dissipation of elastic energy. The specific damping capacity of industrial steels exceeds 40 % and their damping properties are close to those of highpurity damping alloys based on the Fe-Al system. Mechanical properties of damping steels are similar to those of conventional construction steels. High level of properties of damping steels can be explained by their specific crystalline and magnetic structure.