Biagio Carboni

Hysteresis of Multiconfiguration Assemblies of Nitinol and Steel Strands: Experiments and Phenomenological Identification

AbstractAn in-house–built rheological device, made of assemblies of custom-made nickel titanium-Naval Ordnance Laboratory (Nitinol) strands, wires, and steel wire ropes, is experimentally tested in different configurations corresponding to three distinct constitutive behaviors: a strong hardening pinched hysteresis, a quasi-linear–softening behavior, and an intermediate behavior in the range of interest. The nonlinear features of the hysteretic rheological device are the result of geometric hardening of the ropes, interwire friction, and dissipation caused by the phase transformations of the Nitinol wires. These different mechanisms determine a pinching at the origin of the hysteresis force-displacement loops. A phenomenological representation of the experimentally acquired constitutive responses is obtained by an extension of the Bouc-Wen model incorporating a pinching function that depends on two parameters. The responses of the Nitinol wires and strands under uniaxial tension are instead well identifie...

Damage detection by modal curvatures: numerical issues

This work is concerned with modal curvature-based damage detection in slender beam-like structures, whereby the modal curvatures are computed by numerical differentiation of noisy mode shapes sampled at a finite number of measurement points. Within this framework, most common techniques greatly amplify the measurement errors and their application leads to unreliable outcomes, especially when a large set of measurement points is considered. Preliminary signal processing, even if beneficial for reducing the noise level, does not solve the problem in that neither the detection of damaged zones nor the reduction of false alarms exhibit significant improvements. In a comparative fashion, we herein demonstrate that a modified Savitzky–Golay filter and the cubic smoothing spline method can provide a more affordable way for detecting damages when using numerically obtained modal curvatures. In doing so, the robustness against the measurement errors and the role of the adopted formulation for the modal curvature-based damage index are considered. A simple statistical procedure that can further improve the detection of damaged regions together with the identification of possible false positives is also presented.

Nonlinear Vibration Absorber with Pinched Hysteresis: Theory and Experiments

AbstractA nonlinear vibration absorber exploiting the pinched hysteresis of mixed wire ropes made of NiTiNOL and steel is proposed. The mixed wire ropes are assembled in a mechanical device which, by bending them, provides the restoring force to the oscillating mass. The assembly of mixed wire ropes, subject to cyclic end displacements, gives rise to a pinched force-displacement behavior due to the simultaneous occurrence of interwire friction and phase transformations. A modified Bouc-Wen model is adopted to represent the pinched hysteresis while the differential evolutionary (DE) algorithm is employed to identify the constitutive parameters that reproduce the experimental force-displacement cycles. The DE algorithm is also utilized to optimize the restoring force of the absorber toward mitigation of the dynamic response of the main structure to external disturbances of various magnitudes. The pinched hysteresis provides an equivalent damping ratio and resonance frequency, which tend to become almost con...

Data-Based Nonlinear Identification and Constitutive Modeling of Hysteresis in NiTiNOL and Steel Strands

AbstractSeveral different data-driven strategies for nonlinear identification are applied to experimental data exhibiting various types of hysteretic behavior. The experimental data contain displacement and restoring force information for several tests conducted using different configurations of a rheological testing device with various assemblies of nickel titanium-Naval Ordnance Laboratory (NiTiNOL) and steel wire strands. Among the different configurations, the response of the wire strands shows three distinct forms of nonlinear behavior: classical quasi-linear softening hysteresis; strongly pinched, hardening hysteresis; and slightly pinched, hardening hysteresis. The data-driven methods applied for nonlinear identification include polynomial basis functions and neural networks. The polynomial basis nonlinear identification methods are used for the construction and characterization of reduced-order models to gain insight into the physical modeling of the hysteretic phenomena. The neural network method...

Hysteretic beam model for steel wire ropes hysteresis identification

A nonlinear hysteretic beam model based on a geometrically exact planar beam theory combined with a continuum extension of the Bouc-Wen model of hysteresis is proposed to describe the memory-dependent dissipative response of short wire ropes which have the unique feature of exhibiting hysteretic energy dissipation due to the interwire friction. With the proposed model, hysteresis is introduced in the constitutive equation between the bending moment and the curvature within the special Cosserat theory of shearable beams. The model is indeed capable of describing the hysteretic behavior exhibited by short steel wire ropes subject to flexural cycles. The model parameters which best fit a series of experimental measurements for selected wire ropes are identified employing the Particle Swarm Optimization method . The identified parameters are used to reproduce other experimental tests on the same wire ropes obtaining a good accuracy.

Tailoring of Hysteresis Across Different Material Scales

Hysteresis is discussed as a multi-scale material feature that can strongly affect the dynamic performance of a structure. It is shown that the hysteresis exhibited by assemblies of short wire ropes can be tailored via a synergistic use of different dissipation mechanisms (inter-wire frictional sliding, phase transformations) combined with geometric nonlinearities. The blend of material and geometric nonlinearities is a powerful and promising way to design new advantageous types of hysteretic responses in macro- or micro-scale devices and structures. Indeed, moving from macro-scale structures towards much smaller material scales, carbon nanotubes in nanocomposites are shown to dissipate energy through stick-slip with the polymer chains. The hysteresis of these materials can be largely modified and optimized by adjusting the micro-structural constitutive features. Recent experimental and modeling efforts are discussed in the context of new directions in material design and dynamic behavior of nanocomposites.

Identification of energy dissipation in structural joints by means of the energy flow analysis

In this paper, identification of energy dissipation in the joints of a lab-scale structure is accomplished. The identification is carried out by means of an energy flow analysis and experimental data. The devised procedure enables to formulate an energy balance in the vicinity of the joints to obtain local energy dissipation. In this paper, a damping matrix based on the locally identified damping coefficients is formulated. The formulated damping matrix is later used in a five-degrees-of-freedom (5DOF) system for validation. The results obtained with the proposed method are in good agreement with the experimental data, especially in the low frequency range.

Dynamic Response of Nonlinear Oscillators With Hysteresis

The nonlinear features of the steady-state periodic response of hysteretic oscillators are investigated. Frequency-response curves of base-excited single-degree-of-freedom (SDOF) systems possessing different hysteretic restoring forces are numerically obtained employing a continuation procedure based on the Jacobian of the Poincare map. The memory-dependent restoring forces are expressed as a direct summation of linear and cubic elastic components and a hysteretic part described by a modified version of the Bouc-Wen law. The resulting force-displacement curves feature a pinching around the origin. Depending on the hysteresis material parameters (which regulate the shapes of the hysteresis loops), the oscillator exhibits hardening, softening and softening-hardening behaviors in which the switching from softening to hardening takes place above certain base excitation amplitudes. A comprehensive analysis in the parameters space is performed to identify the thresholds of these different behaviors. The restoring force features here considered have been experimentally obtained by means of an original rheological device comprising assemblies of steel and shape memory wire ropes. This study is carried out also with the aim of designing the restoring forces which give rise to dynamical behaviors useful for a variety of applications.Copyright