Negative and positive stiffness in auxetic magneto-mechanical metamaterials

Abstract

This work discusses the concept of allowing the control of the stiffness of a particular class of re-entrant auxetic magneto-mechanical metamaterials through the introduction of magnets to the system. It is shown, through experimental testing backed up by a theoretical model, that the appropriate insertion of magnets in such a system will alter its stiffness, possibly even making it exhibit ‘negative stiffness’. This leads to a completely different behaviour of the structure in terms of stability. It is also reported that the investigated mechanical metamaterials may exhibit both negative stiffness and negative Poisson's ratio at the same time. Moreover, it is shown that the effect which magnets have on the stiffness of the system may be fine-tuned upon replacing magnets with electromagnets. Such systems have the potential to be used in a wide range of practical applications such as vibration damping devices where achieving a negative stiffness is of fundamental importance.

Reversible signal transmission in an active mechanical metamaterial

“…Parameters used are ν = 4, η = 2 and κ = 0.01. The signal is initiated using the initial condition described by equations (8) and (9) with Q = 1.…”

“…Mechanical metamaterials are artificially constructed and have mechanical properties defined by their structure [1]. Simple metamaterials consist of a one, two, or three-dimensional array of elements connected by links [1][2][3] that may be elastic [4][5][6][7], magnetic [8,9] or electrostatic [4]. Mechanical metamaterials are highly tuneable [10][11][12] and by altering the structure of these elements, and the properties of the links, materials have been developed that selectively transmit signals [13,14], behave as logic gates [5,15] or buckle after the application of external stimulus [2].…”

Planar Mechanical Metamaterials with Embedded Permanent Magnets

“…Moreover, the insertion of permanent magnets into the structure of a metamaterial can enhance the impact resistance [38]. In practice, mechanical metamaterials consisting of re-entrant unit cells with embedded magnets are able to exhibit negative stiffness and auxetic behavior simultaneously [39]. Moreover, the incremental stiffness of the system can be adjusted by changing the orientation of the magnets [40].…”

Auxeticity and stiffness of random networks: Lessons for the rational design of 3D printed mechanical metamaterials

“…Mechanical metamaterials are a class of advanced engineered materials whose unprecedented properties originate from their geometrical design at smaller scales. [1][2][3] Some of the examples of these unusual properties include a negative Poisson's ratio (i.e., auxetic metamaterials), [4][5][6][7][8] shape morphing, 9,10 negative compressibility, [11][12][13] and negative stiffness. 14 Mechanical metamaterials may be directly 3D printed 6,15,16 or be fabricated using crumpling-, 17 origami-, 18,19 or mechanism-based 20 approaches.…”