The octopus is a marine animal whose body has no rigid structures. It has eight arms composed of a peculiar muscular structure, named a muscular hydrostat. The octopus arms provide it with both locomotion and grasping capabilities, thanks to the fact that their stiffness can change over a wide range and can be controlled through combined contractions of the muscles. The muscular hydrostat can better be seen as a modifiable skeleton. Furthermore, the morphology the arms and the mechanical characteristics of their tissues are such that the interaction with the environment (i.e., water) is exploited to simplify control. Thanks to this effective mechanism of embodied intelligence, the octopus can control a very high number of degrees of freedom, with relatively limited computing resources. From these considerations, the octopus emerges as a good model for embodied intelligence and for soft robotics. The prototype of a robot arm has been built based on an artificial muscular hydrostat inspired to the muscular ...

Soft Robot Arm Inspired by the Octopus

Covid-19 face masks: A potential source of microplastic fibers in the environment.

Meso-FE modelling of textile composites: Road map, data flow and algorithms

X-ray computed tomography of polymer composites

Soft electronics are intensively studied as the integration of electronics with dynamic nonplanar surfaces has become necessary. Here, a discussion of the strategies in materials innovation and structural design to build soft electronic devices and systems is provided. For each strategy, the presentation focuses on the fundamental materials science and mechanics, and example device applications are highlighted where possible. Finally, perspectives on the key challenges and future directions of this field are presented.

Materials and Structures toward Soft Electronics.

Braiding is a relatively less explored textile process for producing composite preforms. Biaxial braids can be produced as hoses and subsequently be draped over different three-dimensional surfaces. However, triaxial braids are relatively stable structures and should be produced to the desired shape during the braiding process. This is achieved by over-braiding on mandrels that either form part of the finished composite or removed before the moulding process. Triaxial braided composites have superior mechanical properties due to fibre orientations along three directions. Geometry of a braided structure depends on the number of yarn carriers, rotational speed of the carriers, take-up speed and the effective perimeter of the cross-section of a mandrel. In the present work, a VRML based geometrical visualisation tool has been developed to simulate a braid structure on any predefined mandrel geometry, and using a predefined yarn cross-section. Braid angles, cover factors and yarn volume fractions can be computed from these simulations. A triaxial braiding machine has been developed with an independent servo control of the carrier movement and the take-up mechanism; geometrical simulation is used as an input to the control system to continuously vary the braid structure along the length of a mandrel. Flexible tooling is important for rapid product development. A flexible mandrel has been developed that can be mechanically adjusted to change the cross-section and the taper. This system enables rapid development of braided preforms.

Geometrical modelling and control of a triaxial braiding machine for producing 3D preforms

Novel stitch-bonded sandwich composite structures

Modelling the forming process for engineering fabrics and textile composites using a mechanical approach, such as the finite element method, requires characterisation of the material’s behaviour under large shear deformation. For woven engineering fabrics, a coupling between in-plane tension and both shear compliance and the onset of wrinkling is to be expected. This paper focuses on a novel testing technique, the biaxial bias extension test, as a means to investigate this shear–tension coupling and fabric wrinkling. Novel methods of determining the wrinkling behaviour are demonstrated. The main difficulty with the technique lies in extracting the material contribution to the recorded signal. To do this, an experimental method is proposed and demonstrated using a plain weave glass fabric. Biaxial bias extension test results are compared against picture frame and uniaxial bias extension results.

Characterising the shear–tension coupling and wrinkling behaviour of woven engineering fabrics

Compaction modelling of textile preforms for composite structures

Textile preforms undergo complex in-plane and out-of-plane deformations during forming processes. In-plane shear is the most significant mode of deformation during draping or forming around double-curvature surfaces. This paper reports an improved method for measuring the constitutive shear properties of textile preforms—a wide strip bias extension test has been found to give significantly better results in comparison to conventional narrow strip bias test. Shear angles, computed directly from global strains, were in close agreement to those measured using an optical method. Constitutive shear stress–strain relation, computed from the bias extension test data, was in good agreement with KES (Kawabata Evaluation System) test results. Meso-scale tow deformations have been measured using two techniques: an inexpensive flatbed scanner-based full-field strain measurement technique for measuring in-plane tow deformations and a strain-freezing technique for measuring through-thickness tow deformations. With this data, a 3D Representative Volume Element (RVE) can be constructed for each stage of shear deformation. Beyond the geometric shear limit, tow deformations during bias extension appear to be somewhat different from those normally expected from pure shear—a reduction in tow thickness and tow cross-sectional area and a corresponding increase in packing factor.

Prasad Potluri

Papers

Geometrical modelling and control of a triaxial braiding machine for producing 3D preforms

Novel stitch-bonded sandwich composite structures

Characterising the shear–tension coupling and wrinkling behaviour of woven engineering fabrics

Compaction modelling of textile preforms for composite structures

Measurement of meso-scale shear deformations for modelling textile composites