This paper presents a novel approach for active structures driven by soft dielectric electro-active polymers (EAPs), which can perform contractive displacements at external tensile load. The active ...structure is composed of an array of equal segments, where the dielectric films are arranged in a pile-up configuration. The proposed active structure has the capability of exhibiting uniaxial contractive deformations, while being exposed to external tensile forces. The serial arrangement of active segments has one contracting degree of freedom in the thickness direction of the dielectric EAP film layers.
Due to the envisaged tension force transmission capability, special attention is paid to the electrode design which is of paramount importance with regard to functionality of the actuator. A compliant electrode system with anisotropic deformation properties is presented based on nano scale carbon powder. In experiments, the free deformation as well as the contractive motion under external tensile loading of several actuator configurations with different setups is characterized. These involve the study of various sizes and numbers of stacked film layers as well as different electrode designs.
► Cyclic fatigue loading in mode II yields lower delamination rates at comparable Gmax than mode I. ► The three-point end-notched flexure set-up for cyclic mode II fatigue requires a specimen ...fixation. ► There is a correlation between quasi-static and cyclic fatigue behavior for mode I and mode II.
Delamination resistance testing of fiber-reinforced polymer–matrix laminates under fatigue loads is important for materials development and structural design. Mode II in-plane shear fatigue test development using three-point bending end-notched flexure (3-ENF) and two-point bending end-loaded split (ELS) set-ups is performed in a round robin. Effects of specimen restraint observed earlier in ENF tests are confirmed and preliminary data indicate differences between the two set-ups, if simple beam theory or experimental compliance analyses are applied. Possible reasons for the observed disagreement are discussed.
•Gravure printed stretchable electrodes on polydimethylsiloxane.•Development of MWCNT-based ink for gravure printing of the electrodes.•Electro-mechanical behavior of stretchable electrodes under ...uniaxial and biaxial strain.•Plasma activation influence on electrode resistance under strain.
Dielectric elastomer transducers are promising devices for a growing field of applications. However, to be competitive with established electromechanical transducer technologies, low-cost and efficient fabrication process is needed. In particular, the electrode composition and deposition method seem to be the key elements in this context. In this paper, authors use gravure printing for the deposition of thin and compliant MWCNT electrodes on PDMS films. Gravure printing is a high through put deposition method which allows printing complex electrode patterns whit high resolution and, therefore, is well suited for large scale production of dielectric elastomer transducers. Special attention was given to the adaptation of the MWCNT-based ink to the specific requirements of the gravure printing process in order to achieve stable and high quality printing. Furthermore, the effect of oxygen plasma treatment of the silicone substrate on the electro-mechanical behavior of electrode was investigated. In this context a comprehensive characterization of the electrodes behavior under uniaxial and biaxial strain was carried out. Two mechanisms that explain specific aspects of electro-mechanical behavior of electrodes are proposed.
The knowledge of spinal kinematics is of paramount importance for many aspects of clinical application (i.e. diagnosis, treatment and surgical intervention) and for the development of new spinal ...implants. The aim of this study was to determine the translational and rotational stiffnesses of a functional spinal unit (FSU) L4–L5 using a specimen-specific finite element model. The results are needed as input data for three-dimensional (3D) multi-body musculoskeletal models in order to simulate vertebral motions and loading in the lumbar spine during daily activities. Within the modelling process, a technique to partition the constitutive members and to calibrate their mechanical properties for the complex model is presented. The material and geometrical non-linearities originating from the disc, the ligaments and the load transfer through the zygapophysial joints were considered. The FSU was subjected to pure moments and forces in the three anatomical planes. For each of the loading scenarios, with and without vertical and follower preload, the presented technique provides results in fair agreement with the literature. The novel representation of the nonlinear behaviour of the translational and rotational stiffness of the disc as a function of the displacement can be used directly as input data for multi-body models.
Summary
Reasons for performing study: There are no detailed studies describing the resistance of equine tibiae and radii to side impact loads, such as a horse kick and a better understanding of the ...general long bone impact behavioural model is required.
Objectives: To quantify the typical impact energy required to fracture or fissure an equine long bone, as well as to determine the range and time course of the impact force under conditions similar to that of a horse kick.
Methods: Seventy‐two equine tibiae and radii were investigated using a drop impact tester. The prepared bones were preloaded with an axial force of 2.5 kN and were then hit in the middle of the medial side. The impact velocity of the metal impactor, weighting 2 kg, was varied within the range of 6–11 m/s. The impact process was captured with a high‐speed camera from the craniomedial side of the bone. The videos were used both for slow‐motion observation of the process and for quantifying physical parameters, such as peak force via offline video tracking and subsequent numerical derivation of the ‘position vs. time’ function for the impactor.
Results: The macroscopic appearance of the resultant bone injuries was found to be similar to those produced by authentic horse kicks, indicating a successful simulation of the real load case. The impact behaviours of tibiae and radii do not differ considerably in terms of the investigated general characteristics. Peak force occurred between 0.15–0.30 ms after the start of the impact. The maximum contact force correlated with the 1.45‐power of the impact velocity if no fracture occurred (Fmax≅ 0.926 ·vi1.45). Peak force scatter was considerably larger within the fractured sub‐group compared with fissured bones. The peak force for fracture tended to lie below the aforementioned function, within the range of Fmax= 11–23 kN (‘fracture load’). The impact energy required to fracture a bone varied from 40–90 J.
Conclusions: The video‐based measuring method allowed quantifying of the most relevant physical parameters, such as contact force and energy balance.
Potential relevance: The results obtained should help with the development of bone implants and guards, supporting theoretical studies, and in the evaluation of bone injuries.
The effectiveness of fastening of high-strength unidirectional CFRP/epoxy rods in potted anchors was investigated experimentally. The rods had splitted ends, in which duralumin wedges were glued. The ...experiments, performed for three types of contact between the composite rods and the potted material, showed that the most effective were full adhesion and adhesion–friction contacts, when the maximum load-carrying capacity of CFRP rods under tension could be reached. The full friction contact was ineffective because of the shear failure of CFRP rods inside the anchorage zone.
•Reviewing state-of-the-art of fatigue delamination test development.•Discussing problems of fatigue delamination test under load control.•Unidirectional CFRP laminates tend to yield low threshold ...values in fatigue.•Fatigue delamination of CFRP is compared for different loading modes.
Activities toward standardization of fracture mechanics tests on carbon fiber-reinforced polymer-matrix (CFRP) composites have recently focused on cyclic fatigue under mode I (tensile opening), mode II (in-plane shear) and mixed-mode I/II loading. Data from recent round robins performed by Technical Committee 4 (TC4) of the European Structural Integrity Society (ESIS) and from preliminary testing of additional CFRP epoxy laminates at the authors’ laboratories are analyzed with different approaches in attempts to reduce scatter and to identify parameters for CFRP structural design. Selected test data comparing load and displacement control for the cyclic fatigue tests are also discussed. Specifically, threshold values from Paris-law data fitting are compared with values from fitting with a modified Hartman–Schijve approach. Independent of the approach used for the analysis, mode I threshold values of selected CFRP seem to be in the range between about 30 and 100J/m2, i.e., roughly around the range of critical mode I energy release rate values (denoted by GIC) obtained from fracture testing of neat commercial epoxy resins, but clearly below quasi-static initiation GIC-values for unidirectional CFRP composites. Implications for CFRP structural design based on mode I fatigue fracture mechanics test data are briefly discussed.
This paper presents the results of an experimental study into the effects of including different types (cross section, diameter, length and supplier) and dosages of polypropylene (PP) fibres on the ...occurrence of heat-induced concrete spalling. A new fire testing methodology named the Heat-Transfer Rate Inducing System (H-TRIS) was developed and used in an attempt to tackle some of the shortcomings of standard furnace fire testing in the practical study of heat-induced concrete spalling.
The probability of in-vivo failure of ceramic hip joint implants is very low (0.05–0.004 per cent). Besides material flaws and overloading, improper handling during implantation may induce fractures ...of the ceramic ball head in the long term. This study focuses on the influence of contaminants located in the stem—ball interface and on the use of damaged metal tapers on the strength of ceramic ball heads. Mechanical tests on alumina ball heads according to the standard ISO 7206-10 were performed to identify their effect on the static fracture load. A decrease of up to 90 per cent with respect to the reference static fracture load was found when contaminants such as bone chips, soft tissue, or blood were present. Reductions of 57 per cent and 27 per cent were observed for deformed stem cross-sections (from circular to elliptical) and for flattened stems respectively, making deformed stems another influential parameter. Since any alteration of the interface between the metal taper and the ceramic ball head yields a non-uniform load introduction and hence results in stress concentrations, its presence has to be avoided.
A finite element analysis is carried out to determine the stress-strain state of anchors for round rods made of a high- modulus, high-strength unidirectional carbon-fiber reinforced plastic. The rods ...have splitted ends in which Duralumin wedges are glued. Three types of contact between the composite rods and a potted epoxy compound are considered: adhesion, adhesion-friction, and friction ones. The corresponding three-dimensional problems in the elastic statement are solved by the finite-element method (FEM) with account of nonlinear Coulomb friction. An analysis of stresses on the surface of the composite rod revealed the locations of high concentrations of operating stresses. The results of FEM calculations agree with experimental data.
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