Incremental Displacement Research Articles

ВДОСКОНАЛЕННЯ СПОСОБІВ ЗБЕРЕЖЕННЯ СТІЙКОСТІ ПІДГОТОВЧИХ ВИРОБОК З УРАХУВАННЯМ ДЕФОРМАЦІЙНИХ ВЛАСТИВОСТЕЙ ОХОРОННИХ СПОРУД

Purpose. To evaluate the deformation properties of protective constructions of preparatory workings to maintain their stability in the excavation areas of coal mines with steep coal seams. Methodology. To achieve this goal, laboratory and field studies of the deformation properties of protective constructions have been performed. Results. It has been established that under uniaxial compression, under the action of a statistical external force, which manifests itself in the conditions of uniaxial compression and relative deformation of wood chocks within 0.1<λ<0.2, their stiffness decreases, and then it increases at 0.4<λ<0.7, which creates conditions for ensuring the bearing capacity of protective constructions. Under field conditions, when using the method of protecting the slope drifts with wood chocks made of sleepers, after their deformation of more than 40% in the zone of influence of mining works (0<l<100 m), a gradual decrease in the increase in the displacement of side rocks on the contour occurs during the compaction process, due to which the operational condition of the preparatory workings along the length of the excavation section is ensured. To study the deformation characteristics of the protective constructions, we used the function of the incremental displacement of the side rocks on the contour of the workings at the section of 0<l<100 m behind the face. Scientific novelty. The regularities of deformation of protective constructions of preparatory mine workings under uniaxial compression with regard to changes in their stiffness have been established. Practical significance. When mining steep coal seams, using the peculiarities of geomechanical phenomena manifested in the coal massif, it is advisable to use compressible protective constructions of preparatory mine workings.

Practical macro‐element for vertical and batter pile groups

AbstractThis paper presents a novel macro‐element for vertical and batter pile groups. The numerical scheme is based on de‐coupled, single pile response. Each pile consists of two separate load‐displacement formulations (axial and transverse) that take a displacement increment as input and return a diagonal tangent stiffness value. The effect of rotation is implicitly incorporated in the transverse load‐displacement formulation. The presented macro‐element does not require pre‐defined failure surfaces or other parameters, and is therefore not restricted to a specific foundation configuration, soil profile or soil type. The macro‐element may be calibrated using any type of non‐linear pile‐soil model. The developed macro‐element is validated using rigorous numerical models for a variety of configurations.

Effect of Frequency Content of Earthquake Ground Motions on Structures with Varying Dimension

An earthquake is a catastrophe which is always a topic of concern for structural designers and civil technocrats. Not only it causes physical damage to the structures but also successful to impart psychological disorder in human minds for long-run. In order to mitigate the devastating effects of earthquake on society, it is eminent to study the dynamic characteristics in detailed manner i.e. to examine how the structure responds owing to the seismic characteristics. The various ground motion characteristic includes time-duration and velocity, frequency content and amplitude, displacement, incremental velocity and incremental displacement, peak ground accelerations (PGAs), etc. Out of these, effect of frequency content and maximum amplitude value of earthquake ground motions on the seismic response of structures is often underestimated. This paper investigates the effect of frequency content and maximum amplitude value on the seismic response of structures which is dominant of all characteristics. The study proceeds with recording time-history of acceleration obtained from conventional unidirectional harmonic shake table. Further, FFT (Fast Fourier Transform) analysis of applied time-history is done and the effect of frequency content and the maximum amplitude value of applied time-history on the seismic responses of structures is investigated and studied. For this, structures with varying dimensions (height, length, and width) are modelled and time-history analysis of structural models has been carried out in SAP2000v19. Seismic responses of analysed structures are represented in the form of fundamental natural frequency, storey displacement, and base shear. It is reported that out of many earthquake indices, frequency content and amplitude of earthquake ground motions are the most dominating. It is reported that the resonance phenomena occurs for the less height structure and thus it shows maximum displacement and base shear responses. Also, as height, length, and width of structure increases; displacement, base shear, and fundamental time-period of structure increases.

Role of surgical hyoid bone repositioning in modifying upper airway collapsibility.

Background: Surgical hyoid bone repositioning procedures are being performed to treat obstructive sleep apnea (OSA), though outcomes are highly variable. This is likely due to lack of knowledge regarding the precise influence of hyoid bone position on upper airway patency. The aim of this study is to determine the effect of surgical hyoid bone repositioning on upper airway collapsibility. Methods: Seven anaesthetized, male, New Zealand White rabbits were positioned supine with head/neck position controlled. The rabbit's upper airway was surgically isolated and hyoid bone exposed to allow manipulation of its position using a custom-made device. A sealed facemask was fitted over the rabbit's snout, and mask/upper airway pressures were monitored. Collapsibility was quantified using upper airway closing pressure (Pclose). The hyoid bone was repositioned within the mid-sagittal plane from 0 to 5mm (1mm increments) in anterior, cranial, caudal, anterior-cranial (45°) and anterior-caudal (45°) directions. Results: Anterior displacement of the hyoid bone resulted in the greatest decrease in Pclose amongst all directions (p = 0.002). Pclose decreased progressively with each increment of anterior hyoid bone displacement, and down by -4.0 ± 1.3cmH2O at 5mm. Cranial and caudal hyoid bone displacement did not alter Pclose (p > 0.35). Anterior-cranial and anterior-caudal hyoid bone displacements decreased Pclose significantly (p < 0.004) and at similar magnitudes to the anterior direction (p > 0.68). Conclusion: Changes in upper airway collapsibility following hyoid bone repositioning are both direction and magnitude dependent. Anterior-based repositioning directions have the greatest impact on reducing upper airway collapsibility, with no effect on collapsibility by cranial and caudal directions. Findings may have implications for guiding and improving the outcomes of surgical hyoid interventions for the treatment of OSA.

Fast staggered schemes for the phase-field model of brittle fracture based on the fixed-stress concept

Phase-field models are promising to tackle various fracture problems where a diffusive crack is introduced and modeled using the phase variable. Owing to the non-convexity of the energy functional, the derived partial differential equations are usually solved in a staggered manner. However, this method suffers from a low convergence rate, and a large number of staggered iterations are needed, especially at the fracture nucleation and propagation. In this study, we propose novel staggered schemes, which are inspired by the fixed-stress split scheme in poromechanics. By fixing certain invariants of the stress when solving the damage evolution, the displacement increment is expressed in terms of the increment of the phase variable. The relation between these two increments enables a prediction of the displacement and the active energy based on the increment of the phase variable. Hence, the maximum number of staggered iterations is reduced, and the computational efficiency is improved. We present three fast staggered schemes by fixing the first invariant, second invariant, or both invariants of the stress, denoted by S1, S2, and S3 schemes. The performance of the schemes is then verified by comparing with the standard staggered scheme through three benchmark examples, i.e., tensile, shear, and L-shape panel tests. The results exhibit that the force–displacement relations and the crack patterns computed using the fast schemes are consistent with the ones based on the standard staggered scheme. Moreover, the proposed S1 and S3 schemes can largely reduce the maximum number of staggered iterations and total cpu time in all benchmark tests. The S2 scheme performs comparably except in the L-shape panel test, where the underlying assumption is violated in the region close to the crack.

A transition scheme from diffusive to discrete crack topologies at finite strain during the course of a staggered iterative procedure

AbstractThis study presents a novel transition scheme that can trace an actual crack path as closely as possible and stably update its explicit crack tip even in a large deformation regime. The crack initiation and propagation processes are determined from an energy minimization problem with respect to the displacement field and crack phase‐field, and the predicted path represented by a diffuse crack topology is replaced by a discrete path by applying the finite cover method. By developing a technique for determining explicit crack tips, the crack topology is updated from diffusive to discrete intermittently during the course of the staggered iterative procedure. Therefore, even a curved crack path that evolves significantly within a single time increment can be explicitly captured. Additionally, to stably update an explicit crack tip within the finite strain framework, we introduce a stabilization technique. Specifically, pseudo‐stiffness is applied to severely damaged elements around the discrete crack path to prevent excessively large deformations, and the corrector of the displacement increment in the global Newton–Raphson iterative procedure is intentionally diminished so that the discrete crack opens in a gradual and stable manner. After describing the individual techniques devised in the proposed scheme for achieving these features based on their algorithmic aspects, we present several representative numerical examples to demonstrate the performance and capability of the developed approach.

Dynamic Response Characteristics of Roadway Surrounding Rock and the Support System and Rock Burst Prevention Technology for Coal Mines

Anchor cables (bolts) act as the main support system and play an important role in improving the rock burst resistance and stability of the roadway surrounding the rock. In this study, the dynamic response characteristics of the roadway surrounding the rock and the support system under different shock intensities were investigated. The following findings were obtained. The stress wave propagation process under dynamic shock was divided into a stress vibration initiation stage, a stress fluctuation stage, and a stress adjustment stage. In the stress vibration initiation stage, the surface mass of the roadway surrounding the rock started to vibrate, and the pretension of the anchor cables (bolts) was reduced; in the stress fluctuation stage, the failure of the roadway surrounding the rock intensified, and the anchor cables (bolts) were damaged to some extent; and in the stress adjustment stage, the roadway deformation of the surrounding rock and the axial forces of the anchor cables (bolts) tended to stabilize. As the dynamic shock intensity increased, the vibration velocity, displacement increment, and acceleration amplitude of the mass of the roadway surrounding the rock increased exponentially. The critical shock energy of the roadway surrounding the rock was 105 J, above which the damage to the rock was aggravated. The larger the pretension of the anchor cables (bolts) was and the higher the dynamic shock intensity was, the more severe the damage to the anchor cables (bolts) was. Given the dynamic response characteristics of the roadway surrounding the rock and support elements under shock, a full anchor cable yielding support technology is proposed to effectively control the stability of the roadway surrounding the rock under dynamic shock, providing a reference for the construction of the support systems for preventing rock bursts in similar roadways.

In-plane cyclic behavior of brick walls strengthened with CFRP plates embedded in the horizontal mortar joint

Unreinforced masonry (URM) buildings exhibit significant vulnerability under in-plane seismic loads due to poor tensile strength and integrity. An experiment was carried out to investigate the effectiveness of embedding carbon fiber reinforced polymer (CFRP) plates in the horizontal mortar joint on improving the in-plane seismic performance of URM wall that was prone to fail by diagonal shear failure mode. A total of five half-scale specimens, each measuring 2250 mm × 1500 mm × 240 mm, including two un-strengthened brick walls and three strengthened walls, were tested undergoing pre-compression stress combined with incremental lateral displacement. The CFRP plates were only embedded in the wall on one side in order to reduce the impact on building appearance and different reinforcement ratios were adopted. The failure mode, hysteretic behavior, shear strength, ductility, stiffness degradation and energy dissipation capacity of the specimens were discussed. The results showed that reinforcement can control the initiation and rapid growth of diagonal shear cracks. The strengthened masonry walls exhibited flexural rather than brittle shear failure with good ductility and energy dissipation. The ductility of the strengthened walls increased significantly with the increased reinforcement ratio and there was an optimal reinforcement ratio that maximized the ductility. The strengthened wall with medium reinforcement ratio showed the highest increase in ductility factor of 45.71% compared with the control specimen. The strengthened specimens displayed greater bearing capacity compared with the un-strengthened specimen. The largest increase in the shear strength of the strengthened walls was 10.16%, which indicates the effectiveness of the reinforcement method of used to embed CFRP in the horizontal joint to improve the in-plane seismic performance of URM walls. In addition, the abilities of several analytical models used to predict the shear capacity of the URM and strengthened walls were analyzed.

An analytical model of time-dependent elastoplasticity with hydraulic–mechanical coupling for wellbore stability in hydrate exploitation

Natural gas hydrates have potential economic and environmental significance. However, wellbore instability likely occurs during drilling due to the deterioration in the geomechanical properties of formation caused by hydrate dissociation. In this study, a time-dependent elastoplastic analytical model for wellbore stability is proposed under overbalanced and underbalanced drilling, considering the hydrate dissociation-induced changes in the geomechanical properties and full coupling between hydraulic–mechanical fields. The analytical solutions are verified with the finite element results under the same conditions and validated with the results from complex numerical simulations. According to the analytical solutions, the difference in pore pressure relative to the initial pore pressure decreases, and accordingly, the incremental displacement decreases (by approximately 39.54% for the maximum displacement) after the influence of the mechanical field on pore pressure is considered. The influence is greater far from the wellbore and smaller around the wellbore due to the constant drilling fluid pressure. The risk of wellbore instability increases with time, and the safe drilling window of drilling fluid pressure will be narrowed by hydrate dissociation (by −5.90%), the increase in the drilling fluid temperature (by −12.64% from the temperature of 20 °C to 30 °C) and the reduction in cohesion (by −47.43% at most).

Quasi-static cyclic loading assessment of GFRP single-lap adhesive joints reinforced with z-pins

Numerous studies have focused on the bond behavior of z-pinned composite joints under monotonic and fatigue loading. Despite this, research on quasi-static cyclic loading is still limited. In order to improve our understanding of the mechanical behavior of glass fiber reinforced polymer (GFRP) single-lap adhesive joints subjected to quasi-static cyclic loading, an experimental study was conducted, and the effects of z-pinning and the adhesive thickness of the bonding area on the strength and stiffness of joints were examined. In this regard, a series of the single-lap joints with 0.5 and 1 millimeter adhesive thickness without z-pin and reinforced with 9 and 16 z-pins were fabricated and monotonic, quasi-static cyclic, and monotonic after cyclic loadings were applied to each. It was found that in conditions where monotonic loading is only the case, and there is no quasi-static cyclic loading, the use of single-lap joints with 16 z-pins is recommended due to their effect on enhancing the ultimate load. For deciding on the adhesive thickness, the shear stiffness of the joint should be taken into consideration, as thinner adhesive thickness resulted in lower shear stiffness but higher ultimate load with the same number of z-pins. In the presence of quasi-static cyclic loading, inserting 16 z-pins along with 1 mm adhesive thickness is proposed. This number of z-pins significantly increased the ultimate load and the number of cycles the joint could tolerate. The impact of this thickness on reducing the level of stiffness degradation and displacement increment is noticeable as the cyclic loads progress.

Study on collapse settlement and cracks of core wall rockfill dams under wetting deformation

AbstractThe safety and stability of core wall rockfill dams during impoundment are threatened by the wetting deformation of up‐stream shell materials. The serious wetting deformation not only aggravates the collapse settlement of upstream rockfill but also intensifies differential settlement of the dam crest during impoundment, and then causes cracks on the dam crest. On the basis of the proposed wetting deformation model and its simulation method of wetting deformation, this paper simulated the impoundment process of Guanyinyan core wall rockfill dam and studied the deformation characteristic of the dam during impoundment. In addition, the smeared cracking model was used to simulate the crack propagation on the dam crest, and the crack develop and spread mechanism was analysed. The results show that the simulated deformation can fit the in‐situ data well, and the simulated crack propagation is in good agreement with the actual situation. Once watered, the upstream rockfill and core wall have significant settlement, and the whole dam crest has obvious horizontal displacement towards the upstream. It is on the same order of magnitude that the increment of horizontal displacement and settlement at the top of the dam during impoundment. In the process of impoundment, the upper part of the dam tends to deform towards the reservoir area, which will lead to tensile cracks appearing in the rockfill areas on both upstream and downstream sides of the core wall of the dam crest, and the propagation direction of the cracks is basically parallel to the adjacent core wall surface. With the water level rising, the cracks on the downstream side of the dam crest mainly extend vertically, and the cracks on the upstream side of the dam crest not only extend vertically, but also extend horizontally.

An energy-based computational scheme for the analysis of reinforced concrete structures with geometric and material nonlinearities

ABSTRACT This paper proposes a new energy-based numerical technique for the nonlinear analysis of reinforced concrete beam elements. The mathematical concept and equations are presented in detail for a general nonlinear quasi-static problem. This method can create a physical sense of the types of energy in a system for an analyst to easily consider any material type and geometric nonlinearity effects from the analysis of reinforced concrete members. The governing equations of this computational scheme have a quadratic form, which leads to proving a complementary relationship for a stability check. In other words, a distinguishing feature of the proposed method is paving the path for selecting the optimum size of displacement increments during a nonlinear numerical analysis. In the proposed method, the steps have been made easier for analysts. Unlike several existing methods, the formulation has also considered the shear and normal deformations, making the analysis results closer to experimental realities. Moreover, the results obtained from solving, evaluating, and comparing several examples demonstrate the acceptable accuracy and convergence of this energy-based approach for reinforced concrete beams. In addition, the quadratic nature of its formulation provides an analyst with information about the accuracy and stability of the obtained structural responses.

Immiscible Viscous Fingering: The Simulation of Tertiary Polymer Displacements of Viscous Oils in 2D Slab Floods.

Immiscible viscous fingering in porous media occurs when a high viscosity fluid is displaced by an immiscible low viscosity fluid. This paper extends a recent development in the modelling of immiscible viscous fingering to directly simulate experimental floods where the viscosity of the aqueous displacing fluid was increased (by the addition of aqueous polymer) after a period of low viscosity water injection. This is referred to as tertiary polymer flooding, and the objective of this process is to increase the displacement of oil from the system. Experimental results from the literature showed the very surprising observation that the tertiary injection of a modest polymer viscosity could give astonishingly high incremental oil recoveries (IR) of ≥100% even for viscous oils of 7000 mPa.s. This work seeks to both explain and predict these results using recent modelling developments. For the 4 cases (µo/µw of 474 to 7000) simulated in this paper, finger patterns are in line with those observed using X-ray imaging of the sandstone slab floods. In particular, the formation of an oil bank on tertiary polymer injection is very well reproduced and the incremental oil response and water cut drops induced by the polymer are very well predicted. The simulations strongly support our earlier claim that this increase in incremental oil displacement cannot be explained solely by a viscous “extended Buckley-Leverett” (BL) linear displacement effect; referred to in the literature simply as “mobility control”. This large response is the combination of this effect (BL) along with a viscous crossflow (VX) mechanism, with the latter VX effect being the major contributor to the recovery mechanism.

A molecular dynamics study of evaporation mode transition of hydrocarbon fuels under supercritical conditions

The mode transition of evaporation for single- and multi-component hydrocarbon fuels is investigated at the molecular level. This study scrutinizes first the subcritical and supercritical evaporation of n-hexadecane droplets and liquid films by molecular dynamics (MD) simulations. The mode regime map of n-hexadecane droplets is obtained. Then the mode transition of evaporation of a three-component droplet and a six-component droplet is studied. A critical dimensionless number τ0.9P of 0.5 based on the average displacement increment (ADI) of fuel atoms is used to identify the evaporation mode transition of fuels with any type and number of components. It is found that in the diffusion mode of evaporation, the entropy becomes the dominant factor in the evaporation of fuels, and the disorder of the fuel molecules increases significantly compared with that in the classic evaporation mode. Compared with the case of the quiescent droplet, with increasing relative velocity between the droplet and the ambient gas, the mode transition becomes easier, although this is a non-linear process. Fuel droplets and liquid films with different initial sizes are investigated to understand the size effect. In addition, for the same ambient temperature and pressure, the smaller the normalized specific heat transfer surface area of the fuel is, the easier the mode transition of evaporation is. A correlation was proposed to compare the possibility of mode transition of evaporation for single- and multi-component fuels.

Volumetric element with vector approximation of the desired values for nonlinear calculation of the shell of rotation

The usage of traditional approximating functions directly to the desired displacement vector of the internal point of a finite element to determine it through nodal unknowns in the form of displacement vectors and their derivatives is described. To analyze the stress state of a geometrically non-linearly deformable shell of rotation at the loading step, the developed algorithm for forming the stiffness matrix of a hexagonal finite element with nodal values in the form of displacement increments and their derivatives was used. To obtain the desired approximating expressions, the traditional interpolation theory is used, which, when calculated in a curved coordinate system, is applied to the displacement vector of the internal point of a finite element for its approximation of class C(1) through nodal displacement vectors and their derivatives. For the coordinate transformation, expressions of the bases of nodal points are obtained in terms of the basis vectors of the inner point of the finite element. After the coordinate transformations, approximating expressions of class C(1) are found for the components of the displacement vector of the internal point of the finite element, leading in a curved coordinate system to implicitly account for the displacement of the finite element as a rigid whole. Using calculation examples, the results of the developed method of approximation of the required values of the FEM with significant displacements of the structure as an absolute solid are obtained.

Reformulation of a phenomenological model for symmetric rate-independent hysteresis

The present paper enhances, both theoretically and numerically, a recent uniaxial phenomenological model aiming to reproduce complex hysteretic behaviors of seismic isolation devices, including steel- and fiber-reinforced elastomeric bearings, presenting smooth hysteresis loops with hardening and/or softening regions. The investigated constitutive model is based on five parameters that can be directly related to the experimentally observed hysteresis loops. Moreover, because of its analytical nature, the presented formulation is capable of computing in closed form the generalized response relevant to any displacement increment starting from a known equilibrium state. Hence, differently from the original differential formulation of the investigated model as well as from popular materials such as the celebrated Bouc–Wen, the presented formulation does not require any iterative strategy for computing the hysteretic force. Finally, the investigated model is validated by numerical simulations compared with experimental tests selected from the literature.

Mechanical fracture parameters of hemp fibre reinforced cement-based composites with recycled aggregate

This paper aims to evaluate the effect of replacement of aggregate by recycled one on fracture response of selected composites. These are hemp fibre reinforced cement-based composites. Four different mixtures were prepared: in reference one, the only natural aggregate was used whereas in the other three mixtures, the natural aggregate was replaced by recycled one in the amount of 10, 25 and 50 %, respectively. All mixtures contained hemp fibres with a length of 10 mm in the dosage of 1 % by volume. In order to determine the selected mechanical fracture characteristics of the investigated composites, three-point bending fracture tests were carried out on prismatic specimens with nominal dimensions 40 × 40 × 160 mm3 provided with an initial notch. During the whole course of the testing, the loading process was governed by a constant displacement increment of 0.02 mm/min. The vertical displacement (midspan deflection) was measured using the inductive sensor mounted on a special measurement frame placed on the specimens. The fracture tests were terminated when the midspan deflection reached 0.5 mm. The mechanical fracture parameters were obtained through a direct evaluation of the fracture test data via the effective crack model and the work-of-fracture method. The paper shows that composites with a higher dosage of recycled aggregate (25 and 50 wt%) achieve similar values of mechanical fracture properties, so this replacement can be recommended.

Effect of Various Rainfall Conditions on the Roadside Stabilisation of Slopes in Gippsland

A distinctive slope stabilisation method that integrates two well-developed methods for slope stabilisation is analysed in this paper. The slope stabilisation method utilises embedded piles and geogrid-reinforced retaining walls with gabion basket wall facing. To study the effect of this integrated slope stabilisation method on the stability of the slope under the negative impacts of rainfall, a three-dimensional finite element model with fluid–solid coupling is adopted to indicate the rainfall infiltration process and investigate the corresponding slope responses. The shear strength reduction method is applied after fluid–solid coupling analysis to investigate the impact of various rainfall intensities and rainfall patterns on the stability of slopes with different configurations. The results from the comparison of slope responses among various configurations indicate that under the highest rainfall intensity, the integrated method improves the stability of the slope up to 41.2% and restrains the displacement increment of the road edge to a maximum of 12.5 mm. The most critical rainfall pattern for the stability of the slope has also been recognised in terms of the factor of safety and the variation in the negative pore-water pressure of the slope. The numerical results indicate that the back-loaded rainfall pattern always yields the lowest factor of safety and induces the highest loss of matric suction, which can be 23 kPa at the toe of the slope. Moreover, a comparison between two construction scenarios under various rainfall intensities was also conducted, which demonstrates that the reinforced filled slope configuration is preferable when the site conditions permit.

Energy-based method for the assessment of the cumulative slip increment in frictional contacts subjected to cyclic loadings

The cumulative slip phenomenon is often observed as a limit state in mechanical assemblies involving interference or press-fits and subjected to cyclic thermomechanical loadings. In engineering structural applications, it may prove very difficult to annihilate completely the occurrence of this phenomenon by targeting a slip-shakedown limit state, due to design and other mechanical constraints. Consequently, the cumulated relative slip magnitude on the contact interface, after a given of applied cycles, should be anticipated to prevent any unexpected contact with other mechanical components that may result in seizure or affect the normal structural behaviour of the assembly. In this paper, a novel theoretical approach is proposed to derive the cumulative relative slip increment from the frictional dissipated energy per cycle. In particular, two independent methods – one based on the rigid body slip property and the other using the unified energy-based approach from fatigue crack growth theory – are considered here to determine the same expression of the expected quantity. The obtained formula is evaluated through various analytical examples with a special focus on bushing migration in interference-fit assemblies. It is shown, in each case, to be in perfect agreement with the incremental displacement calculation of the cumulative slip increment when the cumulative slip phenomenon occurs.

Increasing displacement range in 3D printed compliant joints via bio-inspired slot patterns: An exploratory study

Compliant joints own their motion performance to three main aspects: base material, geometrical design, and dimensions. When aiming to increase their motion range without affecting the overall assembly of the system in which they are employed, modifying the design or dimensions is not appropriate anymore. To overcome this, the current work presents a novel strategy for increasing the motion range of the split tube flexural pivots joint based on removing material from the complaint joint using two specific bio-inspired patterns. These bio-inspired patterns are based on the shells encountered in Testudines (tortoise) and Dasypodidae (armadillo). Then, these patterns were parametrized, and their effective mechanical properties evaluated on 3D printed samples. Features of the flexible region of the flexural pivot joint were varied to identify the conditions in which the motion range increases. A factorial analysis was made to obtain the angular displacement response based on the determined parameters, which depend on the flexible region features. The use of these patterns successfully demonstrated the reduction in stiffness of the joints, obtaining increments in displacements twice in the stiffest case and 4.25 times in the most flexible one. Secondary displacements were also analyzed. Displacements measured were characterized via computationally analyzed images and recordings. Finally, the mechanical properties measured were compared to computationally predicted properties via Finite Element Models. Predictions resulted in good agreement with the experimental measurements with errors below 10% in most cases and up to 15% in the worst cases. These were attributed to manufacturing defects in the samples.