Mechanical Properties Of Objects Research Articles

Undulations in tubular origami tessellations: A connection to area-preserving maps

Origami tessellations, whose crease pattern has translational symmetries, have attracted significant attention in designing the mechanical properties of objects. Previous origami-based engineering applications have been designed based on the “uniform-folding” of origami tessellations, where the folding of each unit cell is identical. Although “nonuniform-folding” allows for nonlinear phenomena that are impossible through uniform-folding, there is no universal model for nonuniform-folding, and the underlying mathematics for some observed phenomena remains unclear. Wavy folded states that can be achieved through nonuniform-folding of the tubular origami tessellation called a waterbomb tube are an example. Recently, the authors formulated the kinematic coupled motion of unit cells within a waterbomb tube as the discrete dynamical system and identified a correspondence between its quasiperiodic solutions and wavy folded states. Here, we show that the wavy folded state is a universal phenomenon that can occur in the family of rotationally symmetric tubular origami tessellations. We represent their dynamical system as the composition of the two 2D mappings: taking the intersection of three spheres and crease pattern transformation. We show the universality of the wavy folded state through numerical calculations of phase diagrams and a geometric proof of the system’s conservativeness. Additionally, we present a non-conservative tubular origami tessellation, whose crease pattern includes scaling. The result demonstrates the potential of the dynamical system model as a universal model for nonuniform-folding or a tool for designing metamaterials.

Feasibility of nondestructive testing using transient vibrations excited by acoustic radiation force

The use of the transient response in vibro-acoustography to image the mechanical properties of objects was investigated. Verification of the proposed method using aluminum foil showed that transient vibrations are generated by a step-function acoustic radiation force exerted on an object. These vibrations can be used to obtain the frequency characteristics of the object. The proposed method was applied to the one-dimensional imaging of aluminum foil with various mechanical properties. This method captured the distributions of the vibrational amplitude and resonant frequencies, which vary according to local mechanical properties. These results show that the proposed method effectively visualizes the mechanical properties of objects.

Hand explorations are determined by the characteristics of the perceptual space of real-world materials from silk to sand

Perceiving mechanical properties of objects, i.e., how they react to physical forces, is a crucial ability in many aspects of life, from choosing an avocado to picking your clothes. There is, a wide variety of materials that differ substantially in their mechanical properties. For example, both, silk and sand deform and change shape in response to exploration forces, but each does so in very different ways. Studies show that the haptic perceptual space has multiple dimensions corresponding to the physical properties of textures, however in these experiments the range of materials or exploratory movements were restricted. Here we investigate the perceptual dimensionality in a large set of real materials in a free haptic exploration task. Thirty-two participants actively explored deformable and non-deformable materials with their hands and rated them on several attributes. Using the semantic differential technique, video analysis and linear classification, we found four haptic dimensions, each associated with a distinct set of hand and finger movements during active exploration. Taken together our findings suggest that the physical, particularly the mechanical, properties of a material systematically affect how it is explored on a much more fine-grained level than originally thought.

Exploratory study on the perception of additively manufactured end-use products with specific questionnaires and eye-tracking

The outreach of application domains for Additive Manufacturing (AM) is expanding and end-use products represent their next frontier. Contextually, design methods are developed for exploiting the unique AM capabilities. They largely benefit from the knowledge about peculiarities, constraints and technical performances of the various AM processes and devices. However, while the mechanical properties of objects created with AM are widely studied, there is lack of research on emotional and perceptual aspects. This is of great relevance in the mentioned perspective of employing AM for end-use products. The paper aims to elucidate which perceptual mechanisms are activated when a user observes an object generated with AM instead of traditional technologies. An experiment has involved 43 participants who have evaluated ten pairs of objects, constituted by a commercial product and a replica made with Fused Deposition Modelling. Testers have answered a questionnaire, as well as their visual behavior has been recorded with eye-tracking glasses. Based on results, replicas suffer from poor attractiveness and especially low perceived quality. They have also given rise to more careful exploratory behaviors because they likely require a lengthier examination for testers’ assessment or they arouse curiosity. It can be inferred that Fused Deposition Modelling does not exhibit sufficient accuracy to achieve acceptability with reference to everyday products. Nevertheless, it is also deemed that limited improvements might compensate for the perception of technical unsuitability this technology engenders. This can be verified by repeating the experiment with more sophisticated and precise AM devices.

Microstructure and Mechanical Properties of Objects Prepared by Selective Laser Melting of AKD12 Powder

The morphology and elemental composition of Al–12% Si powder grade AKD12 of three fractions are studied. Powder is prepared in an original molten metal gas spraying unit UR-9 in a high-purity nitrogen atmosphere. Results are provided for measurement of mechanical properties, a study of outer surface morphology and the failure surface of objects prepared by selective laser melting from AKD12 powder fraction less than 45 μm. It is shown that the mechanical properties of these objects surpass these indices for analogs produced overseas, i.e., ultimate strength σu = 245 MPa with relative elongation δ = 12%.

Inferring Object Properties with a Tactile-Sensing Array Given Varying Joint Stiffness and Velocity

Whole-arm tactile sensing enables a robot to sense contact and infer contact properties across its entire arm. Within this paper, we demonstrate that using data-driven methods, a humanoid robot can infer mechanical properties of objects from contact with its forearm during a simple reaching motion. A key issue is the extent to which the performance of data-driven methods can generalize to robot actions that differ from those used during training. To investigate this, we developed an idealized physics-based lumped element model of a robot with a compliant joint making contact with an object. Using this physics-based model, we performed experiments with varied robot, object and environment parameters. We also collected data from a tactile-sensing forearm on a real robot as it made contact with various objects during a simple reaching motion with varied arm velocities and joint stiffnesses. The robot used 1-nearest-neighbor (1-NN) classifiers, hidden Markov models (HMMs), and long short-term memory (LSTM) networks to infer two object properties (hard versus soft and moved versus unmoved) based on features of time-varying tactile sensor data (maximum force, contact area, and contact motion). We found that, in contrast to 1-NN, the performance of LSTMs (with sufficient data availability) and multivariate HMMs successfully generalized to new robot motions with distinct velocities and joint stiffnesses. Compared to single features, using multiple features gave the best results for both experiments with physics-based models and a real-robot.

Three-Dimensional (3D) Printing of Polymer-Metal Hybrid Materials by Fused Deposition Modeling.

Fused deposition modeling (FDM) is a three-dimensional (3D) printing technology that is usually performed with polymers that are molten in a printer nozzle and placed line by line on the printing bed or the previous layer, respectively. Nowadays, hybrid materials combining polymers with functional materials are also commercially available. Especially combinations of polymers with metal particles result in printed objects with interesting optical and mechanical properties. The mechanical properties of objects printed with two of these metal-polymer blends were compared to common poly (lactide acid) (PLA) printed objects. Tensile tests and bending tests show that hybrid materials mostly containing bronze have significantly reduced mechanical properties. Tensile strengths of the 3D-printed objects were unexpectedly nearly identical with those of the original filaments, indicating sufficient quality of the printing process. Our investigations show that while FDM printing allows for producing objects with mechanical properties similar to the original materials, metal-polymer blends cannot be used for the rapid manufacturing of objects necessitating mechanical strength.

Use of Centrifugal Electroslag Casting for Producing Cold-Resistant Steel Grade Ring Blanks of Flange Objects

A method is considered for preparing objects of the flange type made of steel of grades 09G2S and 10G2 by centrifugal electroslag casting (CESC). Results are given for chemical analysis and mechanical properties of objects prepared by different methods. The advantage of CESC technology is demonstrated making it possible to prepare cast blanks that with respect to production parameters and physicomechanical properties correspond to the GOST and TU for the given forms of steel having configuration and dimensions close to a finished object.

Methods of reconstructing complex multi-structural anatomical objects with RP techniques

Abstract This article presents reconstruction methods applied to a (geometrically and physically) complex structural object with the use of RP and RT techniques. The methods are innovative due to their hybrid - multi-model and multi-material - approach to reconstruction, as well as the application of multiple technologies. An experimental analysis was conducted to verify the feasibility of rapid prototyping (RP) techniques in the reconstruction of complex internal structures using materials of diverse properties. Some RP techniques offer the possibility of discriminating between diverse objects through the use of different colours. Such models are well-suited for diagnostic purposes, for better visualisation of complex clinical problems, pathological alterations, etc. Nevertheless, they fail to fully reflect physical and mechanical properties of objects, which renders them useful in experimental analysis only to a limited extent. Their basic drawback is that they merely reflect geometrical features of the examined object. The methods discussed in the present article enable modelling multi-object structures in a single process based on the PolyJet Matrix technology and materials of different physical properties by means of a hybrid method. The article also describes the process of modelling complex anatomical structures of soft tissues and bones using models of the maxilla and the mandible as examples. The study is based on data acquired through standard computed tomography (CT). In addition, the article addresses selected aspects of CT acquisition, generation of numerical models composed of several anatomical structures (objects) and fabricating physical multi-object models.

Synthesis of Vibration Damping Control Systems based on the Identified Model of a Mechanical Construction at Broadband Disturbance Influence

changing of certain types of energy into other types in machines and mechanisms, the transformation of movement forms and carrying out certain working processes inevitably causes the emergence of variable forces and vibration-causing momentum. Vibration control and management are important tasks in aerospace field. This thesis solves the problem of the development of an effective control system based on the active method used for vibration reduction in a mechanical construction of a cantilever fixed metal plate broadband disturbance lab device. In the system synthesis process a carry out structural and parametric identification of the mathematical model of the controlled object using experimental data. LabVIEW 10.0 development environment and FPGA hardware technology from National Instruments were used to create a spectrum analyzer measurement system, which allows solving problems of experimental acquisition and identification of the dynamic properties of mechanical objects. With the help of MATHLAB environment mathematical apparatus and Optimization and Control System Toolbox packages, a mathematical model of the control object, regulators' synthesis was built; their optimal parameters were searched for, and system operation with different object structures and regulators (PID, LQG) was modeled. Keywordssystem, regulator, PID, LQG, vibration, control object, mathematical model, LabVIEW, MATHLAB.

Perceptually salient haptic rendering for enhancing kinesthetic perception in virtual environments

Kinesthetic or dynamic touch involves the use of muscle sensitivity to perceive mechanical properties of objects that are gripped in the hand and wielded in space. Many previous studies with real objects have investigated the mechanical properties that underlie human haptic perception. Few virtual environments, however, have systematically incorporated the relevant mechanical parameters underlying kinesthetic perception. In this study, the ability of a haptic device to render kinesthetic information regarding the inertial properties of virtual objects was tested. Results suggest that users were able to perceive length of rendered virtual objects via the haptic device. Further, users can be trained using the haptic device to increase sensitivity to specific mechanical parameters (like inertia) that are perceptually salient in perceiving properties of rendered objects. The primary implication of this finding is that rendering kinesthetic parameters and employing feedback in a systematic manner may increase the realism of virtual environments and also improve haptic perception.

A study of the mechanical properties of objects built through weld-deposition

Hybrid layered manufacturing, an automatic layered manufacturing process for metallic objects, combines the best features of two well-known and economical processes, namely, weld-deposition and milling. A study of the mechanical properties like hardness and tensile strength of objects made through hybrid layered manufacturing is presented in this article. It was found that the interior matrix has negligible hardness variations in all directions. The tensile strength of the matrix displays negligible variations in the horizontal plane. However, the same for the vertical direction initially was found to be slightly lower, but this could be rectified by increasing the weld-deposition current. The ability of hybrid layered manufacturing to make composite material matrix with good material bonding has also been demonstrated. These studies help in understanding and controlling the anisotropic behavior of objects built using weld-deposition–based rapid prototyping and manufacturing techniques.

Intermanual transfer of sensorimotor memory for grip force when lifting objects: The role of wrist angulation

To investigate the mechanisms underlying the intermanual transfer of sensorimotor memory when lifting an object. Twenty healthy subjects grasped and lifted an object with constant mechanical properties with the right hand (RH) first and then with the left hand (LH). Ten of the subjects lifted the object with the RH in a regular wrist angulation (WA), followed by lifts with the LH in a regular WA. The remaining 10 subjects lifted the object with the RH in a hyper-flexed WA, followed by lifts with the LH in a regular WA. Subjects generated greater peak grip force (GF) rates, grip and lift forces when lifting the object with the wrist in a regular WA compared to lifts with the wrist in hyper-flexion. Importantly, subjects transferred the predictive scaling of GF from the RH to the LH, regardless of the WA. Biomechanical properties of the object do not seem to be used by the CNS as a first line information to evaluate GF when handling an object or transferring information about the grasp to the opposite hemisphere. The predictive scaling of GF rather reflects an internal sense of effort than an internal representation of the mechanical object properties.

Interhemispheric Transfer of Predictive Force Control During Grasping in Cerebellar Disorders

When an object is repeatedly grasped and lifted, the balance between grip force (normal to the object's surface) and lift force (tangential to the object's surface) is programmed according to the mechanical object features within a few lifts. Information related to the mechanical object properties is easily transferred in between both hands, and the cerebellum may play an essential role for the integration and generalization of this information. Recently, we have shown that the transfer of weight-related information in between both hands is impaired in cerebellar degeneration (Nowak et al., Neuropsychologia, 43:20-27, 2005). Here, we investigated the role of the cerebellum for the inter-manual transfer of friction-related information. Healthy subjects and patients with either focal or generalized cerebellar disorders first repeatedly lifted an object with one hand followed by a series of lifts of the same object with the opposite hand. The experiments were performed with the object's grip surfaces covered with either silk or sandpaper. Patients and healthy subjects scaled grip force differentially to surface friction within a few lifts. However, the ability to transfer friction-related information from one hand to the other was disturbed in cerebellar patients. We interpret these data within the recent concept that the cerebellum is essential for the rapid integration and generalization of mechanical object features in between both hemispheres when handling objects in the environment.

Nanonewton force-controlled manipulation of biological cells using a monolithic MEMS microgripper with two-axis force feedback

As mechanical end-effectors, microgrippers enable the pick–transport–place of micrometer-sized objects, such as manipulation and positioning of biological cells in an aqueous environment. This paper reports on a monolithic MEMS-based microgripper with integrated force feedback along two axes and presents the first demonstration of force- controlled micro-grasping at the nanonewton force level. The system manipulates highly deformable biomaterials (porcine interstitial cells) in an aqueous environment using a microgripper that integrates a V-beam electrothermal microactuator and two capacitive force sensors, one for contact detection (force resolution: 38.5 nN) and the other for gripping force measurements (force resolution: 19.9 nN). The MEMS-based microgripper and the force control system experimentally demonstrate the capability of rapid contact detection and reliable force-controlled micrograsping to accommodate variations in size and mechanical properties of objects with a high reproducibility.

Sensorimotor memory for fingertip forces during object lifting: The role of the primary motor cortex

When an object is repetitively lifted, the scaling of grip force is influenced by the mechanical properties of the preceding lift, suggesting the formation of a sensorimotor memory. Similar effects on force scaling are observed when the subsequent lift is performed with the hand opposite to the preceding lift. We used neuronavigated rTMS over the hand area of the dominant primary motor cortex to investigate its role in setting up sensorimotor memory. After ten lifts of a novel object with the dominant hand either rTMS or a period of motor rest commenced, until another set of lifts was performed with either the same or opposite hand. Compared to motor rest, rTMS caused underestimation of the object's weight when given 10 or 30s after the previous set of lifts, but overestimation of the object's weight when applied 60 or 120s after the previous set of lifts, regardless of the hand performing the lift. Our interpretation of the data is that (a) the primary motor cortex is essential for setting up sensorimotor memory related to the mechanical object properties during manipulation and (b) rTMS can induce bidirectional changes of grip efficiency within the dynamics of sensorimotor integration.

High‐frequency repetitive transcranial magnetic stimulation over the hand area of the primary motor cortex disturbs predictive grip force scaling

When we repetitively lift an object, our grip force is influenced by the mechanical object properties of the preceding lift, irrespective of whether the subsequent lift is performed with the same hand or the hand opposite to the preceding lift. This study investigates if repetitive high-frequency transcranial magnetic stimulation (rTMS) over the dominant primary motor cortex affects this relationship. After completion of 10 lifts of an object using the dominant hand, rTMS was applied over the dominant primary motor cortex for 20 s. On the first lift following rTMS, the peak grip force was significantly higher than on the lift preceding rTMS. Moreover, this measure remained elevated throughout the following set of lifts after rTMS. rTMS did not change the peak lift force generated by more proximal arm muscles. The same effect was observed when the lifts following rTMS over the dominant motor cortex were performed with the ipsilateral hand. These effects were not observed when subjects rested both hands on their lap or when a sham stimulation was applied for the same period of time. These preliminary data suggest that rTMS over the sensorimotor cortex disturbs predictive grip force planning.

Grip force behavior during object manipulation in neurological disorders: toward an objective evaluation of manual performance deficits.

The control of prehensile finger forces is an essential feature of skilled manual performance. The basic aspects of healthy grip force behavior have been well documented. In healthy subjects, grip force is precisely adjusted to the mechanical object properties. Grip force is always slightly higher than the minimum necessary to prevent the object from slipping. When we move a hand-held object, grip force is modulated in parallel with movements-induced load fluctuations without an obvious delay. The absence of a temporal delay between grip and load force profiles suggests that the central nervous system is able to predict the load variations before the intended manipulation and consequently regulates grip force in anticipation. Feedback from the grasping fingertips is used to adjust the level of applied fingertip force efficiently to the actual loading requirements. Pathologic grip force control affects the efficiency of produced force and the precision of the temporal coupling between grip and load force profiles. Here, we review the characteristics of pathologic grip force behavior in various neurological disorders. Detailed examination of grip force control is simple and well suited for the objective evaluation of impaired motor function of the hand and its rehabilitation.

Analysis of grip force during object manipulation. Method for the objective measurement of physiological normal and impaired hand function

The control of prehensile finger forces is an essential feature of all skilled manual performance. The basic aspects of healthy grip force control have been well documented within the past two decades. In healthy subjects, grip force is accurately adjusted to the mechanical object properties such as weight, surface friction, and shape: when we move a hand-held object, grip force is modulated in parallel with movement-induced load fluctuations without an apparent temporal delay. At all phases of the movement, grip force is always slightly higher than the minimum necessary to prevent the object from slipping. The absence of a temporal delay between grip and load force profiles implies that the central nervous system is able to predict load variations precisely before the intended manipulation, and consequently regulates grip force in anticipation. Feedback from the grasping fingertips is used to adjust the force level efficiently to the actual load requirements. Pathologic grip force control affects the efficiency of the forces produced and the predictive temporal coupling between grip and load force profiles. Here we demonstrate pathologic grip force control in various neurologic disorders. The analysis of grip force control is simple and highly sensitive for detecting healthy and pathologic motor behaviour. The examination of grip force control is well suited for an objective evaluation of therapy during sensorimotor rehabilitation of deficient hand function.

Memory for fingertip forces: passive hand muscle vibration interferes with predictive grip force scaling.

When subjects repetitively lift an object, the grip force they select is influenced by the mechanical object properties of the preceding lift. Similar effects on grip force scaling are observed whether the subsequent lift is performed with the same hand or the hand contralateral to the preceding lift. Here we demonstrate that passive vibration of the hand muscles involved in the generation of grip force in the interval between two blocks of lifting trials interferes with predictive grip force scaling. Following ten trials in which subjects lifted an object with constant mechanical properties with the dominant hand, muscle vibration was given to the first interosseus and adductor pollicis muscles of the dominant hand during a 10-min rest period. Compared with the last lift preceding vibration, peak rates of grip force increase and peak grip forces were scaled too high during the first lift following vibration whether the lift was made with the dominant or non-dominant hand. Subjects scaled grip force accurately to the object properties within three lifts following vibration. If subjects rested for 10 min after the first ten trials and received no vibration, then there was no significant difference in the peak grip force or its rate of increase between the last lift preceding rest and the first lift following it. We suggest that vibration impairs the memory processes responsible for predictive grip force scaling. Our data are consistent with the recent suggestion that these memory processes are neither specific for a certain motor action nor do they reflect internal representations of mechanical object properties.