Calculation of stress intensity factors for an interfacial crack

Ph.D.SN Atlur

Stress analysis of a rectangular implant in laminated composites using 2-D and 3-D finite elements

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992.Includes bibliographical references (leaves 235-237).by Wai Tuck Chow.M.S

Soft-stable interface in grasping multiple objects by wiring-tension

Efficiently manipulating objects in a group state poses an emerging challenge for soft robot hands. Overcoming this problem necessitates the development of hands with highly stable structures to bear heavy loads and highly compliant designs to universally adapt to various object geometries. This study introduces a novel platform for the development of robot hands aimed at manipulating multiple objects in each trial. In this setup, the objects come into soft contact with an elastic wire affixed to the finger skeletons. This combination results in a harmonious hybrid finger, inheriting both the soft, flexible properties of the wire and the robust stability provided by the finger skeleton. To facilitate this approach, a theoretical model was proposed to estimate the kinematics of manipulating multiple objects using wiring-based fingers. Based on this model, we designed a hybrid gripper comprising two wiring-based fingers for conducting experimental evaluations in manipulating four groups of samples: a pair of bevel gears, a pair of bevel gears plus a pneumatic connector, a pair of glue bottles, and a pair of silicon bottles. The experimental results demonstrated that our proposed gripper reached good performance with high success rates in durability tests conducted at various lifting velocities and high adaption with objects in soft-friendly ways. These findings hold promise for efficiently manipulating multiple complex objects in each trial without the need for complex control systems.Agency for Science, Technology and Research (A*STAR)Published versionThis work is partly supported by the Schaefer Hub for Advanced Research at NTU, under the ASTAR IAF-ICP Programme ICP1900093

Increasing the interlayer strength of 3D printed concrete with tooth-like interface: an experimental and theoretical investigation

In 3D concrete printing, layer interface and interlayer notch are generated by the layer-by-layer process. Therefore, the 3D printed concrete is anisotropic with the interlayer strength lower than the strengths measured in the other two directions. In order to adequately address this issue, tooth-like layer interface is adopted in the present study for higher interlayer strength. It is found that the tooth-like interface with tooth angle of 45° increases the interlayer tensile and shear strengths by 294% and 89% respectively, and shifts the failure mode from pure adhesive failure to a mixture of adhesive and cohesive failures. Moreover, a theoretical model is developed for the relationship between the interlayer strength and interfacial tooth angle, and then validated by the experimental data with a relative error of about 5%. By this model, further design and optimization of the interfacial geometry would be possible, for higher interlayer strength subject to different parameters and conditions of 3D concrete printing.Nanyang Technological UniversityNational Research Foundation (NRF)Published versionThe authors acknowledge the financial and technical supports from National Research Foundation of Singapore, SempCorp Design & Construction Pte Ltd., and Singapore Centre for 3D Printing (SC3DP). This work is also supported by Young-scientist Research Cultivation Program of South China Normal University under Grant 21KJ15, in part by the Guangdong Basic and Applied Basic Research Project under Grant 2021A1515011171, and in part by the National Natural Science Foundation of China under Grant 62076103

Universally grasping objects with granular-tendon finger: principle and design

Nowadays, achieving the stable grasping of objects in robotics requires an increased emphasis on soft interactions. This research introduces a novel gripper design to achieve a more universal object grasping. The key feature of this gripper design was a hybrid mechanism that leveraged the soft structure provided by multiple granular pouches attached to the finger skeletons. To evaluate the performance of the gripper, a series of experiments were conducted using fifteen distinct types of objects, including cylinders, U-shaped brackets, M3 bolts, tape, pyramids, big pyramids, oranges, cakes, coffee sachets, spheres, drink sachets, shelves, pulley gears, aluminium profiles, and flat brackets. Our experimental results demonstrated that our gripper design achieved high success rates in gripping objects weighing less than 210 g. One notable advantage of the granular-tendon gripper was its ability to generate soft interactions during the grasping process while having a skeleton support to provide strength. This characteristic enabled the gripper to adapt effectively to various objects, regardless of their shape and material properties. Consequently, this work presented a promising solution for manipulating a wide range of objects with both stability and soft interaction capabilities, regardless of their individual characteristics.Agency for Science, Technology and Research (A*STAR)Published versionThis research is supported by the Agency for Science, Technology and Research (A*STAR) under its IAF-ICP Programme I2001E0067 and the Schaeffler Hub for Advanced Research at NTU. Nguyen was fully supported by Japan Society for Promotion of Science (JSPS PD program) and JSPS Kakenhi Grants No. 20J14910

Design of novel nozzles for higher interlayer strength of 3D printed cement paste

In this study, novel nozzles for cement paste 3D printing are designed and optimized for higher interlayer strength via experiment and volume-of-fluid (VOF) based simulation, in terms of various outlet shapes and two nozzle components namely the interface shaper and the side trowel. These nozzles are evaluated experimentally and theoretically based on their performances in the specimen interlayer strength, interfacial shear stress, and cross-sectional geometry. It is concluded that the “Cir3” and the “Kidney” outlet shapes achieve the best performance with the paste water-cement (w/c) ratio ranging from 0.21 to 0.23, subject to the nozzle stand-off distance of 12 mm and printing speed of 60 mm/s. In addition, the interface shaper and the side trowel are able to further enhance the interlayer strength significantly by up to 2 times, through optimization of the interfacial geometry and minimization of the interlayer notch of 3D printed cement paste. It is also confirmed that the optimal nozzle varies with the w/c ratio of cement paste due to different notch depths that are generated, such that nozzle optimization is required along with material development for cement paste 3D printing

Bioinspiration and Biomimetic Art in Robotic Grippers

The autonomous manipulation of objects by robotic grippers has made significant strides in enhancing both human daily life and various industries. Within a brief span, a multitude of research endeavours and gripper designs have emerged, drawing inspiration primarily from biological mechanisms. It is within this context that our study takes centre stage, with the aim of conducting a meticulous review of bioinspired grippers. This exploration involved a nuanced classification framework encompassing a range of parameters, including operating principles, material compositions, actuation methods, design intricacies, fabrication techniques, and the multifaceted applications into which these grippers seamlessly integrate. Our comprehensive investigation unveiled gripper designs that brim with a depth of intricacy, rendering them indispensable across a spectrum of real-world scenarios. These bioinspired grippers with a predominant emphasis on animal-inspired solutions have become pivotal tools that not only mirror nature’s genius but also significantly enrich various domains through their versatility

Large-Scale Piezoelectric-Based Systems for More Electric Aircraft Applications

A new approach in the development of aircraft and aerospace industry is geared toward increasing use of electric systems. An electromechanical (EM) piezoelectric-based system is one of the potential technologies that can produce a compactable system with a fast response and a high power density. However, piezoelectric materials generate a small strain, of around 0.1–0.2% of the original actuator length, limiting their potential in large-scale applications. This paper reviews the potential amplification mechanisms for piezoelectric-based systems targeting aerospace applications. The concepts, structural designs, and operation conditions of each method are summarized and compared. This review aims to provide a good understanding of piezoelectric-based systems toward selecting suitable designs for potential aerospace applications and an outlook for novel designs in the near future

A 3D printing-enabled artificially innervated smart soft gripper with variable joint stiffness

The manufacturing industry has witnessed advancements in soft robotics, specifically in robotic grippers for handling fragile or irregular objects. However, challenges remain in balancing shape compliance, structural rigidity, weight, and sensor integration. To address these limitations, a 3D-printed multimaterial gripper design is proposed. This approach utilizes a single, nearly fully automated 3D printing process to create a universal gripper with almost no assembly work. By processing functional polymer, polymer nanocomposite, and metal wire simultaneously, this technique enables multifunctionality. The gripper achieves different gripping configurations by adjusting joint stiffness through Joule heating of conductive polylactic acid material, ensuring shape conformance. Embedded metal wires, created using an in-house wire embedding technique, form reliable high-current-loading interconnections for the conductive joints acting as the heater. Additionally, an integrated soft sensor printed in thermoplastic polyurethane (TPU) and conductive TPU detects compression levels and discerns handled samples. This study showcases the potential of 3D multimaterial printing for on-demand fabrication of a smart universal gripper with variable stiffness and integrated sensors, benefiting the automation industry. Overall, this work presents an effective strategy for designing and fabricating integrated multifunctional structures using soft, rigid, and conductive materials, such as polymer, polymer nanocomposite, and metal through multimaterial 3D printing.Agency for Science, Technology and Research (A*STAR)Nanyang Technological UniversityThis research was supported by the Agency for Science, Technology and Research(A*STAR) under its IAF-ICP Programme Grant No. I2001E0067 and the Schaeffler Hub for Advanced Research at NTU