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Recently, cellular lattice structures are gaining research attention due to their lightweight and high energy absorption. Interpenetrated lattice structure is a combination of two or more regular lattices with the same volume and without any contact at the unit level. The interpenetrated tessellated lattice (I-PTL) structures are better known for load sharing and energy absorption applications. In the current research, regular unit cell lattices such as cubic, beam lattice, body-centered cubic, and octahedron are considered to fabricate penetrated and interpenetrated cellular lattice structures and tested for energy absorption on quasi-static loading. These structures were fabricated using a Vat polymerization three-dimensional printer and tested as per the American Society for Testing and Materials (ASTM) standards, and the results were compared with numerical simulation using ANSYS. The penetrated tessellated lattice structural and I-PTL behavior deliver energy transfer controlled by the surface and solid joint interactions. The enhancement in mechanical properties is observed with the controllable compliance and specific energy absorption of the lattice structure.

Energy absorption is a key performance criterion for several engineering structures. Lightweight lattice structures are better suited for this purpose. The convolute design patterns that exist in nature are proven effective for several engineering applications. In this paper, a George lily flower leaf is considered to build a novel 3D open lattice pattern for specific energy absorption (SEA) purposes. A multi-cellular specimen is designed and fabricated using Vat photopolymerization 3D printing process. Quasi-static compression tests have been conducted and the performance of proposed structure is compared with 2.5D closed thin-walled structures and found the proposed 3D open lattice structure has shown significant improvement in SEA over other thin-walled structures.

PurposeThis research work aims to determine the maximum load a thermoplastic gear can withstand without the occurrence of extended contact. The extended contact of polymer gears is usually overlooked in basic design calculations, although it considerably affects the gear's load-carrying ability. Although various researchers highlighted the phenomenon, an extensive investigation of the extended contact behaviour is limited. Hence the work aims to investigate the premature and extended contact behaviour of thermoplastic gears and its effect in the gear kinematics, bending stiffness, stresses induced and the roll angle subtended by the gear pair.Design/methodology/approachThe work uses finite element method to perform quasi-static two-dimensional analysis of the meshing gear teeth. The FE model was developed in AutoCAD and analysed using ANSYS 19.1 simulation package. A three-dimensional gear model with all the teeth is computationally intensive for solving a static analysis problem. Hence, planar analysis with a reduced number of teeth is considered to reduce the computational time and difficulty.FindingsThe roll angle subtended at the centre by the path of approach is higher than the path of recess because of the increased load sharing. The contact stress profile followed a unique R-F-R-F pattern in the premature and extended contact regions due to the driven tip-driver flank surface contact. A non-dimensional parameter was formulated correlating the young's modulus, the load applied and deflection induced that can be utilised to predict the occurrence of premature and extended contact in thermoplastic gears.Originality/valueThe gear rating standards for polymer gears are formulated from the conventional metal gears which does not include the effect of gear tooth deflection. The work attempts to explain the gear tooth deflection for various standard thermoplastics and its effect in kinematics. Likewise, a new dimensionless number was introduced to predict the extended contact that will help in appropriate selection of load reducing the possibility of wear.

Manufacturing industries are aiming to reduce weight of the products at uncompromised structural performance. Topology optimization is a reliable technique to achieve the improved topologies at minimum material utilization. Nature is known as best manufacturer to bring complex structures with the existed materials. The present research is aimed to identify the constructal design patterns that existed in nature through topology optimization. Structures with different boundary conditions are modeled and optimized using Solid Isotropic Material Penalization (SIMP) method through ANSYS software under structural and thermal loading conditions. The performed case studies revealed that the optimized topologies are very close to the nature inspired patterns.

Two-dimensional Finite Element Analysis is frequently utilized to determine the behaviour of gear contact stress due to its computational time and higher efficiency. Based on the gear tooth-to-face width ratio, either plane stress or plane strain was selected in the investigations. However, the existing investigations failed to explain the above selection criteria. Thus, the present work attempted to do detailed contact stress investigations for all thermoplastic gears using 3D FEA and compared them with 2D FEA. Based on the criteria, the face widths of 5 and 20 mm were selected during the 3D analyses, replicating the plane stress and plane strain conditions of the 2D analysis. Contact stress variations with respect to face width were extracted at 10 distinct locations. For both 5 and 20 mm gears, higher contact stresses were obtained on gear edges, whereas lesser contact stresses were in the centre regions of the gear. For all the analysed thermoplastic gears, 5 and 20 mm face-width gears exhibited plane stress conditions. Subsurface and surface stress was detected during 3D and 2D analysis for both gears. For PP, the maximum contact stress occurred at the lowest depth value of 0.15–0.155 mm, and PC exhibited maximum contact stress at 0.275–0.28 mm depth. A dimensionless ratio of proportional limit – to – young’s modulus was introduced to predict the maximum contact stress depth for the thermoplastic gears. And it was observed that the ratio is directly proportional to the maximum contact stress depth value.

Short fibre reinforced thermoplastics are being considered for light- and medium-duty engineering applications because of their improved mechanical strength combined with cost-effective advantages. In recent years, the carbon nanotube reinforced thermoplastics are being preferred over the short fibre reinforced thermoplastics because of the absence of directional shrinkage characteristics, directional mechanical and tribological properties. In this work, 1 wt% carbon nanotube–polypropylene material was injection-moulded to spur gears and evaluated for the durability using in-house developed power absorption gear test rig. During testing, the net surface temperature of the test gears and in-line torque available at the driver and driven shafts were continuously measured. The measured torque was used to evaluate the transmission efficiency of the test-steel gear pair. The measured net surface temperature was correlated with the gear failure mode. Test gears were run up to failure or up to 8.6 × 105 cycles, whichever occurred first. Worn-out gear tooth surfaces were observed using an optical and scanning electron microscope to understand the wear mechanism. In the initial stage of service, test gears exhibited less wear near the pitch region compared to the tip and root regions. This behaviour is due to the maximum sliding velocities at the tip and root regions compared to the pitch region. The carbon nanotube–polypropylene gears exhibited lower surface temperature (5−10 ℃), improved service life (30%−80%) and higher transmission efficiency (1−1.5%) compared to the polypropylene gear.

In the recent years, utilization of non-standard gears have increased due to the improved load carrying capacity and improved durability. However, these non standard gears are manufactured by non-conventional manufacturing process including wire cut electric discharging machining (WEDM). Standard gears are manufactured by conventional machining process, hobbing. This work reported the performance of injection molded polymer gear paired with a steel gear manufactured by conventional hobbing and wire cut electric discharge machining process. WEDM steel gear surface exhibited poor surface topology and higher hardness when compared to that of conventional machined steel gear. Measured net surface temperature of polymer gear at various loads (2-3 Nm) confirmed a temperature rise of 10-15°C when paired with WEDM gear compared to that of hobbed and ground gear. Polymer gear paired with WEDM exhibited inferior fatigue performance when compared to the polymer gear paired with hobbed and ground gear.

Polymer gears can replace metallic gears in many engineering applications; however, thermal sensitive mechanical properties of the polymers limit its wide application. Gear tooth surface interaction as well as material hysteresis generates heat in the gear operation. There have been many attempts to improve the gear performance by design modifications as well as with new materials to withstand against thermal damages. In this work, compressed air cooling method is adopted to improve the wear resistance of injection molded polypropylene spur gears. For the chosen gear and test conditions, continuous measurement of gear surface temperature confirmed that compressed air cooling lowers the temperature up to 15 ℃. Periodical measurement of gear tooth thickness confirms that wear resistance increases up to 100%. Continuous measurements of torque available in driver and driven end confirmed that a 2% increase in transmission efficiency of the gear pair. Test gear tooth surface after a finite number of cycles also confirms the effect of compressed air cooling on wear resistance. Mao model is used to predict the gear surface temperature and found to be in close agreement with experimental results.

The measurement from the indentation process depends on the amount of pile-up or sink-in around the contact impressions. In this paper, finite element concept is utilized to study the pile-up and sinkin behaviour for the wide range of materials with different young\'s modulus, yield stresses, strain-hardening exponents and co-efficient of friction values. The exact indentation model is created by using the two dimensional axisymmetrical model for simulating the spherical indentation process on the lines of Taljat and Pharr (2004) work. The result shows that during spherical indentation process the amount of pile-up is greatly influenced by the strain hardening exponents in addition to other material properties and depth of penetration. The numerical results from the finite element analysis are also validated using the exact multilinear material properties obtained from the tensile testing for the materials like mild steel, brass and aluminium.

Asymmetric tooth profiles with different pressure angle at drive and coast sides are being considered to enhance the gear performance. In this work, experimental investigations were carried out to evaluate the fatigue and wear performance of injection moulded asymmetric polypropylene spur gears using the power absorption gear test rig. Test gears exhibited wear failure at lower loads and tooth bending failure at higher loads. Periodic measurement of gear tooth thickness and weight loss was carried out to quantify gear tooth wear. Sudden rise in measured gear temperature and failure morphology confirmed bending failure at higher loads. The results revealed that asymmetric gears exhibited inferior performance than that of symmetric gears. This behaviour is due to the reduced contact ratio, increased normal load and increased height at which worst load act on the gear tooth profile for the considered test conditions.