Excellent Shock Resistance Research Articles

Micromechanics of kink-band formation in bimetallic layered composites

Bimetallic layered composites with ultrathin layers possess high strength and hardness, and excellent shock resistance and radiation damage tolerance. However, they are prone to deformation localization and readily form kink-bands when subjected to layer parallel compression. Following this, we carried out extensive plane strain finite element finite deformation analyses to understand and rationalize the experimentally observed kink-band formation in these composites. In the calculations, both constituent materials were assumed to follow a rate-independent isotropic elastic-plastic constitutive relation with an ad-hoc thickness dependent yield strength. Our results demonstrate that in these composites, layer refinement, together with the strength differential between the layers of the constituent materials, is sufficient to trigger kink-banding. Importantly, this phenomenon occurs even in the absence of elastically stiff layers, geometrical imperfections (such as waviness of the layers), and extreme plastic anisotropy within the layers. Additionally, we performed parametric studies to investigate the individual effects of layer thickness, strength differential between the two constituent materials, and strain-hardenability of the materials on kink-band formation. The outcomes of our parametric studies reveal that the strain-hardenability of the constituent materials stabilizes the formation of kink-bands. Furthermore, it leads to a transition from the abrupt formation of through-width kink-bands to the onset and propagation of stable inclined wedge-shaped kink-bands, similar to the experimental observations.

Characterization of underwater shock transient effects on naval E-glass biaxial fiberglass laminates: An experimental and numerical method

Non-contact underwater explosions (UNDEX) can cause extremely large deformations on naval composite structures related to heavily nonlinear phenomena. For this reason, for military purposes, used materials must have excellent shock resistance properties. Historically, the underwater shock transient effects on fiberglass laminates are predicted using quasi-static approaches. In this paper, the composite materials are characterized by experimental modal analysis as well as by a comprehensive series of shock tests, whose results are compared with numerical models. Namely, the MIL S 901 D Medium Weight Shock Machine (MWSM) was used to perform dedicated shock tests, in which composite specimens are supported on a special constraining structure designed to create large deflections and providing reproducible results. A dynamic implicit finite element model has been set, validated by modal analysis at first, and then applied to simulate the MWSM test behavior and to predict the structural response of different E-Glass polyester resin laminates. In the end, the complete comparison of numerical results and experimental data is reviewed to validate the modeling strategies for shock design of navy ships.

A New Inspiration in Bionic Shock Absorption Midsole Design and Engineering

Inspired by the performance of the ostrich in terms of loading and high-speed moving ability, the purpose of this study was to design a structure and material on the forefoot and heel of the middle soles of sports shoes based on the high cushioning quality of the ostrich toe pad by applying bionic engineering technology. The anatomical dissection method was used to analyze the ostrich foot characteristics. The structure and material of the bionic shock absorption midsole were designed according to the principles of bionic engineering and reverse engineering. F-Scan and numerical simulation were used to evaluate the bionic shock absorption midsole performance. The results showed that the bionic shock absorption midsole decreased the peak pressure (6.04–12.27%), peak force (8.62–16.03%), pressure–time integral (3.06–12.66%), and force–time integral (4.06–10.58%) during walking and brisk walking. In this study, the biomechanical effects to which the bionic shock absorption midsole structure was subjected during walking and brisk walking exercises were analyzed. The bionic midsole has excellent shock resistance. It is beneficial for the comfort of the foot during exercise and might reduce the risk of foot injuries during exercise.

Soft Jumping Robot Using Soft Morphing and the Yield Point of Magnetic Force

In this paper, soft-morphing, deformation control by fabric structures and soft-jumping mechanisms using magnetic yield points are studied. The durability and adaptability of existing rigid-base jumping mechanisms are improved by a soft-morphing process that employs the residual stress of a polymer. Although rigid body-based jumping mechanisms are used, they are driven by multiple components and complex structures. Therefore, they have drawbacks in terms of shock durability and fatigue accumulation. To improve these problems, soft-jumping mechanisms are designed using soft polymer materials and soft-morphing techniques with excellent shock resistance and environmental adaptability. To this end, a soft jumping mechanism is designed to store energy using the air pressure inside the structure, and the thickness of the polymer layer is adjusted based on the method applied for controlling the polymer freedom and residual stress deformation. The soft jumping mechanism can transfer energy more efficiently and stably using an energy storage and release mechanism and the rounded ankle structure designed using soft morphing. Therefore, the soft morphing and mechanisms of energy retention and release were applied to fabricate a soft robot prototype that can move in the desired direction and jump; the performance experiment was carried out.

Influence of SiC Addition on Mechanical Behavior of Thermal Barriers with the Aid of Acoustic Emission

The improvement of high temperature materials with lower heat transfer coefficients lead to the development of thermal barrier coatings (TBCs). One of the most widely used materials for thermal barrier coatings is Y2O3 stabilized ZrO2 (Y-TZP) because of its excellent shock resistance, low thermal conductivity, and relatively high coefficient of thermal expansion. The aim of this work is to study the TBCs mechanical behavior with the addition of SiC into the suspension of Y-TZP/Al2O3 by acoustic emission (AE). Additionally, a microstructural analysis and a finite elements model were carried out in order to compare results. The coatings were made by suspension plasma spray (SPS) on metal plates of 70 × 12 × 2 mm3. An intermetallic was deposited as a bond coating, followed by a coating of Y-TZP/Al2O3 with and without 15 wt.% SiC, with thicknesses between 87 and 161 μm. The AE becomes a fundamental tool in the study of the mechanical behavior of thermal barriers. The use of wavelet transforms streamlines the study and analysis of recorded sound spectra. The crack generation arises at very low stress levels.

Compressive behavior and energy absorption of polymeric lattice structures made by additive manufacturing

Lattice structures have numerous outstanding characteristics, such as light weight, high strength, excellent shock resistance, and highly efficient heat dissipation. In this work, by combining experimental and numerical methods, we investigate the compressive behavior and energy absorption of lattices made through the stereolithography apparatus process. Four types of lattice structures are considered: (i) Uniform body-centered-cubic (U-BCC); (ii) graded body-centered-cubic (G-BCC); (iii) uniform body-centered-cubic with z-axis reinforcement (U-BCCz); and (iv) graded body-centered-cubic with z-axis reinforcement (G-BCCz). We conduct compressive tests on these four lattices and numerically simulate the compression process through the finite element method. Analysis results show that BCCz has higher modulus and strength than BCC. In addition, uniform lattices show better energy absorption capabilities at small compression distances, while graded lattices absorb more energy at large compression distances. The good correlation between the simulation results and the experimental phenomena demonstrates the validity and accuracy of the present investigation method.

High strain rate compressive response of the Cf/SiC composite

Carbon fiber reinforced ceramic owns the properties of lightweight, high fracture toughness, excellent shock resistance, and thus overcomes ceramic's brittleness. The researches on the advanced structure of astronautics, marine have exclusively evaluated the quasi-static mechanical response of carbon fiber reinforced ceramics, while few investigations are available in the open literature regarding elastodynamics. This paper reports the dynamic compressive responses of a carbon fiber reinforced silicon carbide (Cf/SiC) composite (CFCMC) tested by the material test system 801 machine (MTS) and the split Hopkinson pressure bar (SHPB). These tests were to determine the rate dependent compression response and high strain rate failure mechanism of the Cf/SiC composite in in-plane and out-plane directions. The in-plane compressive strain rates are from 0.001 to 2200 s−1, and that of the out-plane direction are from 0.001 to 2400 s−1. The compressive stress-strain curves show the Cf/SiC composite has a property of strain rate sensitivity in both directions while under high strain rate loadings. Its compressive stiffness, compressive stress, and corresponding strain are also strain rate sensitive. The compressive damage morphologies after high strain rate impacting show different failure modes for each loading direction. This study provides knowledge about elastodynamics of fiber-reinforced ceramics and extends their design criterion with a reliable evaluation while applying in the scenario of loading high strain rate.

Cutting Performance and Tool Failure in Intermittent Turning Processes of an Al<sub>2</sub>O<sub>3</sub>-Based Micro-Nano-Composite Ceramic Tool

An Al2O3-based micro-nano-composite ceramic cutting tool material reinforced with (W, Ti)C micro-particles and Al2O3 micro-nano-particles was fabricated by using hot-pressing technique, the composite was denoted as AWT. The cutting performance, failure modes and mechanisms of the AWT micro-nano-composite ceramic tool were investigated via intermittent turning of hardened AISI 1045 steel (44~48 HRC) in comparison with those of an Al2O3/(W, Ti)C micro-composite ceramic tool SG-4 and a cemented carbide tool YS8. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy (SEM). The results of intermittent turning revealed that shock resistance of the AWT ceramic tool was higher than that of the SG-4 and YS8 tools at all the tested cutting speeds. The excellent shock resistance of the AWT composite ceramic tool was attributed to its synergistic strengthening/toughening mechanisms induced by the (W, Ti)C micro-particles and Al2O3 nano-particles.

YTTRIA-STABILIZED ZIRCONIA THERMAL BARRIER COATINGS — A REVIEW

Thermal barrier coatings (TBCs), which protect metallic components from high-temperature environments, have been widely applied to the fields of high-temperature and corrosion-resistant structural parts such as gas turbine engines, diesel engines, and power generation systems. Yttria-stabilized zirconia (YSZ) is one of the most widely used materials for TBCs owing to its excellent shock resistance, low-thermal conductivity, and relatively high coefficient of thermal expansion. In this paper the properties of YSZ and the recent developments of YSZ-TBCs are reviewed. The failure mechanism of YSZ-TBCs and corresponding methods for lengthening the lifetime of YSZ-TBCs are discussed. The advantages of graded thermal barrier coatings and the problems in processing are elucidated.

RECENT DEVELOPMENTS IN ZIRCONIA THERMAL BARRIER COATINGS

Thermal barrier coatings (TBC) are finding increasing applications in aeronautical, chemical, metallurgy industries, etc. As a ceramic material, ZrO 2 is one of the most widely used for TBCs owing to its excellent shock resistance, low thermal conductivity and relatively high coefficient of thermal expansion (CTE). In this paper the thermomechanical properties of ZrO 2 and the evolution of ZrO 2-TBCs are reviewed. The failure mechanism of TBCs and corresponding methods for lengthening the lifetime of TBCs are discussed. The advantages and disadvantages of graded thermal barrier coatings (GTBC) as well as the problems to be solved in fabricating advanced TBCs are elucidated.

Temperature and seed layer effects on the magnetics of sputtered glass-ceramic disks

Glass-ceramic substrates show excellent shock resistance and low glide performance. To achieve good magnetics, two types of seed layers, A and B, and no seed layer were deposited on glass-ceramic substrates with following Cr and CoCrPtTa layers. The effects of the seed layers on the substrate temperature, the subsequent Cr and CoCrPtTa crystallographic orientations, anisotropy K u , media noise and the signal-to-noise ratio (SNR) were measured. The seed layer reduces the emissivity of the glass and increases the substrate temperature by more than 100°C during the Co layer deposition. Significant differences in media noise performance were observed among the three seed layer materials and processes. The textures of the Cr underlayer and the Co alloy depend on the surface of the seed layer. Samples with Ni 3P seed layers have a structure with Co(11 2 0)/Cr(200) on Ni 3P and show SNR values 2–6 dB higher than those with Cr seed layers. However, the Δ M curves show that samples with Ni 3P seed layers have higher Δ M. The Δ M value may not be a necessary condition for determining the mechanism of media noise.

Airbag application: a microsystem including a silicon capacitive accelerometer, CMOS switched capacitor electronics and true self-test capability

A low cost, high reliability accelerometer microsystem designed for crash sensing in automotive airbag electronic control units is presented. The proposed microsystem offers high level output, on-line self-test function, small size (3.5 mm × 3.5 mm × 1.15 mm), and high design flexibility thanks to a two-chip construction. The sensitive part is a surface micromachined capacitive interdigitated structure realized from a SIMOX SOI substrate. The accelerometer operates in a closed loop mode using electrostatic feedback with conditioning circuitry realized in a 2 μm CMOS process. A high performance readout circuit using switched capacitors has been developed. Behavioural simulation results show a bandwidth of 630 Hz at ±50g with 5 V power supply. The fabrication process includes the realization of a free-standing seismic mass by means of reactive ion etching and sacrificial oxide etching, the mechanical protection of the sensing element with a thin silicon cap bonded onto the structured SOI wafer, and eventually the electrical connection with the ASIC by flip-chip bonding. Preliminary results are very encouraging: dynamic actuation of the sensing elements is optically tested, with a yield of 70% at a prototype level. Excellent shock resistance and low internal stress are observed.

MR Sensor for Magnetic Encoder

Recent work on magnetoresistive elements for use in magnetic encoders is reviewed. Magnetic encoders are often used as position and speed detectors in motor control systems. They have attracted attention because of their durability in dirty environments, their low temperature dependence, excellent shock resistance, and compatibility with a wide variety of designs. Much of the current work on such detectors aims at high resolution using smaller equipment. In studying suitable constructions for such detectors, the magnetoresistive elements must be considered.

Defect characterization of graphite/epoxy and carbon/carbon composite structures using acoustic techniques

Graphite/epoxy (Gr/Ep) and carbon/carbon (C/C) composite structures possess properties of small thermal expansion, high heat of ablation, excellent shock resistance, high damping, high specific stiffness, and strength. Material and manufacturing anoamalies, however, cannot be avoided in these composites and a knowledge of the integrity of the structure at various stages of its performance is mandatory. The purpose of this paper is to present experimental studies on defects encountered in Gr/Ep and C/C composites. This paper reviews nondestructive evaluation techniques of composites, such as acoustic emission (AE) and acoustoultrasonics (AU). Experimental results obtained using AU and AE on tensile samples of unidirectional Gr/Ep with artificially induced defects are presented. Stress wave factor (SWF), a parameter in AU testing, was found to reduce at the location of the defects. The peak amplitude distribution of AE hits was indicative of the type of failure mechanism occurring in the Gr/Ep composites. AU studies on C/C composites, prior to carbonization and after carbonization, are also presented.

Development of the Absolute Type Magnetic Encoder Suitable for Thinner Structure

Rotary encoders are often used as position detectors in robot control systems and are of two types: optical encoders and magnetic encoders. Magnetic rotary encoders have attracted attention for their durability in unclean environments, reliability at low temperatures, excellent shock resistance, and wide variety of designs. Such encoders can function in two different ways; detecting either relative or absolute positions. In this paper, an absolute position-detecting magnetic encoder with high resolution and a thin construction is proposed, and such an encoder (100 mm dia. × 20 mm) with 11 bits, only one-fourth as thick as conventional magnetic encoders, has been trial-fabricated.

薄型アブソリュート磁気エンコーダの試作

Rotary encoders are often used as position detectors in robot control systems and are of two types: optical encoder and magnetic encoder. The magnetic rotary encoder has been noticed from the viewpoint of its durability in an unclean environment, low temperature dependence, excellent shock resistance and wide variety of desings. This encoder can function in two different ways: detecting either reference or absolute position. In this paper, an absolute magnetic encoder suitable for higher resolution and of thinner structure has been suggested, and an absolute magnetic encoder (φ 100×20 mm) with 11bit, which is one-fourth as thick as a conventional magnetic encoder, has been prepared successfully.

NODULOY

Abstract NODULOY is a magnesium inoculated ductile cast iron in which the graphite is in the nodular form. It offers excellent castability, high mechanical properties, good machinability, pressure tightness, high modulus, and excellent shock resistance. It has extraordinary high ductility in the annealed state. This datasheet provides information on composition, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as casting, heat treating, and machining. Filing Code: CI-1. Producer or source: Dominion Wheel & Foundries Ltd.