High Load Applications Research Articles

Performance analysis of liquid desiccant dehumidification systems

Desiccant systems find applications in a very large variety of industrial and daily usage products including the new HVAC installations. An overview of liquid desiccant technology has been presented in this paper along with a compilation of experimental performance data of liquid desiccant dehumidifiers, empirical dehumidification effectiveness and mass transfer correlations in a useful and easy to read tabular format. The latest trends in this area suggest that hybrid systems are of current interest to HVAC industry, not only for high latent load applications but also for improving indoor air quality. The paper presents a comprehensive comparative parametric analysis of packed bed dehumidifiers for three commonly used desiccant materials viz. triethylene glycol, lithium chloride and calcium chloride, using empirical correlations for dehumidification effectiveness from the literature. The analysis reveals significant variations and anomalies in trends between the predictions by various correlations for the same operating conditions, and highlights the need for benchmarking the performance of desiccant dehumidifiers.

Preparation of titanium diboride TiB2 by spark plasma sintering at slow heating rate

A systematic study of the spark plasma sintering of TiB2 starting from mixture of elemental powders was performed to investigate the temperature distribution between pressing tool and sinter body. The reaction mechanism and time-dependant evolution of the sintering behavior are established. The simultaneous application of pulsed high dc current and load leads to a microstructure with needle-shaped grains. Electron backscattering diffraction analyses show the preferred orientation of small crystallites parallel to the pressing direction.

Superfast densification of nanocrystalline oxide powders by spark plasma sintering

Spark plasma sintering (SPS) is a newly discovered old technique which recently has been used for superfast densification of ceramic powders. Simultaneous application of pulsed high dc current densities and load is the necessary condition for rapid and full densification of ceramic powders by SPS. Commercial nanocrystalline magnesium oxide (nc-MgO) and yttrium aluminum garnet (nc-YAG) powders were densified to optical transparency using spark plasma sintering at distinctly different homologous temperatures (0.3 Tm for nc-MgO and 0.7 Tm for nc-YAG). The observed microstructure, density and grain size evolutions versus the SPS temperature were analyzed. The enhanced densification of the nc-MgO powder at the present SPS conditions was related to plastic deformation followed by diffusion processes. Densification of nc-YAG powder was described by the formation of viscous layer at the particle surfaces and corresponding densification by grain rotation and diffusion through the liquid phase. Densification by normal grain growth takes place at higher relative densities, regardless of the material.

Dual hydroxyapatite composite with porous and solid parts: Experimental study using canine lumbar interbody fusion model

Hydroxyapatite (HA) has been evaluated for use in a variety of applications in bone reconstruction surgery because of its high affinity with host bone and biocompatibility. However, because of the difficulty in combining porosity (for bone ingrowth) and strength in HA, it is generally considered inappropriate to use HA for high-load applications such as spinal interbody fusion. In the present study, we constructed a HA implant for spinal interbody fusion, composed of a dual HA composite (DHC) that combines two HA materials with different porosities: HA with 75% porosity, for bone ingrowth; and HA with 0% porosity, for load bearing. We used a canine lumbar interbody fusion model to evaluate bone conduction of the implant and its efficacy for bony fusion. Six months after the operation, DHC exhibited almost the same efficacy for bony fusion as iliac bone grafts. Moreover, pores of the porous part of the DHC were completely filled with newly formed bone and bone marrow cells. The present findings indicate that DHC is suitable for use as an implant material for spinal interbody fusion as a substitute for iliac bone grafts, which could eliminate the disadvantages associated with autograft harvesting.

NIROSTA 4568

Abstract Nirosta 4568 is a higher-carbon alloy used primarily in high mechanical loading applications for strength retention. It is often supplied in the strained condition and used as springs. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SS-949. Producer or source: ThyssenKrupp Nirosta GmbH.

One-dimensional dynamic microslip friction model

A one-dimensional dynamic microslip friction model, including the damper inertia, is presented in this paper. An analytical approach is developed to obtain the steady-state solution of the resulting nonlinear partial differential equations when subjected to harmonic excitation. In the proposed approach, according to the excitation frequency, a single mode of the system is considered in the steady-state solution for simplicity; consequently, phase difference among spatially distributed points is neglected. Three types of normal load distributions, resulting in distinct stick–slip transitions along the contact interface, are studied. The resulting hysteresis curves and the associated Fourier coefficients are obtained and compared with each other. An equivalent point contact friction model is established and compared with the proposed microslip model, illustrating the effects of partial slip in the contact interface for low amplitude or high normal load applications.

Assessment of Stiffness and Strength of 4 Different Implants Available for Equine Fracture Treatment: A Study on a 20° Oblique Long‐Bone Fracture Model Using a Bone Substitute

To compare the mechanical properties of 4 stabilization methods for equine long-bone fractures: dynamic compression plate (DCP), limited contact-DCPlate (LC-DCP), locking compression plate (LCP), and the clamp-rod internal fixator (CRIF--formerly VetFix). In vitro mechanical study. Bone substitute material (24 tubes) was cut at 20 degrees to the long axis of the tube to simulate an oblique mid-shaft fracture. Tubes were divided into 4 groups (n=6) and double plated in an orthogonal configuration, with 1 screw of 1 implant being inserted in lag fashion through the "fracture". Thus, the groups were: (1) 2 DCP implants (4.5, broad, 10 holes); (2) 2 LC-DCP implants (5.5, broad, 10 holes); (3) 2 LCP implants (4.5/5.0, broad, 10 holes) and 4 head locking screws/plate; and (4) 2 CRIF (4.5/5.0) and 10 clamps in alternating position left and right of the rod. All constructs were tested in 4-point bending with a quasi-static load until failure. The implant with the interfragmentary screw was always positioned on the tension side of the construct. Force, displacement, and angular displacement at the "fracture" line were determined. Construct stiffness under low and high loads, yield strength, ultimate strength, and maximum angular displacement were determined. None of the implants failed; the strength of the bone substitute was the limiting factor. At low loads, no differences in stiffness were found among groups, but LCP constructs were stiffer than other constructs under high loads (P=.004). Ultimate strength was lowest in the LCP group (P=.01), whereas yield strength was highest for LCP constructs (409 N m, P=.004). CRIF had the lowest yield strength (117 N m, P=.004); no differences in yield strength (250 N m) were found between DCP and LC-DCP constructs. Differences were found for maximum angular displacement at the "fracture" line, between groups: LPC<DCP<LC-DCP<CRIF (P< or =.037). DCP, LC-DCP, and LCP constructs provided sufficient biomechanical stability to withstand single-cycle loads that might be experienced postoperatively. LCP constructs showed the best performance because of the highest yield strength, above which irreversible deformation occurred. Inadequate biomechanical properties, excessive motion, and shape of the device create concern about the use of CRIF in these large sizes. CRIF does not meet the demands for equine long-bone fracture treatment. With respect to biomechanical properties, DCP, LC-DCP, and LCP constructs did not show critical differences so other factors may direct clinical selection of these implants. We prefer the LCP implants because of the high yield strength, high stiffness under high-load application, and the least movement at the fracture line.

Experimental implementation of complex path tracking control for large robotic hydraulic excavators

The experimental implementation of the path tracking control of a real hydraulic excavator with an operating weight of 4,500 kg for realising a large hydraulic servo robot with a high loading ability is described in this article. The three working arms are driven by hydraulic valve-controlled cylinders with boom structure systems to achieve rotational motion. Accordingly, the non-linearity of the boom mechanisms, large masses, large dimensions and low natural frequency of the working arms, as well as the coupling influence between the multi-body systems of the three working arms make it difficult to realise high accuracy path tracking control. The control strategy of the model reference adaptive control, which has a simple algorithm and on-line self-tuning ability, is used. Complex path profiles tracking can be achieved by the combination of the path tracking control of the three working arms. Consequently, the large hydraulic excavator can be used as large multi-purpose robots for high loading and high precision applications.

Tribological characterization of diamond-like carbon (DLC) coatings sliding against DLC coatings

Two different qualities (single-layer and multi-layer) of thick diamond-like carbon (DLC) coatings were prepared on both extremely polished ( R a ∼0.01 μm) stainless steel disks and 6 mm diameter stainless steel balls. Morphological and micro-structural evaluations reveal that multi-layer DLC coatings are superior in nature compared to the single-layer coatings. Tribological characterisations using a pin (ball)-on-disk tribometer shows that, even though the multi-layer DLC coating exhibits superior qualities, when it slides against the same displays relatively higher friction and wear compared to that of single-layer DLC sliding against the same. Multi-layer DLC coated steel ball sliding against the single-layer DLC coated disk displays the best tribological performance. However, stress cracking was observed very rarely at the sliding edge of the multi-layer film prepared on the ball and is believed to be due to the relatively higher compressive stress in the film combined with the applied stress. The tribological performance of the single-layer DLC sliding against the same is also found to be excellent, and is comparable to that of the multi-layer DLC coated ball against the single-layer DLC coated disk. No cracks were observed on the low stress single-layer DLC coated ball after the friction test. The study reveals that the single-layer DLC sliding against the same would provide the best tribological DLC pair for relatively higher load applications such as in orthopaedic implants.

Use of desiccant dehumidification to improve energy utilization in air-conditioning systems in Beirut

Humidity and indoor moist surrounding affect air cleanliness and protects harmful microorganisms when relative humidity is above 70%. In humid climates, the humidity issues are a major contributor to energy inefficiency in HVAC devices. The use of liquid desiccant dehumidification systems of supply air is a viable alternative to reduce the latent heat load on the HVAC system and improve efficiency. Thermal energy, at a temperature as low as 40–50°C, required for the operation of a liquid desiccant hybrid air conditioner can be efficiently obtained using a flat-plate solar collector. In this work a model of a solar-operated liquid desiccant system (using calcium Chloride) for air dehumidification is developed. The system utilizes packed beds of counter flow between an air stream and a solution of liquid desiccant for air dehumidification and solution regeneration. The desiccant system model is integrated with a solar heat source for performance evaluation at a wide range of recorded ambient conditions for Beirut city. Standard mass and energy balances are performed on the various components of the system and a computer simulation program is developed for the integrated system analysis. The desiccant system of the current study replaces a 3 TR (10.56 kW) vapour compression unit for a typical house as low latent load application, and is part of a hybrid desiccant–vapour compression system for a high latent load application, namely a small restaurant with an estimated cooling load of 11.39 TR (40 kW), including reheat. The relevant parameters of the desiccant system are optimized at peak load, and it is found out that there is an important energy saving if the ratio of the air flow rate in the regenerator to that in the dehumidifier is about 0.3 to 0.4. The COP of the desiccant unit is 0.41 for the house, and 0.45 for the restaurant. The size of the vapor compression unit of the restaurant is reduced to 8 TR when supplemented by a desiccant system. The performance is studied of the desiccant system integrated with a solar collector system and an auxiliary natural gas heater to heat the regenerator. The transient simulation of the solar desiccant system is performed for the entire cooling season. The solar fraction for the house is equal to 0.25, 0.47, and 0.68 for a collector area of 28.72, 57.44, and 86.16 m2, respectively. The solar fraction for the restaurant is 0.19, 0.38, and 0.54, for the same collector areas. The life cycle savings for the house run solely on desiccant system were positive only if natural gas is available at a cheap price. For the restaurant, the economic benefit of the desiccant system is positive, because the need for reheat in the vapor compression system is eliminated. For a gas price of 0.5638 $/kg, the payback period for the restaurant turned out to be immediate if the energy is supplied solely by natural gas, and 11 years if an 86.16 m2 solar collector is implemented to reduce the fuel consumption. Copyright © 2003 John Wiley & Sons, Ltd.

Variable Structure Control of a Differentially Steered Wheeled Mobile Robot

This paper discusses dynamic modeling and robust control of a differentially steered mobile robot subject to wheel slip and external loads. Consideration of wheel slip and external loads is crucial for high load and/or high speed applications because they act as disturbances to the system. Furthermore, a tire model that adequately accounts for the tire/ground interaction is essential and Dugoff's pneumatic tire friction model is utilized herein in deriving the dynamic equations of motion of the mobile robot. It is shown that the dynamic equations satisfy the matching condition, and the variable structure control method is employed to design a tracking controller of the mobile robot. Numerical simulation shows the promise of the developed control algorithm.

Critical measurements for validation of constitutive equations under shock and impact loading conditions

Interpretation of the data often requires numerical simulations of the experiments and comparisons with the data. However, determination of an appropriate set of values for parameters in constitutive equations valid under shock and high strain rate loading remains one of the most difficult tasks for material model developers. Most researchers employ experimental data obtained under idealized stress/strain states in the model parameter calibration scheme. Since the dynamic response of materials is very complex, especially the failure response, the generality of the model parameters is highly questionable. For example, the fracturing of ceramic materials involves nucleation, propagation, and coalescence of microcracks under shock and impact. The dynamic deformation processes in ceramics include dynamic pore collapse, dislocation generation, twinning, and microcracking. When shocked above the Hugoniot elastic limit, the ceramic deformation becomes inelastic; therefore, the constitutive model formulation should consider modeling the effects of these various processes on the degradation of strength and stiffness of ceramic. This paper presents a brief summary of diagnostic measurements and modeling techniques associated with validation and verification of ceramic constitutive/damage models under high strain rate, shock, and penetration loading applications.

The friction and wear of different polymers under high‐load conditions

AbstractEngineering polymers are increasingly being used as self‐lubricating materials in demanding high‐load applications. In this study, a comparison has been made of the tribological behaviour under high‐load conditions of two grades of polyamide and polyethylene terephthalate as well as polyacetal. Large‐scale testing is used to reduce edge effects. It has been found that the two grades of polyamide and pure polyethylene terephthalate are prone to stick—slip, while internally lubricated polyethylene terephthalate and polyacetal show low friction and wear and no stick—slip.

Control of an operator-assisted mobile robotic system

In this paper, two different control methods are developed for an operator-assisted mobile robotic system for high load applications. For high load applications of mobile robots, an accurate tire model that considers wheel slip needs to be studied to achieve robustness of the system response. First, a simple operator-manipulator coordination system is developed based on explicit force control. Then, a position controller for the platform is designed to minimize the effect of wheel slip on control performance and integrated with the force controller for the operator-manipulator subsystem based on a motion coordination scheme. Then, a new type of human-robot coordination control method is developed, in which robust force control of the manipulator and impedance control of the mobile platform are integrated to achieve robust response and smooth interaction between the operator, the manipulator and the mobile platform. In simulation, the developed methods are compared for control performance on following the operator's motion intention.

Atomic Force Microscope Images of Nanobubbles on a Hydrophobic Surface and Corresponding Force−Separation Data

Domains, apparently nanobubbles, have been observed on a hydrophobic glass surface in water using an atomic force microscope operated in tapping mode. Phase images show the domains to be softer than the underlying substrate. Complementary force curves between a silica colloid probe and the glass surface display features characteristic of the hydrophobic interaction, including a jump-in distance that is comparable to the height of the imaged domains. Images and force curves have been acquired over a range of pH conditions to probe the nature of the overall interaction and gain some insight into the conformation of nanobubbles on the sample surface. The bubbles appear to regrow following their removal by the application of high loads through either contact mode imaging or tapping mode imaging at high drive amplitudes. They are not present in a solvaphilic fluid (ethanol) but regrow following the subsequent reintroduction of H2O. The correlation between image and force data, supported by existing results in the literature, provides strong evidence to favor nanobubbles as the origin of the hydrophobic force.

Densification route and mechanical properties of Si 3N 4–bioglass biocomposites

The processing route and the final microstructural and mechanical characteristics of a novel biomaterial composite are described. This new material is composed of 70 wt% Si 3N 4 ceramic phase and 30 wt% bioglass, the later performing as a liquid sintering aid system and simultaneously providing bioactivity characteristics to the composite. The conditions for fabrication of an almost fully dense material (∼98% of relative density) were pursued. Optimised parameters were 1350°C–40 min–30 MPa by hot-pressing technique. The very fast densification rate of the process avoided the crystallisation of the bioglass intergranular phase and therefore its intrinsic properties were maintained. Also, the large amount of glassy phase assured the densification by liquid phase assisted grain rearrangement without Si 3N 4 phase transformation. The final mechanical properties of the Si 3N 4–bioglass were as follows: fracture toughness, K IC=4.4 MPa m 1/2; Vickers hardness, H V=10.3 GPa; Young's modulus, E=197 GPa; bending strength, σ R=383 MPa; Weibull modulus, m=8.3. These values provide an attractive set of properties among other bioactive materials, namely by upgrading the main drawback of bioceramics and bioglasses for high-load medical applications, which is the lack of satisfactory fracture toughness.

Drag torque in high Tc superconducting magnetic bearings with multi-piece superconductors in low speed high load applications

The design of superconductor magnet bearings for high load applications such as flywheel kinetic energy storage necessitates the use of large pieces of high quality high temperature superconductors. Limitations on the size of one continuous block of HTS materials that can be produced make it very attractive to use contiguous pieces of high quality HTS materials to provide the same large amount of HTS surface that can interact with magnets to give as high a levitation force. More often than not, the shape of such a composite piece is not symmetric about any axis of rotation. Variations in the drag torque are observed within each rotation cycle of the magnet above the composite HTS piece. The authors show that part of this drag torque variation originates from the nonaxisymmetric shape of the composite HTS piece. Implications of this drag torque variation on the power loss of superconductor magnet bearings made with composite HTS pieces are discussed.

A stiffness-based quality measure for compliant grasps and fixtures

This paper presents a systematic approach to quantifying the effectiveness of compliant grasps and fixtures of an object. The approach is physically motivated and applies to the grasping of two- and three-dimensional objects by any number of fingers. The approach is based on a characterization of the frame-invariant features of a grasp or fixture stiffness matrix. In particular, we define a set of frame-invariant characteristic stiffness parameters, and provide physical and geometric interpretation for these parameters. Using a physically meaningful scheme to make the rotational and translational stiffness parameters comparable, we define a frame-invariant quality measure, which we call the stiffness quality measure. An example of a frictional grasp illustrates the effectiveness of the quality measure. We then consider the optimal grasping of frictionless polygonal objects by three and four fingers. Such frictionless grasps are useful in high-load fixturing applications, and their relative simplicity allows an efficient computation of the globally optimal finger arrangement. We compute the optimal finger arrangement in several examples, and use these examples to discuss properties that characterize the stiffness quality measure.

AFM characterization of the structure of Au-colloid monolayers and their chemical etching

Modification of a glass support with triethoxy propylaminosilane yields an active interface for the assembly of Au colloids. The colloids are imaged by AFM using a low applied load (0.5–0.7 nN). The lateral Au-colloid dimensions, 33±3 nm, deviate from the particle dimensions determined by TEM (19±2 nm) and absorption spectroscopy (15 nm). This deviation is attributed to the intrinsic curvature of the AFM tip. Application of higher loads on the tip (3 nN) results in the sweeping of Au colloids from the monolayer. The Au colloid monolayer is etched in the presence of CN −. The etching proceeds by the initial coincidental etching of Au particles followed by the kinetically favored etching of particles at the edges of the etched domains. This provides means for the micro machining and the chemical manipulation of Au colloids of controlled spatial arrangement.

Fixation of femoral shaft osteotomy with an intramedullary composite rod: An experimental study on dogs with a two-year follow-up

A novel composite material with an ultra-high strength and a low elastic modulus called carbon fibre-reinforced liquid crystalline polymer (LCP/CF) has been developed. An experimental diaphyseal osteotomy of the proximal femur in fourteen Beagle dogs was fixed with an intramedullary LCP/CF rod of 4.5 mm in diameter and 80 mm in length. The radiological follow-up intervals were 1, 3, 6, 12, 24, 52, and 104 weeks. Five dogs were killed at 1 year and three dogs at 2 years for histological studies; six dogs were retained for longer follow-up. Radiographs showed an uncomplicated healing of the diaphyseal osteotomy with an external callus formation in all dogs in 12 weeks. Histological analysis revealed a benign host tissue response with few in flammatory cells. Both bone and fibrous tissue were seen at the LCP/CF-host tissue interface. The cross-sectional cortical area of the operated femur was slightly greater than that of the control femur in the 2-year follow-up. LCP/CF showed promising properties for high-load applications.