High Normal Force Research Articles

Controlling the pressure force to obtain a better quality of aluminum 6061 friction stir welded joint

Friction stir welding (FSW) is one of the mechanical joint methods that need no filler metal. The heat is obtained from the friction force between the base metal and friction tool. The FSW is proposed by The Welding Institute – TWI in 1991 which is hoped to overcome problems to weld metals with low weldability. Parameters of FSW determine the quality of the joint and in this paper the normal force as an independent parameter varied at 13,000, 14,000 and 15,000 N. The rotation and feeding speeds are controlled at 1,092 RPM and 200 mm/min respectively. From the experimental results, it is found that 15,000 N provided the strongest joint (specimen 1). The highest heat input was claimed to cause a better joint. This high heat input provides enough weld nugget and time for the aluminum to grow its grains, which in turn increase the tensile strength of the FSW joint.However, from the average values and the trend line it cannot be assumed that the greater pressure force always produces higher tensile strength. The tensile strengths were almost at the same level (115.44±1.56 MPa) meanwhile the calculated heat input is linearly dependent on the pressure force: 73.59, 79.25 and 84.91 J/mm for pressure forces equal to 13,000, 14,000 and 15,000 respectively. The recorded temperature, which indicates heat input showed the same trend with tensile strength, it was on the same level, those are: 491.55±2.22 °C. There must be some aspects which were not taken into account in the heat input mathematical model. Or maybe, the assumption of higher heat input is not always accomplished by the higher pressure force. Based on the literature, it is found that the yield strength is mitigated at a higher temperature. This lower yield strength decreases the friction force for a constant normal force which in turn causes declining heat input which contradicts the previous assumption.Another literature that inspected the coefficient of friction as a function of temperature showed that the coefficient is altered due to temperature.And finally, the higher normal force does not mean a stronger joint can be produced by means of Friction Stir Welding

Performance comparison and optimisation of dual mover linear permanent magnet flux switching machine

Short moving primary and rigid low-cost secondary are important requirements of linear machines designed for long stroke applications. In the race, linear permanent magnet flux switching machine (LPMFSM) is a competitive candidate by confining excitation sources to short mover, thus making stator robust and low cost (made of only iron). However, single-sided LPMFSM exhibit a demerit of high normal (attraction) force due to its topology. In order to rectify the problem and enhance thrust force profile, two novel double-sided LPMFSMs are proposed with dual stator and dual mover topologies. After stator pole study, both topologies with same design dimensions are analysed and compared by 2-D finite element method here. Detailed analysis revealed that 12/14 DMLPMFSM exhibit low numerical values of thrust force ripples and detent force while maintaining average thrust force value. Hence, 12/14 DMLPMFSM is selected and optimised by structure-based deterministic optimisation (SBDO) approach to further enhance thrust force profile. Finally, comparison of initial and optimised design of 12/14 DMLPMFSM is presented to validate optimisation procedure.

Micromechanical behaviour of a polymer-coated sand

Polymers, such as polydimethylsiloxane, can be utilised as functional coatings with water repellent properties in granular materials. These new surface-modified granular materials have potential applications in barriers to control wetting. However, limited knowledge exists on the mechanical behaviour of particles with synthetic coatings. Here, a fundamental insight is provided by investigating the micromechanical behaviour of a coated sand with extreme water repellency by means of a custom-built inter-particle loading apparatus. To synthesize the water repellent coatings, an industrial sand was subjected to 3% mass ratio of dimethyldichlorosilane. In a comparative investigation between coated and uncoated (natural) sand particles, the results revealed (1) a decrease of the normal stiffness and (2) a dependency of the inter-particle friction coefficient on the normal force for the coated sand particles. In particular, the inter-particle friction coefficient significantly increased at low normal forces (lower than 2 N) with this effect decreasing as the coatings were damaged under a high normal force (over 5 N), and with the micromechanical behaviour of the coated sand converging towards that of the uncoated (natural) sand. The results are compared to theoretical models and mechanisms are proposed to explain the findings. By changing the nature of the coatings, this paper provides a basis for future research on granular materials with functional coatings for other applications.

Characterizing and modeling wear-recovery behaviors of acid-induced casein hydrogels

Hydrogels are soft materials with applications in multiple industries, but their fundamental wear behaviors are relatively unknown. Studies on hydrogel wear behaviors generally use empirical measurements. Additionally, it can be difficult to measuring hydrogel wear rates by traditional mass loss measurements because wear debris cannot always be removed without disturbing intact sample. Therefore, the objective of study was to develop a method for more precise calculation of soft material wear rates. The method developed compared creep-recovery and wear-recovery behaviors of casein hydrogels to separate deflection of the material under an applied load from the amount of material removed. Casein hydrogels were prepared at different concentrations (8%, 10%, and 15% w/w) and pH (2.3, 3.6, 4.8), and tested under a range of normal loads (0.3, 0.4, 0.5 N). Wear-recovery behaviors were fit to an exponential model. Maximum penetration depth during wear and creep, creep-recovery, and wear-recovery increased with lower casein concentration and higher normal force and pH. Exponential models for casein gel wear-recovery behaviors indicated good fit (R2 > 0.99). This wear measurement method is useful for developing food products with specific oral and industrial processing behaviors.

Influence of WC on third body behaviour during fretting of cold-sprayed Cu MoS2WC composites

Abstract Fretting wear of cold-sprayed Cu MoS2 and Cu MoS2 WC composites rubbing against AISI 440C was studied under gross slip regime at a high normal force of 150 N. Third body rheology was expressed using tribological circuit according to morphology observations of the contact. WC particles boosted generation and ejection of large wear particles during running-in and early steady state yet promoted more stable and lower third body formation and ejection over subsequent test. This led to a considerably reduced wear rate (∼80 × 10−6 mm3/Nm) comparing to that of Cu MoS2 (∼210 × 10−6 mm3/Nm) during steady state. The 12 wt% WC particles were able to prevent rapid detachment that was induced by MoS2, which was resulted from microwedging and pinning of the WC fragments.

Textural modification of 3D printed dark chocolate by varying internal infill structure

This study aimed to create an intricate internal structure of 3D printed chocolate by varying the infill construction. Three intricate infill patterns designed were star, Hilbert curve and honeycomb with infill percentage of 5%, 30%, 60% and 100%. Cadbury dark chocolate (Choc-1) and Callebaut bittersweet dark chocolate (Choc-2) powders were used by incorporating magnesium stearate (Mg-ST) and plant sterol (PS) powders as food additives. Printing parameters were set up with an extrusion temperature of 32 °C, nozzle size of 0.78 mm and printing speed of 70 mm/s. The results showed that voids in printed samples of all three pattern with 5% infill density ranged from 60.8 ± 2.1% to 72.2 ± 1.8%. Voids in samples with 30% infill density ranged from 20.9 ± 2.1% to 49.2 ± 3.6% while with 60% infill density it ranged from 11.6 ± 2.3% to 19.4 ± 4.2%. Additionally, star and honeycomb infill pattern produced the most stable and tough structure at 60% infill as indicated by a higher normal force (N) to break the printed sample. Moreover, even at 100% infill percentage, 3D printed chocolate were found less hard (ranged from 82.2 ± 2.2 N to 92.2 ± 1.3 N) as compared to cast samples (>110 N) in the snap test. The results obtained in this study provide a useful insight in creating various internal structures of 3D printed dark chocolate with different textural characteristic and physical stability.

On-machine texturing of PCD micro-tools for dry micro-slot grinding of BK7 glass

While using diamond micro-tools for micro-grinding, tool re-clamping errors and low chip removal space from machining zone are the primary factors which cause large vibrations, higher grinding forces and poor surface quality. On-machine tool preparation and tool texturing prior to micro-grinding can reduce tool re-clamping error. It can further help to reduce the tool-workpiece contact area along with enhanced chip removal from the machining zone specifically essential during dry micro-grinding as usage of the cutting fluid should be minimized or completely avoided for environmental aspects. In this study, end faces of polycrystalline diamond (PCD) micro-tools have been on-machine textured using micro electro-discharge machining (micro-EDM) process. Four types of textured tools are envisaged viz. tool with one micro-cavity at the center of the end face (T2), one micro-groove along the end face diameter (T3), two intersecting micro-grooves at the end face (T4) and four intersecting micro-grooves at the end face (T5). A new term “contact area ratio” is defined to explain the texture dimension on the end face of the micro-grinding tools. Performances of different micro-textured tools (T2, T3, T4 and T5) with respect to a normal commercial tool (T1) in terms of grinding force, surface roughness and micro-slot quality are investigated for micro-slot grinding of BK7 glass. It is observed that micro-textured micro-grinding tool efficiently serves the purpose of provisional chip collection in passive grinding areas of the tool whereas chip adhesion or wear on the active grinding areas significantly gets reduced as compared to un-textured tools. Maximum reductions in the x and y direction forces are observed with tool type T5 compared to all other tool types. Reduction in z direction force is comparable for both tool types T2 and T3. Average surface roughness decreased from tool type T1 to type T2, T3 and up to tool type T4 whereas it again increased for tool type T5. The current study shows that textured micro-grinding tools are capable of reducing high normal forces, surface roughness and material dragging which are major concerns during micro-grinding with flat-end polycrystalline diamond tools.

Influence of morphology on the micro-mechanical behavior of soil grain contacts

The development of the discrete element method (DEM) has provided important insights into the micro-scale behavior of geological materials with major applications in geotechnical, geological and petroleum engineering. Mechanical response of grain contacts including normal and tangential behavior are given as input quantities in various DEM applications. However, it was only achieved in recent years to properly capture the real soil grain behavior in the laboratory and provide useful input parameters to be further utilized in DEM analyses. In this paper, an experimental study was conducted investigating the normal and tangential contact behavior of soil grains composed of limestone sand (denoted as LS), which is a material of biogenic origin and it may find applications, for example, in offshore engineering. In their previous work (Senetakis et al. in Tribol Int 111:1–8, 2017), the authors reported on the dynamic inter-particle friction of this material and concluded that due to the smooth surface of the brand of grains they tested, the inter-particle friction was found lower in comparison to quartz grains of Leighton Buzzard sand (LBS). That study quantified friction at relatively large displacements of shearing, of the order of 80 μm or above, where a steady state sliding was observed. In the present work, the mechanical behavior of LS sand grains was enhanced with additional test data to further explore normal and tangential behavior. The focus of the study was to investigate the differences in inter-particle friction at different reference displacements, termed as small displacement range, where the behavior exhibited a peak, and large displacement range, where a fairly steady state sliding was occurred as well as to stress the differences in the observed responses between LS and LBS grains in terms of tribological and contact mechanics behavior. It is shown in the study that very high friction angles may be observed at displacements of about 10–30 μm for LS grain contacts when sheared under low normal forces, with a substantial drop of the mobilized friction leading to a steady state at much greater sliding displacements. This drop of friction with shearing displacement was not observed when the grains were sheared at higher normal forces. The morphological effects on friction were more evident at low normal forces for LS grains. In the normal loading tests, the LS sand grains exhibited significant plastic behavior. After the conduction of a number of normal loading–unloading cycles, the observed plastic deformations continued to increase, even though this observed trend was dominant at the first cycle. The observed apparent contact Young’s moduli of LS grains were found to be much lower than those of LBS grains. These observations should not be ignored by DEM modelers when the numerically created sample targets to represent a granular material such as crushed LS.

The Magnetorheological Performance of MRFs Based on Different Types of Carbonyl Irons

Abstract Magnetorheological fluid (MRF) is a kind of promising smart functional material with significant magnetorheological (MR) performance. MRFs are typically fabricated by mixing magnetizable microparticles into a base oil. As the most important part of MRFs, magnetizable carbonyl iron (CI) particles show an obvious impact on the performance of MRFs. In this work, MRFs based on six types of CI particles were fabricated, and their MR performance was tested under both rotational and oscillatory modes by a parallel plate rheometer coupled with an MR device. The results indicate that MRFs based on big particles with high iron content present more significant MR performance in both rotational and oscillatory modes. Conversely, small particles were likely to form weaker structures that displayed lower shear stress and storage modulus. Meanwhile, silicon dioxide–coated CI particles led to decreased shear stress and storage modulus but dilated the linear viscoelastic range of MRFs. MRFs based on phosphate-modified CI particles presented a high storage modulus but low shear stress. Moreover, the normal force test results also suggest that big particles with high iron content are likely to form stronger microstructures that macroscopically present relatively higher normal forces. The suspension stability of MRFs was measured by direct observation. The results indicate that MRFs based on surface-modified and small particles have better suspension stability.

Influence of Calf Serum on Fretting Behaviors of Ti–6Al–4V and Diamond-Like Carbon Coating for Neck Adapter–Femoral Stem Contact

Influences of newborn calf serum on the fretting behaviors of Ti–6Al–4V and diamond-like carbon coating were investigated using a fretting-wear test rig with a cylinder-on-flat contact. The results indicated that, for the Ti–6Al–4V/Ti–6Al–4V contact, the friction coefficients were high (0.8–1.2) and the wear volumes presented an increase with the increase in the displacement amplitude under dry laboratory air conditions. Under serum-liquid conditions, the Ti–6Al–4V/Ti–6Al–4V contact presented significantly larger wear volumes under the displacement of ± 40 µm; however, it presented significantly lower friction coefficients (0.25–0.35) and significantly smaller wear volumes under the displacement of ± 70 µm. For the DLC coating/Ti–6Al–4V contact, the coating response wear maps could be divided into two areas: the coating working area (low normal force conditions) and the coating failure area (high normal force conditions). In the coating working area, the DLC coating could protect the substrate with low friction, low wear volume, and mild damage in the coating. The presence of serum had a positive influence on the tribological performance of the DLC coating. Furthermore, the positive influence was more significant under larger displacement amplitudes condition.

The Experimental Investigations into Dry Turning of Austempered Ductile Iron

Austempered ductile iron (ADI) formed by austempering of nodular cast iron (NCI). ADI has good mechanical properties due to the matrix of ausferrite.Use of carbide forming elements such as molybdenum and manganese while alloying form carbide. This carbide segregates towards cell boundaries during casting and form carbide in metal matrix. When high normal force is applied to ADI while machining, austenite on surface undergoes strain induced transformation (SIT) and form martensite. This transformation right in front of tool face makes it more difficult to machine. These issue reducing tool life significantly and making hurdle for further applications of ADI.In the present work, experimental investigations have been carried out into dry turning of ADI using response surface methodology(RSM) with central composite design(CCD). The performance of cemented carbide tool while machining ADI (austenitised at 850 °C for 2 hr, austempered at 350 °C for 1 hr) has been presented. The effects of speed, feed and depth of cut on cutting force, surface finish and microhardness have also been investigated with surface plots. The adequacy of these models has been checked by using analysis of variance. The predictability of main cutting force has been found to be greater than 95 %. The R- squared value for surface roughness model has found to be 0.9288. The main cutting force found to be influenced mainly by depth of cut while, the surface roughness by cutting speed.

Fatigue assessment of EMPT-welded joints using the reference radius concept

The electromagnetic pulse technology (EMPT) is a joining process similar to the explosion welding. In the process, a flyer-sheet is accelerated towards a target-sheet using electromagnetic fields. During impact high normal and lateral contact forces are generated which join the sheets on an atomic level. This process can be automated for joining thin sheets and is therefore especially suited for mass production, e.g. in the automotive industry. The resulting joints are not comparable to ones made by common MIG/MAG or laser welding processes since no heat is induced. This leads to the question if the standard approaches to assess the weld in terms of their fatigue behavior can be used also and if a reliable fatigue assessment can be achieved. In the paper, the fatigue strength of EMPT-welded connections under constant amplitude loading is presented. Common assessment approaches like the notch stress approach are applied to assess the fatigue life. A comparison between numerically derived fatigue life and experimental tests shows a good agreement and proves the applicability of established approaches.

Conditioning exercises in ski jumping: biomechanical relationship of squat jumps, imitation jumps, and hill jumps

As hill jumps are very time-consuming, ski jumping athletes often perform various imitation jumps during training. The performed jumps should be similar to hill jumps, but a direct comparison of the kinetic and kinematic parameters has not been performed yet. Therefore, this study aimed to correlate 11 common parameters during hill jumps (Oberstdorf Germany), squat jumps (wearing indoor shoes), and various imitation jumps (rolling 4°, rolling flat, static; jumping equipment or indoor shoes) on a custom-built instrumented vehicle with a catch by the coach. During the performed jumps, force and video data of the take-off of 10 athletes were measured. The imitation and squat jumps were then ranked. The main difference between the hill jumps and the imitation and squat jumps is the higher maximal force loading rate during the hill jumps. Imitation jumps performed on a rolling platform, on flat ground were the most similar to hill jumps in terms of the force–time, and leg joint kinematic properties. Thus, non-hill jumps with a technical focus should be performed from a rolling platform with a flat inrun with normal indoor shoes or jumping equipment, and high normal force loading rates should be the main focus of imitation training.

Austempering Parameters and Machinabilityof Austempered Ductile Iron: AComprehensive Review on EffectiveParameters

Austempered ductile iron (ADI) formed by austempering of nodular cast iron (NCI). ADI has good mechanical properties due to the matrix of ausferrite (austenite, ferrite and graphite nodules). It gives good combination of high strength to weight ratio, fatigue resistance, ductility and toughness. Austempering process offer ability to access to a wide range of characteristics with appropriate selection of heat treatment parameters. Graphite nodules give ductility to material and also act as crack arrester and give good fatigue strength. ADI is strain hardening or work hardening material, it has property to go for strain induced transformation (SIT) while straining. When high normal force is applied to ADI while machining, austenite on surface undergoes to SIT and form martensite. This makes further machining even more difficult and reduces performance of cutting tool. This paper deals with detail study of ADI, effective austempering parameters and performance of different cutting tools at various input machining parameter while machining ADI.

Bioinspired, Highly Stretchable, and Conductive Dry Adhesives Based on 1D-2D Hybrid Carbon Nanocomposites for All-in-One ECG Electrodes.

Here we propose a concept of conductive dry adhesives (CDA) combining a gecko-inspired hierarchical structure and an elastomeric carbon nanocomposite. To complement the poor electrical percolation of 1D carbon nanotube (CNT) networks in an elastomeric matrix at a low filler content (∼1 wt %), a higher dimensional carbon material (i.e., carbon black, nanographite, and graphene nanopowder) is added into the mixture as an aid filler. The co-doped graphene and CNT in the composite show the lowest volume resistance (∼100 ohm·cm) at an optimized filler ratio (1:9, total filler content: 1 wt %) through a synergetic effect in electrical percolation. With an optimized conductive elastomer, gecko-inspired high-aspect-ratio (>3) microstructures over a large area (∼4 in.(2)) are successfully replicated from intaglio-patterned molds without collapse. The resultant CDA pad shows a high normal adhesion force (∼1.3 N/cm(2)) even on rough human skin and an excellent cycling property for repeatable use over 30 times without degradation of adhesion force, which cannot be achieved by commercial wet adhesives. The body-attachable CDA can be used as a metal-free, all-in-one component for measuring biosignals under daily activity conditions (i.e., underwater, movements) because of its superior conformality and water-repellent characteristic.

Reinforced bending load‐stressed masonry – Suggestions for future designs / Bewehrtes biegedruckbeanspruchtes Mauerwerk – Vorschläge für zukünftige Bemessungen

AbstractEuropean standardization bodies are currently working on the amendment to EN 1996‐1‐1, which will also affect the evaluation of reinforced masonry in Germany. For that reason, discussion suggestions are being made here for revisions to lay the groundwork for building materials evaluations and especially, evaluations of bending load‐stressed masonry walls or beams at their serviceability limit state (SLS) for load‐bearing capacities. Information already presented in E DIN 1053‐3:2008‐03 [N3] is being incorporated as well.Characteristic values for the compressive strength of the masonry parallel to the bed joints fk,∥ are essential for the design of reinforced masonry, although they are currently not included in national application documents for Germany. For the time being, they can be mathematically calculated using conversion factors for the characteristic compressive strength values vertical to the bed joints fk or by using the declared axial compressive strengths of the masonry units.The ultimate strains for masonry in general should be set consistently at ϵmu = ∣–0.002∣ as several masonry types do not exhibit higher compressive strain values. The use of steel strains higher than ϵsu = 0.005 does not change any measurement results. Varying stress‐strain curves of the constitutive equations on masonry under compressive strain (parabolic, parabolic‐rectangular, tension block) lead to differing values of recordable bending moments despite having the same mechanical reinforcement percentage at higher normal forces. Therefore, clear guidelines should be made for the type of applicable constitutive equation for masonry walls under compressive strain. With the introduction of a tension block, the number values of the reduction factors λ for the compression zone height x, which is dependent on limit strains, and where applicable, reduced compressive strength, need to be determined, as with reinforced concrete construction.A modification of the bending moment based on the second order theory according to [N4] is presented for the calculation of reinforced masonry walls in danger of buckling. The use of reduction factors for the load capacity of the masonry cross section, such as for unreinforced masonry, does not appear to be appropriate as buckling safety evidence because here, the design task is the determination of a required reinforcement cross section.

A novel all-elastomer MEMS tactile sensor for high dynamic range shear and normal force sensing

A novel all-elastomer MEMS tactile sensor with high dynamic force range is presented in this work. Conductive elastomeric capacitors formed from electrodes of varying heights enable robust sensing in both shear and normal directions without the need for multi-layered assembly. Sensor geometry has been tailored to maximize shear force sensitivity using multi-physics finite element simulations. A simple molding microfabrication process is presented to rapidly create the sensing skins with electrode gaps of 20 m and sensor spacing of 3 mm. Shear force resolution was found to be as small as 50 mN and tested up to a range of 2 N (dynamic range of ). Normal force resolution was found to be 190 mN with a tested range of 8 N (dynamic range of ). Single load and multiload tests were conducted and the sensor exhibited intended behavior with low deviations between trials. Spatial tests were conducted on a sensor array and a spatial resolution of 1.5 mm was found.

Experimental and numerical analysis of three-point bending fracture of pre-notched asphalt mixture beam

The experiments are combined with the discrete element simulations to investigate the three-point bending fracture of pre-notched asphalt mixture and evaluate the effects of aggregate distribution and pre-notch dislocation on fracture. Compared with aggregate distribution, pre-notch location is a more important effect factor for the crack path. The crack-path deviation angle, the critical fracture load, and the critical fracture displacement generally increase with the increasing pre-notch offset. The three-point bending fracture of asphalt mixture is of Mode I and induced by high normal contact force concentration. Due to some random factors and the narrow limitation of 2D simulations, two discrepancies are also found in the crack-path deviation angle and the critical fracture load.

Extreme load scratch testing

Downhole oil well piping has the potential to scrape against a myriad of objects, from geological debris to drilling components such as detached tools or the edges of machined, casing-exit penetrations. This project quantified the type and extent of damage that occurs on tubing when scratched with very high normal forces similar to those experienced downhole.A scratch test machine was designed and fabricated that used weights and lever arm to apply up to 11,120N (2500lbf) on a sharpened tool point. The point was forced into the rotating surfaces of bare and protected oil well pipe. The pipe protection hardfacings were proprietary thermal sprayed coatings in several thicknesses from 0.018mm to 0.165mm (0.007–0.065in.).The scratch testing quantified the hardfacing thickness that was required to prevent the tool from penetrating into the base metal. The minimum protective thicknesses were not equal among the three hardfacings. Likewise, the maximum load that each hardfacing was able to withstand was not the same. The test rig demonstrated that it is possible to clearly delineate hardfacing type and thickness that are effective in protecting well casing components from high-load scratching damage.

Plastic properties of polytetrafluoroethylene (PTFE) under conditions of high pressure and shear

We investigate experimentally the behavior of a thin sheet of PTFE between a steel plate and a cylindrical steel indenter under combined action of high normal force and torsion. Under these actions, the PTFE layer is partially squeezed out of the contact area. The thickness of the remaining layer is studied as function of the applied normal force, the torsion angle, and the radius of the indenter. We suggest a simple semi-empirical material model which describes both the process of squeezing out of the layer and the force of friction produced by the layer.