Elastic Recovery Effect Research Articles

Mechanistic Fatigue Performance Evaluation of Stone Mastic Asphalt Mixtures: Effect of Asphalt Performance Grade and Elastic Recovery.

This study evaluates the crack performance of stone mastic asphalt (SMA) mixtures according to the performance of a modified asphalt binder, evaluated based on the asphalt performance grade (PG) and the elastic recovery of multiple stress creep and recovery (MSCR) according to AASHTO M 320 and T 350. The cracking performance of the mixture was evaluated using the asphalt mixture performance tester (AMPT) according to AASHTO T 378 and T 400 through dynamic modulus and direct tension cyclic fatigue tests. Furthermore, the recently developed viscoelastic continuum damage (VECD) theory was utilized to evaluate the cyclic fatigue index parameter (apparent damage capacity, Sapp) and the permissible heavy vehicle class. For performance evaluation, six modified asphalt mixtures were prepared and tested using SMA aggregate gradation with a nominal maximum aggregate size (NMAS) of 10 mm. The MSCR test results revealed that, of the six asphalt mixtures, the rubber-based PG76-28 exhibited the least initial strain and the highest elastic recovery. The dynamic modulus test results demonstrated that using a rubber-based modifier increased the elastic modulus at high temperatures and decreased it at low temperatures, thereby enhancing resistance to plastic deformation in the summer and reducing low-temperature cracking in the winter. Finally, the correlation between the Sapp performance index and the elastic recovery of modified asphalt and the number of direct tension cyclic loads until failure of the mixture was evaluated as 0.87 and 0.76, respectively.

Molecular dynamics simulation of the effect of tool parameters on nano-cutting of polycrystalline γ-TiAl alloys

As one of the most promising lightweight high-temperature structural materials in the future, the surface quality of γ-TiAl alloys has a great influence on the performance of the workpieces, and the tool parameters are an important factor affecting the machining results. In this study, molecular dynamics simulations of the nano-cutting process of polycrystalline γ-TiAl alloys with different tool parameters were carried out. The results show that increasing the tool rake angle and decreasing the tool edge radius within a certain range helps to reduce the average cutting force, cutting force fluctuation, cutting temperature, and stabilize the cutting process, while the change of the tool clearance angle has less influence on the cutting process. In contrast, negative rake angle cutting is more likely to produce grain rotation and grain boundary steps in the processed substrate and increase the processed surface roughness than positive rake angle cutting; increasing the tool rake angle within a certain range will weaken the elastic recovery effect of the substrate. During cutting at a positive rake angle, whether a portion of the substrate is prone to slip toward the surface of the substrate, thereby reducing the surface quality, depends on the relative state of grain orientation and force applied in the substrate.

Mechanical Dewatering of Homogeneous and Segregated Filter Cakes by Vibration Compaction

The solid volume fraction of a slurry requiring solid–liquid separation often fluctuates in industrial cake filtration processes. For low solid volume fractions, particle segregation arises, resulting in an inhomogeneous filter cake structure. Particle segregation has significant impacts on cake formation such as a longer cake formation time compared to homogeneous cakes. This work addresses the impact of this effect on vibration compaction, which is an alternative deliquoring method applying oscillatory shears to the filter cake. The dewatering results of homogeneous and segregated cakes made of the same material with a broad particle size distribution are compared. Although cake deliquoring is achievable despite particle segregation, vibration compaction is more effective for homogeneous cakes. The reason is that no particle size homogenization within segregated cakes occurs due to oscillatory shear, as particle size analyses indicate. The particle size measurements of cakes before and after vibration compaction reveal that the material’s particle size distribution is preserved despite vibration application. Vibration compaction achieves higher deliquoring than the common compaction method by squeezing, as elastic recovery effects after squeezing lead to the reabsorbing of liquid, already expressed and stored in the filter cloth. This demonstrates that vibration compaction is a real alternative for cake deliquoring.

Damage evolution in spark plasma sintered boron carbide under scratch and indentation loading conditions

Spark plasma sintered boron carbide (B4C) has been tested for damage evolution characteristics. Three distinct failure regions were identified during the scratch process of B4C, based on the observed transitions in the induced tangential force pattern and fracturing. B4C exhibited significant elastic recovery effect (50%) under both scratch (1–50 N) and indentations (5–100 mN) loading conditions. The sequence of transition from the nucleation of cracking and its propagation resulting to amorphization were identified. Scratch grooves were characterized with partial bow type Hertzian cracking, radial cracking and an onset of chipping (up to 75 N) and extensive spallation and fragmentation (76–100 N). The spallation regions were characterized with numerous randomly oriented slip lines suggesting failure dominated by the shear deformation. Raman spectra from spallation regions reveal peaks corresponding to amorphous B4C, inferring the occurrence of amorphization concentrated at the localized shear bands. At higher loads (>75 N), grain boundary fractures were observed in addition to simple cleavage fracture, which contributes for deteriorating material performance, by extensive cracking. The hardness and elastic modulus of B4C measured by nanoindentation were 44 GPa ± 6.6 GPa and 560 GPa ± 47 GPa, respectively.

Adjust operating conditions of an in-made house horizontal hydraulic press for a 90° cold bending process

During the cold-bending process, the tooling suffers considerable damage due to excess pressure. This also causes the machines to break down, causing problems in the precision and quality of the metal parts formed. The precision depends on the operating conditions of the press, the tooling employed, and the elastic recovery effect of the material. This study determines the working conditions for a made-in-house horizontal hydraulic press through an experimental design (DOE). This research carried out the V-forming to 90° (ISO 2768-1) of a hot-rolled carbon steel plate, considering pressure, piston permanence time, and recovery factor (Kr). The experimental and statistical analysis ensures accurate forming while the work pressure decreases by 17% and 33%, respectively, regarding the maximum. This reduction will delay the appearance of fatigue damage and have the operating parameters well established; in turn, it will be possible to design tools according to commercial standards.

Modeling of oscillating bone sawing forces with instantaneous cutting speed and depth of cut

Oscillating bone sawing is a crucial procedure in orthopedic surgery, but excess sawing forces are often detrimental to implant fixation and postoperative patient recovery. Therefore, understanding and controlling sawing forces are critical. However, the conventional bone cutting model is not applicable to the oscillating sawing process, as it requires variable speed cutting with a negative rake angle, which is affected by the difference in viscoelasticity of the bone at different speeds. In this study, an oscillating sawing force model was developed that considered variations in cutting speeds and depth of cut for each saw tooth. A speed-related cutting force model, including ploughing force in the tool edge and rake face, was developed, considering the effect of speeds on fracture toughness and normal stress based on orthogonal cutting experiments. Moreover, the model accounted for each saw tooth's instantaneous depth of cut by considering the depth of elastic recovery and interference effect of adjacent saw teeth, based on a kinematic model of the saw tooth tip. The impact force in the blind groove cut and the acceleration effect on cutting force were also considered in the model. The proposed model accurately predicts sawing forces, offers insights for reducing them through design parameter modifications, and has potential applications in medical training simulations, robotic-assisted surgery, and the optimization of saw blade shapes or movement to reduce sawing forces.

Plastic side flow and elastic recovery influences on optical diffraction effect of diamond turning: theoretical simulation and experimental verification.

Spherical/aspherical mirrors are widely used in optical systems and imaging systems, but their reflectivity is affected by the surface roughness. In this study, the effects of plastic side flow and elastic recovery on the diffraction phenomenon and reflectivity are analyzed systematically. The energy ratio of an ultra-precision turning surface is calculated by rigorous coupled-wave method, the influence of aberration on diffraction efficiency is considered in combination with the specific structural parameters of spherical/aspherical surface, and the appropriate measuring beam diameter is selected. Through predicted results and experimental observations, it can be found that with the increase of plastic side flow height, the energy ratio of zero-order diffracted light reduces, the brightness weakens, and the diffraction light spots become more obvious. This is because large plastic side flow height leads to more complex three-dimensional surface topography and great roughness P-V value. The influence of elastic recovery on the reflectivity is different from that of plastic side flow. As the elastic recovery increases, the roughness P-V value lessens. As a result, the energy ratio of zero-order diffracted light enlarges, and the brightness strengthens. This paper provides a theoretical basis for machining of spherical/aspheric mirrors with high reflectivity.

Accurate measurement of cutting-edge radius on a single-crystal diamond tool

Single-crystal diamond (SCD) tools are hard and can maintain a uniform sharp cutting edge and hence used in ultraprecision machining of optics. The tools typically have edge radii in the range of 10-100 nm. Direct measurement of the cutting-edge radius on the SCD tool accurately in the order of tens of nanometers using a scanning electron microscope (SEM) is not possible and arduous using an atomic force microscope (AFM). In this study, we have demonstrated a more accurate edge reversal technique to measure the SCD tool’s cutting-edge radius. A nano indent is made using the SCD tool on two polished pure copper blocks held together in a precise vise. After the nanoindentation, the copper blocks are separated, and the cross-section profile of the indentation mark, a replica of cutting-edge geometry, is observed in an SEM. A fitted circle on the indentation profile is used to obtain the edge radius. Due to the elastic recovery in the material, the indentation profile geometry changes slightly, and the radius measured from the SEM image is not the same as the actual tool radius of the SCD tool. We performed finite element method (FEM) simulations to quantify the amount of elastic recovery and calculate the elastic recovery factor for a given SCD tool geometry as a function of indentation depth and edge radius. From the simulation results, we found the error due to elastic recovery effect in edge radius measurement is only 10%. Due to the stick-slip condition and high stress concentration factor at the cutting edge of the tool, material pull-out is observed at the middle of the cutting mark on the substrate but at the ends of cutting mark on the substrate material was negligible. In this method, compared to the previous literature work the three primary sources of errors, elastic recovery effect, convolution effect of AFM tip, and material pull-out are eliminated. Hence, this method provides a more accurate measurement of the edge radius and can be adopted by research labs, universities, and industries having ultra-precision machining facilities without needing a special purpose SCD tool edge radius characterization facility.

Improved Cutting Force Modelling in Micro-Milling Aluminum Alloy LF 21 Considering Tool Wear

Aluminum alloy LF 21 has a strong ability to reflect electromagnetic waves. LF 21 waveguide slit array structure is widely used in waveguide radar antenna. The stiffness of the slit array structure is relatively weak. So, the structure is prone to deformation under the cutting force in the conventional milling process. Micro-milling technology can realize high-precision machining of mesoscale parts/structures and is a potential effective machining technology for the waveguide slit array structure. However, the diameter of the micro-milling cutter is small, and the feed per tooth is comparable to the arc radius of the cutting edge, so the micro-milling cutter is prone to wear. In addition, the effects of elastic recovery of material, the minimum cutting thickness and friction of cutting dead zone on micro-milling force cannot be ignored. A simulation model of micro-milling aluminum alloy LF 21 processes based on DEFORM 3D is built by combining the theory of cutting and the technology of process simulation. Prediction of tool wear is achieved. The quantitative relationship between the arc radius of the cutting edge and tool wear is clarified for the first time. The authors built an improved cutting force model in micro-milling LF 21 considering tool wear and cutter runout with the minimum cutting thickness as the boundary. The validity of the built micro-milling force model is verified by experiments.

Effects of structure relaxation and surface oxidation on nanoscopic wear behaviors of metallic glass

Both structure relaxation and oxidation of surface layer induced by thermal treatment or friction heat play significant roles in reducing wear of metallic glasses (MGs). To distinguish the effects of structure relaxation and surface oxidation, we prepared Zr-based MGs at different states, i.e., as-cast MG; the annealed MGs under argon atmosphere (referred to as structure-relaxed MG) and oxygen atmosphere (referred to as oxidized MG). Nano-wear tests were carried out by atomic force microscope (AFM) to quantitatively clarify these two effects on the wear performance. Compared with the as-cast MG, the structure-relaxed MG shows an increased adhesive but slightly decreased ploughing friction. While, the oxidized MG shows the best anti-wear performance with dramatic reductions in both adhesive and ploughing friction. Classic molecular dynamics (MD) and ab initio MD simulations revealed that the introduction of O hinders the MG atoms from forming interfacial bonds with diamond, and reduces significantly the adhesion between the diamond tip and passivated MG. In addition, the synergistic effect of high hardness and elastic recovery associated with oxidization reduces ploughing friction and enhances wear resistance. This finding clarifies the importance of surface chemistry over structure modification during wear, and offers a generic pathway for tailoring ultra-wear resistant MGs.

Conjugation of CMCS to silk fibroin for tuning mechanical and swelling behaviors of fibroin hydrogels

Silk fibroin (SF) attracts great scientific interests as multifunctional biomaterials, owing to its excellent biocompatibility. However, a critical issue with regard to pure SF hydrogels is its poor formability. To address this issue, a composite hydrogel of SF and carboxymethyl chitosan (CMCS) was prepared, via EGDE-assisted conjugation of CMCS to SF chains for tuning the mechanical property and drug-release behavior. The results reveals that molecular weight of SF was noticeably increased after grafting of CMCS, meanwhile, the obtained hydrogel exhibited high structural stability and improved mechanical properties compared to the control. In the range of compression ratio of 10 to 50%, the composite hydrogel exhibited satisfactory elastic recovery effects, meanwhile, increasing CMCS contents was beneficial enhance its water retention ability. Using Trypan blue as the model drug, the sustained release rate of the SF/CMCS hydrogel was approximately 35% higher than that of the SF hydrogel. Moreover, the introduction of CMCS into SF hydrogel also promoted the proliferation of NIH/3T3 cells, revealing excellent biocompatibility of the prepared hydrogel. In summary, an efficient and novel strategy to prepare fibroin hydrogels with desired properties is developed, which might expand the applications of SF in the field of biomedical materials.

Numerical and Experimental Study of Elastic Recovery in Deep Drawing of Low Carbon and Galvanized Steel Sheet Conical Products

Deep Drawing is an important sheet metal forming process. It has numerous applications in different industrial fields. Due to improvements in technological techniques, modern industries focused on products dimensional accuracy especially for the products that have inclined walls since it may suffer from the effect of elastic recovery or what is known as springback. Springback is considered a major defect besides thinning, earing, and other deep drawing defects. It may cause serious deviation from demand dimensions particularly for the products inclined by certain angle such as conical shells or products. This study investigates the effect of wall inclination angle, punch velocity, type and thickness of the sheet material on elastic recovery behaviour. Two types of sheet metal, low carbon (AISI 1008) and galvanized steel sheets, of 110 mm diameters circular blanks at 0.9 and 1.2 mm thickness are formed by tooling set (punch, die, and blank holder). Conical dies were used to execute the experimental work and numerical having inclination angles at 70°, 72°, and 74° where, the punch velocity was 100, 150, and 200 mm/min. Numerical simulation was conducted using ABAQUS 6.14 where dynamic explicit solver was used to preform formation of conical products and static or standard solver to predict the behaviour of springback effect. A comparison between the experimental and numerical simulation was conducted. The results show that elastic recovery decreased with increasing of die wall angle, punch velocity, and sheet or blank thickness while increased with increasing of metal yielding stress. The springback factor rose by 0.003 to 0.007 with die angle increasing by 0.002 to 0.006 with punch velocity and thickness increasing, while it decreased by 0.001 to 0.003 with increasing of yielding point. The numerical simulation results show same tendency and high agreement with experimental results with a maximum discrepancy of 4%.

Prediction of surface roughness in diamond turning of Al6061 with precipitation effect

Aluminum alloy 6061(Al6061) is one kind of precipitation hardening alloy, and its precipitate generation highly influences the mechanical properties and finished surface quality in diamond cutting. To accurately estimate the surface roughness in diamond turning of Al6061, an improved surface roughness prediction model is proposed in this study with the full consideration of the minimum undeformed chip thickness, the materials plastic side flow, elastic recovery and precipitation effect. Pre-heating treatments and diamond turning experiment are conducted on Al6061 samples to build the relationship between pre-heating conditions, precipitation generation and surface roughness in single point diamond turning (SPDT). The experimental results show that precipitation effects are found on both the deformed chips and the fresh generated surface. The effect of pre-heating conditions on precipitates generation agrees well with its effect on surface roughness of Al6061 in SPDT. Compared with the previously proposed models, the developed model considering the precipitation effect of Al6061 remarkably improves the prediction accuracy by 26 %.

Elastic recovery of monocrystalline silicon during ultra-fine rotational grinding

Micromachining of brittle materials like monocrystalline silicon to obtain deterministic surface topography is a 21st Century challenge. As the scale of machining has shrunk down to sub-micrometre dimensions, the undulations in the machined topography start to overlap with the extent of elastic recovery (spring back) of the workpiece, posing challenges in the accurate estimation of the material's elastic recovery effect. The quantification of elastic recovery is rather complex in the grinding operation due to (i) randomness in the engagement of various grit sizes with the workpiece as well as (ii) the high strain rate employed during grinding as opposed to single grit scratch tests employed in the past at low strain rates. Here in this work, a method employing inclination of workpiece surface was proposed to quantify elastic recovery of silicon in ultra-fine rotational grinding. The method uniquely enables experimental extraction of the elastic recovery and tip radius of the grits actively engaged with the workpiece at the end of the ultra-fine grinding operation. The proposed experimental method paves the way to enable a number of experimental and simulation endeavours to develop more accurate material constitutive models and grinding models targeted towards precision processing of materials. It can also be shown that using this method if the tip radius distribution of active grits is measured at different time instances, then this data can be used to assess the state of the grinding wheel to monitor its wear rate which will be a useful testbed to create a digital twin in the general framework of digital manufacturing processes.

Modelling and experimental analysis of the effects of run out, minimum chip thickness and elastic recovery on the cutting force in micro-end-milling

Prediction of cutting force has great significance for controlling the micro-end-milling processes. In this study, a mechanics model for exactly prediction cutting force is comprehensively established by considering the variety of entry and exit angles for each engaged cutting edge and an accurate instantaneous uncut chip thickness (IUCT). The determination of IUCT has considered the combination of the minimum chip thickness, tool run-out, and the material's elastic recovery, which is embedded in the cutting force model. Further, cutting force coefficients as function of uncut chip thickness have been calculated by using finite element method (FEM). To verify the reliability of the presented cutting force model, a series of experiments for cutting force are conducted and experimental results are compared to cutting force predicted. The results demonstrate that the cutting force predicted is well in agreement with that of measured. The effects of elastic recovery and tool run-out on cutting force also are investigated. Some conclusion can be drawn that elastic recovery can more obviously affect the cutting force predicted with smaller the feed per tooth, the errors of experimental and predicted is getting smaller with increasing the cutting depth, the slight change of tool run-out will lead to a great variation in cutting force.

A novel surface roughness model for potassium dihydrogen phosphate (KDP) crystal in oblique diamond turning

KDP crystal is a typical soft-brittle material, and the challenge of predicting its surface roughness at a wide range of feed rates in oblique cutting invokes the comprehensive consideration of various factors, e.g. the plastic behavior in ductile mode and the cracks effect in brittle mode. In this work, a novel theoretical roughness model, into which the components of kinematics, plastic side flow, materials elastic recovery and cracks effect are integrated, is proposed to reveal the underlying mechanisms of surface roughness variation in oblique diamond turning of KDP crystal. In modeling, the duplication effect of the active cutting edge contour is successfully used to calculate the component of kinematics, and an empirical expression with consideration of equivalent cutting edge radius in oblique cutting is reconstructed to estimate the materials elastic recovery. For the component of plastic side flow, the effect of the volume of unremoved materials and the scale coefficient of plastic side flow determined by feed rate and tool inclination angle are taken into account. Moreover, the component of cracks effect is quantified based on the relative length of crack (RLC) model that considers the material properties, tool geometries, process parameters and the suppression of hydrostatic pressure in the cutting area. In experiments, a method of oblique fly-cutting is employed to reduce the impact of material anisotropy on surface roughness. The results show that the RLC model can well predict the distribution of cracks, and the surface roughness model considering these four components has a satisfactory prediction accuracy.

Hardness and friction coefficient of fused silica under scratching considering elastic recovery

Elastic recovery of fused silica under scratching has significant effects on its hardness and friction coefficient. However, the effects are seldom considered in previous calculation models causing misestimation of hardness. In this work, scratching on fused silica with a conical indenter and a Berkovich indenter was investigated by finite element analysis (FEA). Meanwhile, analytical models of apparent friction coefficient were built by modeling the geometry of contact regions as a sector and a triangle for the conical and Berkovich indenters, respectively. With the effects of elastic recovery taken into account, the apparent friction coefficient predicted by these analytical models is consistent with FEA. The results provide a reference for calculating hardness of materials with large E/H (Young's modulus/hardness) like fused silica during scratching, which consider elastic recovery. Besides, by analogues to indentation strain, a new parameter, i.e., sliding strain εs, is proposed. FEA reveals that εs can be used to characterize the effects of indenter geometry and sliding direction on scratching. As demonstrated by the results, the apparent friction coefficient and hardness increase with εs, while the elastic recovery ratio decreases with εs.

High temperature rheological properties of APAO and EVA compound modified asphalt

This study aims to explore the laboratory performance of APAO (Amorphous Poly Alpha Olefin) and EVA (ethylene-vinyl acetate copolymer) compound modified asphalt. Four EVA concentrations (i.e., 0%, 2%, 4%, and 6% by the weight of base asphalt) and four APAO concentrations (i.e., 0%, 2%, 4%, and 6% by the weight of base asphalt) were selected. Conventional tests (penetration, softening point, ductility and viscosity) were conducted. Frequency sweep, temperature sweep and multiple stress creep recovery (MSCR) tests were carried out to investigate the rheological properties of the asphalt binders and the storage stability was measured by cigar tube tests. The aging effect was evaluated by using dynamic shear rheometer (DSR) testing results. Fourier transform infrared spectroscopy (FTIR) test was used to study the chemical reaction of the asphalt. The results represented that the addition of additives (i.e., APAO and EVA) decreased the nonrecoverable creep compliance and aging index while increased softening point, elastic recovery, complex modulus and recovery rates, which indicating that APAO and EVA enhanced the high temperature properties of asphalt. Specially, in the ductility test at 5℃, the addition of APAO/EVA greatly improved the crack resistance at low temperature. The increasing VTS (viscosity-temperature susceptibility) indicated the additives enhanced the resistance to temperature susceptibility of this compound modified asphalt. Besides, the binder with APAO is better than that with EVA alone, especially in the elastic recovery and aging effect. Besides, the storage stability test results showed that the increase of APAO improved the stability of asphalt and the compound modified asphalt binders showed good resistance to cracking at low temperature in ductility test at 5 °C. The FTIR test showed that chemical reactions might happen during the mixing process of asphalt.

A Comparative Study of Forming and Crash Behavior of High Strength Steels

Abstract Advanced high strength (AHS) steel sheets of various grades have been increasingly used in the automotive industries because of their advantageous mechanical properties. High strength and great energy absorption are desired for a structural component design. On the other hand, large formability and strain hardening are necessary for achieving an effective forming process. To apply eligible steel grades, precise understanding of their forming and crash characteristics is needed. In this work, AHS steels with varying strengths, namely grades 780, 980, and 1180, were investigated. First, tensile tests were performed, and mechanical properties, including r-values, of the examined steels were obtained for different loading directions. The forming limit curves (FLCs) and respective forming limit stress curves (FLSCs) were determined by means of a Nakajima forming test and finite element simulation. The cyclic tension-compression tests were conducted to characterize the elastic recovery and Bauschinger effect of steels. Afterward, forming processes of an automotive part were performed, and the forming and springback behaviors of steels were evaluated by using simulations coupled with Hill’48 and Yoshida-Uemori models, determined material parameters, FLCs, and FLSCs. In addition, crashworthiness of steels was numerically studied by means of a crash rectangle profile and simplified side impact pole test. The mechanical, forming, and crash performances of all the investigated AHS steels were evaluated and discussed so that the results can be applied for part design and manufacturing.

Analytical prediction for depth of subsurface damage in silicon wafer due to self-rotating grinding process

Subsurface damage (SSD) induced by silicon wafer grinding process is an unavoidable problem in semiconductor manufacturing. Although experimental attempts have been made on investigation of the influential factors on the SSD depth, however, few theoretical studies have been conducted to obtain SSD depth through grinding parameters. To fill the gap, an analytical model is developed to predict the SSD depth in silicon wafer due to self-rotating grinding process, which can reveal the relationship among SSD depth and the grinding parameters, the size of the abrasive grains and the radial distance from the wafer center. The establishment of the proposed model is based on scratch theory and fracture mechanics of isotropic brittle materials, and we further consider the effects of elastic recovery, cleavage plane and crystalline orientation on SSD formation. To validate the applicability of the proposed predictive model, grinding experiments with varied grinding parameters are performed and the depths of SSD along the <110> and <100> crystal directions are also measured and analyzed. The results given by the proposed model present reasonable accuracy of less than 20% deviation with experimental results. Effects of grinding parameters, wafer radial distance, crystalline orientation, and abrasive grain size on SSD depth are discussed in detail.