kPa Load Research Articles

Numerical analysis of soil reinforced by sand columns using different installation methods

This study involves a finite element numerical simulation of laboratory tests conducted on small-scale models. The tests involved the installation of columns using different techniques: without soil displacement and without column compaction (WR-NC), and without soil displacement but with column compaction (WR-WC). The reinforced soil masses were then subjected to a uniform 150 kPa load. A comparison between the numerical and experimental results showed excellent agreement, validating the simulation. Following this validation, a parametric analysis was carried out to examine the effects of the various parameters on the behavior of the reinforced soil masses. In the first method, three different column diameters were analyzed, focusing on the effects of diameter (area replacement ratio), column length, and geogrid containment benefits. In the second method, three levels of compaction pressure were applied during the column installation. The study evaluated the impact of column installation techniques on the behavior of the reinforced masses. The findings indicate that settlement reduction is proportional to the increase in area replacement ratio and column length. Additionally, confining the columns with geogrid was shown to be effective in further reducing settlements. The results also revealed that increasing compaction stress leads to greater radial expansion of the columns, which densifies and stiffens the surrounding soil, thereby reducing settlement. Overall, the study concludes that column installation techniques significantly influence the behavior of reinforced soil masses.

Improving the properties of hot applied crack sealant by utilizing Pre-activated Crumb Rubber (PCR)

Crack sealing stands as a cost-effective pavement maintenance practice and has a typical life span of 1–3 years. To enhance sealants’ longevity and optimize their performance, evaluating potential material modification, particularly in hot and arid regions, is of interest. In this research study, a comprehensive testing protocol was designed to address prevalent failure modes observed in asphalt crack sealants such as adhesion, cohesion, pumping, and settlement failures. The primary modification involved the incorporation of Pre-activated Crumb Rubber (PCR) at varying concentrations (2.5%, 5%, and 7.5%) by weight of the sealant. Testing was conducted on both unaged and short-term aged sealant samples with different PCR contents. The findings revealed promising improvements associated with PCR concentrations up to 5%, manifesting as enhanced elasticity, toughness, tenacity, flexibility at low temperatures, and resistance to shear thinning at high temperatures. For a content of 5% PCR, the results show a decrease of the non-recoverable creep compliance (Jnr) of 60% for 0.1kPa and 81% for 3.2kPa loading conditions when compared to the control sealant. Furthermore, an increase in toughness and tenacity of 72% and 25% respectively was measured for the aged conditions. In terms of shear thinning resistance, the coefficient “P” increased from 0.75 to 0.83 indicating a greater resistance to tracking. The results indicated favorable trends with the addition of the modifier, yielding potential improved performance in the field.

Analyzing photovoltaic module mechanics using composite plate theories and finite element solutions

Deflection and stress calculated from an experimentally validated, high-fidelity finite element model (FEM) of a photovoltaic module experiencing mechanical load was compared to results from a simplified FEM treating the module laminate as a homogenized composite using a rule of mixtures approach, and further compared to analytical calculations treating the module as a Kirchoff-Love flat plate. The goal of this study was to determine the error incurred by analyzing module mechanics with varying levels of simplification, since resolving the aspect ratios of a module is computationally expensive. Homogenized FEMs were found to underpredict peak deflection under a 1.0 kPa load by between 13 and 19% for lower and upper bound application of the rule of mixtures. However, module shape was captured, implying that a useful replication of a resolved model could be achieved with a reduced, calibrated material stiffness. Homogenized stress results captured glass layer tensile stress components to within 46 to 52% at a sample location of interest, though agreement was poor through the remainder of the laminate due to the lack of material resolution. For plate theory, deflection was overpredicted by 45 to 67% for upper and lower bound homogenizations, and frame-adjacent module shapes were not adequately replicated. Stress results mirrored FEM trends but magnitudes were not well correlated to resolved model values. These results support the use of homogenized laminate models for module shape derivation, though resolved models remain necessary for stress analyses. The accuracy of plate theory was found to be inadequate for most applications.

Mechanical strength testing of ethylene-tetrafluoroethylene film

Mechanical strength testing of ethylene-tetrafluoroethylene (ETFE) film is performed on the test machine INSTRON. The average elastic modulus of the film is 35.8 MPa. Under subsequent loading, the elastic-to-plastic stage transition occurs with decreasing elastic modulus to 1.78–2.71 MPa and then to 0.06–0.086 MPa. Strength testing of the ETFE film 250 µm thick at 8.577 kPa uniformly distributed load does not lead to the film rupture either at positive (15–18 °С) or negative temperatures (–23–29 °С). A multiple damage of the film under an 8.50 kPa load at −26 °С does not lead to its disruption. The film bending at positive and negative temperatures reaches 84 and 58.2 mm, respectively. Strength testing of the ETFE film demonstrates its ultra-high strength properties, and thus predicts its wide use in the formation of comfortable conditions in buildings created in Arctic and other territories of Russia.

Impact of compaction ratio and loading period on compressional behavior of foam glass aggregates

Foam glass aggregates are used as a lightweight material in various civil engineering applications due to their big granular nature. Investigating the impact of compaction ratio, loading period, and environmental condition on the compressional behavior of the material is highly appreciated. In this study, after examining the pore microstructure and elements of the material, a series of static compression loads starting from 50 kPa to 300 kPa with 50 kPa intervals were applied on foam glass aggregate samples which were prepared with four different compaction ratios (10%, 20%, 30%, and 40%). The density and porosity of the material at different compaction ratios were also tested. The results showed a significant decrease in vertical strain values, from 6.2% at 10% compaction to 0.8% at 40% compaction. The compressibility rate significantly reduced, especially after 20% compaction. Calculated Eoed ranged between 7.9 MPa at 10% compaction under 50 kPa loading to 23 MPa at 40% compaction under 300 kPa loading. The long-term loading stage revealed that the material's strain values are not significantly time-dependent, especially when the material has been compacted more than 20%. The porosity of the samples was only reduced by 3% after compacting the aggregate to a 40% ratio. The influence of submergence on the compressional behavior of foam glass aggregate for the given loading range was eliminated when the material was compacted by more than 20%.

Numerical Analysis of Shallow Foundations with Varying Loading and Soil Conditions

The load–deformation relationship under the footing is essential for foundation design. Shallow foundations are subjected to changes in hydrological conditions such as rainfall and drought, affecting their saturation level and conditions. The actual load–settlement response for design and reconstructions is determined experimentally, numerically, or utilizing both approaches. Ssettlement computation is performed through large-scale physical modeling or extensive laboratory testing. It is expensive, labor intensive, and time consuming. This study is carried out to determine the effect of different saturation degrees and loading conditions on settlement shallow foundations using numerical modeling in Plaxis 2D, Bentley Systems, Exton, Pennsylvania, US. Plastic was used for dry soil calculation, while fully coupled flow deformation was used for partially saturated soil. Pore pressure and deformation changes were computed in fully coupled deformation. The Mohr–Columb model was used in the simulation, and model parameters were calculated from experimental results. The study results show that the degree of saturation is more critical to soil settlement than loading conditions. When a 200 KPa load was applied at the center of the footing, settlement was recored as 28.81 mm, which was less than 42.96 mm in the case of the full-depth shale layer; therefore, settlement was reduced by 30% in the underlying limestone rock layer. Regarding settlement under various degrees of saturation (DOS), settlment is increased by an increased degree of saturation, which increases pore pressure and decreases the shear strength of the soil. Settlement was observed as 0.69 mm at 0% saturation, 1.93 mm at 40% saturation, 2.21 mm at 50% saturation, 2.77 mm at 70% saturation, and 2.84 mm at 90% saturation of soil.

Micromachined Tactile Sensor Array for RTSA.

This work presents a polymer-based tactile capacitive sensor capable of measuring joint reaction forces of reverse total shoulder arthroplasty (RTSA). The capacitive sensor contains a polydimethylsiloxane (PDMS) dielectric layer with an array of electrodes. The sensor was designed in such a way that four components of glenohumeral contact forces can be quantified to help ensure proper soft tissue tensioning during the procedure. Fabricated using soft lithography, the sensor has a loading time of approximately 400 ms when a 14.13 kPa load is applied and has a sensitivity of 1.24 × 10−3 pF/kPa at a load of 1649 kPa. A replica RTSA prothesis was 3D printed, and the sensor was mounted inside the humeral cap. Four static right shoulder positions were tested, and the results provided an intuitive graphical description of the pressure distribution across four quadrants of the glenohumeral joint contact surface. It may help clinicians choose a right implant size and offset that best fit a patient’s anatomy and reduce postoperative biomechanical complications such as dislocation and stress fracture of the scapula.

Verifying the Mechanical Performance of Cold and Hot Asphalt Mastics Containing Jet Grouting Waste as a Filler

In the road construction sector, the CO2 emissions that affect global warming are, in most cases, from the asphalt mixtures production activities that are carried out at high temperature (above 160 °C). The research here presented aims to investigate the physical-mechanical properties of asphalt mastics made up using jet grouting waste (JW) as a filler produced through both cold (40–50 °C) and hot mixing process. The first step focused primarily on examining the effects of optimal blending time and curing time of the mastics. The second step focused on the investigation of the rheological properties using a dynamic shear rheometer and carrying out a frequency sweep test at temperatures ranging from 0 to 50 °C with increments of 10 °C, and a multiple stress creep and recovery (MSCR) test under 0.1 and 3.2 kPa load levels at temperatures of 40 and 50 °C. Four cold asphalt mastic solutions were analyzed and then compared to three hot traditional ones, keeping constant, on the one hand, the binder weight and filler over binder weight ratio (0.5), and, on the other hand, changing the type and amount of filler. The compositions of the hot and cold asphalt mastics were as follows: (a) 33% limestone filler (LF) plus 67% bitumen (concerning the cold mixing process, the bitumen content refers to the amount of bitumen into the bitumen emulsion), (b) 33% JW plus 67% bitumen, (c) 16.5% LF plus 16.5% JW and 67% bitumen. The fourth solution designed only for cold asphalt mastic was made up of 33% Portland cement (PC) plus 67% bitumen (referring to the amount of bitumen in the bitumen emulsion). The main findings showed that the optimal performance was achieved at high test temperature by cold and hot asphalt mastics made up adding LF and JW filler, which showed a pronounced elastic behavior. Moreover, the cold asphalt mastic solution made up of LF and JW filler showed better performance than the mastic made up using PC, reaching over 40% increase of the shear modulus and 30% lower non-recoverable creep compliance values at all test temperatures.

Robust and flexible transparent protective film fabricated with an ambient-curable hybrid resin

An ambient-curable hybrid resin (ACHR) terminated with trimethoxysilane functional groups, synthesized through a simple ring-opening reaction between 3-glycidyloxypropyltrimethoxysilane (KH560) and 4,4′-methylenebis (cyclohexylamine) (PACM), was applied to the surface of a transparent organic polymer to produce a robust, flexible, and transparent protective hybrid film, moisture cured at room temperature. The structure, morphology, and optical, mechanical, and thermal properties of the obtained hybrid film were evaluated. The hybrid film allowed the transmittance of more than 87% of visible light (at 600 nm), maintaining almost the same high transparency as bare PET film. The unique flexible segments and rigid segments in the inorganic–organic hybrid structure of the film realized superior resistance to bending and scratching. The hybrid film-coated PET demonstrated excellent flexibility, with an extremely low bending radius, illustrated by wrapping around a 1-mm mandrel bar without cracking. In addition, the hybrid film exhibited superior pencil hardness (of 2H) and excellent wear durability, i.e., no scratching after being subjected to 200 abrasion cycles using #0000 steel wool under a 19.6 kPa load. The robust, flexible, and transparent protective film developed here, and its simple and efficient preparation method, should have extensive application prospects.

Investigating the rheological properties of hot bituminous mastics made up using plastic waste materials as filler

The large amount of plastic waste is currently causing serious pollution to the environment mainly due to long decomposition times and their dispersion. In order to avoid that the pollution by plastics could worsen further, it is trying to encourage companies to recycle existing pallets to create new products.This study investigates the volumetric and mechanical properties of hot bituminous mastics made up using plastic waste materials (PW) as filler. The PW has a maximum size of 2 mm and a melting temperature between 120 and 260 °C. Scanning Electron Microscopy of the PW reveals a mesh structure of elongate elements marked by a much rougher surface than traditional limestone filler (LF).The first step of the study focused primarily on searching for the optimal blending time for the mastics; a total of nine mastics were made up, and no substantial differences were found for any of them on increasing mixing time from 10 up to 60 min in terms of softening point, penetration at 25 °C or dynamic viscosity at 100 °C. Thus, a period of 10 min was selected for mixing all the mastics.The second step focused on the investigation of rheological properties using a dynamic shear rheometer and carrying out a Frequency Sweep (FS) test at temperatures ranging from 0 °C to 50 °C with increments of 10 °C, and a Multiple Stress Creep and Recovery (MSCR) test under 0.1 and 3.2 kPa load levels at temperatures of 40 and 50 °C.The two resulting best solutions are made up of a) 20% PW (HP02), and b) 5% LF plus 15% PW (HLP02), both by the total weight of B5070. Specifically, the shear modulus G* for mastics containing PW showed a distinct increase in G* compared both with B5070 and traditional mastics made up of LF; in particular, the gap becomes more marked moving towards 50 °C, where the best performance of HP02 is obtained.Moving on to illustrate the main results of the MSCR analysis, it was observed that the HP02 and HLP02 solutions showed good recoverable deformation already from the end of the loading phase without waiting for the last step of the unloading cycles at two test temperatures and under two stress levels.

Experimental investigation of the behavior of soil reinforced with waste plastic bottles under cyclic loads

The low natural degradation rate of plastic products makes the recycling or disposal of increasing post-consumer plastic materials, including Plastic Polyethylene Terephthalate (PET) bottles, a global concern. The current capacity of recycling programs for absorbing annual waste PET materials in environmentally friendly ways is limited. As a novel beneficial option, the cellular form of post-consumer bottles might act to provide sufficient confinement for infill soil and hence provide a technique by which the behavior of foundation beds under applied loads could be improved. In this study, a series of full-scale tests were conducted on unreinforced and PET (Plastic Polyethylene Terephthalate) bottle reinforced beds. For each test 100 cycles of 400 kPa load followed by 400 cycles of 800 kPa load was applied to the pavement through loading plate. Experiments were performed in a 2200 × 2200 × 1000 mm test pit on a 300 mm diameter circular loading plate. Three different sizes (i.e., different external diameters and heights) of waste plastic (PET) bottles filled with soil were tested as a reinforcing element. In some tests, a single layer of HDPE (high-density polyethylene) geogrid layer over bottles reinforced zone was examined. The results showed improvement in all reinforcing arrangement, although improvement was slightly higher for smaller bottles. For the reinforced case, a lower settlement accumulation rate and a higher resilient (elastic) settlement was observed compared to the unreinforced condition. In the case of lower cyclic loading (400 kPa amplitude), an average 42% improvement occurred for the three bottle-reinforced scenarios, however this value was 179% for higher cyclic loading (800 kPa), indicating more benefits of bottle-reinforcement in the case of critically loaded conditions. An extra layer of geogrid over the bottle-reinforced zone increases load distribution area and prevents distortion of bottles, leading to as much as 82% more reduction in soil settlement compared to the case without geogrid. The combined use of bottles and single geogrid layer eliminates the need to multilayer geosynthetic reinforcement usage, helps the economy of the project besides avoiding the high cost of waste bottle disposal.

Tunable Electromechanical Liquid Crystal Elastomer Actuators

Liquid crystal elastomers (LCE) are soft materials which anisotropically shape morph in response to external stimuli. Herein, a method to produce large‐area carbon nanotube–LCE nanocomposite films with exceptional electrostrictive properties is examined. A methodology to produce telechelic precursor oligomeric composites at scale (>100 g) is presented along with the continuous casting and photocuring process. The carbon nanotubes are well‐aligned and well‐dispersed in the films, which exhibit exceptional anisotropic thermomechanical, optical, and thermal shape change characteristics. When an electric field is applied through the film thickness, the material quickly and reversibly contracts along the alignment direction. As an example, a compliant carbon nanotube–LCE film contracts >4% against a 140 kPa load, roughly comparable to the blocking force of many natural muscular tissues. Furthermore, it is demonstrated that this tunable contraction is dependent upon the electric field strength, and that the contraction mimics the form function of the input electric field (e.g., a sine wave). These compliant actuators are excellent candidates for incorporation into soft and/or biological systems.

Mechanical abrasion resistant candle soot based superhydrophobic coating over nanosecond laser textured stainless steel

In this report, we show that using naturally hydrophobic wax bound carbon soot nanoparticles (WCN) as fillers over laser ablation textured stainless steel surface, a mechanical abrasion resistant superhydrophobic (SH) surface can be prepared. The abrasion resistance may be due to the fact that during mechanical abrasions, the WCN lying in the lower layers of the laser textured surface get spread over the abraded surfaces and maintain superhydrophobicity. Further, the laser created grooves provide a space for the WCN to stay protected from abrasions so that all the WCN do not get wiped away at once. The developed SH surface when abraded by a sandpaper of 3000 grit loaded with 8 kPa load was found to exhibit ∼157° contact angle and ∼7° sliding angle even after 40 cycles of abrasions which corresponded to ∼400 mm abrasion distance. Further, the SH surface obtained by using WCN over laser textured surface was also found to have better abrasion resistance when compared with the SH surface prepared via the conventional fluorosilane coating over laser textured surface.

Poly-Saora robotic jellyfish: swimming underwater by twisted and coiled polymer actuators

Jellyfish are energy-efficient swimmers due to the muscle-powered flapping of their soft bell that facilitates a unique energy recapture mechanism. In this paper, we present a bio-inspired jellyfish robot named Poly-Saora that mimics the swimming behavior of the jellyfish species Black sea nettle (Chrysaora achlyos). An assembly-based fabrication method is used to create the Poly-Saora that is developed mainly with polymeric materials (95% of the robot by volume). Twisted and coiled polymer (TCP) actuators are successfully implemented in this robot and show great potential for underwater applications. The influence of different parameters such as the amplitude of the input power, the actuation frequency, and the lifecycle of the actuator are investigated underwater. A full characterization of 6-ply TCP muscles is demonstrated. An actuation strain of ∼10% is achieved in water at a frequency of 0.1 Hz and 50 kPa load. When integrated into the jellyfish, the TCP was able to bend a single bell by 17°. Poly-Saora was able to swim a vertical distance of 180 mm in 220 s with four TCP actuators each confined in a separate conduit. The robot mimics the swimming behavior of a real jellyfish by contracting the bell segments through the activation of the actuators, which generates forced water circulation under the bell in a pulsating rhythm, consequently creating a vertical movement of the robot. Overall, Poly-Saora presents a model of an underwater system that is driven by stimuli-responsive polymer materials and has unique advantages over conventional rigid robots due to their lightweight, muscle-like structures, silent actuation and ease of manufacturing. This robot can be used for safe interaction with other underwater species and their natural habitats when fully developed.

Characterization of Perineum Elasticity and Pubic Bone-Perineal Critical Distance with a Novel Tactile Probe: Results of an Intraobserver Reproducibility Study.

Background:Tactile imaging provides biomechanical mapping of soft tissues. Objective biomechanical and anatomical assessment of critical structures within the vagina and pelvis may allow development and validation of a clinical tool that could assist with clinical decisions regarding obstetrical procedures and mode of delivery. Objective: To assess intraobserver reproducibility of measurements of perineal elasticity and pubic bone-perineal critical distance with a novel tactile probe in pregnant women.Methods:An Antepartum Tactile Imager (ATI) was designed with a vaginal probe resembling a fetal skull. The probe comprises 128 tactile sensors on a double curved surface and measures 46 mm in width and 72 mm in length. The probe has a motion tracking sensor that allows acquisition of 3D tactile images. There were two arms of the study. In the first arm, biomechanical mapping of the perineum and pelvic bone location was performed in 10 non-pregnant women for purposes of demonstrating safety and feasibility. In the second arm, biomechanical mapping was performed in 10 pregnant women to explore intraobserver reproducibility. Each subject had two standardized examinations over 3 – 5 minutes by the same observer. Examination comfort and pain levels were assessed by post-procedure survey. Reproducibility was analyzed by intraclass correlation coefficients (ICC) with 95% confidence intervals and Bland-Altman plots. Bias and the 95% limits of agreement were also calculated.Results:The safety and feasibility arm of the study demonstrated high degree of safety and tolerability and reliable acquisition of tactile signals. In the reproducibility arm, 10 pregnant women were recruited at mean gestational age of 34.2 ± 6.5 weeks. The mean perineum elasticity (Young’s modulus, E) was 9.8 ± 5.9 kPa, and the mean pubic bone-perineal critical distance (D) at 20 kPa load was 34.6 ± 6.2 mm. The ICC was 0.97 [95% confidence interval (CI) 0.91, 0.99] and 0.82 [CI 0.44, 0.95] for E and D respectively, consistent with excellent intrarater agreement. The bias and the 95% limits of agreement of E were −6.3% and −29.4% to +16.7%, respectively. The bias and the 95% limits of agreement of D were −2.6% and −25.3% to +20.2%, respectively.Conclusions:The tactile imaging data obtained in the study reproducibly characterized perineal elasticity and pubic bone-perineal critical distance. Further evaluation of this tool in clinical settings is warranted.

Highly stretchable, breathable and negative resistance variation textile strain sensor with excellent mechanical stability for wearable electronics

In recent years, wearable and stretchable electronic devices have attracted great research interest and effort due to their promising applications in electronic skin, wearable health monitoring, human–machine interactions and so on. However, it still remains a great challenge to fabricate highly stretchable and wearable devices with excellent breathability, mechanical robustness and laundering durability. Herein, we fabricated a highly stretchable and breathable textile strain sensor based on conductive polyester fabric (CPF) with weft-knitted structure by chemically growing conductive and transparent Al-doped ZnO (AZO) element via atomic layer deposition (ALD). The CPF strain sensor demonstrates captivating performance, including high stretchability (up to 130%) and long-term stability (3000 cycles), as well as a distinct negative resistance variation with increasing strain owing to its weft-knitted structure. Most importantly, due to the formation of chemical interactions between textiles and AZO films during ALD process, the CPF strain sensor exhibits excellent mechanical robustness and laundering durability under reciprocating rubbing (50 kPa load pressure, 30 cycles), washing (500 r/min for 10 cycles, 200 min) and light fastness (accelerated light aging test for 7 days), thus allowing the fabrication of breathable and comfortable wearable sensor without elastomer encapsulation. Based on its admirable performances, the CPF strain sensor can be easily knitted or sewed on garments or attached on human skin directly for tracking both large and subtle human motions, revealing its numerous prospects in wearable electronics, intelligent robotics and other fields.

Effect of biomechanical stress on endogenous antioxidant networks in bovine articular cartilage

Mechanosensitve pathways in chondrocytes are essential for maintaining articular cartilage homeostasis. Traumatic loading increases cartilage oxidation and causes cell death and osteoarthritis. However, sub-lethal doses of the pro-oxidant molecule tert-Butyl hydroperoxide (tBHP) protects against loading-induced chondrocyte death. We hypothesized that compressive cyclic loading at moderate strains (<20%) causes sub-lethal cartilage oxidation that induces an adaptive increase in the endogenous antioxidant defense network. We tested this hypothesis by subjecting healthy bovine articular cartilage explants to in vitro static or cyclic (1 Hz) compressive loading at 50 kPa (15% strain, "physiologic") versus 300 kPa (40% strain, "hyper-physiologic") for 12 h per day for 2 days. We also treated unloaded explants with 100 μM tBHP for 12 h per day for 2 days to differentiate between biomechanical and chemical pro-oxidant stimulation. All loading conditions induced glutathione oxidation relative to unloaded controls, but only the 50 kPa cyclic loading condition increased total glutathione content (twofold). This increase was associated with a greater expression of glutamate-cysteine ligase, the rate-limiting step in glutathione synthesis, compared to 300 kPa cyclic loading. 50 kPa cyclic loading also increased the expression of superoxide dismutase-1 and peroxiredoxin-3. Like 50 kPa loading, tBHP treatment also increased total glutathione content. However, tBHP treatment and 50 kPa cyclic loading differed in their effect on the expression of genes regulating antioxidant defense and cartilage matrix synthesis and degradation. These findings suggest that glutathione metabolism is a mechanosensitive antioxidant defense pathway in chondrocytes and that intermittent pro-oxidant treatment alone is insufficient to account for all changes in mediators of cartilage homeostasis associated with cyclic loading. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:760-769, 2018.

Comparison of one-step and step-wise compression tests

The primary purpose of this paper is to investigate the influence of loading procedure type. To reach this aim, we have chosen the Baltic Sea Klaipėda sand, due to granulometry composition and particles shape. The paper examines several key aspects of sand compression type, namely comparison between one-step (constant rate loading) and step-wise (incremental loading) oedometer compression tests. In this manuscript, we present investigation of sandy soil compression character up to maximum 400 kPa loading. This research shows the difference between two loading procedures. The main objects of research: investigation of stress jumps during one-step and step-wise soil sample loading. The analysis of the results shows that when soil was compressed by step-wise loading procedure (0.94 mm) displacements were almost twice as big as in case of one-step loading procedure (0.57 mm).

(Invited) Temporary Bonding with Polydimethylglutarimide for Residue-Free Layer Transfer and 3-D Integration

Residue free temporary bonding with Polydimethylglutarimide (PMGI) was studied for a Layer Transfer Platform. Temporary wafer bonding is one of promising technologies for 3D integration, in particular transferring 2D materials such as graphene. PMGI was traditionally applied for lift off resist (LOR) and used as sacrificial layer for undercutting during lift-off processing. However, it has recently been reported that a sacrificial layer of LOR based PMGI (MicroChem) realized a clean graphene surface and free of residue after protolithic-graphic processing1. The practicability of LOR as a temporary wafer bond adhesive is investigated by varying bonding parameters and monitoring the size of the bonded area as well as the bond strength. Bonding of Si wafers using PMGI as a temporary adhesive was performed. Before bonding, Si wafers were cleaned using Standard Clean 1 (H2O:NH4OH:H2O2 = 5:1:1). After surface cleaning, Si wafers are spin coated with LOR 5A (MicroChem), which is based on PMGI, and pre-baked to evaporate the solvent in the resist. Finally, the two PMGI surfaces are brought into contact and the wafer pair was introduced into a bonding machine (EV-501 from EVGroup Inc.). In the bonding machine, the two PMGI layers are compressed face to face with a force of 150 N, under vacuum condition of around 10-3 Pa, and heated to 200-250 ºC. To evaluate these bonded samples, the size of bonded area was observed using an Infrared camera, and the bond strength was evaluated by blade crack test 2. Under optimized process conditions, the wafers are bonded with a few small voids. The size of bonded area covers over 98% of the wafer surface. Also, the wafers are bonded strongly. The bond strength of the sample under optimized conditions is 4.86 J/m2. The surface energy of two Si wafers is 5 J/m2. This means the strength of bonded samples is almost as same as the bulk of Si under the optimized conditions. For an optimization of spinning speed at coating stage, samples are bonded with the spin speed ranging from 2000 to 5000 rpm. This result shows bonded area is large enough (>98%) at spinning speed is between 2000–4000 rpm. However, some voids appear after bonding when spinning speed is higher than 5000 rpm and the bond strength gradually deceased with higher spin speed. From these results, the strongest bonding as well as largest bonded area is obtained when spin speed is 2000 rpm. For an optimization of pre-bake temperature after spinning, samples are bonded with pre-bake temperature from 120 to 220◦C. Bonding quality of the samples baked at 120 ºC was poor in both bond strength and bonded area. However, when the pre-bake temperature is higher than 160◦C, most of the loaded area was bonded and the bond strength is high. One reason for this is that the boiling point of cyclopentanone, the solvent of LOR, is 131◦C. Thus, samples baked at 120 or 140ºC still have residual solvent left in the LOR layer. Therefore, cyclopentanone vapor during bonding prevents successful bonding at the interfaces. Bonding with pre-baking over 160◦C can achieve high quality bonding. Lower process temperature is preferable to reduce thermal damage to bonding materials, so an optimized pre-baking temperature is concluded to be 160◦C. For an optimization of bonding temperature samples are bonded under bonding temperature ranging from 200 to 250 ºC under a 750 KPa load for 30 minutes at a vacuum of around 10−3 Pa. With increasing bonding temperature, the bonding across the LOR surfaces improves. When the bonding temperature was at least 250◦C, most of the loaded area was bonded and bond strength was high. Moreover, contamination after debonding was studied using atomic force microscopy (AFM). Si wafers bonded with PMGI were debonded using N-Methyl-2-pyrrolidone (NMP)-based solvent called Remover PG (MicroChem). Comparison of the Si wafer surface before processes and after bonding-debonding processes shows RMS of surfaces are 0.75 ± 0.06 nm and 0.87 ± 0.36 nm, respectively. Any residue remaining on the Si wafer surface after LOR removal is negligibly small and any resist residue can be 100% removed with a subsequent oxygen plasma ashing process. In conclusion wafer bonding with polydimethylglutarimide (PMGI) has been demonstrated to be suitable for 3-D integration with a temporary bonding process enabling a layer transfer technology. Reference 1. A.Nath,A.D.Koehler,G.G.Jernigan,V.D.Wheeler,J.K.Hite,S.C.Herna andez, Z. R. Robinson, N. Y. Garces, R. L. Myers-Ward, C. R. Eddy, D. K. Gaskill, and M. V. Rao, Appl. Phys. Lett., 104 (2014). 2. W. P. Maszara, G. Goetz, A. Caviglia, and J. B. McKitterick, J. Appl. Phys., 64,4943 (1988).

Measurement of Gas Permeability in Geosynthetic Clay Liners in Transient Flow Mode

Abstract Geosynthetic clay liners (GCLs) are often selected as a part of the barrier layer for cover systems in solid waste landfills to prevent infiltration of rainfall and migration of biogas into the atmosphere. To address the ability of GCLs to mitigate gas flow through cover layers, this paper presents an apparatus and testing method to measure the gas permeability of non-saturated and strained GCLs in the laboratory. The test is performed following a transient gas flow regime, and the test results are interpreted using a simple analytical solution. A series of gas permeability tests was performed on a needle-punched GCL with a degree of saturation between 32 % and 47 %. The specimens were tested under a 20 kPa load and 1.3 % strain in the radial direction, whereas the gas flow was induced by a gas differential pressure of less than 4 kPa. The results show that both the apparatus and the testing method can provide a reliable, fast, and simple method to measure the gas permeability of GCLs.