Instrumented Roller Research Articles

An unsaturated soil mechanics approach for performance-based intelligent compaction

Intelligent compaction involves using instrumented rollers to provide real-time monitoring of the compacted ground using sensors such as accelerometers and GPS. This technology has the potential to improve productivity and uniformity in construction but its advancement is currently impeded due toinaccurate estimation of the physical ground properties, such as dry density, and the absence of robust quantitative models to predict the effect of compaction on the long-term performance of unsaturated soils under repeated loads. In this study, the compaction of the soil layers and subsequent deformations under repeated traffic loads are simulated by using an advanced computational framework and model for unsaturated soils. By employing an effective stress concept, the presented computational approach allows a unified description of soils at various degrees of saturation. In addition, the model can capture plastic deformations at the initiation of loading and thereby offer accurate predictions of soil behaviour under cyclic loads. Several numerical examples will be provided to demonstrate how the initial states of compacted soils affect the compaction efficiency and the long-term performance of compacted soils.

Evaluation of a standardized test protocol to measure wheelchair-specific anaerobic and aerobic exercise capacity in healthy novices on an instrumented roller ergometer.

This study aims to evaluate whether a test protocol with standardized and individualized resistance settings leads to valid wheelchair Wingate tests (WAnT) and graded exercise tests (GXT) in healthy novices. Twenty able-bodied individuals (10M/10F, age 23 ± 2 years, body mass 72 ± 11 kg) performed an isometric strength test, sprint test, WAnT and GXT on a wheelchair ergometer. Using a previously developed set of regression equations, individuals’ isometric strength outcome was used to estimate the WAnT result (P30est), from which an effective individual WAnT resistance was derived. The subsequently measured WAnT outcome (P30meas) was used to estimate the GXT outcome (POpeakest) and to scale the individual GXT resistance steps. Estimated and measured outcomes were compared. The WAnT protocol was considered valid when maximal velocity did not exceed 3 m·s-1; the GXT protocol was considered valid when test duration was 8–12 min. P30est did not significantly differ from P30meas, while one participant did not have a valid WanT, as maximal velocity exceeded 3 m·s-1. POpeakest was 10% higher than POpeakmeas, and six participants did not reach a valid GXT: five participants had a test duration under 8 min and one participant over 12 min. The isometric strength test can be used to individually scale the WAnT protocol. The WAnT outcome scaled the protocol for the GXT less accurately, resulting in mostly shorter-than-desired test durations. In conclusion, the evaluated standardized and individualized test protocol was valid for the WAnT but less valid for the GXT among a group of novices. Before implementing the standardized individual test protocol on a broader scale, e.g. among paralympic athletes, it should be evaluated among different athletic wheelchair-dependent populations.

Proximal Sensing of Density During Soil Compaction by Instrumented Roller

The measurement of density or void ratio during the compaction of geomaterials (soils and unbound granular materials) in the field during road construction is essential for superior performance. The specifications adopted by the road authorities worldwide are exclusively based on density. However, estimating density evolution proximally or non-destructively is challenging. Conventional field-based density measurement techniques are hazardous, slow to use and are point-based measurements. This study developed a novel methodology to estimate the density of geomaterials non-destructively in real-time during the compaction process. The methodology included measuring the surface deformation using Light Detection and Ranging (LiDAR) systems attached to rollers and developing physics-based 1-Dimensional and machine learning (ML) based constitutive models to relate the measured parameters to the density. The developed methodology was validated in an indoor environment where a large soil box (dimensions: 7.5 m×4 m×0.8 m) was fabricated and a well-graded sand in 5 layers of 100 mm was compacted using a 1.5-tonne instrumented roller. The measurement of deformation provided an opportunity to estimate the density in real-time. The estimated density using 1-D model and a ML based classification model had an error of 20% and 16% respectively when compared to density measured from Nuclear Density Gauge (NDG). This novel instrumentation allowed the density to be measured during compaction with high accuracy, which presents an unprecedented advantage over other conventional approaches, which are intrusive and pointwise, thereby ensuring that the road will be constructed expediently and will function satisfactorily, minimising the occurrence of premature failures. The continual measurement of density during compaction will also facilitate maintaining uniformity of the density, thereby reducing the potential for excessive differential deformations.

Experimental and numerical investigation on carbonitrided steel characterization with spherical indentation

This study investigates the mechanical behavior of a carbonitrided steel, plastically graded material, during a spherical indentation test. We demonstrate that the behavior of a carbonitrided steel can be simulated accurately with a seven layer sample, including the surface, five intermediate layers and the substrate. Moreover, for engineering design simulations which require a lot of calculation time, using three layers provides a good compromise for accuracy.A complete experimental procedure involving seven successive identifications with inverse analysis gave the same results as a simpler procedure proposed in a previous paper. It is shown that the assumption of a linear variation of the properties in the intermediate layers between surface and substrate is valid. This is the first time that an instrumented roller indentation test has demonstrated the reliability of the proposed method for the mechanical characterization of carbonitrided steels with spherical indentation.

Changes in Technique and Efficiency After High-Intensity Exercise in Cross-Country Skiers

This study investigated changes in technique and efficiency after high-intensity exercise to exhaustion in elite cross-country skiers. Twelve elite male skiers completed 4 min submaximal exercise before and after a high-intensity incremental test to exhaustion with the G3 skating technique on a 5% inclined roller-ski treadmill. Kinematics and kinetics were monitored by instrumented roller skis, work rate was calculated as power against roller friction and gravity, aerobic metabolic cost was determined from gas exchange, and blood lactate values indicated the anaerobic contribution. Gross efficiency was the work rate divided by aerobic metabolic rate. A recovery period of 10 min between the incremental test and the posttest was included to allow the metabolic values to return to baseline. Changes in neuromuscular fatigue in upper and lower limbs before and after the incremental test were indicated by peak power in concentric bench press and squat-jump height. From pretest to posttest, cycle length decreased and cycle rate increased by approximately 5% (P < 0.001), whereas the amount of ski forces did not change significantly. Oxygen uptake increased by 4%, and gross efficiency decreased from 15.5% ± 0.7% to 15.2% ± 0.5% from pretest to posttest (both P < .02). Correspondingly, blood lactate concentration increased from 2.4 ± 1.0 to 6.2 ± 2.5 mmol/L (P < .001). Bench-press and squat-jump performance remained unaltered. Elite cross-country skiers demonstrated a less efficient technique and shorter cycle length during submaximal roller-ski skating after high-intensity exercise. However, there were no changes in ski forces or peak power in the upper and lower limbs that could explain these differences.

Construction of an instrumented roller ski and validation of three-dimensional forces in the skating technique

The purposes of the present investigation were to construct an instrumented roller ski, validate the force measurements and resolve the forces into three dimensions. To demonstrate the practical applications of the system, this study aimed to distinguish cycle characteristics and kinetics between skiers with different technical characteristics and between skating with and without poling while roller ski skating on a treadmill. It was shown that a roller ski with full bridge strain gauges could provide valid measurements of one-dimensional forces. By recording the orientation of the skis in space using the Qualisys motion capture system, the one-dimensional forces were converted into three dimensions according to the global coordinate system. However, some corrections are still required to obtain valid three-dimensional forces. It was possible to distinguish clear differences in cycle characteristics and roller ski forces between the two skiers with different characteristics and between skating with and without poling. Overall, this instrumented roller ski can be useful for future research and when monitoring elite athletes’ technical development.

Roller compaction of moist pharmaceutical powders

The compression behaviour of powders during roller compaction is dominated by a number of factors, such as process conditions (roll speed, roll gap, feeding mechanisms and feeding speed) and powder properties (particle size, shape, moisture content). The moisture content affects the powder properties, such as the flowability and cohesion, but it is not clear how the moisture content will influence the powder compression behaviour during roller compaction. In this study, the effect of moisture contents on roller compaction behaviour of microcrystalline cellulose (MCC, Avicel PH102) was investigated experimentally. MCC samples of different moisture contents were prepared by mixing as-received MCC powder with different amount of water that was sprayed onto the powder bed being agitated in a rotary mixer. The flowability of these samples were evaluated in terms of the poured angle of repose and flow functions. The moist powders were then compacted using the instrumented roller compactor developed at the University of Birmingham. The flow and compression behaviour during roller compaction and the properties of produced ribbons were examined. It has been found that, as the moisture content increases, the flowability of moist MCC powders decreases and the powder becomes more cohesive. As a consequence of non-uniform flow of powder into the compaction zone induced by the friction between powder and side cheek plates, all produced ribbons have a higher density in the middle and lower densities at the edges. For the ribbons made of powders with high moisture contents, different hydration states across the ribbon width were also identified from SEM images. Moreover, it was interesting to find that these ribbons were split into two halves. This is attributed to the reduction in the mechanical strength of moist powder compacts with high moisture contents produced at high compression pressures.

Instrumented Rollers to Assess Construction Quality on Texas Projects

The concept of using a vibratory compactor as a tool for assessing construction quality by measuring the drum displacement with an accelerometer began decades ago. Initiated in Europe and correlated with plate bearing tests, this technology has advanced to “intelligent” compaction, in which feedback from the instrumentation can control the amplitude of vibration. With the national push to implement such methods in the United States, researchers at the Texas Transportation Institute sought to examine the relationship between the vibration amplitude of the roller drum and pavement layer properties on several Texas construction projects. Testing revealed that although the roller drum vibration amplitudes did relate to pavement layer properties, the correlation was with the stiffness of foundation layers, typically at least 12 in. below the surface. This finding presents at least one significant hurdle to implementing the instrumented–intelligent compaction concept: a change from density-based to stiffness-based specifications would be necessary. In addition, valid approaches to extracting properties of the surface layer are needed. The results from projects tested indicate that the most promising approaches to using this technology are for evaluating uniformity, compaction monitoring (determining when to stop rolling), and proof rolling. The proof rolling application requires validation to determine the depth of the weak spot.

Capturing Nonlinear Vibratory Roller Compactor Behavior through Lumped Parameter Modeling

Continuous monitoring of soil properties using an instrumented roller compactor requires models that can capture the essential features observed during drum/soil vibration. This paper presents the results of lumped parameter modeling of the drum/soil system together with data from complex nonlinear behavior observed experimentally during operation on sandy soil. Model parameters and response were developed using experimental data collected over a wide range of operating frequencies. Three and four-degree-of-freedom (DOF) models with linear and nonlinear soil elements were investigated. The results showed that a 3DOF model incorporating the soil, drum, and frame of the roller was successful in capturing behavior during coupled drum/soil vibration and during decoupling (i.e., loss of contact between drum and soil). Modeling the drum/soil decoupling accounted for most of the experimentally observed nonlinearity. The addition of nonlinear soil stiffness due to the curved drum effect and due to strain hardening soil behavior accounted for additional nonlinearity observed experimentally. Experimentally observed drum rocking during coupled drum/soil vibration was successfully modeled with a 4DOF drum-frame model. The analysis also revealed that commonly observed heterogeneous soil conditions give rise to a transient response that can have a significant influence on vibration behavior.

The effect of lubrication on density distributions of roller compacted ribbons

Roller compaction is a continuous dry granulation process for producing free flowing granules in order to increase the bulk density and uniformity of pharmaceutical formulations. It is a complicated process due to the diversity of powder blends and processing parameters involved. The properties of the produced ribbon are dominated by a number of factors, such as the powder properties, friction, roll speed, roll gap, feeding mechanisms and feeding speed, which consequently determine the properties of the granules (size distribution, density and flow behaviour). It is hence important to understand the influence of these factors on the ribbon properties. In this study, an instrumented roller press developed at the University of Birmingham is used to investigate the effect of lubrication on the density distribution of the ribbons. Three different cases are considered: (1) no lubrication, (2) lubricated press, in which the side cheek plates of the roller press are lubricated, and (3) lubricated powder, for which a lubricant is mixed into the powder. In addition, how the powders are fed into the entry region of the roller press and its influence on ribbon properties are also investigated. It is found that the method of feeding the powder into the roller press plays a crucial role in determining the homogeneity of the ribbon density. For the roller press used in this study, a drag angle (i.e., the angle formed when the powder is dragged into the roller press) is introduced to characterise the powder flow pattern in the feeding hopper. It is shown that a sharper drag angle results in a more heterogeneous ribbon. In addition, the average ribbon density depends upon the peak pressure and nip angle. The higher the peak pressure and nip angle are, the higher the average ribbon density is. Furthermore, the densification behaviour of the powder during roller compaction is compared to that during die compaction. It has been shown that the densification behaviour during these two processes is similar if the ribbons and the tablets have the same thickness.

Field Monitoring of Roller Vibration during Compaction of Subgrade Soil

A field investigation was carried out with an instrumented vibratory roller compactor to explore the relationship between vibration characteristics and underlying soil properties, namely soil stiffness. The roller was outfitted with instrumentation to monitor drum and frame acceleration, as well as eccentric excitation force. Multiple consecutive passes were performed over six test beds on an active earthwork construction site to capture changes in roller vibration during compaction. Using lumped parameter vibration theory, soil stiffness was extracted from the roller data drum and frame acceleration and drum phase lag. Both drum acceleration and drum phase lag were found to be very sensitive to changes in underlying soil stiffness. The drum-soil natural frequency of the coupled roller-soil system varied considerably and increased with compaction-induced soil stiffening. Phase lag always decreased with increasing soil stiffness, whereas drum acceleration trends depended on whether the excitation frequency was less than or greater than resonance. Roller-determined soil stiffness was found to be a function of the eccentric force, and heterogeneity in moisture, lift thickness, and underlying stiffness has a considerable affect on roller vibration behavior. When used as a proof roller, the instrumented roller identified soft areas in the embankment that were not identified by a static proof roll test.

Roller Extrusion of a Ceramic Paste

The roller extrusion of a stiff model ceramic paste has been studied experimentally using a fully instrumented roller apparatus that allows simultaneous measurement of roller separation, separating force, torque, and roll surface pressure. The paste exhibited no noticeable wall slip and little expansion, detaching from the rollers shortly downstream of the nip. Data collected over reduction ratios of 0.92−0.15 and speeds of 1.5−30 rpm (7.9−160 mm s-1) showed consistent trends when plotted against reduction ratio. A small strain rate dependence was observed, which was consistent with the rheological parameters obtained from the Benbow−Bridgwater characterization approach that models the material as a yield strength material. The data were also compared with the results from three models for rolling based on the plasticity approach: an upper bound model, a lower bound model, and a hot metal rolling model originally presented by Orowan. The experimental and predicted results showed good agreement for the latter model, and it was then extended to incorporate a simple strain rate dependency based on the Benbow−Bridgwater characterization approach. These results indicate that this characterization approach can be used to predict or gauge the rolling performance of such soft-solid materials.