Load Penetration Research Articles

Meso-mechanical model of concrete under a penetration load

Abstract The influence of concrete components on projectile penetration is significant. To study the relationship between the equivalent mechanical properties and components of concrete under a penetration load, concrete is simplified as a two-phase composite of coarse aggregate and mortar, and a meso-mechanical model is established, including the equivalent equation of state model, the equivalent confining pressure strength model and the equivalent dynamic tensile strength model, considering shear stress, large deformation and pore compression. Tests of the mechanical properties of mortar, concrete and limestone were conducted; the results show that the equivalent mechanical properties of concrete calculated by the meso-mechanical model are consistent with the test results, and the equivalent mechanical properties of concrete with different volume fractions of coarse aggregate are obtained. Meso-scale and macro-scale numerical simulations of a projectile penetrating into concrete are carried out, the penetration depths obtained by meso-scale and macro-scale numerical simulations are consistent for different volume fractions of coarse aggregate and different velocities of the projectile, which verifies the rationality of the meso-mechanical model.

Experimental evaluation of ultimate bearing capacity of the cutting edge of an open caisson

Open caissons are sunk into the ground by their own weight. A cutting edge of the caisson having a tapered inner face on loading – that is, raising of the steining – results in bearing failure by displacing the soil which is in contact with the cutting edge. The bearing capacity of the cutting edge and the soil flow mechanism depend on the configuration of the cutting edge, sinking depth and soil type. This paper presents the results of a series of 1g model tests, which investigate the effect of varying tapered angles of the cutting edge on the penetration resistance of the open caisson. The vertical failure load and corresponding vertical bearing capacity factor, N′γ, and the soil flow mechanism around the cutting edge are investigated. The soil flow mechanism and the influence of surcharge formed at the top level of the cutting edge due to advancement of the caisson in the ground are examined using the image-based deformation measurement technique. The results highlight that the cutting angle of the cutting edge and sinking depth play important roles in the load–penetration response and soil flow mechanism.

Quasicontinuum multiscale modeling of the effect of rough surface on nanoindentation behavior

Roughness of surface has as an important influence on identifying the mechanical behavior and performance of crystalline metals. In this study, nanoindentation simulations are conducted by the two dimensional quasicontinuum method to determine the load–penetration response and the critical load associated with the onset of plasticity in rough surfaces of a face-centered cubic single crystal copper. The arithmetic roughness index, ranging between 2 and 13 A, is used to specify the roughness of surface. Results of indentation with different roughnesses are in good agreement with previous studies for the indenter size of 10–140 A. The resultant load–penetration scattering, which stems from the roughness, indicates different dislocation nucleation steps, different subsequent dislocations intervals and varying stiffness values of samples. It can be concluded that the surface roughness has a significant effect on the first dislocation emission because of the indenter position and surface interactions beneath it. Moreover, the critical penetration depth for the first dislocation emission increases by the increase of the contact area between the indenter and surface.

The Relation Between the Load, Duration, and Steam Penetration Capacity of a Surface Steam Sterilization Process: A Case Study.

In practice it is claimed that load characteristics influence a surface steam sterilization process. To the best of our knowledge, no information on this topic has been found in the literature. The purpose of this study was to find if a load influences the duration and related characteristics of a surface steam sterilization process. In a case study, every load monitoring using an objective, quantifying steam penetration test was performed during 30 days. This resulted in 98 production processes with load monitoring. The acquired data were analyzed. A relation between the weight of a load and the duration of a surface steam sterilization process has been found. In this case study, it is demonstrated that the process time increases with the weight of the sterilizer load. Additionally, it is concluded that when the duration of a process is longer, diffusion will have a greater effect and steam penetration increases.LAY ABSTRACT: Steam sterilization is applied in most health-care facilities that reprocess medical devices, in pharmaceutical industries, and in labs where specific instrumentation and equipment have to be sterile. Steam sterilization is still not fully understood, as demonstrated in the literature. Our manuscript contributes to understanding the surface steam sterilization process. The information shared in our manuscript demonstrates by a case study that relations exist between the weight of the load which is steam sterilized, the duration of a process, and the steam penetration in a process. A quantitative relation can be used to predict the duration of a process and the steam penetration. It is likely that for other steam sterilizers these relations can be found as well. This is of interest for institutes researching decontamination and sterilization, health-care facilities, developers and manufacturers of medical devices, and committees addressing standards for steam sterilization.

Jinyong Lei ; Chaoyang J

As load and renewable penetration continues to grow, optimal placement and sizing of substations is becoming increasingly important in distribution system planning. This paper presents an improved methodology to solve the substation siting and sizing problem based on geographic information and supervised learning. The proposed approach can optimize the locations, capacities, and power supply ranges of substations with minimum investment and annual operation costs. Capital cost of land adds complexity and difficulty to the substation placement problem, especially for highly developed urban areas. This paper presents a theoretical framework to determine the optimal location of substations considering the cost of land. The state-of-the-art parallel computing techniques are employed so that co-optimization for substations of multiple voltage levels can be directly conducted in a computational efficient way. Case studies are presented to demonstrate the effectiveness of the proposed approach.

Some concerns about the current interpretation and analyses of indentation unloading P – h curves highlighted with Young's modulus studies of single crystals of MgO (100)

Indentation tests using indenter load, P, and indentation penetration, h, curves obtained from instrumented indentation machines have been in use for over 30 years. The unloading part of a P – h curve is frequently used for determining the indentation size at the maximum applied indenter load and for determining the elastic modulus of the test solid. To do this, four fundamental assumptions have been made. We show here experimentally that, unfortunately, none of the assumptions is correct. Therefore, these assumptions lead to incorrect determinations. Examples highlighting the concerns are given from our own work on single crystals of Cu and MgO and from the work of others. It is shown here that for both isotropic and anisotropic solids, the elastic moduli determined using the current methods of data analysis vary very considerably with the applied maximum indenter load. Furthermore, the obtained values do not correlate well with the literature values of the elastic moduli, despite the claim [see abstract of W. C. Oliver and G. M. Pharr (J. Mater. Res. 7, 1564 (1992)] that the agreement is within 5%. To remedy this problem, an alternative approach employing only elastic loading with an elastic sphere is used and the resulting load versus displacement data are analyzed using the Hertzian equation for the normal loading of a sphere on an elastic half-space. This experimental technique yields satisfactory values of the elastic moduli of test surfaces of single crystals of Cu (111), Cu (100), and MgO (100); the elastic moduli thus determined do not vary with the applied indenter load.Indentation tests using indenter load, P, and indentation penetration, h, curves obtained from instrumented indentation machines have been in use for over 30 years. The unloading part of a P – h curve is frequently used for determining the indentation size at the maximum applied indenter load and for determining the elastic modulus of the test solid. To do this, four fundamental assumptions have been made. We show here experimentally that, unfortunately, none of the assumptions is correct. Therefore, these assumptions lead to incorrect determinations. Examples highlighting the concerns are given from our own work on single crystals of Cu and MgO and from the work of others. It is shown here that for both isotropic and anisotropic solids, the elastic moduli determined using the current methods of data analysis vary very considerably with the applied maximum indenter load. Furthermore, the obtained values do not correlate well with the literature values of the elastic moduli, despite the claim [see abstract...

Impact of Iontophoresis and PACK-CXL Corneal Concentrations of Antifungals in an In Vivo Model.

To investigate voriconazole (VRZ) penetration and fungal load in the cornea after applying VRZ therapy with various treatment combinations in a fungal keratitis model. Fifty-four eyes of 27 young albino rabbits were provided for this experimental study. Twelve corneas were inoculated with Candida albicans, 12 corneas were inoculated with Fusarium solani, and 6 eyes were selected as controls. Infected corneas received various treatment combinations including VRZ 1% drop therapy alone, VRZ 1% plus amphotericin B 1% drop combination therapy, iontophoretic VRZ therapy, and VRZ 1% drop therapy after corneal cross-linking. Fungal load was measured by log reduction, and VRZ levels were quantified by liquid chromatography-tandem mass spectrometry. Iontophoresis-assisted VRZ application showed the highest antifungal activity against F. solani keratitis (4-log reduction) and C. albicans keratitis (5-log reduction) compared with other treatment applications. VRZ levels were also found to be the highest in corneas that received iontophoretic VRZ treatment (3.6313 ± 0.0990 ppb for F.solani keratitis and 1.7001 ± 0.0065 ppb for C. albicans keratitis) compared with other treatment applications. Iontophoresis seems to provide the highest VRZ concentration and highest antifungal activity in the cornea compared with other treatment applications for C. albicans and F. solani keratitis.

A combined split-spoon sampler and spherical penetrometer: laboratory trials

Full flow penetrometers (FFPs) such as T-bar and ball penetrometer provide reliable estimates of undrained shear strength (su) of soft-soil deposits. Several studies are reported in the literature on the field application of these penetrometers for offshore applications typically for the deep-water environment. However, the lack of sampling provision creates problem for identifying the accurate soil type from the load–penetration response. Information obtained from the field samples is vital in determining the stratigraphy and conducting several basic laboratory tests. This study proposes a new sampling-cum-penetration testing device, which uses a split-spoon sampler for sampling with a spherical cutting shoe. The cutting shoe was modified to increase the bearing area for enhanced accuracy in soft deposits. Strength assessment study was conducted in the laboratory using remoulded kaolin clay at various undrained shear strengths. To investigate the occurrence of plugging and the extent of influence zone during penetration, image-based deformation measurement technique was adopted. The modified ball penetrometer shows a strength factor of about 14·3 in remoulded kaolin clay.

Size effects in wedge indentation predicted by a gradient-enhanced crystal-plasticity model

A recently developed gradient-enhanced crystal-plasticity model is applied to predict the size effects in wedge indentation. In the model, the internal length scale is defined through standard quantities that appear in the underlying non-gradient hardening law. A careful calibration of the non-gradient hardening law is thus performed, and the model is validated against published experimental results. To this end, a comprehensive computational study of wedge indentation into a nickel single crystal is performed, and the obtained results show a good agreement with the experiment in terms of the load–penetration depth curves for three wedge angles, as well as in terms of the distributions of lattice rotation, GND density, and net Burgers vector. For the indentation depth of about 200 μm, as employed in the experiment, the predicted size effects are insignificant. Accordingly, the size effects are next studied for the indentation depth varied between 200 μm and 1 μm. As an intermediate result, apparently not published to date, the general 3D crystal plasticity model with anisotropic hardening is consistently reduced to a 2D plane-strain model in which plastic deformation is realized by three effective in-plane slip systems, each representing two crystallographic slip systems.

Bilevel Arbitrage Potential Evaluation for Grid-Scale Energy Storage Considering Wind Power and LMP Smoothing Effect

This paper deals with extended-term energy storage (ES) arbitrage problems to maximize the annual revenue in deregulated power systems with high-penetration wind power. The conventional ES arbitrage model takes the locational marginal prices (LMP) as an input and is unable to account for the impacts of ES operations on system LMPs. This paper proposes a bilevel ES arbitrage model, where the upper level maximizes the ES arbitrage revenue and the lower level simulates the market clearing process considering wind power and ES. The bilevel model is formulated as a mathematical program with equilibrium constraints) and then recast into a mixed-integer linear programming using strong duality theory. Wind power fluctuations are characterized by the GARCH forecast model and the forecast error is modeled by forecast-bin-based Beta distributions. Case studies are performed on a modified PJM 5-bus system and an IEEE 118-bus system with a weekly time horizon over an annual term to show the validity of the proposed bilevel model. The results from the conventional model and the bilevel model are compared under different ES power and energy ratings, and also various load and wind penetration levels.

Lateral response of piles subjected to a combination of spudcan penetration and pile head loads

The effects of spudcan penetration on adjacent laterally-loaded piles mainly manifest themselves in the additional lateral shaft loads induced by large soil deformation. This paper presents a procedure to analyze lateral response of piles subjected to a combination of spudcan penetration and pile head loads. First, the Coupled Eulerian-Lagrangian technique (CEL) is post-processed and key model parameters are investigated to generate accurate soil displacement profiles during free-field spudcan penetration. Second, the effects of spudcan penetration on the adjacent piles loaded on the pile head are analyzed in two ways: the passive pile method and the offset p-y curve method. Results of an available centrifuge model test is firstly adopted to certify the effectiveness of the procedure in analyzing piles singly loaded by spudcan penetration. Then a combined-loading 1 g model test is conducted to calibrate the procedure. Agreement between the calculated and measured results is found especially with the combination of the CEL FE method and the passive pile method.

Bilevel Optimization Framework for Smart Building-to-Grid Systems

This paper proposes a novel framework suitable for bilevel optimization in a system of commercial buildings integrated to smart distribution grid. The proposed optimization framework consists of comprehensive mathematical models of commercial buildings and underlying distribution grid, their operational constraints, and a bilevel solution approach which is based on the information exchange between the two levels. The proposed framework benefits both entities involved in the building-to-grid (B2G) system, i.e., the operations of the buildings and the distribution grid. The framework achieves two distinct objectives: increased load penetration by maximizing the distribution system load factor and reduced energy cost for the buildings. This study also proposes a novel B2G index, which is based on building’s energy cost and nodal load factor, and represents a metric of combined optimal operations of the commercial buildings and distribution grid. The usefulness of the proposed framework is demonstrated in a B2G system that consists of several commercial buildings connected to a 33-node distribution test feeder, where the building parameters are obtained from actual measurements at an office building at Michigan Technological University.

Mechanical Properties of Cubic‐BN(111) Bulk Single Crystal Evaluated by Nanoindentation

We performed nanoindentation measurements on the (111) plane of a cubic boron nitride (c‐BN) bulk single crystal and a c‐BN sintered compact at room temperature to evaluate the intrinsic mechanical properties of c‐BN. Our load–penetration depth curves for bulk single crystal feature a low noise level and small variation in the data. These features reflect the perfect phase purity and high crystal coherency of the c‐BN bulk crystal. The hardness and Young's modulus are determined to be 61 ± 1 and 1070 ± 30 GPa, respectively. These values are larger than those corresponding to the c‐BN sintered compact. The obtained Young's modulus followed a similar trend to previous experimental and calculation studies. Hence, we demonstrate the effectiveness of this evaluation method based on high‐quality bulk single crystals. We also compared the mechanical properties with our results for wurtzite boron nitride (w‐BN) bulk crystal.

Smart Grid Constraint Violation Management for Balancing and Regulating Purposes

The gradual active load penetration in low-voltage distribution grids is expected to challenge their network capacity in the near future. Distribution system operators should for this reason resort to either costly grid reinforcements, use of low-voltage boosters, or demand response (DR) mechanisms. Since DR implementation is usually more cost effective, it is the favorable solution to avoid or delay the need for grid reinforcement. To this end, this paper presents a framework for handling grid limit violations, both voltage and current, to ensure a secure and qualitative operation of the distribution grid. This framework consists of two steps, namely a proactive centralized, and subsequently, a reactive decentralized control scheme. The former is employed to balance the 1-h-ahead load, while the latter aims at regulating the consumption in real time. In both schemes, fairness in terms of utilization of demand flexibility among the customers is incorporated. It is demonstrated that the proposed methodology aids in keeping the grid status within preset limits while utilizing flexibility from all flexibility participants.

Assessment of the Local Residual Stresses of 7050-T7452 Aluminum Alloy in Microzones by the Instrumented Indentation with the Berkovich Indenter

The local residual stresses in microzones are investigated by the instrumented indentation method with the Berkovich indenter. The parameters required for determination of residual stresses are obtained from indentation load–penetration depth curves constructed during instrumented indentation tests on flat square 7050-T7452 aluminum alloy specimens with a central hole containing the compressive residual stresses generated by the cold extrusion process. The force balance system with account of the tensile and compressive residual stresses is used to explain the phenomenon of different contact areas produced by the same indentation load. The effect of strain-hardening exponent on the residual stress is tuned-off by application of the representative stress $$\sigma_{0.033}$$ in the average contact pressure assessment using the $$\varPi$$ theorem, while the yield stress value is obtained from the constitutive function. Finally, the residual stresses are calculated according to the proposed equations of the force balance system, and their feasibility is corroborated by the XRD measurements.

Lateral boundary effects in centrifuge foundation tests

Large deformation finite-element analyses were conducted to explore the effect of the container lateral boundary in centrifuge tests where a large offshore foundation is tested. A spudcan foundation, typically used to support jack-up drilling rigs, was penetrated into uniform clay, uniform sand and sand overlying clay stratigraphies under rough and smooth lateral boundary conditions. The effect that the proximity of the container lateral boundary has on the measured load–penetration response is quantified. The boundary impact varies with the soil profile and boundary roughness, and for sand-only or sand-over-clay conditions the required separation between the foundation and the container boundary is far greater than in clay-only conditions. In most cases, during large penetration of the spudcan foundation, the largest influence from the lateral boundary was on peak resistance, and diminished during the subsequent deeper penetration. For practical use, a centrifuge container design chart is proposed to check whether the dimensions are adequate for the foundation and model size to be used in an experiment. It is shown that the results from many earlier studies could have been potentially influenced by container boundary effects.

Foundation punch-through in clay with sand: analytical modelling

Severe punch-through of jack-up rig foundations can occur due to the presence of a stronger sand layer in a bed of relatively soft clay. Analytical estimation of the bearing capacity and leg load–penetration response on such multi-layer stratigraphies is challenging. Accurate mechanism-based models need to be established in each of the layers involved and the effects of the mechanisms in each of the layers on the response in the other layers must be captured. Based on the recently developed failure stress-dependent punch-through models for sand–clay stratigraphies, an extended model is proposed for clay–sand–clay stratigraphies. Half-spudcan particle image velocimetry centrifuge tests and full-spudcan centrifuge tests are used in developing and validating the extended model. The centrifuge test results were discussed in a companion paper and this paper focuses on the analytical developments and prediction assessment. Both spudcan peak resistance (qpeak) and spudcan punch-through depth (dpunch) can be estimated using the model. The predictions by the extended model and by the current industry guidelines are compared against the centrifuge test data. The extended model proposed in this paper outperforms the approaches suggested in the guidelines. An advantage of the proposed approach is that it can be used for either sand–clay or clay–sand–clay scenarios and exhibits excellent performance compared to the model testing dataset considered in this work for both cases. The resulting penetration resistance model is a useful design tool for routine punch-through risk assessment.

EXPERIMENTALLY MEASUREMENT AND ANALYSIS OF STRESS UNDER FOUNDATION SLAB

Understanding of a load redistribution into subsoil below building foundation is an importantknowledge for reliable design and its economy too. The article presents the results of a physical model of afoundation slab and its interaction with the subsoil. The interactions were investigated comprehensively bymonitoring the developments of stress in the subsoil and foundation slab settlement during its loading. Theload acting on the foundation was applied by strutting the hydraulic press against heavy steel frame whichwas established by the Department of Building Structures, Faculty of Civil Engineering of VSB -TU Ostravafor this purpose. The preparatory phase of the present experiment involved the homogenization of soil duringwhich trio pressure cells in three horizons were gradually fitted. The quality of homogenization was checkedon an ongoing basis through field tests: dynamic penetration load test, dynamic plate load test and seismicmeasurement of foundation slab response. Finally, the homogenized soil was subjected to mechanicalanalysis to determine the strength and deformation parameters for basic Mohr-Coulomb constitutive model.

Improving voltage profile of load bus of wind generation system using DSTATCOM

In a low voltage distribution system with integrated wind plant, voltage stability is impacted by the large variation of load and wind penetration. The compensators like SVC and DSTATCOM are currently being used to address such issue of voltage instability. This paper analyses the impact of wind penetration and variation of active and reactive power of the load on voltage profile of a wind generation system with and without DSTATCOM. It also analyses the performance of the system during fault by calculating various parameters of the system. It has been demonstrated that voltage stability margin increases using DSTATCOM at different wind penetration levels. This system has been simulated and analysed in MATLAB 2011b using a power system toolbox under steady state and transient conditions.

Improving voltage profile of load bus of wind generation system using DSTATCOM

In a low voltage distribution system with integrated wind plant, voltage stability is impacted by the large variation of load and wind penetration. The compensators like SVC and DSTATCOM are currently being used to address such issue of voltage instability. This paper analyses the impact of wind penetration and variation of active and reactive power of the load on voltage profile of a wind generation system with and without DSTATCOM. It also analyses the performance of the system during fault by calculating various parameters of the system. It has been demonstrated that voltage stability margin increases using DSTATCOM at different wind penetration levels. This system has been simulated and analysed in MATLAB 2011b using a power system toolbox under steady state and transient conditions.