Monotonic Loading Research Articles

Biomechanical and biochemical changes in murine skin during development and aging

Aging leads to biochemical and biomechanical changes in skin, with biological and functional consequences. Despite extensive literature on skin aging, there is a lack of studies which investigate the maturation of the tissue and connect the microscopic changes in the skin to its macroscopic biomechanical behavior as it evolves over time. The present work addresses this knowledge gap using multiscale characterization of skin in a murine model considering newborn, adult and aged mice. Monotonic uniaxial loading, tension relaxation with change of bath, and loading to failure tests were performed on murine skin samples from different age groups, complemented by inflation experiments and atomic force microscopy indentation measurements. In parallel, skin samples were characterized using histological and biochemical techniques to assess tissue morphology, collagen organization, as well as collagen content and cross-linking. We show that 1-week-old skin differs across nearly all measured parameters from adult skin, showing reduced strain stiffening and tensile strength, a thinner dermis, lower collagen content and altered crosslinking patterns. Surprisingly, adult and aged skin were similar across most biomechanical parameters in the physiologic loading range, while aged skin had lower tensile strength and lower stiffening behavior at large force values. This correlates with altered collagen content and cross-links. Based on a computational model, differences in mechanocoupled stimuli in the skin of the different age groups were calculated, pointing to a potential biological significance of the age-induced biomechanical changes in regulating the local biophysical environment of dermal cells. Statement of significanceSkin microstructure and the emerging mechanical properties change with age, leading to biological, functional and health-related consequences. Despite extensive literature on skin aging, only very limited quantitative data are available on microstructural changes and the corresponding macroscopic biomechanical behavior as they evolve over time. This work provides a wide-range multiscale mechanical characterization of skin of newborn, adult and aged mice, and quantifies microstructural correlations in tissue morphology, collagen content, organization and cross-linking. Remarkably, aged skin retained normal hydration and normal biomechanical function in the physiological loading range but showed significantly reduced properties at super-physiological loading. Our data show that age-related microstructural differences have a profound effect not only on tissue-level properties but also on the cell-level biophysical environment.

Coupled hydro-mechanical hypoplastic model for partially saturated soils under monotonic and cyclic loading

Coupled hydro-mechanical hypoplastic model for partially saturated soils under monotonic and cyclic loading

Cyclic inelastic behaviour of a bonded patch repair system used for pipes with through-wall corrosion damage

Repairs of through-wall corrosion damage in pipes conveying liquids using bonded metallic patches are becoming common in the oil and gas industry. Usually, this kind of patch is used in association with a composite sleeve, and it is essential to assure that the repair wońt leak. The use of bonded metallic patches associated with the composite sleeve is not forbidden in the standards for the design of composite repair systems (such as ASME PCC-2 and ISO 24817). However, they do not address this very frequent practice adopted in industry. Since the patch is responsible for sustaining most of the pressure of the repair, it becomes necessary to further understand its behaviour. This paper investigates the cyclic inelastic behaviour of a metal patch/adhesive system and its effect on the failure pressure. Hydrostatic tests were performed regarding how pressure variations can generate cyclic inelastic strains in the adhesive layer that bonds the metal patch to the pipe, and how this cyclic loading–unloading process ultimately affects the failure pressure. The failure pressure in monotonic burst tests can be reasonably modelled using basic concepts of linear elastic fracture mechanics. Although the assumption of a brittle-elastic behaviour of the repair system seems adequate in the case of monotonic loading, it is not in the case of cyclic tests with high pressure amplitudes. Repairs in steel pipes under pressure with a 25 mm diameter hole failed after a very small number of cycles with pressure amplitude of 80% of the average failure pressure obtained in monotonic burst tests. To help understanding the behaviour of the system, single lap joints were studied. The patch and pipe are not subjected to significant permanent deformations, while the adhesive layer has an inelastic behaviour. Results show that the lap joints present a rate-dependent behaviour in tensile tests and may present highly different cyclic responses which are quite sensitive to very small perturbations in the manufacturing process.

Sustainable Structural System Selection Using Hybrid Fuzzy Multi-Criteria Decision Model Based on Seismic Performance

In the rapidly evolving field of sustainable construction, this study aims to address the critical need for advancement in the building industry, focusing on vital indicators like energy efficiency and cost-effectiveness, as well as improving occupant comfort. This research introduces a novel approach to support the choice of suitable structural systems for mass housing projects, with a case study on Iran’s national housing scheme. This methodology involves a four-phase process, beginning with compiling a database from existing studies to outline primary and secondary indicators affecting structural system selection. It utilizes the fuzzy AHP method for criteria prioritization and the fuzzy TOPSIS technique for alternatives (LSF, 3DP, ICF, TRC, and RCCF). The study identified the light steel framing (LSF) system as the optimal choice for Iran’s housing needs based on various criteria. Then, in the final phase, the study evaluates the seismic performance of cold-formed steel (CFS) frames with various sheathing panel types (OSB, DFP, CSP, and GWB) under monotonic loads, examining key seismic parameters across 38 frame setups. The findings reveal that LSF structures can effectively withstand seismic events within the elastic behavior range, suggesting that this construction approach is viable for enhancing mass housing production in Iran’s construction sector.

Self-sensing performance of concrete columns using Multi-layer Graphene filled cement-based sensors with different arrangements

The Multi-layer Graphene (MLGs) filled cement-based sensor (GCBS) was developed and applied in the concrete columns. The strain-sensing performance of GCBS was investigated under cyclic and monotonic loading after being embedded in the column. Meanwhile, the influence of embedded location and adjacent sensor distance on the piezoresistive performance of the sensor was discussed. The strain measured by the embedded sensor agreed well with that obtained by LVDTs within the elastic regime. However, the embedded sensor underestimated the concrete strain after stepping into the plastic stage because of the increasing transverse deformation coefficient. Moreover, improper arrangement of the sensor resulted in uneven deformation, generating significant strain differences between the sensor with concrete and increasing prediction deviation. To guarantee the predicting accuracy of the sensor, it is recommended that the embedded position of the sensor from the superficial layer of the column should exceed 25 mm, and the distance between adjacent sensors should not be lower than 107.24 mm.

Comparative assessment of load-bearing capacities in bolted laminated bamboo lumber connections: A study on diverse reinforcement techniques

Laminated bamboo lumber (LBL), a renowned engineered bamboo composite known for its outstanding performance and sustainability, is extensively used in modern bamboo structured buildings. This study focuses on examining the effects of diverse reinforcement techniques, particularly self-tapping screws and tension control bolts, on the load-bearing capacity of bolted LBL connections with steel plates. In total, 24 specimens were categorized into 8 groups and subjected to monotonic loading tests. The test results demonstrate that the non-reinforced group clearly shows longitudinal splitting failure at the bolt position, followed by a decrease in load-bearing capacity after failure. In contrast, the group with self-tapping screws (ST) and tension control bolts (BT) exhibited fiber tearing at the lower part of the midspan, accompanied by section bending and damage. The final load-bearing capacity of the groups reinforced with single-row three-bolt self-tapping screws and tension control bolts showed an increase of 67.30 % and 52.95 %, respectively. Likewise, the groups with single-row four-bolt configurations also demonstrated significant reinforcement effects, with increases of 40.52 % and 29.66 %, respectively. Furthermore, DIC-3D analysis was employed to examine the displacement of the connection bolts, and the van der Put model was utilized to estimate the load-bearing capacity of bolted LBL connections under splitting conditions. Subsequently, finite element models were established and calibrated based on the experimental data. The results confirm that self-tapping screws and tension control bolts can serve as structural enhancements in the design of bolted LBL connections, providing effective reinforcement for existing engineering structures.

Digital holographic microscope for high spatial and temporal resolution in situ observation of dynamic phenomena of metals

A digital holographic microscope (DHM) was developed for the purpose of simultaneous observation and measurement of surface relief formation during deformation and phase transformation of steels. It was designed to accommodate the sample mounting component of a custom tensile tester. The Gabor wavelet transform method was used in the image reconstruction. To verify performance, the DHM was used to observe and measure height of slip bands formed during the monotonic loading 316L stainless steel. Data obtained has high temporal resolution (limited only by the camera’s frame rate capability) with lateral resolution approaching the diffraction limit. The results clearly show the evolving microstructures with height information available within each captured image.

Experimental and numerical investigations on shear behavior of RC beams strengthened with U-wrapped PET FRP

This paper reports the investigations of experimental and numerical programs on the shear performance of U-shaped Polyethylene Terephthalate (PET) FRP-retrofitted RC beams. Twelve RC beams were fabricated and tested under monotonic three-point loading with the test parameters being FRP strip width and shear span-to-effective depth ratio. A comprehensive analysis and investigation were conducted in terms of the failure modes, shear load–deflection responses, shear capacities, the strain evolution of FRP and stirrups, and the interaction of shear contributions among FRP, stirrups and concrete. Larger debonding strains were observed for PET FRP. Five design guidelines and two models available in the literature were assessed against the measured PET FRP shear contribution. A modified model of the shear contribution for PET FRP was developed and verified by the test results. Finally, a finite element model was established to further understand the shear performance of retrofitted beams, in which the bond-slip relationship between concrete and FRP was considered. The FE model was validated by comparing the test and FE results. The proposed FE model could accurately capture the propagation of shear critical cracks and FRP debonding failure for the specimens with medium and large shear spans.

Bond properties of deformed steel bars coated with quartz sand modified enamel in concrete under both monotonic and reversed cyclic loading

Reinforced concrete structures located in seismic zones require significant ductility, which is affected by the bond properties between steel and concrete. The bond may be negatively impacted by anti-corrosion coatings. Quartz sand modified enamel (QSME) enhances the bond ductility for steel rebars in concrete under monotonic loading. This study investigates the bond properties of QSME-coated deformed steel rebars under monotonic and cyclic loading. For comparison, uncoated, fusion-bonded epoxy (FBE)-coated, and unmodified enamel-coated steel rebars are also studied. In addition to the coating type, the effects of steel rebar diameter, anchorage length, and concrete strength are considered. Acoustic emission (AE) technique was utilized to capture the AE energy released during the pull-out tests. Results showed that the bond stiffness and strength properties of QSME-coated steel rebars increase when concrete strength increases, while they decrease with rebar diameter under monotonic loading. The energy dissipation capacity of QSME-coated deformed rebar specimens is in average 1.43, 2.11, and 1.56 times greater than that of uncoated, FBE- and enamel-coated specimens, respectively. Among all coating types, the QSME-coated steel rebars exhibit the highest degradation index for the residual bond strength and the most AE activity, attributed to their improved chemical bonding and interfacial friction.

Flexural behavior of finger joint connected glulam wooden beams strengthened with CFRP strips

Laminated wood beams have become a preferred solution compared to standard solid beams due to their ability to carry larger loads and in larger spans (greater distances). The increase in wood usage and the varieties of its applications have highlighted the necessity for the enhancement of the maximum load-carrying capacity and overall load-displacement behavior of laminated wood beams. Among the various strengthening options applied to increase the maximum load-carrying capacity and material performance, the most commonly preferred choice is strengthening with CFRP (Carbon Fiber Reinforced Polymer). Within the scope of this study, a total of 26 glulam wooden beam test specimens were produced. Variations were introduced in terms of the number of laminated layers, the distance between finger joint connection points, finger joint orientation, the use or lack of use of strenghthening, and distance between CFRP strips. The specimens were subjected to monotonic static loading through a four-point bending test, allowing for an examination of how these variables influenced the bending behavior. The values obtained from the experimental study and the numerical study conducted using the finite element software ABAQUS were compared and interpreted. These values included ultimate load capacity, displacement at ultimate load, initial stiffness, displacement ductility, and energy dissipation capacity. Based on the conducted analyses, it was observed that the strengthening method involving CFRP strips developed within the extent of this study significantly increased the load-bearing capacity of finger jointed glulam wooden beams. Furthermore, it was shown to have a highly positive impact on the overall load-displacement behavior.

Mechanical strength of an hot-mix asphalt using recycled concrete aggregate: mass and volume proportioning

The generation of solid waste produced by the construction sector is considered a major problem worldwide. Several studies have been conducted to evaluate the use of construction and demolition wastes (CDW) in pavements. Within CDW, one material with great potential for use is recycled concrete aggregate (RCA). The present study evaluated the mechanical performance of a hot-mix asphalt (HMA) that used RCA as a partial substitute for the coarse fraction of the natural aggregate – Nag (particle size retained on 1/2” and 1/2"+3/8” sieves). The substitution was performed in a conventional way by mass and also by volume. To evaluate the performance under monotonic loading, the stability/flow ratio (S/F) of the Marshall test and the Indirect Tensile Strength (ITS) were measured on dry (ITSd) and conditioned (immersed in water, ITSw) samples. The tensile strength ratio (TSR) was calculated to evaluate the resistance to moisture damage. Under cyclic loading, tests of resilient modulus – RM (three temperatures and three loading frequencies), permanent deformation, and fatigue resistance under controlled-stress were performed. Cantabro tests were performed to measure the resistance to abrasive wear. Conventional characterization tests and imaging processing in a scanning electron microscope (SEM) were carried out on particles of RCA and Nag. A Life Cycle Cost Analysis (LCCA) was performed with the results obtained. The general conclusions were as follows: (i) RCA increases the asphalt content in the mixes, however, volume substitution could help to decrease it; (ii) the mixes with RCA met the volumetric and strength parameters established by the Colombian specification (especially for roads with low traffic volumes); (iii) mixes with RCA undergo better mechanical performance in all tests performed, however, resistance to moisture damage may be compromised when dosing by volume and asphalt content decreases; (iv) substitution by mass or volume did not generate clear trends in the results, but better overall performance is reported in mixes dosed by volume. It is recommended to carry out more studies where Nag is replaced by RCA in volume.

Structural performance of fibre reinforced recycled aggregate concrete road kerb sections under monotonic and cyclic loading

In recent years, there has been a notable emphasis on waste reduction and the adoption of recycled materials within the construction industry to reduce the industry’s overall carbon footprint. This study investigates the structural performances of concrete kerb sections prepared with five different concrete mixes containing recycled concrete aggregate, recycled tyre-derived aggregates and recycled polypropylene fibres. Kerb sections were cast at a road site in a suburb of Adelaide, Australia. After the concrete hardened, sections were cut and brought to the laboratory. A large number of monotonic and cyclic load tests were conducted on the kerb sections. The load-carrying capacity, bending moment capacity, cyclic fatigue capacity, durability properties along with deformation tolerance were evaluated. Kerb sections made with concrete containing recycled aggregate and polypropylene fibre could sustain nearly 2000 cycles of loading. Kerb sections prepared with natural aggregate concrete performed comparatively better. The addition of polypropylene fibre significantly improved the post-cracking behaviour of kerb sections and can delay crack propagation and other distress when subjected to cyclic loadings such as excessive soil movement, e.g., in areas with expansive soils or prone to tree root migration. Long-term observation may be required to confirm the mechanical and durability performance improvement in real field conditions.

The effect of silicon on the critical resolved shear stress of solid solution strengthened ferritic ductile iron

Solid solution strengthened ferritic ductile iron (SSFDI) exhibits improved mechanical properties compared to conventional ductile cast iron (DCI) grades, however, its potential widespread application is hindered by unpredictable brittle fracture which might be attributed to microstructural silicon segregation and associated superstructure formation. The aim of the present study is therefore to deepen the understanding on the effect of local silicon segregation on the mechanical properties of SSFDI, which is crucial especially for the common applications of DCI in cyclically loaded structures. Micropillar compression tests were carried out on three different casts to investigate the solution strengthening effect of silicon in the ferritic matrix. An almost perfect linear relationship between critical resolved shear stress (CRSS) and global silicon content was found. It was also found that the variation of CRSS with silicon content corresponds well to the variation of the macroscopic yield limits (under tension and compression) with global silicon content of different SSFDI alloys. This indicates that the ferritic matrix dominates the yield limit of the DCI alloys investigated in this study, while the morphology of the graphite nodules plays a minor role under monotonic loading conditions.

Comparison between acoustic emission sensors and piezoelectric patches for damage detection in concrete beams

Acoustic emission (AE) sensing is an established technique to monitor crack nucleation and propagation in different types of structural elements and for different damage scenarios. Although effective for crack monitoring in civil infrastructure, off-the-shelf AE sensors can be expensive, discouraging their installation in large numbers for assessing the global structural performance or monitoring multiple assets in the infrastructure network. For this reason, this paper explores the use of piezoelectric patches as an alternative low-cost solution to AE sensors. These patches are considerably cheaper, do not require external power supply and can be easily attached to existing structural elements or embedded into new structures. Moreover, thanks to the direct and inverse piezoelectric effect, the same set of patches can act both as sensors and actuators, meaning that they can be used to “passively” monitor crack propagation over time, as well as to locate and characterize damage in ageing structures at a certain time by using the patches as emitters and receivers of waves. In this framework, this paper proposes a comparison between traditional AE sensors and piezoelectric patches. The comparison is performed on a set of three concrete beams subjected to four-point bending loading, each equipped with two grids of sensors, i.e. 8 AE sensors and 8 patches. The beams are tested under increasing monotonic loading, from zero-load uncracked condition up to collapse.

Contribution to the experimental and theoretical study of the behavior of soil-structure interfaces

Designing civil engineering works often requires taking into consideration the contact and interface conditions between the soil and structure. These may refer to the discontinuity surfaces between the soil and a structure such as foundations, geotechnical works, and others. Current research aims to improve the calculation methods for structures through a better understanding of the behavior of materials and interfaces. The present work falls into this context. It involves two parts. The main purpose of the first part is to present the results of the monotonic and cyclic soil-structure interface tests which were carried out using a modified direct shear box apparatus. The tests were conducted using a local material, namely the sand from the town of Messâad in the Wilaya of Djelfa (Algeria), in accordance with a constant normal stress path. In addition, a parametric study, dealing with the effect of density, interface roughness, and type of adhesive used on the behavior of the interfaces, was carried out as well. As for the second part, it primarily aims to validate the Modjoin interface model, which was developed at the Lille Mechanical Laboratory, based on the tests that were carried out in the first part. It is important to know that this model includes the main concepts used in soil modeling, such as isotropic hardening, characteristic state, critical state, softening, and others. Moreover, several validation tests are also presented in this work in order to describe the behavior of the soil-structure interface under monotonic loading to assess the performance of the model.

Bearing capacity of modified suction caissons in clay overlying sand under monotonic horizontal loading

The modified suction caisson (MSC) is an innovative foundation for fixing offshore wind turbines, consisting of an internal caisson (IC) and an external skirt (ES). In this study, the Plaxis3D is conducted on the bearing capacity of the MSC in clay overlying sand under monotonic horizontal loading. The parameters of the aspect ratio of the IC, the size of the ES, the clay thickness, and the soil strength are considered. Results show that the horizontal ultimate bearing capacity of the MSC decreases as the length ratio of the ES to IC decreases. Moreover, the width of the ES enhances the horizontal bearing capacity of the MSC higher than the length of the ES. With the increase of the clay thickness, the rotation center of the TSC and MSC exhibits two and three stage change patterns, respectively. When the clay and sand are the inhomogeneous soils, the horizontal ultimate bearing capacity of the MSC is enhanced by 8.96% compared to the homogeneous soils. Additionally, the passive and active earth pressures around the MSC are mainly generated at the front and rear side of the loading direction, respectively. This study will provide theoretical guidance for the design of the MSC.

Experimental nonlinear response of a new tensairity structure under cyclic loading

Pneumatic structures are recognized as promising thin-walled structures for their advantageous features such as lightness, portability, versatile design, and ease of installation. Although their bearing capacity under monotonic static loads can be formidable, their inherent dissipation capacity is low and thus entails significant limitations when counteracting dynamic loads. A novel tensairity structure is here proposed to overcome this drawback. The innovative design features a cylindrical inflatable element integrated with NiTiNOL cables wrapped around and affixed to a slender beam positioned along its generatrix. A laboratory-scale prototype is employed to assess how the structure behaves under cyclic loading in comparison to a standalone inflated beam and a conventional tensairity structure outfitted with steel cables. This experimental study delves into the influence of internal pressure and pretension levels of the metallic cables. Experimental results unfold a smooth softening-type hysteretic behavior under cyclic loading, which is accompanied by a slight stiffness degradation and a moderate pinching. The comparative analysis of the experimental results also demonstrates the substantially improved and consistent dissipation capacity of the presented novel concept of tensairity structure, which thus offers superior stability under cyclic loads. A parametric identification based on a modified Bouc–Wen model is finally performed to simulate the hysteretic response of the structure. A correlation is also established between the identified parameters of the phenomenological model and the internal pressure, type and cables pretension levels. The excellent agreement between numerical predictions and experimental force–displacement cycles other than those used for the parametric identification demonstrates the suitability of the adopted phenomenological modeling.

Topology optimization of vertical shear links in eccentrically braced frames

The inclusion of additive manufacturing (AM) in the construction industry has opened new perspectives on the production of structural members. By coupling AM technologies with topology optimization (TO), significant reductions in material usage and weight can be achieved. Although TO has been applied to optimize simply supported beams, additional factors such as stress concentrations, buckling, and low-cycle fatigue from seismic loads require further investigation. This study presents a numerical approach for optimizing shear links subjected to monotonic and cyclic loading. The numerical models for conventional shear links were validated against experimental work, including cyclic loading tests on individual shear links and scaled eccentrically braced frames (EBF). The implementation of TO led to a 12 % volume reduction in the first optimized link. The optimized link demonstrated superior performance, exhibiting higher shear strength and energy dissipation capacity under both monotonic and cyclic loading. Another study examined EBFs with vertical links, achieving 12 % and 30 % reduction in material volume. The optimized links showed improvements that reached 25 % compared to the conventional link in terms of strength and energy dissipation with 12 % volume reduction, while 30 % volume reduction showed slightly less improvement over EBFs with conventional shear links.

RESEARCH OF THE NOISE LOAD OF VEHICLES

Noise can be viewed as an undesirable component of a signal that can affect the quality of perception or transmission of information in a system. In different contexts, the term «noise» may have different meanings, but a common feature is the random impulsive nature of this phenomenon. Automotive noise is sound energy generated by the movement of a vehicle and its components. The study of road traffic noise is an important area, especially in environments where noise can have a significant impact. This includes analyzing noise levels, identifying noise sources, assessing its impact on the environment, and developing strategies to reduce noise. This study analyzes the causes of automobile noise and their noise sources, and provides classification features. The research methodology included measuring the noise level at different points of the bus interior using a specialized acoustic sound level meter Testo 816. The Sound Meter program was additionally used to obtain current time values of noise level changes with graphical data interpretation. When the bus is idling, a monotonous noise load level in the range of 58-63 dB is observed in the cabin, which is typical for a running diesel engine, which is the main source of noise. The movement of the bus in urban conditions is accompanied by a change in traffic conditions, which in turn increases the maximum noise load to 73 dB. The movement of the bus in the city is accompanied by an increase in the noise load up to 74 dB and the equivalent up to 67 dB. This is due to an increase in speed, contact of tires with the asphalt road, interaction of the air environment with bus elements, the appearance of vibrations and other noises.Although the noise load in the bus interior is within the upper permissible limits, it requires the introduction of noise reduction measures, especially for long-distance buses for a comfortable ride for passengers. Therefore, it is important to take noise levels into account when designing and operating vehicles, as well as when planning urban infrastructure projects.

A Griffith description of fracture for non-monotonic loading with application to fatigue

With the fundamental objective of establishing the universality of the Griffith energy competition to describe the growth of large cracks in solids not just under monotonic but under general loading conditions, this paper puts forth a generalization of the classical Griffith energy competition in nominally elastic brittle materials to arbitrary non-monotonic quasistatic loading conditions, which include monotonic and cyclic loadings as special cases. Centered around experimental observations, the idea consists in: (i) viewing the critical energy release rate Gcnot as a material constant but rather as a material function of both space X and time t, (ii) one that decreases in value as the loading progresses, this solely within a small region Ωℓ(t) around crack fronts, with the characteristic size ℓ of such a region being material specific, and (iii) with the decrease in value of Gc being dependent on the history of the elastic fields in Ωℓ(t). By construction, the proposed Griffith formulation is able to describe any Paris-law behavior of the growth of large cracks in nominally elastic brittle materials for the limiting case when the loading is cyclic. For the opposite limiting case when the loading is monotonic, the formulation reduces to the classical Griffith formulation. Additional properties of the proposed formulation are illustrated via a parametric analysis and direct comparisons with representative fatigue fracture experiments on a ceramic, mortar, and PMMA.