Initial Force Research Articles

Crack characteristics analysis and mechanisms in GH3536 alloy manufactured by laser powder bed fusion

The presence of cracks poses a significant challenge in the application of laser powder bed fusion (LPBF) for manufacturing high Ni-base superalloys. The crack characteristics of LPBF-fabricated GH3536 superalloy are investigated in this paper, with a focus on analyzing the generation and expansion mechanism of micro-cracks through an investigation into the evolution of the molten pool, thermal stress and micro-characteristics. The findings suggest that thermal stress serves as the primary driving force for both crack initiation and propagation, with a predominant concentration of thermal stress observed in the heat-affected zone located at the periphery of the molten pool. Grain disorientation is another crucial factor influencing both the initiation and propagation of cracks. The difference in orientation between adjacent grains at the crack exceeds 40°, with the crack primarily originating from large angle grain boundaries (LAGBs) and propagating along them. Furthermore, there exists inconsistency in terms of elastic modulus and deformation coordination between carbides (Mo2C, (Ni, Cr) Mo3C6) particles, and matrix. This inconsistency results in two normal partial stresses acting in different directions, leading to dislocation aggregation and crack nucleation.

Effect of the triangular prism dent on stress corrosion cracking behavior of alloy 690TT heat transfer tube in a lead-containing alkaline solution

In this paper, the microstructural changes and mechanical characteristics of alloy 690TT heat transfer tube with a triangular prism dent are investigated by combining experimental and simulation methods, and subsequently examines their influence on stress corrosion cracking (SCC) behavior. The results indicate that the deformation mechanism caused by impact dent is slip and twinning. The structural transformation of high-density dislocations, as well as Copper and Brass deformation textures, are formed at dent bottom, resulting in stress concentration through work hardening, which greatly increases SCC sensitivity. Oxidation preferentially occurs along grain boundaries and dislocations, and the corrosion products are formed, which exhibit a semi-coherent orientation relationship with the matrix. Oxidation is essentially a de-alloying process in which oxygen diffuses inward and Cr migrates towards the oxidation zone. The wedge force generated by corrosion products provides another driving force for initiation and propagation of SCC cracks, in addition to external loads and residual stress. SCC cracks propagate in the form of intergranular stress corrosion cracking and transgranular stress corrosion cracking in a high temperature lead-containing alkaline solution.

Deformation and Energy Absorption Performance of Functionally Graded TPMS Structures Fabricated by Selective Laser Melting

Triply periodic minimal surface (TPMS) structures have unique geometries and excellent mechanical properties, which have attracted much attention in many fields. However, the relationship between different filling forms and different directions of functionally graded TPMS structures on energy absorption has not been fully studied. In this study, a functionally graded strategy was proposed to investigate the effect of filling form and direction gradient on the energy absorption of TPMS structures. The design of functionally graded Gyroid and Diamond TPMS cellular structures with multiple forms was characterized, and the structures were fabricated using additive manufacturing technology. The effects of uniformity and different directional gradients on the deformation and energy absorption properties of the structures were studied experimentally and numerically. According to the compression test results, it was found that different filling forms of the TPMS structure behave differently in terms of yield plateau and deformation pattern, and the sheet structures can develop a better deformation pattern to enhance energy absorption capacity. Functionally graded sheet Diamond TPMS cellular structures along the compression direction exhibit a 32% reduction in initial peak force, providing more advantages in structural deformation and energy absorption. More closely, it is possible to further reduce the initial peak force, delay the densification point, and thus increase the energy absorption capacity by designing functionally graded sheet Diamond TPMS based cellular structures. The results of this study provide valuable guidance for the design of high-performance impact-protection components.

Numerical and theoretical analysis of the out-of-plane crushing behavior of a sinusoidal-shaped honeycomb structure with tunable mechanical properties

Honeycomb structures are widely utilized for energy absorption in engineering, showing superior crushing strength and energy absorption in the vertical direction, yet their potential as energy absorbers is limited due to a high initial peak force (IPF) in that direction. In this study, a novel honeycomb structure with tunable out-of-plane mechanical properties is developed by incorporating sinusoidal-shaped features into traditional vertically straight-walled cells. Crushing behavior and energy absorption performance of sinusoidal-shaped honeycomb structure (SSHS) under quasi-static out-of-plane compression are investigated numerically and theoretically. Results demonstrate that the IPF and the fluctuation of crushing response of SSHS can be effectively reduced for the introduction of sinusoidal-curved configuration. The predictable collapse mode of SSHS could be achieved for the buckling-induced features of trough and peak of sinusoidal waves. Parametric analyses were carried out to explore the influence of the geometrical topology of sinusoidal waves, namely, wave amplitude (A = 0.6–1.6 mm), wave number (N = 1–6) and the relative density (ρ = 0.05–0.25) on the out-of-plane mechanical properties of SSHS, including IPF, mean crushing force (MCF), specific energy absorption (SEA) and crushing force efficiency (CFE). The results imply properly adjusting topology parameters can determine the collapse patterns and the stress distribution, thereby substantially improving the mechanical properties. Moreover, theoretical investigation was also performed based on the simplified super folding element theory. The calculation of MCF shows a good agreement between the theoretical predictions and the numerical results. The sinusoidally curved-walled topology design strategy provides insights into the development of lightweight structures with controllable and improved crushing performance.

Research on movement of dimensional singularities without elastic interaction in gasketed joints

Loss of clamping force due to elastic interaction is unpredictable and nonnegligible with the typical non-linear characteristics of gasketed joints. It is hard to weaken or eliminate elastic interaction by suitable joint dimensions. An analytical model of elastic interaction with dimensional representation is constructed using gasket deformation as a bridge. The influence of multi-dimensional dimensions on clamping force losses, such as bolt spacing, joint width and thickness, was explored by non-linear finite element analysis for a typical sandwich structure with two-bolt gasketed joints. Dimensional singularities without elastic interaction are validated and their approximate range is determined. It is clarified that initial clamping force or joint material can cause dimensional singularity movement. This paper provides a theoretical basis for solving the problem of clamping force losses and inhomogeneities effected by elastic interactions in engineering.

Study on the Stresses Released in a Notched, Postensioned Concrete Beam

Structural prestressed concrete elements (SPCE) face uncertainties in accurately assessing the actual prestressing force. Over time, the initial prestressing force decreases due to several factors. Incorrect estimation of prestress losses can lead to design inefficiencies or structural issues. Monitoring the prestressing force can be achieved through instrumentation during casting, but existing SPCE lack such devices, necessitating indirect methods to determine prestressing force variations. This study focuses on analyzing stresses released in a notched post-tensioned concrete beam using the saw-cutting technique. Surface notches induce local decompression, allowing for strain measurements in the isolated concrete block. These measurements, considering uncertainties in initial prestress and material properties, are analyzed through backward calculations. The findings enhance understanding of saw-cutting and enable future applications to determine effective prestressing force in unmonitored SPCE. Further experimental studies are required to explore prestressing force consistency under monitored conditions. This research provides valuable insights into the potential of the saw-cutting technique as a non-destructive testing method for assessing prestressing force in unmonitored SPCE. Accurately determining the prestressing force is crucial for evaluating existing SPCE and ensuring their structural integrity. Keywords: prestressed concrete, beam, test, saw-cut, notch

Investigation of mixing miscible liquids with high viscosity contrasts in turbulently stirred vessels using electrical resistance tomography

The time required to attain a sufficient degree of homogeneity i.e., mixing time, is an important parameter in mixing processes. This paper presents results from a study employing an experimental approach to estimate mixing times for a miscible Newtonian liquid mixture system with high viscosity contrasts in a turbulent stirred vessel. An Electrical Resistance Tomography (ERT) based technique has been adopted to monitor dimensionless mixing time across a range of additive viscosities, impeller designs, sizes, and speed. Dimensional analysis has been used to interpret these mixing time results in terms of the magnitude of the bulk inertia forces relative to the initial viscous forces within the added fluid. Critical non-dimensional numbers, uniting the properties of the two liquids, have been proposed as the criterion for avoiding undesirable operating conditions under which the mixing time is much longer than that required for mixing fluids with similar properties. The work proposes novel correlations for mixing time and incorporates a new dimensionless group, thereby enabling a more nuanced and accurate characterisation of mixing behaviours. This research stands to contribute to energy saving and waste minimisation efforts in the industry. It provides insights for process designers and simulation engineers, propelling a leap forward in the design and operation of mixing processes when dealing with liquid systems that have significant viscosity differences.

Preparation, shape memory properties and application research of PLA/PCL‐based shape memory polymers doped with Al2O3 and lignin

AbstractIn this paper, the influence of different material trademarks, mass ratios, the melt mass‐flow rate (MMFR) and molecular weights (MW), mold and injection temperatures, Al2O3 powder and lignin on the shape memory properties of PLA/PCL SMP material (PPSM) were then analyzed in detail by different characteristic methods. Besides, three promising applications (Origami metamaterials and variable‐stiffness grippers) are provided utilizing the PPSM doped with Al2O3/lignin. Eventually, a compensating strategy was discussed to improve the final configuration of the SMP after multi‐cycles. The shape memory recovery ratios could be improved by increasing the MMFR of PLA and the MW of PCL. The addition of 2 g‐Al2O3 could shorten the recovery time, while the addition of 2 g‐lignin could increase the thermal‐recovery force and mechanical performance. The shape memory rate under 20 g weights, initial peak forces at room and high temperatures of the origami metamaterials could reach 57%, 2027.29 N and 17.49 N, respectively. The tensile force of banding rebars could reach 150.29 N, which is promising to apply into the construction field.

Graded in-plane Miura origami as crawling robots and grippers

In this work, we propose a variation of Miura origami which, different from the existing out-of-plane bending Miura origami, has an in-plane bent configuration due to its graded crease pattern. By combining with the one-way shape memory alloy spring, we show that the proposed graded Miura origami can serve as a smart actuator and can be applied to drive crawling robots or grippers. First, we constructed a physical model of the graded Miura origami, from which a curvature-programmable geometric equation is proposed. Then, in addition to providing a mechanical model that can capture the mechanical behavior of the initial force–displacement relationship of the curved beam, we show that the proposed curved origami has a different mechanical behavior compared to the corresponding simple flexible arch, specifically if realized by silicon rubbers. By arranging anisotropic friction to the feet, the origami robot can crawl with an omega-elongation/compression motion like an inchworm. With a closed-loop current source control system using a high-frequency pulse width modulation-based topology, where the strain state of the arched origami is detected by a demodulator-free fiber Bragg grating sensor, the average speed of the origami crawling robot can reach 2.72 mm/s. In addition, by arranging three graded Miura origami, a gripper capable of lifting a weight of 518.5 g can be formed, where the carried load is over 4.5 times its own weight.

Time-dependent force depreciation of intraoral orthodontic elastics of variable force and lumen sizes – An in vitro study

: To evaluate force decay of elastics of different dimensions and different force values over 48-hours.Steps included extension and immersion of elastics in artificial saliva and measurement of force levels at a specified point of time. A model with vertical pins placed at in the oral cavity. The initial force measurement was done using Universal testing machine before the elastics were engaged onto the pins 37⁰C in artificial saliva. The reading was taken after this in the Universal testing machine for the samples. The elastics were then placed back into the static simulation for the next 23 hours and again into the dynamic simulation for the next 1 hour. Statistically significant difference (P<0.05) was observed between force depreciation between rest and maximum stretch of the elastic. Statistically significant difference was observed in force depreciation with varying time intervals of a particular elastic sample. Lumen size and pre-determined force values affect the overall force decrease pattern of elastics. Elastics with higher force and smaller lumen size show comparatively higher loss of force than the lighter elastics with larger internal diameter. The maximum force loss of a particular elastic happens within the first 24 hours of elastic stretch. The study would help provide information about how an elastic's lumen size and initial force are interdependent, giving clinicians a better understanding of how to prescribe the right elastics for the force they need to apply for treatment.

Grey-Taguchi analysis and experimental assessment of 1 GPa HSLA steel treated by quenching and tempering

The effect of quenching and tempering (QT) process on the mechanical properties of the experimental high-strength low-alloy (HSLA) steel was analyzed by Grey-Taguchi method, thus achieving the optimum combination of parameters based on the appropriate nine sets of experiments on an orthogonal array. The grey relational analysis (GRA) reveals that the quenching temperature T1 has the greatest effect on each response variable, followed by the tempering temperature T2, while the quenching time t1 and tempering time t2 have similar and the least effect. Experimental assessment of microstructure evolution was performed by multi-scale characterizations and in-situ investigation combined with modeling, focusing on martensite transfomation kinetics that controlled by the quenching process. Results indicate that the prior austenite grain (PAG) size and the substructure of martensite are significantly refined, as the quenching temperature decreased from 950 to 850 °C. The PAG refinement leads to an increase in driving force for martensite transformation initiation, thus shifting the martensite transformation temperature to lower levels for a higher degree of undercooling, consistent with the experimental and modeling results. The refined microstructure obtained at low quenching temperature contributes to strength improvement, and the various carbides precipitated during tempering process offset the tempering softening of the steels. In general, the value increase of process parameters (T1, T2, t1 and t2) leads to a decrease of strength property, but an increase of ductility and toughness. Based on the theoretical and experimental basis, a 1 GPa grade HSLA steel with improved comprehensive mechanical properties can be produced.

Influence of strand rupture on flexural behavior of reduced-scale prestressed concrete bridge girders with different prestressing levels

In prestressed concrete (PC) bridges, high-strength prestressing steel plays a key role in the flexural response of girders. In both pre-stressed and post-tensioned PC bridge girders, damage induced by corrosion or impact of under-passing high vehicles may led to rupture of one or more strands, significantly affecting the load-carrying capacity against dead and traffic loads. This paper presents an experimental study on the response of PC girders affected by strand rupture at different locations. Four reduced-scale post-tensioned concrete girders with different levels of initial prestressing force were tested under four-point bending. Two specimens with a different level of prestress were initially tested in undamaged configuration to provide a basis for the assessment of damage effects. The other pair of specimens were intentionally damaged - having the same initial prestressing level of their undamaged counterparts - in the lower tendon to investigate their limited flexural response under different performance levels including serviceability and collapse. Damage turned into a different critical cross section outside the loading region, i.e. both cracking and collapse were attained 1.1m away from midspan. In the last section of the paper, a cross sectional analysis of the girder was developed at cracking and ultimate conditions for the prediction of damage impact on failure mechanisms, thus validating the experimental findings.

Investigating the Effect of Vitamin a on Orthodontic Tooth Movement: An Experimental Study.

Vitamin A is essential not only for bone metabolism and development but also for the normal functioning of many physiological processes in the body. Despite vitamin A's important involvement in bone metabolism, its effect on orthodontic tooth movement is not entirely known. Previous studies on animals have suggested that vitamin A may influence alveolar bone remodelling and tooth movement, but the effect of various doses of vitamin A on these processes remains poorly understood. This experiment was designed to examine the effect of vitamin A on the orthodontic tooth movement of male rats. Eighty male rats weighing 200-250 grams were divided into eight equal parallel groups. An initial orthodontic force was applied to all groups with a specific appliance, and six different doses of vitamin A were administered (250-2500 IU/Kg intraperitoneally). Two control groups were also considered. Orthodontic tooth movement was measured at the beginning and end of the study period (day 14), and serum alkaline phosphatase (ALP) level was evaluated. The maxillary sections were also evaluated by histological examination. Although there was a dose-dependent increase in tooth movement observed with vitamin A administration, the differences were not statistically significant. There was no significant difference in the number of osteoclasts or the presence of lacunae on the root surface between the study groups. Root resorption was observed in different areas of the root and was not related to different doses of vitamin A. The serum ALP level did not show any significant difference between the groups treated with different doses of vitamin A. Despite the known effects of vitamin A on bone metabolism, the results of this study suggest that vitamin A did not increase alveolar bone remodeling and orthodontic tooth movement in male rats.

Axial crushing and energy absorption of graded hierarchical hexagonal tubes

The concept of both hierarchy and gradient are incorporated into thin-walled hexagonal tubes for a configuration with optimum crashworthiness and energy absorption. Graded hierarchical hexagonal (GHH) tubes are developed by replacing the corners of an original hexagonal tube with a series of micro hexagonal cells. The total net cross-sectional area as well as the mass are kept the same for all the GHH tubes. The axial crushing behavior of the GHH tubes is investigated in terms of deformation modes, crushing forces and energy absorption. Theoretical solutions are also derived to predict the mean crushing forces (MCFs) of the GHH tubes. Two deformation modes have been identified, a locally layer-by-layer folding deformation (Mode-L) and a globally buckling-like deformation (Mode-G). The hierarchical and graded parameters have significant but quite different influences on the crushing behavior of GHH tubes. The MCF and the specific energy absorption (SEA) can be significantly improved with reasonably hierarchical and graded arrangements, while the initial peak force (PF) remains almost constant.

A 0.05 m Change in Inertial Measurement Unit Placement Alters Time and Frequency Domain Metrics during Running.

Inertial measurement units (IMUs) provide exciting opportunities to collect large volumes of running biomechanics data in the real world. IMU signals may, however, be affected by variation in the initial IMU placement or movement of the IMU during use. To quantify the effect that changing an IMU's location has on running data, a reference IMU was 'correctly' placed on the shank, pelvis, or sacrum of 74 participants. A second IMU was 'misplaced' 0.05 m away, simulating a 'worst-case' misplacement or movement. Participants ran over-ground while data were simultaneously recorded from the reference and misplaced IMUs. Differences were captured as root mean square errors (RMSEs) and differences in the absolute peak magnitudes and timings. RMSEs were ≤1 g and ~1 rad/s for all axes and misplacement conditions while mean differences in the peak magnitude and timing reached up to 2.45 g, 2.48 rad/s, and 9.68 ms (depending on the axis and direction of misplacement). To quantify the downstream effects of these differences, initial and terminal contact times and vertical ground reaction forces were derived from both the reference and misplaced IMU. Mean differences reached up to -10.08 ms for contact times and 95.06 N for forces. Finally, the behavior in the frequency domain revealed high coherence between the reference and misplaced IMUs (particularly at frequencies ≤~10 Hz). All differences tended to be exaggerated when data were analyzed using a wearable coordinate system instead of a segment coordinate system. Overall, these results highlight the potential errors that IMU placement and movement can introduce to running biomechanics data.

Mechanical properties of homogeneous and functionally graded spinodal structures

This paper investigates the compressive mechanical behavior of spinodoid metamaterials in a quasi-static state through experimental and numerical analysis at the macroscopic level. This homogeneous structure exhibits weak strain hardening, resulting in a lower initial peak compression force and higher specific absorption energy compared to other mechanical metamaterials. The homogeneous model has multiple low-density regions uniformly distributed within the three-dimensional space due to the random nature of the Gaussian field. Thus, the transition from low-density to high-density regions is described as a gradual process, implying that the deformation of metamaterial shifts to region-by-region compaction. Besides, the functionally graded spinodoid structure shows strong strain hardening, whose deformation mainly tends to collapse layer by layer along a positive graded direction. The graded structures with low densities have a lower energy absorption capacity than the corresponding homogeneous structure, while higher-density structures show a reverse trend. This phenomenon originates from the superimposed effect of two kinds of strain hardening.

The Impact of Temperature on the Electromagnet and Structural Optimization of a Solenoid Valve

The mathematical model of the solenoid valve under varying temperatures is constructed to investigate itsperformance and enhance heat dissipation balance. The relationship between temperature and electromagnetic force isdetermined. Electrothermal coupling simulation using COMSOL is conducted, optimizing the outer diameter and lengthstructure parameters of the coil. It is established that the heat dissipation of the coil is influenced by its outer diameter.Subsequently, based on optimized coil structure parameters, an orthogonal experimental design method combinedwith Ansys Maxwell is employed for simulation solution analysis to study the impact of structural parameters such aslength, position, front and rear angles of the magnetic barrier ring in the iron core, armature length, and through-holesize on electromagnetic force. Optimal structural parameters are identified. Results indicate a decrease in steady-stateelectromagnet temperature by 3–4℃, an increase in the initial electromagnetic force by 32.63%, and a rise in the maximumelectromagnetic force by 27.10%.

Mechanical response of human thoracic spine ligaments under quasi-static loading: An experimental study

PurposeThis study aimed to investigate the geometrical and mechanical properties of human thoracic spine ligaments subjected to uniaxial quasi-static tensile test. MethodsFour human thoracic spines, obtained through a body donation program, were utilized for the study. The anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL), capsular ligament (CL), ligamenta flava (LF), and the interspinous ligament and supraspinous ligament complex (ISL + SSL), were investigated. The samples underwent specimen preparation, including dissection, cleaning, and reinforcement, before being immersed in epoxy resin. Uniaxial tensile tests were performed using a custom-designed mechanical testing machine equipped with an environmental chamber (T = 36.6 °C; humidity 95%). Then, the obtained tensile curves were averaged preserving the characteristic regions of typical ligaments response. ResultsGeometrical and mechanical properties, such as initial length and width, failure load, and failure elongation, were measured. Analysis of variance (ANOVA) revealed significant differences among the ligaments for all investigated parameters. Pairwise comparisons using Tukey's post-hoc test indicated differences in initial length and width. ALL and PLL exhibited higher failure forces compared to CL and LF. ALL and ISL + SSL demonstrated biggest failure elongation. Comparisons with other studies showed variations in initial length, failure force, and failure elongation across different ligaments. The subsystem (Th1 – Th6 and Th7 – Th12) analysis revealed increases in initial length, width, failure force, and elongation for certain ligaments. ConclusionsVariations of both the geometric and mechanical properties of the ligaments were noticed, highlighting their unique characteristics and response to tensile force. Presented results extend very limited experimental data base of thoracic spine ligaments existing in the literature. The obtained geometrical and mechanical properties can help in the development of more precise human body models (HBMs).

Computationally-efficient high-fidelity nonlinear FEA of seismically isolated post-tensioned RC bridges

This study presents a novel computationally efficient high-fidelity nonlinear FEA (NLFEA) methodology for prestressed RC bridges constructed in the UAE and seismically isolated with elastomeric bearings. Specifically, the presented NLFEA methodology, using 3D solid brick elements, is shown to overcome traditional prohibitive numerical burdens. This is demonstrated without compromising accuracy or upscaling applicability and appropriateness. The proposed NLFEA approach is highlighted through detailed modeling of RC bridges’ non-traditional structural components and loading aspects (elastomeric bearings and post-tension prestressing cables). The mechanical behavior of elastomeric isolators and the RC continua, including cracking and other nonlinear phenomena, are captured via 3D solid brick elements. Moreover, the modeling procedure accurately represents the post-tension tendons’ prestressing forces and the associated effects on the RC elements. The prestressing forces are incorporated within the tendon elements via insightful manipulations of stepwise initial conditions and internal force adjustments. Additionally, load-carrying capacity determination for the elastomeric bearings was achieved by conducting a parametric investigation to capture their mechanical behavior adequately. Eventually, the analysis of a full-scale bridge is presented in this paper. The post-tensioned RC bridge understudy spans 100 m over eight elastomeric (natural rubber) seismic isolator bearings. Twelve post-tension prestressing cables are utilized to provide the bridge with continuous internal tension-balancing forces. A high-fidelity detailed FEA model of the complete bridge is developed and validated against a SAP2000 FEA model. It is shown that reasonable computational efforts can be expected without compromising the accuracy of the results.

Evaluation of retentive force between stud and resilient telescopic crown attachment for implant-retained mandibular overdentures

Purpose This study aimed to evaluate the retentive force between stud and resilient telescopic crown attachments for implant-retained mandibular overdenture. Patients and methods A total of 20 male patients were selected from the Clinic of Removable Prosthodontics Department. Faculty of Dentistry, Sinai University (Kantara). Patients were divided into two equal groups. Group I (control group): patients were treated with two implants of 3.7 mm diameter and 13 mm length (in the canine regions), retaining mandibular overdentures with ball abutments, and by conventional maxillary complete dentures. Group II: patients were treated with two implants of 3.7 mm diameter and 13 mm length (in the canine regions), retaining mandibular overdentures with conical abutments with a 6° taper, and by conventional maxillary complete dentures. Retention force was recorded at the time of insertion (T0), 6 months (T6), and 12 months (T12) later. Results One-way anova revealed significant differences between the two groups in initial retention forces (T0). However, no significant difference was observed between the two groups at T6 and T12. Group II (telescopic attachment) was associated with significantly higher retention losses than Group I (ball attachment). In comparing the mean retention loss values for the two groups at different follow-up periods, significant differences were observed for both groups. Conclusion Within the limitations of this study, it can be concluded that: telescopic attachment with taper 6° can provide acceptable retention compared to ball and socket attachment during 12 months of overdenture use.