Testing Machine Research Articles

Stiffness in compression therapy: Analytical estimation of pressure changes beneath textile compression devices

Compression pressure changes in dynamic conditions under textile compression devices have a critical impact on the success of compression therapy. Models exist to predict the level of compression pressure, but not the actual change in pressure. This paper aims to derive a formula to accurately determine the pressure change under textile compression devices, to investigate the factors influencing the pressure change and to verify their effects through theoretical analysis. Firstly, a formula based on Laplace’s law is presented which mathematically describes the dependencies of pressure changes. Secondly, a simulation is carried out to demonstrate the effect of these dependencies on pressure changes using theoretical textile curve functions. Finally, the effect of these dependencies is demonstrated by testing short- and long-stretch bandages in a tensile testing machine and using the recorded material curves to simulate a theoretical application of these bandages to the lower limbs. The results show that the change in pressure is not solely determined by the intrinsic properties of the material, but is influenced by several variables, including the mechanical performance of the textile materials during stretching, the target pressures for application of the textile material, and the body geometries to which the material is applied. Pressure change cannot be a constant for textile compression devices such as bandages. The research increases the understanding of the factors that influence pressure changes in compression device materials. The findings may have implications for the design and selection of compression textiles in clinical applications.

Fracture resistance and fractographic analysis of pressable glass-ceramics with different partial coverage designs for maxillary premolars

BackgroundPartial coverage concepts have met the main goal of conservative dentistry. Vonlays, which combine features of veneers and onlays, are a recent alternative to full coverage designs and overlay partial coverage restorations. This in vitro study was conducted to compare the fracture resistance of the newly introduced pressable zirconia-reinforced lithium silicate with pressable lithium disilicate ceramic and to determine the optimal preparation design for partial coverage on upper premolars.MethodsFifty-two duplicated epoxy resin dies were prepared following vonlay and overlay preparation guidelines. For each preparation (n = 26), the specimens were divided into two subgroups to be restored with lithium disilicate (IPS e.max Press) or zirconia-reinforced lithium silicate (Vita Ambria) (n = 13 each). Ceramic vonlays and overlays were bonded using dual cure resin cement, subjected to thermomechanical fatigue, and the load to fracture was tested by using a universal testing machine. The specimens were fractographically analyzed via scanning electron microscopy (SEM). The normality of the fracture resistance data was checked using the Shapiro‒Wilk test and Q‒Q plots, and two-way ANOVA was used to assess the effect of the type of preparation and ceramic material on the fracture resistance.ResultsThe group of overlays restored with zirconia-reinforced lithium silicate showed the highest mean fracture load (1218.69 N), while the group of vonlays restored with lithium disilicate had the lowest mean fracture resistance (967.15 N). The effect of preparation design and material type on fracture resistance was significant for both factors, p = 0.003 and p < 0.0001, respectively. Different features of the fracture surfaces, such as arrest lines, hackles, and directions of crack propagation, were observed.ConclusionsZirconia-reinforced lithium silicate exhibited greater resistance to fracture compared to lithium disilicate, making it a potential substitute for partial coverage restorations. Additionally, the overlay showed superior fracture resistance when compared to the vonlay preparation design.

The shear bond strength of orthodontic brackets after surface conditioning of Zirconia, Ceramic and E. max models

The current study aims to evaluate the shear bond strength (SBS) of metal orthodontic brackets after surface conditioning by hydrofluoric acid (HF) and aluminum oxide air abrasion (Al2O3) and using two prime types and to determines the adhesive remnant index (ARI). We compared the bond strength of different types of models (full glazed zirconia, ceramic faced zirconia and E. max faced zirconia) with different surface conditioning methods for attaching metal orthodontic brackets. The study used 60 models for each material, divided into subgroups based on the type of prime material and surface preparation method. The bond strength was measured using a universal testing machine and the results were analyzed using statistical software. Shear bond strength of the Aluminum oxide was statistically (p&lt;0.05) higher than the hydrofluoric acid and control groups in all groups (full glazed zirconia, ceramic faced zirconia and E. max faced zirconia). The Assure® Plus primer with Aluminum oxide surface treatment give rise to the highest shear bond strength than 3M™ Transbond™ XT, while there was no significant difference between Assure® Plus and 3M™ Transbond™ XT primer for both control and hydrofluoric acid groups. The highest shear bond strength was obtained with Aluminum oxide conditioning method for all types of ceramic materials used in this study.

Comparative Evaluation of Orthodontic Bonding Systems for Ceramic Brackets on Zirconia Crowns: A Shear Bond Strength and Adhesive Remnant Index Study

Background The purpose of this research was to compare the adhesive residual score/adhesive remnant index (ARI) and shear bond endurance between the two orthodontic bonding systems for zirconia surface bonding: Self-etch (Scotchbond Universal) and total-etch (Transbond XT). Materials and Methods Color-coded acrylic blocks embedded with zirconia slabs were prepared, and the orthodontic brackets (ceramic) were bonded using either the total-etch or self-etch system. Group 1, represented by pink-colored blocks ( N = 12), accommodated 12 zirconia surfaces using the total-etch system, while Group 2, represented purple-colored blocks ( N = 12), also housed zirconia surfaces using the self-etch system. The shear bond strength was evaluated using an Instron Universal Testing Machine, and ARI scoring was done upon debonding. The statistical software SPSS was used for the analyses. Results The average bonding strength for the Scotchbond Universal etch system was 6.21 ± 0.76 MPa, while for the total-etch system, it was 5.59 ± 1.37 MPa. The ARI scores revealed that 83% of surfaces bonded with the self-etch system had no adhesive residue (ARI score 0), compared to 66% for the total-etch system. Conclusion The self-etch bonding agent demonstrated superior bond strength (6.2 MPa) compared to the total-etch system (5.6 MPa). Furthermore, it exhibited better ARI scores, indicating minimal adhesive residue. These findings suggest that the self-etch system is preferable for bonding ceramic brackets to zirconia crowns, offering improved bonding efficacy and ease of clean-up.

Hot deformation behavior and processing map of the nanocrystalline pure Mg

The thermal compression test of the nanocrystalline, as-extrusion and as-cast pure Mg was carried out by the AGX-XD universal testing machine. The results demonstrated that flow stress of pure Mg with different grain sizes decreased with increasing temperature and decreasing strain rate. Accurate prediction of the thermal deformation behavior was achieved through establishing the constitutive equations. In comparison, the nanocrystalline pure Mg represents stronger strain hardening rate and weaker sensitivity to strain rate. Based on processing map, the optimal processing area for the nanocrystalline pure Mg is at 300–400 °C, 0.01– 0.1 s−1. The grain distribution of the nanocrystalline pure Mg remains stable and uniform after hot compression, and the grain boundary migration is the dominant deformation mechanism.

Retention of implant retained obturator using two implant placement configurations for maxillectomy cases: in-vitro study

BackgroundImplant-retained obturators for maxillectomy cases have several advantages over traditional obturators but prosthetic design for specific conditions after maxillary resection has several challenges and the appropriate implant placement configuration is essential for improving retention and the stability of the implant-retained obturator.ObjectivesThe present study aimed to assess the retention force of using linear and nonlinear implant placement configurations using ball and socket attachment in implant-retained obturators at the initial retention and after simulation of six months of use.Materials and methodsTwo identical epoxy resin maxillary models of a completely edentulous unilateral maxillary defect (Brown’s class IIb) were used for implant placement, in the first model three implants were arranged with linear placement configuration, and in the second model three implants were arranged in nonlinear placement configuration. For proper sample sizing, 26 models and obturator were used. Two equal groups of obturators (13 for each group) were constructed, each with a different implant placement configuration. Both groups used the same attachment design (a non-splinted ball attachment). Using a cyclic loading machine that served as a dental insertion and removal simulator, each study group was subjected to 500 tension-compression cycles simulating 6 months of use. Using the universal testing machine, each obturator was removed at a speed of 50 mm/min for the crosshead. peak load to dislodgement was measured at the initial retention and after the simulations of six months of use. Data were analyzed using independent and paired t-tests while percent change was analyzed using the Mann Whitney U test.ResultsThere were a statistically significant differences in retention between the nonlinear implant placement configuration for Brown’s class IIb maxillectomy and the linear implant placement configuration at initial retention evaluation with p-value of < 0.0001 and after simulation of six months of usage with p-value of < 0.0001 Also, after simulation of 6 months of use group I lose − 24.87 (10.16) % of its retention while group II lose − 17.49 (7.78) %.ConclusionsNon-linear implant placement is more retentive at the initial retention and after simulation of six months of use than linear and loses less retention after usage.

The effect of two preparation designs on the fracture resistance and marginal adaptation of two types of ceramic crowns using CAD/CAM technology (In vitro study)

BackgroundRecently, prosthodontic approaches involve more conservative procedures that include less invasive finish line preparations that use less ceramic thickness.Aim of the studyThis in vitro study aimed to evaluate the effect of vertical preparation and modified vertical preparation designs on the marginal adaptation and fracture resistance of two types of ceramic crowns using CAD/CAM technology.Materials and methodsTwo typodont maxillary first premolars were embedded in acrylic resin. Forty positive replicas of epoxy resin dies were used that were divided into two groups depending on the preparation design (n = 20); Group V (Vertical): dies with feather edge finish line and Group MV (Modified vertical): dies with feather edge finish line, where a reverse shoulder of 1 mm depth was placed on the buccal surface 1.5 mm from the occlusal surface. Each group was further subdivided into two subgroups according to the type of ceramic material (n = 10): Subgroup Va and subgroup MVa for lithium disilicate (e.max CAD) and subgroup Vb and subgroup MVb for zirconia (zolid ht+). Crown restorations were made with CAD-CAM technology. The marginal adaptation was assessed using a stereomicroscope both prior to cementation and after cementation and aging. Fracture resistance was tested with a universal testing machine, and the data were statistically analyzed.ResultsMarginal adaptation showed no significant differences between subgroups before or after cementation and aging. Three-way ANOVA indicated that preparation design (p = 0.516) and material (p = 0.269) had no significant effect, but cementation had a significant effect (p < 0.0001) on the marginal adaptation. According to two-way ANOVA test, Subgroup (MVb) showed the highest result followed by subgroup (Vb) and subgroub (MVa) and the least was subgroub (Va). Fracture modes showed no significant differences among the subgroups (p = 0.982).ConclusionsMarginal adaptation of lithium disilicate and zirconia crowns remained clinically acceptable regardless of preparation design. While the modified vertical preparation with a reverse shoulder notably enhanced the fracture resistance of both materials, with zirconia demonstrating superior fracture resistance compared to lithium disilicate with average values exceeding premolar biting force.

Influence of Fiber Orientation on Mechanical Response of Jute Fiber-Reinforced Polymer Composites

The influence of fiber orientation on the mechanical behavior of a polymer matrix composite reinforced with natural jute fibers is investigated in this study. Two fiber orientation configurations are examined: the first involves woven fibers aligned in the direction of testing, while the second considers a 45° orientation. The research involves manufacturing composite plates using jute fabric with the mentioned orientations, followed by cutting rectangular specimens for tensile testing to determine which orientation yields superior properties. Displacement fields are measured using a digital image correlation technique, synchronized with load data obtained from a universal testing machine equipped with a load cell to obtain stress–strain curves for each configuration. Results indicate that 0° specimens achieve higher stress but lower strain compared to 45° specimens. This research contributes to understanding the optimal fiber alignment for enhancing the mechanical performance of fiber-reinforced polymer composites.

Design and evaluation of self-tuning optimal control for vibration suppression of magnetorheological semi-active suspension

The objective of this paper is to enhance the vibration damping capabilities of magnetorheological (MR) semi-active suspension by utilizing a self-tuning LQG control method. Firstly, to determine the mechanical model of MR damper using the hyperbolic tangent model, mechanical experiments were performed with a damping force test machine under various input excitations. Experimental and simulation data were compared to confirm the accuracy of the mechanical model for MR damper. The MR damper is then incorporated into the vehicle’s semi-active suspension system to create a quarter-car suspension model. In order to tackle the problems associated with low control accuracy and poor dynamic adjustment in traditional LQG controllers where the weighting matrix coefficients are difficult to determine, a self-tuning LQG controller based on gravity search algorithm (GSA-LQG) was designed. Finally, the designed controller performance was evaluated by the simulation and experimental results obtained from the random and sinusoidal excitation roads. Experimental data reveal that when subjected to GSA-LQG control, the suspension control performance is considerably enhanced compared to the passive control, PID control and conventional LQG control suspension. Based on these outcome, it can be concluded that the proposed algorithm is effective and the experimental platform is feasible.

Study on microstructure and properties between alloy steel and powder steel via hot isostatic pressing diffusion bonding

PM23 powder steel and H13 hot working die steel and 9Cr2Mo cold working die steel bimetallic composite components were successfully prepared by hot isostatic pressing powder-solid diffusion bonding process. The interfacial behavior of H13-PM23 and 9Cr2Mo-PM23 bimetals was studied by SEM and EBSD techniques; the mechanical properties of the two bimetals were evaluated by universal testing machine. The results indicated that the element diffusion occurred in the interfacial bonding region, and an obvious decarburized layer was observed in the 9Cr2Mo-PM23 bimetals, whose surface was enriched with small rod-like and dot-like MC and M6C carbides.The tensile strength of H13-PM23 and 9Cr2Mo-PM23 bimetals could reach 882 MPa and 772 MPa, respectively, and the fracture occurred exclusively on the side of PM23 powder steel, which could achieve good metallurgical bonding and stable connection. This study provides potential application guidance for enhancing efficiency while reducing costs in composite bimetallic spinning rollers.

Effects of self-etch adhesive agitation with diode laser on dentin bond strength.

The present study assessed the effect of active application of self-etch adhesives with diode laser irradiation on the shear dentin bond strength. Sixty bovine incisors, each embedded individually in hard plaster blocks, were divided into two groups based on the adhesive system used: Group 1 Adper Easy One and Group 2 Clearfil SE Protect. Based on the application technique of self-etch adhesives, each main group was further divided into three subgroups: passive application, active application with a micro-brush, and active application with a 976-nm diode laser tip (phototherapy active application). Shear bond strength tests were conducted using a universal testing machine and the data were analyzed by two-way ANOVA. Post hoc multiple comparisons were performed with the Tukey HSD test. Additionally, the statistical analysis of failure mode distribution was carried out using the chi-squared test (p < 0.05). While the adhesive system exhibited significant differences in shear dentin bond strengths, there were no significant differences in application techniques. Regardless of the application technique, Clearfil SE Protect demonstrated significantly higher dentin bond strength than Adper Easy One. In the present study, the utilization of phototherapy through a 976-nm diode laser for the active application of the tested self-etch adhesives demonstrated similar initial dentin bond strengths to conventional application methods.

COVID testing hesitancy among pregnant patients: lessons learned from the COVID-19 pandemic about the unique needs and challenges of medically complex populations

BackgroundPregnant patients were a significant population to consider during the pandemic, given the impact of SARS-CoV-2 infection on obstetric outcomes. While COVID testing was a central pillar of infection control, it became apparent that a subset of the population declined to test. At the same time, data emerged about pregnant persons also declining testing. Yet, it was unknown why pregnant patients declined tests and if those reasons were similar or different from those of the general population. We conducted this study to explore pregnant patients’ attitudes, access, and utilization of COVID-19 testing to support healthcare for infection prevention management for this unique and medically complex population.MethodsWe conducted a qualitative study of patients who were currently or recently pregnant during the early stages of the pandemic and received outpatient prenatal care at one of the participating study sites. An interview guide was used to conduct in-depth telephone interviews. Coding was performed using NVivo, and analysis was conducted using Grounded Theory.ResultsThe average age of the participants (N = 37) was 32 (SD 4.21) years. Most were < 35 years of age (57%) and self-described as White (68%). Qualitative analysis identified themes related to barriers to COVID-19 testing access and use during pregnancy, including concerns about test accuracy, exposure to COVID-19 in testing facilities, isolation and separation during labor and delivery, and diminished healthcare quality and patient experience.ConclusionsThe implementation of widespread and universal COVID testing policies did not address the unique needs and challenges of pregnant patients as a medically complex population. It is important to understand the reasons and implications for pregnant patients who declined COVID testing during the current pandemic to inform strategies to prevent infection spread in future public health emergencies.

Electrical and current-carrying tribological properties of CoCrFeNi-(Mo, Ti, W) high-entropy alloy coatings on copper alloys by infrared-blue composite laser cladding

Infrared-blue composite laser cladding technology is used to prepare highly conductive and wear-resistant CoCrFeNi-(Mo, Ti, W) HEA coatings on the surface of the copper alloy to overcome the problem of high reflectivity of copper alloy aiming to enhance the surface performance of copper alloy current-carrying friction part. The microstructure and electrical properties of the high-entropy alloy coating were investigated. The wear resistance of the coatings was tested under high-speed and high-current conditions using a self-made current-carrying friction and wear testing machine. The results show that fine-grain and second-phase strengthening significantly enhances the hardness of the high-entropy alloy coating. The high-entropy alloy coating maintains the excellent electrical conductivity of the copper alloy, with an overall conductivity remaining above 60 % IACS. During the current-carrying friction process, the CoCrFeNi-(Mo, Ti, W) HEA coatings exhibited good wear resistance, with wear rates of 0.84 g/h, 1.08 g/h, and 1.32 g/h, respectively. The wear mechanisms observed included varying degrees of adhesive wear, abrasive wear, fatigue wear, and arc erosion.

Fuzzy PCA based Image Matching and Flexible Flying Probe are Used in Embedded Based PCB Bare Board Testing Machine

Fuzzy PCA based Image Matching and Flexible Flying Probe are Used in Embedded Based PCB Bare Board Testing Machine

The Effect of Multiple-Time Applications of Metal Primers Containing 10-MDP on the Repair Strength of Base Metal Alloys to Resin Composite

This experimental study was performed to assess whether applying a metal primer containing 10-MDP multiple times affected the repair shear bonding ability of base metal alloys to resin composites. Ten base metal alloys were randomly assigned to each group in the manner described, following multiple applications of a metal primer (Clearfil Ceramic Primer Plus), namely one to five applications, and no primer application as a negative control. On the specimens’ prepared surfaces, the resin composite was pushed into the mold and then light-activated for 40 s. The bonded samples were kept for 24 h at 37 °C in distilled water in an incubator. The shear bond strength was determined using a universal testing device. A stereomicroscope was used to determine the debonded surface. The one-way ANOVA and Tukey’s test were implemented to statistically analyze. The lowest shear bond strength was found in group 6 (6.14 ± 1.12 MPa), demonstrating a significant difference (p = 0.000) when compared to groups 1 to 5. The shear bond strength of group 3 was highest at 21.49 ± 1.33 MPa; there was no significant difference between group 3 and groups 4 and 5 (20.21 ± 2.08 MPa and 20.98 ± 2.69 MPa, respectively) (p = 0.773, p = 1.000, respectively). All fractured specimens in groups 1, 2, and 6 were identified as adhesive failure. Groups 3 and 4 exhibited the highest percentage of mixed failures. To achieve the repair shear bonding ability of base metal alloys to resin composites, the sandblasted base metal alloys should be coated with three applications of a metal primer before applying the adhesive agent.

Evaluation of the physical properties of bromelain-modified biodentine for direct pulp capping

BackgroundThis study aims to evaluate the compressive strength, solubility, radiopacity, and flow of Bromelain (BR)-modified Biodentine (BD) for direct pulp capping (DPC). This is suggested to determine the impact of BR on the physical properties of BD.MethodsEighty samples were prepared according to the ISO and ADA specifications and evaluated for compressive strength, solubility, radiopacity, and flow. The compressive strength was evaluated at 24 h and 21 days via a universal testing machine. The solubility was determined by weight loss after 24-hours immersion in deionized water. Radiopacity was assessed via X-ray with aluminum step-wedges, and flow was measured by the diameter of the discs under a standard weight. Independent sample t-tests were used to statistically assess the data. A significance level of 5% was considered.ResultsThe compressive strength was 41.08 ± 1.84 MPa for BD and 40.92 ± 1.80 MPa for BR + BD after 24 h, and 88.93 ± 3.39 MPa for BD and 87.92 ± 3.76 MPa for BR + BD after 21 days, with no significant differences. Solubility was slightly greater in the BR + BD (2.75 ± 0.10%) compared to BD (2.62 ± 0.25%), but not significantly different. The radiopacity was similar between BD (2.82 ± 0.11 mm) and BR + BD (2.73 ± 0.10 mm). BR + BD resulted in significantly greater flow (9.99 ± 0.18 mm) than did BD (9.65 ± 0.27 mm) (p ≤ 0.05).ConclusionBR-modified BD maintains BD’s physical properties, with improved flow, making it a promising DPC agent that warrants further study.

Comparative Evaluation of the Effect of Various Irrigating Solutions on the Push-Out Bond Strength of Biodentine and Mineral Trioxide Aggregate: An In Vitro Study

Introduction: A successful endodontic treatment is ba¬sed on combination of adequate instrumentation, irrigation and obturation of canal system. The objectives of endodontic irrigants are lubrication of root canal, removal of microorganisms, pulp, dentinal remnants and dissolution of tissues. The objective of root-end filling is establishment of proper apical hermetic seal. Aim: To evaluate and compare the effect of various irrigating solutions on push-out bond strength of Biodentine and Mineral trioxide aggregate (MTA). Materials and Method: Sixty-four extracted human single rooted teeth were decoronated 1.5-2 mm coronal to cemento-enamel junction. The root canals were prepared and divided into four groups (n=16): Group I- Normal Saline (Control group), Group II- Triple antibiotic solution, Group III- 2% Chlorhexidine, Group IV- Morinda citrifolia solution. Mid root dentin was sectioned horizontally and irrigated further with respective irrigating solutions for 5 minutes and divided into 2 subgroups: Subgroup A- Biodentine and Subgroup B- MTA. The root-end filling material was incrementally placed and embedded in acrylic blocks. Samples were tested for push-out bond strength using universal testing machine. Results: The highest push-out bond strength was shown by 2% Chlorhexidine group when used with Biodentine and lowest when normal saline was used with Biodentine. Conclusion: All experimental irrigating solutions increased the push-out bond strength of MTA and Biodentine.

Micro- and macro-scale fracture behaviour of brittle rocks: Comparison between the conventional Brazilian test and the advanced universal snap-back indirect tensile test (AUSBIT)

Post-peak behaviour is crucial for the estimation of rock mass fracturing in cave mining operations where hard rocks can exhibit class-II or snap-back response when subjected to loading. Despite the rapid development of research into class-II rocks under compression, the corresponding behaviour in tensile tests has rarely been investigated, which is critical considering the complexity of rock mass fracturing under various stress states. The post-peak response of brittle rocks involves abrupt micro-fracturing, leading to brittle macro-scale behaviour. Controlling the fracture process using the Advanced Universal Snap-Back Indirect Tensile test (AUSBIT) allowed the acquisition of the complete macro-scale class-II behaviour in the post-peak regime, facilitating the use of advanced techniques for insights into both micro and macro-scale fracture. In this study, the AUSBIT tests with digital image correlation (DIC) and acoustic emission (AE) instrumentation were conducted to analyse the progressive failure in Calca granite and Gosford sandstone specimens. Post-test observations of the fracture surfaces were performed using a scanning electron microscope (SEM). From a macroscale viewpoint, the lateral strain control in AUSBIT enabled controlled cracking with significant lateral strain extension prior to failure accompanied by gradual energy dissipation and higher rates of AE activity as smaller magnitudes of energy are being released by each AE hit or microcrack compared to conventional Brazilian tests. The stable microcrack propagation was also identified from SEM observations with more uniform profiles of microcracks and less debris observed in AUSBIT specimens. These findings were more significant in Calca granite, which verified its extreme class-II behaviour while also demonstrating the efficiency of AUSBIT in controlling the violent failure of high-strength brittle rocks commonly encountered in deep mining projects, leading to the acquisition of more accurate material behaviour in terms of micro and macro-scale post-peak features which was unattainable from conventional indirect tensile tests.

Horizontal Test Stand for Bone Screw Insertion

Screws are a versatile method of fixation and are often used in orthopaedic surgery. Various specialised geometries are often used for bone screws to optimise their fixation strengths in limited spaces at the expense of manufacturing costs. Additionally, ongoing research is looking to develop systems/models to automatically optimise bone screw tightening torques. For both applications, it is desirable to have a test rig for inserting screws in a regulated, instrumented, and repeatable manner. This work presents such a test rig primarily used for the validation of optimal torque models; however, other applications like the above are easily foreseeable. Key features include controllable insertion velocity profiles, and a high rate measurement of screw torque, angular displacement, and linear displacement. The test rig is constructed from mostly inexpensive components, with the primary costs being the rotational torque sensor (approx. 2000 €), and the remainder being approximately 1000 €. This is in comparison to a biaxial universal testing machine which may exceed 100,000 €. Additionally, the firmware and interface software are designed to be easily extendable. The angular velocity profiling and linear measurement repeatability of the test rig is tested and the torque readings are compared to an off-the-shelf static torque sensor.

Dynamic Monitoring of Steel Beam Stress Based on PMN-PT Sensor

Steel beams are widely used load-bearing components in bridge construction. They are prone to internal stress concentration under low-frequency vibrations caused by natural disasters and adverse loads, leading to microcracks and fractures, thereby accelerating the instability of steel components. Therefore, dynamic stress monitoring of steel beams under low-frequency vibrations is crucial to ensure structural safety. This study proposed an external stress sensor based on PMN-PT material. The sensor has the advantages of high sensitivity, comprehensive frequency response, and fast response speed. To verify the accuracy and feasibility of the sensor in actual engineering, the LETRY universal testing machine and drop hammer impact system were used to carry out stress monitoring tests and finite element simulations on scaled I-shaped steel beams with PMN-PT sensors attached. The results show that: (1) The PMN-PT sensor has exceptionally high sensitivity, maintained at 1.716~1.726 V/MPa in the frequency range of 0~1000 Hz. The sensor performance is much higher than that of PVDF sensors with the same adhesive layer thickness. (2) Under low-frequency random vibration, the sensor’s time domain and frequency domain output voltages are always consistent with the waveform of the applied load, which can reflect the changes in the structural stress state in real time. (3) Under the impact of a drop hammer, the sensor signal response delay is only 0.001 s, and the sensitivity linear fitting degree is above 0.9. (4) The simulation and experimental results are highly consistent, confirming the superior performance of the PMN-PT sensor, which can be effectively used for stress monitoring of steel structures in low-frequency vibration environments.