Effects of Al-Si Coating on Static and Dynamic Strength of Spot-Welded Hot-Stamping Steel Joints

Al-Si is the most popular coating used to prevent oxidation on the surfaces of hot-stamped steel sheets during the heating process. However, like other coatings, it affects the strength of the spot welds in joining the hot-stamped steel parts. In this study, the effects of Al-Si coating on the tensile strength of the resistance spot-welded joints in hot-stamped steel are discussed. Two types of 1.8 mm hot-stamped steel, in uncoated and Al-Si coated forms, were resistance spot-welded, and the tensile shear behavior of the welded joints was studied in both static and dynamic tests. To do this, a special fixture for impact tensile shear tests was designed and fabricated. In the case of the Al-Si coated steel, the presence of the molten Al-Si over the fusion zone, especially its aggregation in the edge of the weld nugget, caused a decrease in the maximum tensile load capacity and a failure of energy absorption in static and dynamic tests, respectively. Additionally, it increased the probability of changing its failure mode from pull out to interfacial fracture in the dynamic test. This study shows that the tensile strength behavior of the welded joints for the Al-Si coated hot-stamped steel is lower than the uncoated steel during static, and especially dynamic, force.

Energy Absorption in Actual Tractor Rollovers with Different Tire Configurations

In order to better understand the complexities of modern tractor rollover, this paper investigates the energy absorbed by a Roll-Over Protective Structure (ROPS) cab during controlled lateral rollover testing carried out on a modern narrow-track tractor with a silent-block suspended ROPS cab. To investigate how different tractor set-ups may influence ROPS and energy partitioning, tests were conducted with two different wheel configurations, wide (equivalent to normal ‘open field’ operation) and narrow (equivalent to ‘orchard/vineyard’ operation), and refer to both the width of the tires and the corresponding track. Dynamic load cells and displacement transducers located at the ROPS-ground impact points provided a direct measurement of the energy absorbed by the ROPS cab frame. A trilateration method was developed and mounted onboard to measure load cell trajectory with respect to the cab floor in real-time. The associated video record of each rollover event provided further information and opportunity to explain the acquired data. The narrow tire configuration consistently subjected the ROPS cab frame to more energy than the wide tire arrangement. To better evaluate the influence of the ROPS cab silent-blocks in lateral rollover, static and dynamic tests were performed. The results confirm that tires influence the energy partition significantly and that further understanding of silent-blocks’ dynamic performance is warranted.

Performance Evaluation of a Novel Optical Sensing System for Detecting Rail Lubricity Conditions

This paper presents a laboratory evaluation of a novel optical sensing system mounted on a moving platform for detecting the presence and adequacy of Top-of-Rail (TOR) friction modifiers and flange greases. The friction modifiers are applied on the top of rail for managing the coefficient of friction to reduce wear while maintaining stable traction. Flange greases are intended to reduce wear that happens when wheel flange makes contact with the rail gage-face during curving. Additionally, friction modifiers and flange greases could influence fuel consumption. The U.S. railroads have made the application of TOR adopted on the mainlines. The tools, however, for evaluating the rail lubricity condition are limited and there is often uncertainty about the required or “optimal” amount of friction modifiers, except for the trained eye of the track engineer. The proposed sensing system provides an innovative non-contact method by using the optical laser’s reflective and scattering properties when directed at the rail surface to assess the friction modifiers’ conditions. In addition, the laser’s near-UV (Ultraviolet) wavelength is able to excite fluorescent elements in the flange grease and detect any top-of-rail contamination of grease that may exist. The design and working principles of the system are demonstrated and explained in this paper. Static and dynamic tests are performed in the lab under a controlled environment for various lubricity conditions, in order to experimentally validate and evaluate the performance of the optical sensing system. The lab evaluation indicates that the proposed optical sensing system is capable of successfully detecting the diverse lubricity conditions and shows a great potential to be widely tested and used in the field on revenue-service tracks.

Preliminary Study on Psychomotor Abilities Decisive for Technical Routines in Rhythmic Gymnastics

The aim of the research is to establish the level of some psychomotor abilities by determining the rhythmic gymnasts’ capability to perform apparatus-specific technical skills within the composition of their routines, according to the provisions of the 2017-2020 Code of Points. The Wireless training timer (Witty) testing equipment was used to assess relevant types of speed in junior rhythmic gymnasts. The reaction time, execution time and travel speed time were measured in similar technical conditions or close to those encountered in training and competitions. The 14 gymnasts included in the research, aged between 13 and 15 years, are part of the National Olympic Centre for juniors in Arad, all being enrolled in the preparatory stage of training. The analysis of the data from both static and dynamic tests established a referential for the forms of speed to be enhanced by means of apparatus-specific technical routines. Results provide interesting information on the average values, inter-individual differences and homogeneity-related issues (which are relevant especially for gymnasts performing in the group event). The key features of these data, as well as previous analysis of junior routines for the 2017-2020 Olympic cycle, have led us to the conclusion that, in order to get a high score for apparatus difficulty/mastery, more difficulty elements should be added, which requires an increase in all kinds of speed involved by the technique of a specific event.

BILATERAL INSTRUMENTED WHEEL SYSTEM FOR MEASURING HANDRIM FORCES DURING MANUAL WHEELCHAIR PROPULSION

The purpose of this study was to design and validate a new bilateral instrumented wheel system (IWS) to measure triaxial handrim forces and torques simultaneously during the wheelchair propulsion. The designed and implemented system measures the force applied to the handrims on both sides of a manual wheelchair using 6-axis force/torque sensors. In addition, a user interface receives the measurements from the left and right IWSs. To verify the accuracy of the wheel system, we evaluate force and torque measurements during the static and dynamic tests. The maximum error in static measurements of force and torque are 4.29% and 1.95%, respectively. Likewise, dynamic tests using planar forces and axle torques provide low errors and measurements that are highly correlated with the expected values ([Formula: see text]). The results revealed that the proposed IWS can be used to measure bilateral 3D handrim reaction forces with acceptable accuracy.