Impact extractive fracture of jointed steel plates of a bolted joint

This study is concerned with the development of a fracture criterion for the impact fracture of jointed steel plates of a bolted joint used in a car body. For the accurate prediction of crash characteristics of car bodies by computer-aided engineering (CAE), it is also necessary to examine the behavior and fracture of jointed steel plates subjected to impact loads. Although the actual impact fracture of jointed steel plates of a bolted joint used in cars is complicated, for simplifying the problem it might be classified into the shear fracture and the extractive fracture of jointed steel plates. Attention is given to the extractive fracture of jointed steel plates in this study. The extractive behavior and fracture of three kinds of steel plates used for cars are examined in experiments and numerical simulations. The impact extraction test of steel plates jointed by a bolt is performed using the one-bar method, together with the static test. In order to understand the mechanism of extractive fracture process of jointed steel plates, numerical simulations by a FEM code LS-DYNA are also carried out. The obtained results suggest that a stress-based fracture criterion may be developed for the impact extractive fracture of jointed steel plates of a bolted joint used in a car body

Thermoelastic Damping in Micro- and Nano-Mechanical Systems

The importance of thermoelastic damping as a fundamental dissipation mechanism for small-scale mechanical resonators is evaluated in light of recent efforts to design high-Q micrometer- and nanometer-scale electro-mechanical systems (MEMS and NEMS). The equations of linear thermoelasticity are used to give a simple derivation for thermoelastic damping of small flexural vibrations in thin beams. It is shown that Zener's well-known approximation by a Lorentzian with a single thermal relaxation time slightly deviates from the exact expression.Comment: 10 pages. Submitted to Phys. Rev.

Behaviour of Crack-Rate Sensitive Brittle Materials in Dynamic Lateral Compression

In order to investigate the behaviour of brittle tubular materials in static and dynamic lateral compression tests (LC tests), an analytical technique including crack-rate sensitivity of brittle materials was applied. From the analysis, it was found that the maximum load, Pmax, in LC tests increases with the increase of the loading rate and this tendency is more remarkable when the crack-rate sensitivity of a brittle material is large. The results from dynamic and static experiments using a mullite ceramic tubes support reasonably the results obtained from the analysis.Dans le but d'étudier le comportement des matériaux fragiles en forme de tube, en essais de compression latérale (essais CL) en estimation statique et dynamique, une technique analytique incluse la sensibilité de la vélocité de la fissure des matériaux fragiles a été appliquée. Du point de vue de l'analyse, il a été observé que la charge maximale, Pmax, en essais CL croît avec l'augmentation de la vitesse du chargement. Cette tendance est plus remarquable quand la sensibilité de la vitesse de la fissure des matériaux fragiles est grande. Les résultats expérimentaux obtenus à partir de l'estimation statique et dynamique en utilisant les tubes en céramique-mullite, supportent bien les résultats obtenus à partir de l'analyse

Dynamic and quasi-static lateral compression tests of ceramics tubes

Dans le but d'étudier la déformation des tubes céramiques en compression latérale, une série d'expérience a été conduite en velocité dynamique et statique. Il a été constaté que la charge et la deflection quand la fracture s'est produite en essais dynamiques sont plus grandes que celles obtenues en essais statiques. Cependant, aucune différence dans le module d'Young n'est apparue dans les deux cas. En utilisant la theorie des poutres en coubes primaires, la pression de fracture des tubes ceramiques pourraient être dérivée des resultats expérimentaux. Le module d'Young a montré une bonne concordance avec les resultats obtenus à partir des essais de tension. La pression de fracture a aussi montré la valeur proche de la resistance au fléchissement des tubes céramiques.In order to investigate the deformation of ceramics tube in lateral compression, a series of experiments was carried out at dynamic and static rates. It was observed that the load and deflection when fracture occurred in dynamic tests were greater than those obtained in static tests. However, a difference between Young's moduli obtained dynamically and statically was not found. By using a primary curved beam theory, Young's modulus and the fracture stress of ceramics tube could be derived from the results of experiments. The Young's modulus showed reasonable agreement with that obtained from tensile tests. The fracture stress also showed the value close to the bending strength of the ceramics tube

Impact extractive fracture of jointed steel plates of a bolted joint

This study is concerned with the development of a fracture criterion for the impact fracture of jointed steel plates of a bolted joint used in a car body. For the accurate prediction of crash characteristics of car bodies by computer-aided engineering (CAE), it is also necessary to examine the behavior and fracture of jointed steel plates subjected to impact loads. Although the actual impact fracture of jointed steel plates of a bolted joint used in cars is complicated, for simplifying the problem it might be classified into the shear fracture and the extractive fracture of jointed steel plates. Attention is given to the extractive fracture of jointed steel plates in this study. The extractive behavior and fracture of three kinds of steel plates used for cars are examined in experiments and numerical simulations. The impact extraction test of steel plates jointed by a bolt is performed using the one-bar method, together with the static test. In order to understand the mechanism of extractive fracture process of jointed steel plates, numerical simulations by a FEM code LS-DYNA are also carried out. The obtained results suggest that a stress-based fracture criterion may be developed for the impact extractive fracture of jointed steel plates of a bolted joint used in a car body

Impact behavior and fracture of jointed steel plates

The present study is concerned with the impact behavior and fracture of jointed steel plates used in cars. The strength and failure of joint parts subjected to impact loads are examined for an accurate prediction of crash characteristics of car bodies by CAE. Members of lap-bolted joints in the suspension of a car are modeled as a pair of steel plates connected by a bolt. One of the plates is the specimen subjected to plastic deformation and fracture and the other is a jig which is subjected to elastic deformation only. We focus our attention on the impact shear deformation and fracture of the specimen plate. The specimens are made of a steel plate with a tensile strength of 270 MPa, while the jig plate is made of high tensile strength steel of 780 MPa. The impact shear test was performed using the Split Hopkinson bar technique for tensile impact. The behavior of the shear stress and deformation up to rupture taking place in the joint. Numerical simulations were also carried out to compare with experimental results and to understand the mechanism of the fracture process in plates of a bolted joint

Dynamic and quasi-static deformation of aluminium honeycomb sandwich panel in three point bending

In this research, the dynamic and quasi-static deformations of aluminium honeycomb sandwich panels in three point bending were investigated experimentally. The load, the deflection of a loading point and the strain response of the rear surface plate at various locations were measured. A peak load caused by local plastic buckling of the cores just under the loading point appeared in the early stage of both dynamic and quasi-static bending. The peak load observed at dynamic rates was about $10\sim20$ % greater than that obtained from static tests. The absorbed energy in the dynamic deformation was also larger than that obtained in static tests. From the change of the strains of the rear surface plate, it was found that the third or higher deformation mode occurred during the early stage of dynamic bending, although only the first mode was observed in static tests. The difference of the bending mode may be one of the principal reasons of greater peak load and absorbed energy in dynamic bending

Effects of strain-rate and pre-fatigue on tensile properties of laser welded joint of high strength steel plates

The impact tensile properties of laser welded butt joints of two kinds of high strength steel plates with the tensile strength level of 590 MPa and 780 MPa (denoted by HR590 and HR780, respectively), were investigated using split Hopkinson bar tensile testing apparatus. Impact tension tests for the joint specimens pre-fatigued were also carried out to examine the effect of pre-fatigue. There were no significant effects of strain-rate and pre-fatigue on the dynamic and quasi-static tensile strength of laser welded butt joints. However, the decrease in the elongation of HR780 welded joints subjected high cycle pre-fatigue was observed only at a high strain-rate. From the observation of fracture surface, it was found that the decrease in the elongation may be caused by a number of damages due to the combination of high cycle pre-fatigue and high strain-rate