In this study, impact behavior of triggered and non-triggered tubes with and without auxetic filler are examined by using numerical methods. Material properties of tubes made of aluminum alloy and auxetic lattices utilizing ABSplus plastics are determined by using tensile tests. Finite element analyses are performed by using LS-DYNA software at 5 m/s impact velocity. Two different trigger shape are suggested and compared each other and discussed the advantages and disadvantages over nontriggered tubes. For these loading conditions, trigger mechanism provides lower peak forces and higher crash force efficiency (CFE), but lower specific energy absorption (SEA). Also, the effects of using auxetic fillers in these triggered tubes are investigated in terms crashworthiness characteristics.

This paper presents the effect of tamper weight shape on the dynamic compaction method in granular soils. Although the dynamic compaction method appears to be very simple, it requires careful design of the compaction process. The aim of this study is to improve the efficiency and decrease the cost of deep compaction by using cylinder-shaped tamper weights. The influence of the shape of the bottom of the tamper weight on dynamic compaction efficiency was evaluated experimentally on sandy soils. Sands of three different densities were used to evaluate the compaction efficiency. Conical-bottom tamper weights were studied with the conic angle approximately the same values as the internal friction angles of the three different densities of soil. Also, in order to compare results, a flat-bottom tamper was used with the same weight. The results indicated significant increases of the amount of ground improvement by using a conical rather than a flat-bottom load.Cet article traite de l'effet de la forme du poids de dameuse sur la méthode de compactage dynamique sur les sols granulaires. Bien que cette méthode apparaisse très simple, elle demande une conception soignée du processus de compactage. Cette étude a pour objectif d'améliorer l'efficacité et de réduire le coû t du compactage profond en utilisant des poids de dameuse de forme cylindrique. Elle évalue expérimentalement l'influence de la forme de la base du poids de dameuse sur l'efficacité du compactage dynamique pour des sols sablonneux. Des sables de trois densités différentes ont été utilisés pour déterminer l'efficacité du compactage. L'étude porte sur des poids de dameuse de forme conique avec un angle conique correspondant approximativement aux mêmes valeurs que les angles de frottement interne des trois différentes densités de sable. Une dameuse de base plate, de même poids, a également été utilisée en vue d'établir une comparaison. Les résultats indiquent une augmentation significative de l'amélioration du sol lorsque l'on utilise une charge à base conique plutô t que plate.

It is interesting to note that the authors carried out laboratory dynamic compaction model tests with conical-bottom tampers. It would be more beneficial to the readers if the authors had explained in the paper the backgound to the use of a conicalbottom tamper in dynamic compaction. In this regard, it is helpful to point out a paper published in 2000 in Géotechnique by the discusser and co-workers 1 on the same topic of conicalbottom tampers. The idea of using a conical-bottom tamper was explained in that paper. In principle, the partition of tamper impact energy into Rayleigh waves and body waves is better for a conical-bottom tamper than for a flat-bottom tamper. The discusser and co-workers have conducted laboratory dynamic compaction model tests using conicalbottom tampers with apex angles of 608, 908 and 1208. It was our experience that the 908 conical-bottom tamper worked the best, regardless of the type of sands used in our model test programme. The 608 conical-bottom tamper penetrated excessively into the specimen. The 1208 conical-bottom tamper created craters smaller than that created by the 908 conicalbottom tamper.The cone angle used by the authors is equal to 1808 minus the apex angle. For example, the 908 apex angle refers to a cone angle of 458. The authors proposed determining the cone angle of the conical-bottom tamper according to the internal friction angles of the sands. However, judging from our experience, this may lead to a conservative design of the tamper. For a loose sand with internal friction angle of 308, the cone angle is 308 and the apex angle is 1208. The efficiency of the 1208 tamper is likely to be smaller than that of a 908 tamper. Furthermore, it should be simple and practical to build only a tamper with a proper apex angle for general applications. In this regard, the discusser would suggest that the 908 apex angle conical-bottom tamper be considered. Authors' replyThe discusser proposes that the efficiency of the 1208 tamper is likely to be smaller than that of a 908 tamper. The discusser's comments show that an intensive philosophical debate is going on as to whether or not to consider the effect of different components on tamper weight shape. The discusser suggests our agreeing that the 908 apex angle conical-bottom tamper be considered. However, it is as yet impossible to make such a general statement.There are many factors that have a great effect on dynamic compaction efficiency. Two most important considerations regarding the applicability of dynamic compaction are the type of soil being densified and the in situ water content. Our experimental conditions considered only one type of granular soil and a constant water content. Thus we were not able to investigate the effect of different parameters on dynamic compaction efficiency using a conical-angle tamper. We did not propose a best shape for the tamper. It may not be possible to make such a statement with such limited information. The discussion shows that the utilisation of conical-bottom tampers requires more resea...