Church bells may be subject during the course of years to structural fatigue, too. But they are such an important part of our cultural heritage that we want them to last for centuries. Researchers have been investigating the damage caused to bells when they are rung.
Nowadays, many people only hear the ringing of bells on important days in the Christian church calendar, such as Christmas Day. And yet for centuries the bells have rung not only to call the faithful to prayer but also to warn the inhabitants of the town of impending danger, to tell them the time and to announce happy events such as a birth or marriage. Each bell had its own special sound, and even its own name. And that's still the case today. But, like everything else, church bells too can fatigue over the years. However, they are such an important part of our cultural heritage that we want them to last for centuries. For this reason, on behalf of the Verein Deutscher Gießereifachleute (VDG) - the German federation of foundry experts -, researchers at the Fraunhofer Institute for Structural Durability LBF in Darmstadt have been assessing the damage caused to bells when they are rung - experimentally and using numerical simulation.
The aim of the project was to analyze the effect of various factors on the wear and tear of a bell, and to find ways of reducing damage that may be attributable to the shape and weight of the clapper, for example, or to the angle of the bell when it is struck and the ambient temperature,. As part of the investigation, the researchers analyzed samples of bell bronze to determine their metallic composition. They also ascertained the strength of the material in fatigue tests at different temperatures. Other experiments were carried out on a moving bell. The scientists used strain gauges and accelerometers to identify the places where tension and expansion forces act, which may cause the bell to crack. In addition, the phases of the ringing cycle were simulated numerically on the computer. "Our investigations proved the effectiveness of a practice that has been in common use for some time. Turning the bell through an angle of about 30 degrees at longish intervals can increase its useful life by up to a third", reports Dr Dietrich Flade of the LBF. "Parameters such as the shape and weight of the clapper don't have any significant effect on damage. Contrary to expectations, the ambient temperature is not of great significance either." The greatest risk to church bells used to be sheer over-enthusiasm on the part of the bell ringers. Nowadays e. g. attempts to make the bells heard over the noise of local traffic by ringing them even harder will result in reduced life span. The higher the bell swings, the greater the force and speed with which the clapper strikes the bell. Increasing the angle of the bell when it is struck by just one degree reduces its useful life by an average of 14 per cent. These findings ensure that it will be a long time before the final hour strikes for many a bell.
For further information:
Dr.-Ing. Dietrich Flade
Phone: +49 61 51/7 05-2 67
Fax: +49 61 51/7 05-2 14
Phone: +49 61 51/7 05-2 68
Fax: +49 61 51/7 05-2 14
© Fraunhofer LBF. Finite-element methods were used to determine the characteristic overtones produce ...
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