Prediction of the character of tempered glass fracture

Abstract

The mechanismoftempered glass fracture is analyzed. Calculationmethods are proposed for determining the degree of tempering required to ensure the safe character of glass fragmentation, the number of glass fragments resulting from fracture, and their average size.The fracture of tempered glass is the self-supporting fracture ofa fragile body, and one can talk of the appearance ofa fracture wave [9]. Consider a plate of thickness h that is situated in a uniform field of main tensile stresses cr m • The stationary character of propagation of the fracture wave is possible only when its velocity is equal to the velocity of propagation of longitudinal elastic waves Co which can be determined by formula [10] where 0 is the thickness of the glass.It would be correct to make the calculation relating the number ofthe fragments N to the stresses in the central (mid. dIe) layer cr c in the case ofunifonn strain of the plate across the entire thickness h. However, in tempered glass the stresses across the plate thickness vary. Let us introduce the average stress value over the plate thickness [8] for industrially tempered glassThe purpose of the present paper is to elucidate the interrelation between the degree of tempering of glass and the number of the fragments resulting from fracture, and to determine the minimum degree of tempering required to ensure the safe character of fragmentation of tempered glass.In fracture of tempered glass, cracks propagate in its middle layer, which is in a state of strain [6]. Let us represent this layer as a separate plate, whose thickness for glass temperedThe nature of fracture of tempered glass determines its degree of safety, The minimum number of fragments oftempered glass for a prescribed area of 5 x 5 ern? is limited by GOST 5727-88. It is known that the number of fragments is proportional to the degree of tempering of the glass, i.e., to the tensile stresses in the middle layer of the tempered glass. However, in spite of the fact that standards similar to the one quoted here exist in all industrial countries, the problem of the minimally required degree of tempering which ensures the safety of glass of different thickness or composition remains unanswered.The reason for that is probably as follows. Although the problem of the interrelation between the degree of tempering and the number of the fragments resulting from fragmentation ofa specific glass was first studied by P. Acloque in 1956 [1], that paper, as well as some later works, were based on the experimental investigations. Owing to the difference in the experimental methods used and the glass compositions investigated, the data obtained by J. Barsom, K. Akeioshi and E. Kanai, do not provide an answer to the question mentioned above.In [5], the method for predicting the number of fragments makes it possible to account for the physical properties ofdifferent glass compositions (namely, the modulus of elasticity of the glass). However, the calculations were based on the Rittinger law of comminution (the law of surfaces). Theref...

Glass Thickness and Fragmentation Behavior in Stressed Glasses

“…Several studies on the interrelation among tempered level, glass thickness, and the number of fragments have been reported since P. Acloque's first report on the fragmentation test in 1956 [2][3][4]. The study described in this first report, however, did not provide readers with a clear answer to the abovementioned correlation [5]. In recent years, R. Tandon and S. J.…”

Remaining stress-state and strain-energy in tempered glass fragments

“…Several models for relating the fragment size to the residual stress state have been suggested in the litterature, e.g. (Barsom 1968;Gulati 1997;Shutov et al 1998;Warren 2001) some of which incorporate the possibility of a remaining strain energy in the fragment. Then the question arises: what is then the strain energy left in a fragment?…”

Statistische Auswertung und Vorhersage des Bruchbildes von thermisch vorgespanntem Glas

“…In der Literatur sind mehrere Modelle zur Bestimmung der Bruchstückgröße aus dem Eigenspannungszustand bekannt, wobei insbesondere [6,7,8,9,10,11] die Bruchstückgröße basierend auf einem Energieansatz vorhersagen. In [14,15,16] Wesentliche Teile dieses Artikels basieren auf den in [14,15,16] dargestellten Ergebnissen.…”

“…In der Literatur sind mehrere Modelle zur Bestimmung der Bruchstückgröße aus dem Eigenspannungszustand bekannt, wobei insbesondere [6,7,8,9,10,11] die Bruchstückgröße basierend auf einem Energieansatz vorhersagen. In [14,15,16] wurde ein theoretisches Modell zur Vorhersage der Fragmentierung von thermisch vorgespanntem Glas vorgestellt, welches ein Energiekriterium der linear-elastischen Bruchmechanik mit der statistischen Analyse des Bruchbildes verbindet.…”