A Model for the Stochastic Fracture Behavior of Glass and Its Application to the Head Impact on Automotive Windscreens

verfasst von: Christopher Brokmann

Verlag: Springer Fachmedien Wiesbaden

Buchreihe : Mechanik, Werkstoffe und Konstruktion im Bauwesen

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

Einloggen, um Zugang zu erhalten

Über dieses Buch

The book deals with the stochastic strength of glass and the application to the automotive windscreen. A finite element model is derived. This is then validated using known phenomena in connection with the fracture behaviour of glass. After the strength of a windscreen has been intensively investigated, experiments with wind windscreen, experiments with windscreens are simulated by means of the model. Finally, the probability of a pedestrian suffering a head injury on impact with a windscreen is predicted. of a pedestrian hitting a windscreen is predicted, taking into account the stochastic breakage behaviour of glass. Up to now, this has not been taken into account in EuroNCAP crash tests, for example.

Inhaltsverzeichnis

Frontmatter

1. Introduction

Abstract

Traffic accidents claim an estimated 1.35 million lives worldwide every year. Approximately 26 % of these victims are pedestrians and cyclists [1]. This corresponds to 970 deaths per day. Around 80 % of all serious injuries to a pedestrian in an accident occur in the head region [2, 3]. Depending on the size of the pedestrian and the vehicle, the head hits the windscreen with a certain probability. Despite these enormous numbers, the stochastic fracture behavior of glass is not considered in crash tests and crash simulations regarding automotive windscreens.

Christopher Brokmann

2. Theoretical Background

Abstract

The definition of glass is not uniformly regulated. The German standard DIN 1259-1:2001-09 [85] defines glass as „an inorganic product of fusion which has been cooled to a rigid condition without crystallizing“. [86] gives the definition of glass as a frozen super-cooled liquid in the physic-chemical sense. Although the atomic structure of glass is comparable to that of a liquid, the mechanical properties are those of a solid. When liquid glass cools, no phase transition is achieved. The transition from liquid to solid takes place in a temperature range, beginning at the glass transition temperature [87, 88]. No crystallization occurs during the entire cooling process. A definition of glass as materials that have a glass transition temperature would include organic glasses, for example PMMA. The quest for a general definition is going on worldwide. Although the general usage of the word glass has changed considerably over the last centuries, in a scientific context, it usually depends on whether the macro- or microscopic behavior is considered [37, 86, 89, 90].

Christopher Brokmann

3. A Stochastic Fracture Model for Glass

Abstract

While the strength of most materials is considered as a material constant, the strength of glass depends on microscopic flaws on the glass surface. These flaws are created during the production and handling of the glass. When mechanical stress is applied, these flaws grow subcritically. Depending on the initial crack depth, the fracture stress of glass shows very large scatter. Chap. 5 will show that the strength between two samples can vary by more than a factor of 15 under identical test conditions.

Christopher Brokmann

4. Mechanical Parameter Quantification

Abstract

Quantitative studies of parameters describing the mechanical behavior of glass are important for several reasons. For one thing, there is the influence of the chemical composition of the glass which can exert a considerable influence on the mechanical behavior [86]. Often, mechanical parameters are found in publications in which the chemical composition of the investigated glass is not stated. Therefore, the parameters are subject to unknown uncertainties. Furthermore, there are different approaches to determining parameters. A pertinent example is the terminal subcritical crack velocity. Several methods of determining the terminal velocity can be found. such as in-situ observation [164], analytical solutions [155, 170] or comparsion of the two [77].

Christopher Brokmann

5. Stochastic Strength of an Automotive Windscreen

Abstract

The strength of glass is defined by microscopic flaws. These flaws are significantly influenced in geometry and frequency by the manufacturing and handling of the glass. It is therefore a logical conclusion that with regard to different areas on automotive windscreens, different populations must be assumed for the fracture strength. Such different populations may originate from the silkscreen process, the cover of the PVB layer or the glass edge processing. Furthermore, the tin and air side from the float process is a non-negligible influence.

Christopher Brokmann

6. Displacement-Controlled Windscreen Tests

Abstract

The present chapter focuses on the stochastic fracture behavior of automotive windscreens by displacement-controlled impact. Windscreens are tested on a test rig with an electrical cylinder at different constant impact velocities. Windscreens in convex and concave orientation are tested and are monitored by an acoustic emission localization device to calculate the origin of fracture. Subsequently, the stochastic scatter of fracture from experiments is numerically reproduced with the stochastic fracture model. The scatter of displacement effected by the impactor until fracture and the location of fracture are compared.

Christopher Brokmann

7. Free-Flying Head Impact

Abstract

The following chapter provides an investigation on dynamic head impact tests on automotive windscreens. This chapter is divided into two parts. The first part investigates head impact replacement tests. These tests consist of a free-flying impactor and an impact velocity according to the European NCAP [191]. The difference between European NCAP experiments and the test conducted within this investigation, is the four-point-support of the windscreens. Subsequently, numerical results are calculated using the stochastic fracture model. The experimental and numerical results were compared and discussed afterwards. In the second part, a pedestrian head impact is simulated under in-service conditions. The aim is to calculate the HIC, taking into account the stochastic fracture behavior of glass. A stochastic distribution of the HIC is presented.

Christopher Brokmann

8. Summary and Future Research Topics

Abstract

The main objective of this thesis was to develop a numerical model that is capable of reproducing and predicting the stochastic fracture behavior of glass.

Christopher Brokmann

Backmatter

Titel: A Model for the Stochastic Fracture Behavior of Glass and Its Application to the Head Impact on Automotive Windscreens
verfasst von: Christopher Brokmann
Verlag: Springer Fachmedien Wiesbaden
Electronic ISBN: 978-3-658-36788-6
Print ISBN: 978-3-658-36787-9
DOI: https://doi.org/10.1007/978-3-658-36788-6