IFMASS8

353

PREDICTION OF THE FRACTURE AND FATIGUE PROPERTIES OF

WELDED JOINTS BY HEAT-AFFECTED-ZONE SIMULATION

Vladimir Gliha, Faculty of Mechanical Engineering, Maribor, Slovenia

INTRODUCTION

Welding is the best practical way of joining two or more metallic pieces to make them

act permanently as a single piece. Elements of huge steel constructions and heavy

machinery are mostly joined by fusion welding, using arc welding with the consumable

electrodes. Arc fusion welding is an efficient and simple joining technique enabling high

commercial effects because of achievable good quality joints produced in workshop con-

ditions (industrial production) as well as on-site (erection).

Many metallic structures are made of steel. Nowadays, high strength low alloy

(HSLA) structural steels are increasingly used all over the world. They have some funda-

mental practical advantages over plain carbon structural steels as higher strength and

improved toughness, and due to good weldability are extraordinary well suited to design

and manufacture welded products which will be subjected to the most demanding condi-

tions. If designers, technologists, and inspectors are really familiar with all peculiarities of

processing these steels, a painless confrontation of industry with the world market is

guaranteed. The successful competition in this market is then quite possible.

A serious problem when welding with the HSLA structural steels is to ensure the

adequate toughness of all zones in the joint. Besides, some kinds of weld defects are

always present in commercial welded joints. Existence of defects and weak zones at the

same time can promote fracture of the welded joint during production, testing by loading,

or in normal exploitation. Failure occurs with crack initiation. Crack initiation is the

consequence of an over-critical interaction between stresses and inconveniently oriented

crack-like defects. The basic function of welded joints is jeopardised if any kind of the

crack, which could not be arrested, initiates during loading. The final result of this

process is namely disintegration of the joint. The type of interaction between stresses and

defects mainly depends on the character of the loading, on the temperature, and effects of

environment. Thus, the effects of cyclic mechanical loading on welded joints are different

than effects of static, quasi-static, or dynamic loading.

Feasibility to prepare samples with the microstructure of potential weak zones of

welded joints which extensions enable mechanical testing were a welcome step to the

experimental studies of welded joint properties and effects of welding on metals. Such an

approach is possible because of the available equipment which is purposely designed for

these tasks, i.e. thermal cycle simulators. This computer controlled equipment is used for

the simulation of thermal conditions during welding on samples of the material with the

appropriate starting microstructure. The fracture and fatigue properties of different zones

in welded joints will be successfully predicted if appropriate specimens are made of these

samples and tested in accordance with their size. The limited size of specimens is the

main obstacle in the intention to determine relevant welded joint properties by testing.

The size of samples with the simulated microstructure depends on the heating and cooling