African Fusion March 2017

the mechanical properties of the material used, the type of welded joints, the cyclic loading parameters and other factors. For the effective application of the UP, depending on the above-mentioned factors, a software package for optimum application of ultrasonic peeningwas developed that is based on an original predictive model. In the optimum application, a maximum possible increase in fatigue life of welded ele- ments with minimum time, labour and power consumption is predicted [4]. Manufacturing and rehabilitation The effectiveness of UP treatment applications to as-manu- factured parts and in rehabilitation of parts that have already served a considerable amount of their useful fatigue life was studied. Rehabilitation is considered as the prevention of pos- sible fatigue crack initiation in existing welded elements and structures that are in service. UPwas applied to newparts and to parts after 50% of their expected fatigue life. Three series of large-scale welded samples imitating the transverse non-load-carrying attachments (Figure 2) were subjected to fatigue testing in 1: The as welded condition; 2: After UP was applied before fatigue testing; and 3: After UP was applied after fatigue loading with the number of cycles corresponding to 50% of the expected fatigue life of samples in the as-welded condition [8]. Tables 1 and 2 present themechanical and chemical prop- erties of the materials used for preparation of the samples. The results of the conducted fatigue testing with UP applied to specimens in the as-welded condition and also after 50% of expected fatigue life are presented in Figure 3. As can be seen from Figure 3, UP caused a significant increase in fatigue strength of the welded elements for both series of UP treated samples. The increase in the limit stress range at N=2×10 6 cycles of welded samples is 49% (from 119 MPa to 177 MPa) for UP treated samples before fatigue loading; and 66% (from 119 MPa to 197 MPa) for UP treated samples after fatigue loading – with the number of cycles cor- responding to 50% of the expected fatigue life of the samples in the as-welded condition. The higher increase of fatigue life of UP treated welded elements for fatigue curve No 3 could be explained by a more beneficial redistribution of residual stresses and/or ‘healing’ of fatigue-damaged material by UP in comparison with the fatigue curve No 2. Use of UIT/UP for weld repair UP could also be effectively used during the weld repair of fatigue cracks [3, 5]. Figure 4 shows the drawings of large-scale

Figure 2: A schematic view of the welded sample used in fatigue testing.

Figure 3: Fatigue curves of welded elements (transverse non-load carrying attachment). 1: In the as welded condition; 2: UP was applied before fatigue testing; 3: UP was applied after fatigue loading with the number of cycles corresponding to 50% of expected fatigue life of samples in as-welded condition.

Mechanical Properties

σ

σ

δ (%)

Ψ (%)

(MPa)

(MPa)

y

u

260

450

37.6

63

Table 1: The mechanical properties of base material.

Chemical composition (%)

C

Si

Mn

S

Figure 4. Drawings of the welded specimens for fatigue testing at different conditions: W: As-welded condition; R: Repair by gouging and welding; R/UP: Repair by gouging, welding and UP. welded specimens containing non-load carrying longitudinal attachments for fatigue testing [3]. These specimens were

0.210

0.205

0.520

0.019

P

Cr

Ni

Cu

0.007 <0.010 Table 2: The data on chemical composition of base material 0.040 0.040

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March 2017

AFRICAN FUSION