**5.1 Influence of an in lying drilled hole**

The aim of this study is to investigate the effects of an in lying drilled hole that is used for an improved quality of the temperature control device, presented in (Riedler & Eichlseder, 2004). The behaviour of the hollow drilled sample is calculated with the finite element method, tested with special LCF test series as well as analyzed by means of fractured surfaces on one wrought and one cast alloy. Whereas the influence on AlCuBiPb is visible, even though, marginally in respect on the lifetime behaviour analyzed with the Manson-Coffin-Basquin (Manson, 1954; Lemaitre & Chaboche, 1985; Basquin, 1910). Approach and the cyclic deformation behaviour analyzed with the Ramberg-Osgood (Ramber & Osgood, 1943) approach, at the Aluminium cast alloy AlSi7MgCu0.5 no difference can be ascertained between the test series of the hollow and solid samples (Riedler & Eichlseder, 2004).

Comparison of Energy-Based and Damage-Related

on LCF is investigated by means of non pre-aged specimens.

few cycles, what can be seen in an increase of the plastic strain part.

 **AlCuBiPb, R=-1, T=25°C / 200°C / 250°C (in each case tot./el./pl. strain ampl. ) Strain-life curves acc. Manson-C.-Basquin** 

1,E+00 1,E+01 1,E+02 1,E+03 1,E+04 1,E+05 1,E+06  **Number of cycles to failure Nf [-]**

al., 2005)

1,E-01

right)

1,E+00

25 °C 200 °C 250 °C

**5.4 Influence of mean strain** 

 **Strain amplitude** ε

 **a,x at N f/2 [‰]** 

1,E+01

1,E+02

**5.3 Influence of temperature** 

Fatigue Life Models for Aluminium Components Under TMF Loading 335

The differences in lifetime for the dwell time of 8 s and 144 s decreases from a factor more than 6 to a factor of 2, when the specimens are pre-aged for 500 h at 250°C before being tested. After extensive pre-aging the influence of dwell time completely disappears in face of the cyclic deformation and the lifetime behaviour (Riedler & Eichlseder, 2004; Riedler et

A constant elevated temperature influences firstly the quasi static material behaviour and secondly has a time-dependent effect because of hardening vs. softening effects during service life. In this section the time-dependent influence of a constant elevated temperature

A constant elevated temperature of 200°C leads to a higher damage of the material with differences in the lifetime of about one decade compared to the room temperature results. At 250°C the effect is even more drastically, as figure 5 (left) shows. Although at the high strained area the lifetime is a little higher than for 200°C, after the point of intersection at about 100 cycles there is a tremendous drop in the lifetime. Figure 5 (right) shows the summarized presentation of the influences of pre-aging, constant elevated temperature and applied mean strain on the LCF deformation behaviour by means of the plastic strain amplitude part. At a constant temperature of 200°C the stress softening phase starts after a

0

1,E+00 1,E+01 1,E+02 1,E+03 1,E+04 1,E+05 **Number of cycles N [-]**

ε **a,t = 10 ‰ (1)**

ε **a,t = 10 ‰ (3)**

ε **a,t = 10 ‰ (4)**

ε **a,t = 10 ‰ (2)**

ε **a,t = 3.75 ‰ (1)**

ε **a,t = 3.75 ‰ (2)**

 **AlCuBiPb - LCF T = 25 / 200°C R = -1 / 0 pre-aged: 0 h vs. 500 h at 250°C** ε **a,t = 3.75 / 10‰**

ε **a,t = 3.75 ‰ (3)**

ε **a,t = 3.75 ‰ (4)**

3

6

**Plastic strain amplitude** ε

Fig. 5. Influence of elevated temperature on the LCF lifetime (on the left) and influence of pre-aging, elevated temperature and mean strain on the LCF deformation behaviour (on the

Impressed mean strains in the manner of pulsating LCF tests (strain ratio=0) show a visible decrease in lifetime for higher strain levels and only a slight lifetime decreasing effect at lower strain levels. At latest from the half of the number of cycles to failure *Nf/2* on, the cyclic stress deformation curves follow a common progression. Some slight lifetime-decreasing effects ascertainable at pulsating executed test series mostly result from the first few cycles, where the higher tensile stresses and plastic strains (see figure 5 (right)) cause higher damage rates. The comparison of alternating and pulsating executed TMF test series shows the same tendencies as at the LCF results. At latest from *Nf/2* on, the cyclic stress deformation

9

 **a,p [‰]** 12

**(1) T = 25°C - R = -1 - 0 h (2) T = 25°C - R = -1 - 500 h at 250°C (3) T = 25°C - R = 0 - 0 h (4) T = 200°C - R = -1 - 0 h**

Moreover the analysis by means of fractured surfaces of AlSi7MgCu0.5 of the solid and hollow sample of three LCF strain levels shows assimilable fractured surfaces for each strain level. When decreasing the strain level to lower values, a crack propagation area can be seen beginning at the outside of the specimens. The finite element method shows differences that are of the size of less than one per cent from the maximum axial stress (Minichmayr, 2005).
