6.1 Evaluation of forming limit diagram

Tension-compression, tension-tension and plane strains are the three regions of strain conditions formed due to the variation in the width of the specimen. The forming limit diagram was plotted based on the grid circles from Figure 5a and stretched various ellipses from Figure 5b with respect to the strain condition as a base.

regions to plot the forming limit diagrams. These strains were measured in three distinct regions like safe region, neck region and fracture region using the formulae natural log of deformed to the original dimension, whereas thickness strain (ε3) was determined at fracture region. The limiting strains and major strains at fracture were calculated for Al alloy sheets from major and minor dimensions at four differ-

The minor and major diameters of ellipse were measured using different mode of strain conditions. They are tension-tension (TT), plane strain (PS) and tensioncompression (TC). The grid circles were etched over the shape of the plate and became elliptical with different major and minor diameters based on the strain

Studies on ductile material models have been used to investigate the nucleation of voids and void coalescence as well as the interaction between different size and scales of voids [2]. This could be used to predict fracture mechanisms in structural components or test specimens. Ductile crack growth by void coalescence is an application [26]. Hence, fractography and void coalescence properties are analysed

The forming and fracture limit diagrams of various grades of aluminium alloys chosen have been presented in Figure 7 along with the limiting strains of various grades of aluminium at different annealing temperatures. A minor strain of 19% and major strain of 21% have been recorded at the lowest temperature of 200°C. The major strain of the same sheet at PS condition was 31%. In TC region major and minor strains were found to be 33% and 3% respectively. Due to the presence of cold rolled refined grains in microstructure, poor formability was shown by the

ent annealing temperatures and have been presented in Table 4.

The maximum major strain at fracture for Al 1350 alloy sheets.

Tension-tension strain condition

Value of limiting strain in percentage for various strain conditions of Al 1350 alloy sheets.

TC region at minor strain 0.075

 109 98 83 111 102 85 116 108 91 125 116 99

Minor strain

 35 18 17 28 3 38 17 21 32 6 43 15 29 38 13 50 13 31 45 14

Major strain Plane strain condition

Major strain values in percentage

PS region

Major strain Major

Tension-compression strain condition

TT region at minor strain 0.15

Minor strain

strain

in the following sections.

7. Limiting strains

39

Annealing temperature (°C)

Aluminium and Its Interlinking Properties DOI: http://dx.doi.org/10.5772/intechopen.86553

Table 4.

Table 5.

Annealing temperature (°C)

conditions, which is the input to plot forming limit diagram (Table 5).

Using a travelling microscope, the ellipse dimensions like minor and major diameters were measured with an accuracy of 0.01 mm. These measurements of major and minor diameters were used to calculate the major strain (ε1) and the minor strain (ε2). The strains ε<sup>1</sup> and ε<sup>2</sup> were measured at the safe, neck and fracture

Figure 5. Chemically etched grid circles (a) before and (b) after the forming process.

#### Aluminium and Its Interlinking Properties DOI: http://dx.doi.org/10.5772/intechopen.86553


#### Table 4.

strain ratio) and percentage elongation, were evaluated in this work. Since the sheet metals were anisotropic in nature, the normal anisotropy parameters such as rav,

Formability parameters of Al 1350 alloy sheets annealed at different temperatures.

Annealing temperature (°C) Orientation nrav Δr rav 300 0° 0.10994 0.0005 0.738

350 0° 0.15448 0.0050 0.851

45° 0.12103 90° 0.20272 Average 0.13868

45° 0.14928 90° 0.22359 Average 0.169153

The n-value and k-value were found to be maximum at 90°C to the rolling direction (RD) and minimum along the RD for the Al 1350 alloy sheet annealed at 200°C. Under similar conditions, the r-value was maximum along the RD and minimum at 90°C; the n-value showed similar observations, whereas the k-value and r-value were maximum at 45° to the RD and minimum at 90° to the RD.

Tension-compression, tension-tension and plane strains are the three regions of strain conditions formed due to the variation in the width of the specimen. The forming limit diagram was plotted based on the grid circles from Figure 5a and stretched various ellipses from Figure 5b with respect to the strain condition as a

Using a travelling microscope, the ellipse dimensions like minor and major diameters were measured with an accuracy of 0.01 mm. These measurements of major and minor diameters were used to calculate the major strain (ε1) and the minor strain (ε2). The strains ε<sup>1</sup> and ε<sup>2</sup> were measured at the safe, neck and fracture

nrav and Δr were also evaluated.

Aluminium Alloys and Composites

6. Forming properties

base.

Table 3.

Figure 5.

38

6.1 Evaluation of forming limit diagram

Chemically etched grid circles (a) before and (b) after the forming process.

Value of limiting strain in percentage for various strain conditions of Al 1350 alloy sheets.


Table 5.

The maximum major strain at fracture for Al 1350 alloy sheets.

regions to plot the forming limit diagrams. These strains were measured in three distinct regions like safe region, neck region and fracture region using the formulae natural log of deformed to the original dimension, whereas thickness strain (ε3) was determined at fracture region. The limiting strains and major strains at fracture were calculated for Al alloy sheets from major and minor dimensions at four different annealing temperatures and have been presented in Table 4.

The minor and major diameters of ellipse were measured using different mode of strain conditions. They are tension-tension (TT), plane strain (PS) and tensioncompression (TC). The grid circles were etched over the shape of the plate and became elliptical with different major and minor diameters based on the strain conditions, which is the input to plot forming limit diagram (Table 5).

Studies on ductile material models have been used to investigate the nucleation of voids and void coalescence as well as the interaction between different size and scales of voids [2]. This could be used to predict fracture mechanisms in structural components or test specimens. Ductile crack growth by void coalescence is an application [26]. Hence, fractography and void coalescence properties are analysed in the following sections.
