MATERIALS ENGINEERING CONCEPTS - Materials for Civil and Construction Engineers - page 31

40

UCL 38

35

Target 30.5

30

25

LCL 23

20

0 5 10 15 20 25 30 35 40

Sample number
(a)

25

UCL 24

20

15

Target 11

10

5

0

LCL 0

0 5 10 15 20 25 30 35 40

Sample number
(b)

FIGURE 1.21 Statistical control charts: (a) X-bar chart and
(b) R chart. UCL indicates upper control limit; LCL indicates lower
control limit.

(a) (b) (c)

(d) (e) (f)

FIGURE 1.22 Possible trends of means and ranges in statistical control
charts: (a) sudden change in mean, (b) gradual change in mean, (c) irregular
change in mean, (d) sudden change in range, (e) gradual change in range, and
irregular change in mean and range.