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Table 4: Materials are used for the kiln Component
Material
Shells Tires
Rollers Pinion
ASTM A.36 Low alloy steel casting
Low alloy steel casting 30 Cr Ni Mo 8 ISO R 638 =
II-68 Type 3 As mentioned earlier there are mainly four
methods to predict fatigue of welded components:
Nominal Stress
Structural Stress
Effective Notch Stress
Linear Elastic Fracture Mechanics LEFM The effects of welding residual stresses, R-ratio, wall
thickness and improvement techniques are included in this research. In case of variable amplitude loading,
Palmgren- Miner´s linear damage rule is used when the design methods nominal, structural and effective
notch stress are applied.
3.0 RESULTS AND DISCUSSION
The results obtained in this research are taken based on the simulation and experimental work. This chapter
discusses only the simulation work. The simulation works are performed to evaluate the fatigue of the
kiln shell. To validate the characteristic of fatigue problem simulation, the mechanical and thermal
load are implemented on the shell of kiln. The results are analyzed in detail in this chapter for fatigue life for
the kiln shell.
In this work, the kiln shell has been modeling by Autodesk Inventor 2014. All the boundary conditions
mechanical load, thermal load, Young’s modulus, density, etc. must be evaluated such as the actual
condition. The simulation of the kiln shell is only conducted to determine the fatigue life of the kiln
shell.
The development of modeling is the initial work that marks the natural condition of the designed
software into the simulation platform. In this phase all algorithms of simulation condition are implemented
using a standard Finite Element Analysis. Within this development model, the architecture is validated
and the main functions and algorithms are tested. During the design, by using static analysis which has
been implemented in the kiln shell. The model of the kiln shell, boundary conditions and initial crack as
shown in Figure 3 and 4 are used in order to achieve robust performance, high reliability and minimal
computational cost.
Figure 3. Model of the kiln shell
a b
c d
e f
Figure 4. Boundary Conditions BC and Initial Crack
Considering the cracked elastic plate shown on the following page, with Young’s modulus
E
and Poisson’s ratio
ν. The height is small compared to the
dimensions
a
and
c
, and the thickness is small enough that p la ne stre ss conditions. If the crack grows all the
way across the plate and the plate separates into two pieces, the system will have zero strain energy. So the
strain energy decreases as the crack grows. Calculating the change in strain energy of the plate if
the crack grows by some amount
d r
. Using the same assumptions used previously to calculate the total
strain energy. Considering of a finite element analysis,
characteristics of a kiln shell are a pretension and a mating part contact Figure 4.a. The pretension can
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generally be modeled with static loading, thermal deformation, a constraint equation, or an initial strain.
For a thermal deformation method, the pretension is generated by assigning virtual different temperatures
and thermal expansion coefficients to the shell, clinker and temperature of gases. In this work, in order to
generate a finite element model for the kiln shell with clinker and temperature of gases Figure 4.b and 4.c,
two kinds of models are introduced. All the proposed models are taken into account above primary
characteristics such as a pretension effect and a contact behavior between shell, clinker and
temperature of gases see Figure 4.d. The prediction of the crack propagation are considered on crack
emanating from contact surface between kiln shell and clinker and welded joint on the kiln shell surface
Figure 4.e. On this Finite Element model, the final mesh consisted of 40.856 elements and 45.245 nodes.
The elements along the direction of crack advance had a length of 28 mm. Following the stress and
deformation simulation, fatigue crack growth was modeled by repeated loading mass of clinker and
thermal gases, unloading, advancing the crack and then the loading again.
Under static analysis, stress and deformation in the kiln is obtained as shown i n F i g u r e 5 . From the
simulation results, it is found that t h e critical area is occurred in the kiln. B y u s i n g the static value,
subsequent fatigue analysis can be performed.
The calculated loads and stresses were used to perform a low cycle fatigue evaluation b y using the
actual operating data. The operating temperatures were lower than the temperatures anticipated in the
design specifications. There were unknown cycles corresponding to the anticipated 450°C gas inlet
temperature upset condition, and only three cycles to the normal operating temperature. Hence, the actual
operating cycles were used to evaluate the fatigue damage.
Figure 5. Stress, displacement and strain of the static
analysis Since local stresses were far in excess of the yield
strength of the materials at the stitch welds, elastic- plastic analyses were used to obtain the strain ranges
needed to perform a low cycle fatigue evaluation. The evaluation was made using fatigue design
curves obtained by applying a factor of cycles to the theoretical failure curves. Based on the design
curves, a cumulative fatigue usage had been reached when failure occurred. This is consistent with
the knowledge that cracks had initiated and grown to a critical size and propagated as fast fractures at this
usage as shown in Figure 6. Actual failure occurred between the design fatigue curve and the theoretical
mean failure data for small polished laboratory test specimens. Failure below the mean laboratory failure
curve is expected due to size effects, surface finish effects, environmental effects and scatter in the data.
a
b
Figure 6. Crack growth and Transition of stress
intensity factor
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The results of the structural analyses of the original design showed that the flexibility of the weight stresses
and reduced thermal bending stresses in the duct. Hence, bending of the duct imposed high cyclic
loads and stresses on the support truss, buckling several truss members. With properly designed duct supports.
Bending of the duct does not bend the supporting truss. Moreover, the flexibility of the truss would have
no effect on dead weight stresses in the duct. This is important since the typical design sequence involves
first designing the duct, and then using the resulting weight to design the truss.
4.0 CONCLUSION
