# Investigation of Debonding Effect in Internal Replacement Pipe System Under Lateral Loading
## 3 Surface Preparation and Its Impact on Debonding
### Behaviour of IRP System in 152.4 Mm (6 inch) Discontinuous Host Pipe
#### 3.2.4 Maximum Stress and Failure Mechanism  
Figures 32-34 present the stress distribution in the IRP layer for a 152.4 mm (6 inch) discontinuous system with various adhesive shear strengths, loaded to a maximum of 56.9 kN (12.8 kip). The analyses indicate that the local deformation phenomenon primarily occurs at the crown of the IRP for all cases. This critical deformation point could potentially lead to a catastrophic failure of the system under loads of approximately 56.9 kN (12.8 kip) or higher. Although lower shear strength adhesives tend to cause more debonding, as shown in Table 11, they have a negligible effect on the failure of the IRP under the maximum load. Local deformation mainly occurs at the crown of the IRP midspan. To improve the local deformation bearing capability, it may be considered to use a thicker IRP for the 152.4 mm (6 inch) discontinuity to increase the bending stiffness of the system.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Shear Strength** & **5** & **20** & **40** \\
**MPa** & **5** & **20** & **40** \\ \hline
**Maximum Normal Stress** & & & \\ MPa (ksi) & 27.308 (3.961) & 26.924 (3.095) & 26.924 (3.095) \\
**Predicted life cycles to failure** & 432,419 & 510,812 & 510,812 \\ \hline \hline \end{tabular}
\end{table}
Table 12: Predicted fatigue life of a 152.4 mm (6 inch) discontinuous IRP system for various levels of adhesive strength.  
Figure 32: Equivalent stress results in the IRP layer of a 152.4 mm (6 inch) discontinuous IRP system employing the adhesive shear strength of 20 MPa (2.9 ksi) at a maximum load of 56.9 kN (12.8 kip) (magnified 5.6 times).  
A similar experimental setup was employed, utilizing the ALTRA10 and a 152.4 mm (6 inch) discontinuous host pipe. This arrangement was positioned in a four-point bending configuration measuring 26 inches by 40 inches by 26 inches. Prior to data collection, it was reported that the system underwent several loading cycles, as shown in Figure 1. This preliminary loading revealed comparable deflection behavior and local deformation failure, as depicted in Figure 35. Local deformation failure was observed both at the crown midspan of the IRP layer under a load of 54.7 kN (12.3 kip), resulting in a deflection of 33.858 mm (1.333 inches) at the invert midspan. The obtained FEA results and experimental findings exhibited substantial agreement, particularly concerning the local deformation outcomes. Specifically, FEA indicated a local deformation load of 56.9 kN (12.8 kip), whereas the experimental result was 54.7 kN (12.3 kip), yielding a difference of 4.065%.  
Figure 34: Equivalent stress results in the IRP layer of a 152.4 mm (6 inch) discontinuous IRP system employing the adhesive shear strength of 40 MPa (5.8 ksi) at a maximum load of 56.9 kN (12.8 kip) (magnified 6.6 times).  
Figure 33: Equivalent stress results in the IRP layer of a 152.4 mm (6 inch) discontinuous IRP system employing the adhesive shear strength of 5 MPa (0.7 ksi) at a maximum load of 56.9 kN (12.8 kip) (magnified 4.5 times).