PSI - Issue 5

Smail Sahnoun et al. / Procedia Structural Integrity 5 (2017) 1065–1071 Asseya El-amiri et al./ StructuralIntegrity Procedia 00 (2017) 000 – 000

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consist of a uniform threaded screw, a flat end or threaded rod, and a nut which are often exposed to corrosion attacks. This defect can cause serious economic and social damage, This is why it is so important to detect it as soon as possible (He, Yunze et al.(2014), Laaidi and Sougrati (2012)). In this regard, the purpose of this study is to demonstrate the ability of the non-destructive thermal control method to detect the depth and thickness of corrosion in bolts. In this paper, we consider a nut and a flat-end screw fixed in a concrete slab as our structure. This latter is simulated using the finite element method and an analysis of its thermal response in steady state is also carried out.

Nomenclature Gt

big size bolt

Mt

medium size bolt

q 0 K

The general inward heat flux The thermal conductivity in (W/m.K)

ρ

The density in (kg/m 3 ) The Specific heat in (J/kg.K) The estimated rust depth

C P T

The heated surface temperature in k

e

The thickness of the rust

2. Model Description

We considered two bolts, one large and one medium, to see if the dimensions of the bolts have an influence on the detection of rust. The structure studied consists of a nut, a flat end screw and a square washer. All these elements are fixed in a concrete slab. Due to the shape of the studied structure, the rust has the shape of a cylinder of diameter d centered on the screw axis. The geometry is illustrated in Fig. 1. The assembly elements studied are the most used in the industry. Their geometrical characteristics are described in Table 1 (Colin H and al. (2012), Kim, Jeong et al. (2007)).

Table 1. The geometric dimensions of the studied elements.

Characteristics

Screw (cm)

Nut (cm)

Plate (cm)

Slab (cm)

External diameter (Gt)

16

23

__________

__________

External diameter (Mt)

1.4

2.6

__________

__________

Length (Gt)

37.8

12.8

50

100

Length (Mt)

2

0.68

5

10

Width (Gt)

__________

__________

50

100

Width (Mt)

5

10

Thickness (Gt)

__________

__________

5

30

Thickness (Mt)

0.4

2

To control the structure formed by the assembly elements, we have heated its upper side by a constant heat flow q0=1000 w/m2. Its lower side is maintained at a constant temperature T0= 20°C and the side faces are thermally insulated (q=0). The initial temperature of the assembly is T0=20°C.