**3.1 Directions and magnitudes**

The evaluation of RS states is often uncertain and the reason for this is related to several specific aspects that should be considered in the measurement of residual stress, since analyses are sometimes problematic and dubious and that residual stress notation is not always used adequately by some authors [30]. Because there is no standardization system that convinces and guides the distribution of residual stresses, each author uses what suits him. However, this point is paramount for proper understanding and knowing the possible effects that can cause on a welded part or structure. Thus, considering that there is no right or wrong way, the criterion used is based on the one most referenced by the specialized academic community, according to the model in **Figure 1**. Generally, the analyses are performed two-dimensionally, considering the longitudinal (σy) and transverse (σx) directions studied, always having as reference the weld bead. The stresses of the normal plane (σz) are less measured, but should not be discarded in any hypothesis, even though the thickness of the plate is conditioned. Finally, it is important mentioning that, in practice, the most significant component is composed of longitudinal stresses, and generally equals, on average, three times the transverse stresses to the weld bead, where welds of a single pass are considered and that there are no temperature gradients on the z axis [25, 31].

Still, within the study of residual stress generated by arc welding two parameters are essential for understanding it: (i) the behavior of this RS (in MPa), that is, if it

is tensile to positive (+) or compressive values for negative (−) values; (ii) and its effect on the welded component, i.e. defects or failures related to residual stresses. Therefore, it is worth mentioning that the relationship between tensile and compressive residual stresses lies in the fact that the first has a degradative effect on the welded part, while the other can contribute in a beneficial way in many cases [3, 32]. However, this statement is often justified, due to the absence of knowledge of the existing residual stress state and its consequences, which is used to explain unexpected failures most often.

Based on the various works already published, it is possible to have a predictability of RS profiles in any of the directions of the plane, considering the metal alloy and the geometry of the welded joint, with this, represents a pattern of longitudinal residual stresses for certain alloys considering plates with butt welds [11].

When it comes to the effect of residual welding stresses on the behavior of materials, depending on their magnitude these stresses affect not only the welded joint, but also, on some occasions, the entire structure. Generally, tensile stresses are attributed to decreased fatigue life and corrosion resistance (cracks by stress corrosion), in addition to hydrogen embrittlement, etc. It is often suggested that the maximum magnitude of the tensile residual stresses should not approach the yield limit of the material, which would lead this or the welded joint to premature failures, especially near the weld. On the other hand, compressive residual stresses when at high magnitudes are usually attributed to decreased buckling resistance of the base metal, provided that the component is subject to compressive loading. Finally, in this way, it is expected that any welded structure, the simplest, will have residual stresses at any magnitude at controlled levels, or that approach the neutral line, since the peaks, even unprovoked, only increase the risk of unwanted and un predictable failures.

### **3.2 Measurement techniques**

There are different measurement techniques to evaluate the residual welding stresses in a welded component. Some are based on the measure of relieved deformation, due to localized removal of material, called destructive techniques. Others are based on the interaction between the residual stress field and the physical properties of the material, called non-destructive (NDT). However, numerous authors also classify some techniques as semi-destructive, since their use does not compromise the physical structure of the material.

### *3.2.1 Destructive techniques*

Among the various techniques for measuring residual stresses considered destructive, there is the sectioning technique that is based on the measurement of deformation due to the release of residual stress after removal of the material from the sample. The sectioning method consists of making a cut with appropriate instrument in the sample in order to release the residual stresses that are present in the cutting line. For this purpose, the cutting process used must not introduce plasticity or heat into the sample, so that the original residual stress can be measured without the influence of the effects of plasticity on the surface of the cutting planes [33]. In [32, 34], a cut-off sequence used by the technique to measure residual stress is shown schematically in literature.

Another technique belonging to this classification is the contour technique, which is based on solid mechanics, which determines RS through an experiment that involves carefully cutting a sample into two parts, measuring the resulting deformation due to the redistribution of residual stresses. The measured strain

**241**

*Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

analysis, providing only one result [32].

*3.2.2 Non-destructive techniques (NDT)*

magnetic induction of the material [34].

which acted on that layer.

semi-destructive.

data is used to calculate residual stresses through an analysis that involves a finite element model that considers stiffness and geometry as just one parameter in the

in the removal of material that contains residual stress, this removal of material causes unbalance in the workpiece that may result in deformation of the same. Removal of the tensioned material is performed continuously and the measurement of the curvature (deflection) of the sample is also done at the same time of removal, the residual stresses originally present can be deduced. Therefore, this technique provides a quick determination of residual stress as a function of the depth below the surface [35]. According to [34], the variation of deflection (curvature) after the removal of a layer of material, from a thickness e', can be related to the stress σe,

Other destructive techniques are the Hole-Drilling Method and the Ring Core Method. The hole-drilling technique is the most used general technique for measuring residual stresses in materials. It uses standardized procedures and has good accuracy and reliability. The test procedure involves some damage to the sample, but this is often tolerable or repairable. For this reason, the technique is sometimes called

Otherwise, the hole-drilling technique is the most used due to its greater ease of use and to cause less damage to the sample. Finally, there is the Deep Hole Drilling Method, which is considered a variant of the hole-drilling and ring core techniques, with the difference of performing an analysis on thicker materials [33]. According to [36] the basic procedure involves the machining of a reference hole through the sample and the subsequent removal of a column of material, centered on the reference hole, using a trepanning technique. The diameter of the reference hole is accurately measured along its length before the material column is removed. Because, when the material column is removed, the stresses are relaxed, the dimensions of the hole diameter of the reference column are changed. In this context, the dimensions of the column and the reference hole are measured again and the residual stresses are calculated from the dimensional changes caused by the removal of the material from the greatest deformation of the sample in the analyzed area.

Within this classification of techniques, there are the magnetic techniques that are based on the relationship between magnetization and the elastic deformation existing in ferromagnetic materials, as experiments demonstrate that a piece of steel wire, once magnetized, will undergo elongation in the direction of magnetization, while once pulled it will magnetize in the direction of the pull. Two techniques have been extensively explored in the literature, in addition to being applicable in industry: the Barkhausen noise technique and the magneto-striction technique. The first is based on the change in the magnetic microstructure caused by the presence of stresses, while the second is based on measurements of the permeability and

The most common magnetic technique is the Barkhausen noise magnetic technique. Ferromagnetic materials present magnetically ordered microscopic regions, called domains, where each domain is magnetized based on the crystallographic directions preferred to the magnetization. Furthermore, a domain does not coincide with a grain, since within a grain there are several domains, which are separated by walls, in which the direction of magnetization generally changes by 90° or 180°. In [34] also states that when a magnetic field or mechanical stress is applied to a ferromagnetic material, changes occur in the structure of the domains

There is also the technique of removal of layers, whose principle of action consists

#### *Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

*Welding - Modern Topics*

pected failures most often.

predictable failures.

**3.2 Measurement techniques**

the physical structure of the material.

is shown schematically in literature.

*3.2.1 Destructive techniques*

is tensile to positive (+) or compressive values for negative (−) values; (ii) and its effect on the welded component, i.e. defects or failures related to residual stresses. Therefore, it is worth mentioning that the relationship between tensile and compressive residual stresses lies in the fact that the first has a degradative effect on the welded part, while the other can contribute in a beneficial way in many cases [3, 32]. However, this statement is often justified, due to the absence of knowledge of the existing residual stress state and its consequences, which is used to explain unex-

Based on the various works already published, it is possible to have a predictability of RS profiles in any of the directions of the plane, considering the metal alloy and the geometry of the welded joint, with this, represents a pattern of longitudinal

When it comes to the effect of residual welding stresses on the behavior of materials, depending on their magnitude these stresses affect not only the welded joint, but also, on some occasions, the entire structure. Generally, tensile stresses are attributed to decreased fatigue life and corrosion resistance (cracks by stress corrosion), in addition to hydrogen embrittlement, etc. It is often suggested that the maximum magnitude of the tensile residual stresses should not approach the yield limit of the material, which would lead this or the welded joint to premature failures, especially near the weld. On the other hand, compressive residual stresses when at high magnitudes are usually attributed to decreased buckling resistance of the base metal, provided that the component is subject to compressive loading. Finally, in this way, it is expected that any welded structure, the simplest, will have residual stresses at any magnitude at controlled levels, or that approach the neutral line, since the peaks, even unprovoked, only increase the risk of unwanted and un

There are different measurement techniques to evaluate the residual welding stresses in a welded component. Some are based on the measure of relieved deformation, due to localized removal of material, called destructive techniques. Others are based on the interaction between the residual stress field and the physical properties of the material, called non-destructive (NDT). However, numerous authors also classify some techniques as semi-destructive, since their use does not compromise

Among the various techniques for measuring residual stresses considered destructive, there is the sectioning technique that is based on the measurement of deformation due to the release of residual stress after removal of the material from the sample. The sectioning method consists of making a cut with appropriate instrument in the sample in order to release the residual stresses that are present in the cutting line. For this purpose, the cutting process used must not introduce plasticity or heat into the sample, so that the original residual stress can be measured without the influence of the effects of plasticity on the surface of the cutting planes [33]. In [32, 34], a cut-off sequence used by the technique to measure residual stress

Another technique belonging to this classification is the contour technique, which is based on solid mechanics, which determines RS through an experiment that involves carefully cutting a sample into two parts, measuring the resulting deformation due to the redistribution of residual stresses. The measured strain

residual stresses for certain alloys considering plates with butt welds [11].

**240**

data is used to calculate residual stresses through an analysis that involves a finite element model that considers stiffness and geometry as just one parameter in the analysis, providing only one result [32].

There is also the technique of removal of layers, whose principle of action consists in the removal of material that contains residual stress, this removal of material causes unbalance in the workpiece that may result in deformation of the same. Removal of the tensioned material is performed continuously and the measurement of the curvature (deflection) of the sample is also done at the same time of removal, the residual stresses originally present can be deduced. Therefore, this technique provides a quick determination of residual stress as a function of the depth below the surface [35]. According to [34], the variation of deflection (curvature) after the removal of a layer of material, from a thickness e', can be related to the stress σe, which acted on that layer.

Other destructive techniques are the Hole-Drilling Method and the Ring Core Method. The hole-drilling technique is the most used general technique for measuring residual stresses in materials. It uses standardized procedures and has good accuracy and reliability. The test procedure involves some damage to the sample, but this is often tolerable or repairable. For this reason, the technique is sometimes called semi-destructive.

Otherwise, the hole-drilling technique is the most used due to its greater ease of use and to cause less damage to the sample. Finally, there is the Deep Hole Drilling Method, which is considered a variant of the hole-drilling and ring core techniques, with the difference of performing an analysis on thicker materials [33]. According to [36] the basic procedure involves the machining of a reference hole through the sample and the subsequent removal of a column of material, centered on the reference hole, using a trepanning technique. The diameter of the reference hole is accurately measured along its length before the material column is removed. Because, when the material column is removed, the stresses are relaxed, the dimensions of the hole diameter of the reference column are changed. In this context, the dimensions of the column and the reference hole are measured again and the residual stresses are calculated from the dimensional changes caused by the removal of the material from the greatest deformation of the sample in the analyzed area.

## *3.2.2 Non-destructive techniques (NDT)*

Within this classification of techniques, there are the magnetic techniques that are based on the relationship between magnetization and the elastic deformation existing in ferromagnetic materials, as experiments demonstrate that a piece of steel wire, once magnetized, will undergo elongation in the direction of magnetization, while once pulled it will magnetize in the direction of the pull. Two techniques have been extensively explored in the literature, in addition to being applicable in industry: the Barkhausen noise technique and the magneto-striction technique. The first is based on the change in the magnetic microstructure caused by the presence of stresses, while the second is based on measurements of the permeability and magnetic induction of the material [34].

The most common magnetic technique is the Barkhausen noise magnetic technique. Ferromagnetic materials present magnetically ordered microscopic regions, called domains, where each domain is magnetized based on the crystallographic directions preferred to the magnetization. Furthermore, a domain does not coincide with a grain, since within a grain there are several domains, which are separated by walls, in which the direction of magnetization generally changes by 90° or 180°. In [34] also states that when a magnetic field or mechanical stress is applied to a ferromagnetic material, changes occur in the structure of the domains

caused by the sudden movement of the walls. These changes cause variations in the average magnetization of the component, as well as in its dimensions. Thus, if a conductive coil is placed close to the sample while the domain wall is moving, the resulting change in magnetization will induce electrical pulses in the coil. When these electrical pulses are produced by the movement of all domains, a signal is generated, called "Barkhausen noise." The extent of movement of the domain walls, that is, the intensity of Barkhausen noise, depends on the stresses present and the material's microstructure. The measurement depth for practical applications of this technique on steel varies between 0.01 and 1 mm. The authors [2] present results of stresses measured by this technique.

Another non-destructive technique is Neutron Diffraction, which, similarly to the X-ray diffraction technique, measures the crystallographic spacing between the crystalline planes. This spacing is affected by RS or applied stress [37]. This technique can measure the elastic deformations induced by residual stresses in the entire volume of the relatively thick steel components with a spatial resolution as small as 1 mm3 [2]. The authors [3, 36] claim that the greatest advantage of neutron diffraction over x-ray diffraction is the great depth of penetration that neutrons can obtain, which makes it capable of measuring a greater depth, reaching 25 mm in aluminum and 25 cm in steel. According to [36], due to the high spatial resolution, neutron diffraction can provide complete three-dimensional deformation maps in an engineering component, that is, for each measurement point, the deformation can be measured in three orthogonal directions along the axis Sample. Practical applications of the technique and the theoretical background can be seen in [34, 38, 39].

There is also the x-ray diffraction technique (XRD). This XRD technique was first proposed by Lester and Aborn in 1925 [34]. However, the technique is restricted, its main restriction being the depth of analysis of the samples, since the beam of x-rays can only penetrate the distance of some atomic planes, about 1–50 μm [36]. For [40], the penetration is around 25 μm and for [41] it ranges from 5 to 20 μm, that is, the XRD makes a subsurface assessment of the stresses. To overcome this restriction, [37] states that for measurements at a greater depth, that is, greater than 0.013 mm, destructive techniques such as the layer removal technique should be used. In the evaluation by XRD, the residual stress is calculated from the measurement of the deformation in the crystal of the polycrystalline aggregate, compared to the network parameters of the crystal of this same material without suffering deformation. When a beam of x-rays is directed towards the surface of a body, a part of these rays is absorbed by the atoms while another part is sent back in all directions of the irradiated area. This technique basically measures the maximum diffracted ray intensity for a given scanning angle. From this angle it is possible to obtain the interplanar spacing of the diffraction planes determined by Bragg's Law [5, 42]. For the measurement of residual stresses using XRD, there are three basic techniques [3, 42]. Techniques, double exposure, single exposure, and multiple exposures or sen2ψ. The amount of exposure refers to the amount of exposure angles, such as angles between the normal at the surface of the part and the plane formed by the incident X-ray beam and the diffracted beam. The sen2ψ technique is one of the most classic [43]. This method is capable of measuring stresses with an accuracy of ±20 MPa, with a penetration depth in the order of microns under the sample surface [2, 4]. This technique and its history of development are described in [5, 43, 44].

Finally, there are the ultrasonic techniques, which are based on the acustoelastic effect, which is the influence of the state of stress on changes in the speed of propagation of the ultrasonic wave as it travels through the material, developed

**243**

same line.

*Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

such as [41, 50–52].

according to Eq. (5) [61].

by [45], using the theory of finite strain and third order terms of [46] elastic strain. The techniques that use Critically Refracted Longitudinal Waves (Lcr) and shear waves [32] stand out. The ultrasonic technique that uses Lcr waves, according to [47], is a special case, as these to be generated, must be introduced into the material with an angle of incidence slightly greater than the critically refracted angle (first critical angle), based in Snell's Law. This wave propagates parallel to the surface of the material to be analyzed, as can be seen in the works of [47–49]. In addition to these, numerous studies are available in the literature,

The other ultrasonic technique is acoustic birefringence (AB), which relates the relative difference between the velocities or the time of two shear ultrasonic waves with polarization directions orthogonal to each other, indicating the degree of anisotropy of the material, where birefringence is determined by (Eq. (4)) [53–59]. In this equation, Vl is the velocity of the shear ultrasonic wave with the polarization direction aligned with that of the lamination, Vt is the velocity of the shear ultrasonic wave with the transverse to lamination polarization direction, tl is the travel time of the ultrasonic wave with the polarization direction aligned with the material lamination direction and tt the travel time of the ultrasonic wave with the polariza-

<sup>−</sup> − − ( ) = = + +

*l t l t l t lt V V t t*

*<sup>B</sup> VV t t* (4)

) (5)

2 2

The acoustic birefringence B depends, therefore, on the initial anisotropy B0 and on the main difference in tension (σ1-σ2), as well as the anisotropic speed of the wave not being directly linked to the effect of stress due to the presence of this initial anisotropy of the material [60]. When the directions of the principal stresses coincide with the axis of the initial anisotropy, the relationship between the difference of the principal stresses with the birefringence is established

> *BB k* =+ − 0 12 (σ σ

In this equation, B0 is the birefringence for the material in the stress-free state and k is the acustoelastic constant that relates the stress variations with the birefringence. This technique has been used a lot lately in practical measurements of residual stresses. In Brazil, since the end of the 1990s by [62] in projects with Petrobras. More recently, by [63], where the technique was used to measure residual stresses generated by GMAW and CW-GMAW welds. **Figure 2** shows the assembly of the RS measurement equipment by acoustic birefringence, identical to that used by researchers. A comparison between non-destructive methods can be seen in **Figure 3**, where x-ray diffraction techniques (the mean between σy and σx) and acoustic birefringence (the difference between σy and σx in MPa), in order to verify the main similarities and differences regarding the values obtained and the magnitudes found. The measurement was made on naval steel plate (ASTM A131 grade AH32) with a thickness of 9.5 mm and dimensions of 1200 mm by 800 mm, considering 3 equidistant lines separated by 300 mm and 100 mm from the edge in the longest direction. Each line has 9 points separated by 120 mm from each other on the

tion direction perpendicular to the lamination direction.

#### *Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

*Welding - Modern Topics*

stresses measured by this technique.

ground can be seen in [34, 38, 39].

ment are described in [5, 43, 44].

tion as small as 1 mm3

caused by the sudden movement of the walls. These changes cause variations in the average magnetization of the component, as well as in its dimensions. Thus, if a conductive coil is placed close to the sample while the domain wall is moving, the resulting change in magnetization will induce electrical pulses in the coil. When these electrical pulses are produced by the movement of all domains, a signal is generated, called "Barkhausen noise." The extent of movement of the domain walls, that is, the intensity of Barkhausen noise, depends on the stresses present and the material's microstructure. The measurement depth for practical applications of this technique on steel varies between 0.01 and 1 mm. The authors [2] present results of

Another non-destructive technique is Neutron Diffraction, which, similarly to the X-ray diffraction technique, measures the crystallographic spacing between the crystalline planes. This spacing is affected by RS or applied stress [37]. This technique can measure the elastic deformations induced by residual stresses in the entire volume of the relatively thick steel components with a spatial resolu-

of neutron diffraction over x-ray diffraction is the great depth of penetration that neutrons can obtain, which makes it capable of measuring a greater depth, reaching 25 mm in aluminum and 25 cm in steel. According to [36], due to the high spatial resolution, neutron diffraction can provide complete three-dimensional deformation maps in an engineering component, that is, for each measurement point, the deformation can be measured in three orthogonal directions along the axis Sample. Practical applications of the technique and the theoretical back-

There is also the x-ray diffraction technique (XRD). This XRD technique was first proposed by Lester and Aborn in 1925 [34]. However, the technique is restricted, its main restriction being the depth of analysis of the samples, since the beam of x-rays can only penetrate the distance of some atomic planes, about 1–50 μm [36]. For [40], the penetration is around 25 μm and for [41] it ranges from 5 to 20 μm, that is, the XRD makes a subsurface assessment of the stresses. To overcome this restriction, [37] states that for measurements at a greater depth, that is, greater than 0.013 mm, destructive techniques such as the layer removal technique should be used. In the evaluation by XRD, the residual stress is calculated from the measurement of the deformation in the crystal of the polycrystalline aggregate, compared to the network parameters of the crystal of this same material without suffering deformation. When a beam of x-rays is directed towards the surface of a body, a part of these rays is absorbed by the atoms while another part is sent back in all directions of the irradiated area. This technique basically measures the maximum diffracted ray intensity for a given scanning angle. From this angle it is possible to obtain the interplanar spacing of the diffraction planes determined by Bragg's Law [5, 42]. For the measurement of residual stresses using XRD, there are three basic techniques [3, 42]. Techniques, double exposure, single exposure, and multiple exposures or sen2ψ. The amount of exposure refers to the amount of exposure angles, such as angles between the normal at the surface of the part and the plane formed by the incident X-ray beam and the diffracted beam. The sen2ψ technique is one of the most classic [43]. This method is capable of measuring stresses with an accuracy of ±20 MPa, with a penetration depth in the order of microns under the sample surface [2, 4]. This technique and its history of develop-

Finally, there are the ultrasonic techniques, which are based on the acustoelastic effect, which is the influence of the state of stress on changes in the speed of propagation of the ultrasonic wave as it travels through the material, developed

[2]. The authors [3, 36] claim that the greatest advantage

**242**

by [45], using the theory of finite strain and third order terms of [46] elastic strain. The techniques that use Critically Refracted Longitudinal Waves (Lcr) and shear waves [32] stand out. The ultrasonic technique that uses Lcr waves, according to [47], is a special case, as these to be generated, must be introduced into the material with an angle of incidence slightly greater than the critically refracted angle (first critical angle), based in Snell's Law. This wave propagates parallel to the surface of the material to be analyzed, as can be seen in the works of [47–49]. In addition to these, numerous studies are available in the literature, such as [41, 50–52].

The other ultrasonic technique is acoustic birefringence (AB), which relates the relative difference between the velocities or the time of two shear ultrasonic waves with polarization directions orthogonal to each other, indicating the degree of anisotropy of the material, where birefringence is determined by (Eq. (4)) [53–59]. In this equation, Vl is the velocity of the shear ultrasonic wave with the polarization direction aligned with that of the lamination, Vt is the velocity of the shear ultrasonic wave with the transverse to lamination polarization direction, tl is the travel time of the ultrasonic wave with the polarization direction aligned with the material lamination direction and tt the travel time of the ultrasonic wave with the polarization direction perpendicular to the lamination direction.

$$B = \frac{V\_l - V\_t}{\frac{V\_l + V\_t}{2}} = \frac{-\left(t\_l - t\_t\right)}{\frac{t\_l + t\_t}{2}}\tag{4}$$

The acoustic birefringence B depends, therefore, on the initial anisotropy B0 and on the main difference in tension (σ1-σ2), as well as the anisotropic speed of the wave not being directly linked to the effect of stress due to the presence of this initial anisotropy of the material [60]. When the directions of the principal stresses coincide with the axis of the initial anisotropy, the relationship between the difference of the principal stresses with the birefringence is established according to Eq. (5) [61].

$$B = B\_\circ + k \left(\sigma\_\circ - \sigma\_\circ\right) \tag{5}$$

In this equation, B0 is the birefringence for the material in the stress-free state and k is the acustoelastic constant that relates the stress variations with the birefringence. This technique has been used a lot lately in practical measurements of residual stresses. In Brazil, since the end of the 1990s by [62] in projects with Petrobras. More recently, by [63], where the technique was used to measure residual stresses generated by GMAW and CW-GMAW welds. **Figure 2** shows the assembly of the RS measurement equipment by acoustic birefringence, identical to that used by researchers.

A comparison between non-destructive methods can be seen in **Figure 3**, where x-ray diffraction techniques (the mean between σy and σx) and acoustic birefringence (the difference between σy and σx in MPa), in order to verify the main similarities and differences regarding the values obtained and the magnitudes found. The measurement was made on naval steel plate (ASTM A131 grade AH32) with a thickness of 9.5 mm and dimensions of 1200 mm by 800 mm, considering 3 equidistant lines separated by 300 mm and 100 mm from the edge in the longest direction. Each line has 9 points separated by 120 mm from each other on the same line.

#### **Figure 2.**

*Ultrasonic system used to measure RS by acoustic birefringence.*

#### **Figure 3.**

*Comparative measurement in a naval steel sheet (ASTM A131 grade AH32) between the methods: (a) X-ray diffraction (XRD) and (b) acoustic birefringence (AB).*

Through **Figure 3**, there is a reasonable difference between the data obtained, where the plate measured by XRD is predominated by yellow and some peaks in more orange, however the range of residual stresses varied from −17 MPa to 50 MPa, while measuring with AB, it showed the central line with more compressive points, in green and other red peaks indicating tensile stresses, with values ranging from −112 MPa to 103 MPa. However, this disagreement in the results is mainly due to two factors, first, due to the difference in the depths analyzed between the measurement techniques, where the XRD method is more superficial and the AB method analyzes the entire plate thickness. Second, due to the specific methodology of each technique, that is, the XRD shows the punctual and unidirectional RS, while the AB shows the average difference of the main RS, but this result was already predicted. Although both techniques were able to clearly show the presence of RS in the component welded by CW-GMAW.

**245**

**Figure 4.**

*Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

**distortions**

**weldment**

**4. Techniques for controlling or reducing residual stresses and** 

conventional alternative techniques will be approached.

The relief of residual stress in welding has as premise the production of a rearrangement of atoms or molecules from their position of momentary equilibrium, from where the material leaves from a larger state to another of lower tension (lower potential energy), a more stable position. The analysis of residual stress and welding distortion, seen from a historical perspective, developed largely independently of each other, although, from the physical point of view, they are closely related [11]. To design and manufacture a structure with the least number of defects it is essential to have: an appropriate design; an appropriate selection of materials; suitable welding equipment and procedures; good manpower; and strict quality control [1]. The authors [64] showed that the procedures for reducing RS's are directly linked to the reduction of deformations generated during the joining process. There are several examples of methodologies that can be used to perform the relief of RS's, classified into three major categories: Thermal, Mechanical and Chemical, which can be performed before, during and after welding. There are many stress relief techniques that can be classified as conventional, due to their extensive use and the most varied applications in welded components, such as: hammering, heat treatment (pre- and post-heating), shot peening, mechanical tensioning, among others. However, non-

**4.1 Procedures for the adequacy of the quantity of material deposited in the** 

Since the RS in welding are the result of non-uniform deformations caused by the thermal gradient of the process, which can be attenuated by reducing the volume of weld metal deposited and adapting the chamfer design, which tends to decrease the heat transferred to the part and consequently, it causes a decrease in the RS levels and the degree of distortion of the weldment. The adequacy of the quantity of material must be chosen at the stage of development of the project and welding procedures. **Figure 4a** shows the representation of angular deformations in butt welds with various thicknesses, demonstrating that the angular distortion increases as a thicker plate is used, due to the greater amount of deposited material, resulting in a greater contraction during the solidification process. For small thicknesses, the angular deformation is not significant due to the high homogeneity of the temperature field through the thickness of the sheet. Plates with

*Representation of angular distortions. (a) plate distortions in butt joints with various thicknesses and (b)* 

*angular distortion depending on the thickness of the plate and the heat input qw.*

*Welding - Modern Topics*

**244**

**Figure 3.**

**Figure 2.**

welded by CW-GMAW.

*diffraction (XRD) and (b) acoustic birefringence (AB).*

*Ultrasonic system used to measure RS by acoustic birefringence.*

Through **Figure 3**, there is a reasonable difference between the data obtained, where the plate measured by XRD is predominated by yellow and some peaks in more orange, however the range of residual stresses varied from −17 MPa to 50 MPa, while measuring with AB, it showed the central line with more compressive points, in green and other red peaks indicating tensile stresses, with values ranging from −112 MPa to 103 MPa. However, this disagreement in the results is mainly due to two factors, first, due to the difference in the depths analyzed between the measurement techniques, where the XRD method is more superficial and the AB method analyzes the entire plate thickness. Second, due to the specific methodology of each technique, that is, the XRD shows the punctual and unidirectional RS, while the AB shows the average difference of the main RS, but this result was already predicted. Although both techniques were able to clearly show the presence of RS in the component

*Comparative measurement in a naval steel sheet (ASTM A131 grade AH32) between the methods: (a) X-ray* 
