Fatigue Life Improvement Using Mechanical Post Treatment for Weldment

2008 ◽  
Vol 580-582 ◽  
pp. 97-100
Author(s):  
Seung Ho Han ◽  
Jeong Woo Han ◽  
Yong Yun Nam
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Residual Stresses ◽  
Quantitative Measure ◽  
Fatigue Strength Improvement ◽  
Weld Profile ◽  
Weld Toe ◽  
Life Improvement ◽  
Hammer Peening ◽  
Compressive Residual Stresses

Mechanical post treatments for welded structures have been applied in various industrial fields and, in most cases, have been found to cause substantial increase in their fatigue strength. These methods, generally, consist of the modification of weld toe geometry and the introduction of compressive residual stresses. In hammer peening, the weld profile is modified due to removal or reduction of minute crack-like flaws; compressive residual stresses are also induced by repeated hammering of the weld toe region with blunt-nosed chisel. In this study, a hammer peening procedure, using commercial pneumatic chipping hammer, was developed; a quantitative measure of fatigue strength improvement was performed. The fatigue life of hammer-peened specimen was prolonged by approximately 10 times in S=240MPa, and was doubled for the as-welded specimen.

Residual Stresses in Welded Joints after Different Mechanical Surface Treatments

2006 ◽  
Vol 524-525 ◽  
pp. 401-406
Author(s):  
Thomas Nitschke-Pagel ◽  
Hamdollah Eslami-Chalandar
Keyword(s):  
Residual Stresses ◽  
Welded Joints ◽  
Shot Peening ◽  
Depth Of Penetration ◽  
Fatigue Strength Improvement ◽  
Weld Toe ◽  
Cold Worked ◽  
Hammer Peening ◽  
Compressive Residual Stresses ◽  
Strength Improvement

Investigations on welded joints of a low strength steel and of an age-hardened aluminium- alloy have been performed to compare the effects of different post-weld treatment methods. The experimental results show, that the methods which are working with help of ultrasonic activation lead to a higher depth of penetration of the compressive residual stresses as shot peening does. The cold worked surface area is deeper and the hardening effect can be found in deeper layers. Furthermore the shape of the weld toe is changed strongly due to the cold working of the surface with the consequence of a change of the weld toe geometry. Anyway the fatigue strength improvement is comparable to that which is generated by shot peening (steel) or less than after shot peening (aluminium). The reason is, that the shape of the treated weld toe profile must not be necessarily smoother due to the ultrasonic hammer peening. Depending on the treatment parameters also sharp defects can be produced at the boarder of the treated zone which may compensate the beneficial effect of the compressive residual stresses.

Fatigue Life Improvement of Welded Elements and Structures by Ultrasonic Impact Treatment

2011 ◽  
Author(s):  
Yuriy Kudryavtsev ◽  
Jacob Kleiman
Keyword(s):  
Mechanical Properties ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Residual Stresses ◽  
Fatigue Testing ◽  
Highway Bridges ◽  
Surface Layers ◽  
Ultrasonic Impact Treatment ◽  
Stress Relieving ◽  
Life Improvement

The ultrasonic impact treatment (UIT) is relatively new and promising process for fatigue life improvement of welded elements and structures. In most industrial applications this process is known as ultrasonic peening (UP). The beneficial effect of UIT/UP is achieved mainly by relieving of harmful tensile residual stresses and introducing of compressive residual stresses into surface layers of a material, decreasing of stress concentration in weld toe zones and enhancement of mechanical properties of the surface layers of the material. The UP technique is based on the combined effect of high frequency impacts of special strikers and ultrasonic oscillations in treated material. Fatigue testing of welded specimens showed that UP is the most efficient improvement treatment as compared with traditional techniques such as grinding, TIG-dressing, heat treatment, hammer peening and application of LTT electrodes. The developed computerized complex for UP was successfully applied for increasing the fatigue life and corrosion resistance of welded elements, elimination of distortions caused by welding and other technological processes, residual stress relieving, increasing of the hardness of the surface of materials. The UP could be effectively applied for fatigue life improvement during manufacturing, rehabilitation and repair of welded elements and structures. The areas/industries where the UP process was applied successfully include: Shipbuilding, Railway and Highway Bridges, Construction Equipment, Mining, Automotive, Aerospace. The results of fatigue testing of welded elements in as-welded condition and after application of UP are considered in this paper. It is shown that UP is the most effective and economic technique for increasing of fatigue strength of welded elements in materials of different strength. These results also show a strong tendency of increasing of fatigue strength of welded elements after application of UP with the increase in mechanical properties of the material used.

Characteristics of High Frequency Peening Methods and their Effects on the Fatigue Strength of Welded Details

2007 ◽  
Vol 348-349 ◽  
pp. 429-432
Author(s):  
Imke Weich ◽  
Thomas Ummenhofer
Keyword(s):  
Fatigue Strength ◽  
Residual Stresses ◽  
High Frequency ◽  
Crack Detection ◽  
Surface Hardness ◽  
Detection Methods ◽  
Laser Measurements ◽  
Mechanical Effects ◽  
Weld Toe ◽  
Compressive Residual Stresses

Research has been initiated on the effects of high frequency peening methods on the fatigue strength. These methods combine an improvement of weld toe profile with an initiation of compressive residual stresses and surface hardening. The effects of two techniques, High Frequency Impact Treatment (HiFIT) and Ultrasonic Impact Treatemnt (UIT) are compared. Laser measurements of the weld seam prove that both methods increase the overall weld toe radii. Further, residual stress measurements verify the introduction of compressive residual stresses at least up to a depth of 1 mm. The values meet the yield strength combined with an increase of the surface hardness. These material mechanical effects cause an increased crack resistance. Crack detection methods prove that the material mechanical effects yield to a retarded crack initiation. Experimental results show that these effects lead to a significant increase of the fatigue strength and reduced slopes of the SN-curves.

Fatigue Improvement of Welded Elements and Structures by Ultrasonic Peening

2013 ◽  
Author(s):  
Yuri Kudryavtsev ◽  
Jacob Kleiman
Keyword(s):  
Mechanical Properties ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Residual Stresses ◽  
Fatigue Testing ◽  
Fatigue Improvement ◽  
Surface Layers ◽  
Ultrasonic Peening ◽  
Stress Relieving ◽  
Life Improvement

The ultrasonic impact treatment (UIT) is relatively new and promising process for fatigue life improvement of welded elements and structures. In most industrial applications this process is known as ultrasonic peening (UP). The beneficial effect of UP is achieved mainly by relieving of tensile residual stresses and introducing of compressive residual stresses into surface layers of a material. The secondary factors in fatigue improvement by UP are decreasing of stress concentration in weld toe zones and enhancement of mechanical properties of the surface layers of the material. Fatigue testing of welded specimens showed that UP is the most efficient improvement treatment as compared with traditional techniques such as grinding, TIG-dressing, heat treatment, hammer peening and application of LTT electrodes. The developed computerized complex for UP was successfully applied for increasing the fatigue life and corrosion resistance of welded elements, elimination of distortions caused by welding and other technological processes, residual stress relieving, increasing of the hardness of the surface of materials. The UP could be effectively applied for fatigue life improvement during manufacturing, rehabilitation and repair of welded elements and structures. The areas/industries where the UP process was applied successfully include: Shipbuilding, Railway and Highway Bridges, Construction Equipment, Mining, Automotive, Aerospace. The results of fatigue testing of welded elements in as-welded condition and after application of UP are considered in this paper. It is shown that UP is the most effective and economic technique for increasing of fatigue strength of welded elements in materials of different strength. These results also show a strong tendency of increasing of fatigue strength of welded elements after application of UP with the increase in mechanical properties of the material used.

Underwater Stress Relief and Fatigue Improvement by Ultrasonic Peening

2012 ◽  
Author(s):  
Jacob Kleiman ◽  
Yuri Kudryavtsev ◽  
Alexander Lugovskoy
Keyword(s):  
Residual Stresses ◽  
Stress Relief ◽  
Fatigue Improvement ◽  
Water Cooling ◽  
Surface Layers ◽  
Welded Structures ◽  
Ultrasonic Peening ◽  
Weld Toe ◽  
Life Improvement ◽  
Compressive Residual Stresses

A new ultrasonic peening instrument was developed for underwater treatment of welds and welded structures. The Ultrasonic Peening (UP) established itself as a promising process for fatigue life improvement of welded elements and structures. The beneficial effect of UP is obtained through relieving of harmful tensile residual stresses and introducing of compressive residual stresses into surface layers of materials, and through decreasing of stress concentration in weld toe zones and enhancement of mechanical properties of the surface layers of the materials. In the design of the underwater UP instrument specially selected anti-corrosion materials are used. The underwater UP instrument can be used for treatment of welds at depths up to 30 meters or, if required, with certain modifications, even deeper. Acoustic pump principle is used in the originally developed system for water cooling of the transducer. The developed UP system allows for improvement treatments at four different power levels and is using replaceable working heads that come in various configurations with variable numbers of pins, depending on the application.

Evaluation of Fatigue Strength Improvement of Ship Structural Details by Weld Toe Grinding

2006 ◽  
Vol 324-325 ◽  
pp. 1079-1082 ◽  
Author(s):  
Myung Hyun Kim ◽  
Sung Won Kang ◽  
Jae Myung Lee ◽  
Wha Soo Kim
Keyword(s):  
Fatigue Strength ◽  
Surface Defects ◽  
Quantitative Measure ◽  
Fatigue Tests ◽  
Weld Bead ◽  
Fatigue Strength Improvement ◽  
Structural Details ◽  
Weld Toe ◽  
Loading Modes ◽  
Strength Improvement

In order to strengthen or repair the welded structural members or fatigue damaged areas, various surface treatment methods such as grinding, shot peening and/or hammer peening are commonly employed among other methods available. While the weld toe grinding method is known to give 3~4 times of fatigue strength improvement, this improvement may significantly vary according to weld bead shapes and loading modes. In this context, a series of fatigue tests is carried out for three types of test specimens that are typically found in ship structures. Weld burr grinding is carried out using an electric grinder in order to remove surface defects and improve weld bead profiles. The test results are compared with the same type of test specimen without applying the fatigue improvement technique in order to obtain a quantitative measure of the fatigue strength improvement. Moreover, structural stress method is employed to evaluate the effectiveness of the method in evaluating the fatigue strength improvement of welded structures.

Fatigue Life Improvement of Laser Clad 7075 Aluminium Alloy by Deep Surface Rolling Technique

2014 ◽  
Vol 891-892 ◽  
pp. 115-120
Author(s):  
Qian Chu Liu ◽  
Wyman Zhuang ◽  
Peter Khan Sharp
Keyword(s):  
Heat Treatment ◽  
Fatigue Life ◽  
Residual Stresses ◽  
Aluminium Alloy ◽  
Laser Cladding ◽  
High Strength ◽  
Post Heat Treatment ◽  
Deep Surface ◽  
Life Improvement ◽  
Compressive Residual Stresses

The Deep Surface Rolling (DSR) technology can substantially increase the fatigue life of metallic materials due to the introduction of deep compressive residual stresses in the material surface. These beneficial compressive residual stresses can be achieved up to a depth of 1 mm. The DSR technology also produces a good surface finish unlike bead peening technology. In this study, the main objectives were: (1) to study the feasibility of DSR for fatigue life improvement of high strength aluminium alloy (7075-T651) repaired with laser cladding technology, and (2) to investigate the effect of thermal stressing on the fatigue life improvement of DSR. Previously published results have shown that post-heat treatment of laser clad high strength Al alloy coupons improved their fatigue life. The experimental results in this paper show that the fatigue life was substantially increased using the DSR technique on laser clad 7075-T6 aluminium alloy compared to laser cladding alone and laser cladding followed by post heat treatment.

Simplified FEA Models in the Analysis of the Redistribution of Beneficial Compressive Stresses in Welds During Cyclic Loading

2018 ◽  
Author(s):  
B. L. Josefson ◽  
J. Alm ◽  
J. M. J. McDill
Keyword(s):  
Cyclic Loading ◽  
Residual Stresses ◽  
Compressive Stress ◽  
Welding Process ◽  
Plastic Behavior ◽  
Element Analysis ◽  
Compressive Stresses ◽  
Static Contact ◽  
Weld Toe ◽  
Compressive Residual Stresses

The fatigue life of welded joints can be improved by modifying the weld toe geometry or by inducing beneficial compressive residual stresses in the weld. However, in the second case, the induced compressive residual stresses may relax when the welded joint is subjected to cyclic loading containing high tensile or compressive stress peaks. The stability of induced compressive stresses is investigated for a longitudinal gusset made of a S355 steel. Two methods are considered; either carrying out a high frequency mechanical impact (HFMI) treatment after welding or alternatively using low transformation temperature (LTT) electrodes during welding. The specimen is then subjected to a cyclic loading case with one cycle with a tensile peak (with magnitude reaching the local yield stress level) followed by cycles with constant amplitude. A sequential finite element analysis (FEA) is performed thereby preserving the history of the elasto-plastic behavior. Both the welding process and the HFMI treatment are simulated using simplified approaches, i.e., the welding process is simulated by applying a simplified thermal cycle while the HFMI treatment is simulated by a quasi-static contact analysis. It is shown that using the simplified approaches to modelling both the welding process and HFMI treatment gives results that correlate qualitatively well with the experimental and FEA data available in the literature. Thus, for comparison purposes, simplified models may be sufficient. Both the use of the HFMI treatment and LTT electrodes give approximately the same compressive stress at the weld toe but the extent of the compressive stress zone is deeper for HFMI case. During cyclic loading it is shown that the beneficial effect of both methods will be substantially reduced if the test specimen is subjected to unexpected peak loads. For the chosen load sequence, with the same maximum local stress at the weld toe, the differences in stress curves of the HFMI-treated specimen and that with LTT electrodes remain. While the LTT electrode gives the lowest (compressive) stress right at the well toe, it is shown that the overall effect of the HFMI treatment is more beneficial.

The Effect of Several Finishing Processes on the Fatigue Resistance of Hole Surfaces

1989 ◽  
Vol 111 (1) ◽  
pp. 71-73 ◽  
Author(s):  
M. O. Lai ◽  
A. Y. C. Nee
Keyword(s):  
Surface Roughness ◽  
Plastic Deformation ◽  
Fatigue Life ◽  
Residual Stresses ◽  
Fatigue Resistance ◽  
Radial Direction ◽  
Fatigue Loading ◽  
Steel Plates ◽  
Finishing Processes ◽  
Compressive Residual Stresses

This investigation examines the effects of different finishing processes on the fatigue life of premachined holes in Assab 760 steel plates. The finishing processes studied were reaming, ballizing, and emery polishing. A general decrease in fatigue life with increase in surface roughness is observed for all the processes employed. In comparing the different processes, for a constant surface roughness, polishing is generally found to give the longest fatigue life while ballizing, in spite of the greater compressive residual stresses induced on the surface of the finished hole, the shortest. The surprising phenomenon was found to be attributed to the amount of plastic deformation occurred before fatigue loading. For Assab 760 steel, a prestrain in the radial direction of less than about 2.5 percent appeared to reduce the fatigue resistance of the material.

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