Shear Fatigue Test Research Articles

Accelerated lifetime estimation of thermosonic Cu ball bonds on Al metallization

In this study a fast mechanical shear fatigue test technique for the quality assessment of thermosonic ball bonded interconnects was developed to estimate their lifetime behavior. The micro-interconnects were subjected to cyclic shear stress using a special specimen set-up in combination with an ultrasonic resonance fatigue system at a frequency of 20kHz and a laser Doppler vibrometer for velocity measurements. Two different types of power semiconductor devices comprising single and multiple Cu ball bonds on Al pads of the same dimension and bonding quality were tested to validate the proposed testing technique. Due to the dimensional restrictions of both specimen types, suitable sample preparation techniques were designed to induce cyclic shear stresses in the interface of the ball bonded interconnects. The obtained high cycle fatigue life curves could be related to the specimen design and the resulting loading modes. Using FEM simulations the loading modes and fatigue response of both set-ups were analyzed. Life-time prediction curves based on a Basquin type relationship (von Mises stress - loading cycles) were obtained in which dissimilar geometries and loading modes could be equated. Additional SEM investigations of the fractured areas were compared and discussed to understand the microstructural failure mechanisms occurring during fatigue loading. It can be concluded that this new fatigue testing technique accompanied by FEM simulations and subsequent inspection of the fractured area is a suitable time saving and economic testing method for the assessment of the reliability and fatigue life response of small micro-interconnects.

Experimental Study on the Ultimate Shear Performance of Elastomeric Bearings of Doublefold Elastomeric Layer

The elastomeric bearings shall not fail nor degrade the durability of the bridge due to the loss of its properties during its service life. Since the elastomeric bearings can be used in the seismic design complementarily to seismic devices, even if it is not a seismic isolator, they particularly should secure high shear performance. For elastomeric bearings to behave monolithically, the internal rubber which is located between the steel plates should be single rubber layer. In this study, a series of elastomeric bearings were fabricated and ultimate shear performance was investigated. Some specimens are of single elastomeric layer, the other are of doublefold elastomeric layer. Shear fatigue tests and ultimate shear tests were carried out. Tests results show that the elastomeric bearings whose internal rubber layer is formed by agglomeration of several rubber pads is likely to experience significant loss of its shear performance or early failure.

GS27 改良型ラップジョイント試験片によるはんだ接合部のせん断疲労試験方法

This paper presents the shear fatigue test method of the solder joint by the advanced lap joint specimen. The advanced lap joint specimen was developed for purpose of stiffness improvement and manufacturing of solder joint thickness equivalent to an actual solder joint of an electric board. The usefulness of the advanced lap joint specimen was checked by FEM analysis and the tensile test, and the test method was considered.

PS14 セルフピアスリベット継ぎ手部の塑性ひずみ量の推定と疲労強度の検討

Society of Automotive Engineers of Japan (JSAE) tested fatigue strength by shear fatigue test for mild steel, 270, and high tensile steel, 590, joined by rivets. As the result of the tests, fatigue strength was independent on the strength of base materials. JSAE reported pre-strain of the rivet affect the fatigue strength. This study estimated the distribution of pre-strain of rivet for 270 and 590 joints by indentation method and simulate pre-strain levels of the rivets. Instead of placing the rivet on the base materials, fatigue strength of the rivet was tested after applying pre-strain. As a result of fatigue test of the rivet, there is a little difference in the fatigue strength by pre-strain. The stress distribution of the rivet for the fatigue testing was analyzed by FEM, and it was found that pre-strain caused larger stress concentration, which resulted in different fatigue lives of the rivet.

Precise Chip Joint Method with Sub-micron Au Particle for High-density SiC Power Module Operating at High Temperature

In this work, a novel precise chip joint method using sub-micron Au particle for high-density silicon carbide (SiC) power module operating at high temperature is proposed. A module structure of SiC power devices are sandwiched between two silicon nitride-active metal brazed copper (SiN-AMC) circuit boards. To make a precise position and height control of the chip bonding, the top side (gate/source or anode pad side) of SiC power devices are flip-chip bonded to circuit electrodes using sub-micron Au particle with low temperature (250°C) and pressure-less sintering. The accuracy of the bonding position of chips was less than 10 μm and the accuracy of the height after bonding chips was less than 15 μm. Mechanical shear fatigue tests for flip-chip bonded SiC Schottky barrier diode (SBD) were carried out. As a result, initial shear strength of the joint was 36 MPa. The shear strength of 43 MPa is obtained after storage life test (500 hours at 250°C), and also 35 MPa is obtained even after thermal cycle stress test (1000 cycles between −40°C and 250°C). The flip-chip bonding of SiC-JFET is successfully realizedon the substrate without short or open failure electrically. Finally we joint the backside of the SiC-JFET (drain side) and the SiC-SBD (cathode side) to each circuit electrodes at once by means of reflow process with Au-12%Ge solder. The structured sandwich SiC power module was also successfully formed.

Influence of rivet to sheet edge distance on fatigue strength of self-piercing riveted aluminium joints

Self-piercing riveting (SPR) is one of the main joining methods for lightweight aluminium automotive body structures due to its advantages. In order to further optimise the structure design and reduce the weight but without compromising strength, reduction of redundant materials in the joint flange area can be considered. For this reason, the influence of rivet to sheet edge distance on the fatigue strengths of self-piercing riveted joints was studied. Five edge distances, 5mm, 6mm, 8mm, 11.5mm and 14.5mm, were considered. The results showed that the SPR joints studied in this research had high fatigue resistance and all specimens failed in sheet material along joint buttons or next to rivet heads. For lap shear fatigue tests, specimens failed in the bottom sheet at low load amplitudes and in the top sheet at high load amplitudes except for specimens with very short edge distance of 5 and 6mm; whereas, for coach-peel fatigue tests, all specimens failed in the top sheet. For both lap shear and coach-peel fatigue tests, specimens with an edge distance of 11.5mm had the best fatigue resistance. It was found that for coach-peel fatigue, length of crack developing path before specimens lost their strengths was the main factor that determined the fatigue life of different specimens; for lap shear fatigue, the level of stress concentration and subsequent crack initiation time was the main factor that determined the fatigue life.

Comparative study of fatigue behaviour in dissimilar Al alloy/steel and Mg alloy/steel friction stir spot welds fabricated by scroll grooved tool without probe

Aluminium alloy A6061-T6 or magnesium alloy AZ31 sheet was welded to steel sheet by a friction stir spot welding technique using a scroll grooved tool without a probe. The material flow in the nugget of the Mg/steel weld was less than that in the Al/steel one. The Al/steel weld exhibited higher static tensile–shear strength than the Al/Al weld, while the strengths of Mg/steel and Mg/Mg welds were comparable. Tensile–shear fatigue tests were performed using lap shear specimens of both dissimilar and similar welds. The dissimilar welds exhibited nearly the same fatigue strengths as the similar ones. The effective nugget size in the dissimilar welds was defined as the area where Al or Mg alloy remained on the steel side after static fracture. When the fatigue strengths of dissimilar welds were evaluated based on the effective nugget size, the normalised fatigue strengths of Al/steel and Mg/steel welds were comparable.

Mode II fatigue delamination resistance of advanced fiber-reinforced polymer–matrix laminates: Towards the development of a standardized test procedure

Delamination resistance testing of fiber-reinforced polymer–matrix laminates under fatigue loads is important for materials development and structural design. Mode II in-plane shear fatigue test development using three-point bending end-notched flexure (3-ENF) and two-point bending end-loaded split (ELS) set-ups is performed in a round robin. Effects of specimen restraint observed earlier in ENF tests are confirmed and preliminary data indicate differences between the two set-ups, if simple beam theory or experimental compliance analyses are applied. Possible reasons for the observed disagreement are discussed.

In vitro cyclic shear fatigue of the bracket-adhesive complex: a pilot study

The aim of this study was to describe the effect of fatigue on the shear strength of the bracket-adhesive complex. Brackets with laser-structured (Discovery®, Dentaurum) and foil mesh bases (Ultra-Minitrim®, Dentaurum) were bonded onto silanized stainless steel flat plates with two chemically curing adhesives (No-Mix Bonding System, Dentaurum; Concise™, 3M Unitek) and aged in distilled water at 37°C for 3 days. One group of specimens was used to determine shear-bond strength. The second group underwent shear-fatigue testing with a testing machine (Zwick 1445) according to the staircase method for 1,000 cycles, and the surviving specimens were subjected to shear-strength testing. The shear strength of the fatigued and non-fatigued specimens were then compared. Fatigued specimens demonstrated an 8% gain in shear strength in material group A (Discovery®/No-Mix) and a 10% loss of shear strength in material group D (Ultra-Minitrim®/Concise™) compared to the non-fatigued group. We observed no statistically significant differences in material groups B (Ultra-Minitrim®/No-Mix) and C (Discovery®/Concise™). The fatigue ratio varied between 60% and 67%. Among the non-fatigued specimens, the bracket Discovery® with laser-structured base showed circa 59% greater shear strength than the foil-mesh bracket Ultra-Minitrim®, and the adhesive Concise™ about 66% more shear strength than the No-Mix. Shear fatigue of the bracket-adhesive complex for 1,000 cycles revealed a variable, material-dependent influence on the shear strength of the bracket-adhesive complex. However, the effect of fatigue on shear strength was less significant than the effect of other factors such as bracket and adhesive type.

A Method to Test Anterior-Posterior Construct Shear Fatigue Based on the Vertebrectomy Model

Abstract Dynamic stabilization systems may be subject to anterior-posterior shear loading. However, there is no standard method established for testing a vertebrectomy model in anterior-posterior translation (as may be seen with dynamic spondylolisthesis). A new anterior-posterior shear fatigue test was devised to test one such dynamic stabilization system in anterior-posterior translation. Similar to ASTMF1717 assemblies, constructs were assembled so that screws were placed in ultra high molecular weight polyethylene blocks to attach to the test fixture. The test setup ensures that the entire shear load is transmitted by the implant system. Unlike ASTMF1717 assemblies, the blocks were rotated 180 deg from each other to facilitate loading in the test frame. This configuration is modified from an expected in vivo usage. However, the resultant load vectors are appropriately similar to the shear loads being simulated. The constructs include polymeric components and thus were tested at body temperature in a fluid bath. The blocks were moved ±5 mm with respect to each other. The constructs were cycled at 2 Hz for a minimum of 5 × 106 cycles. The constructs successfully survived 10 × 106 cycles of anterior-posterior shear displacement. Examination of the constructs demonstrated similarities between components tested via this new method and components retrieved from patients. Comparisons indicate that the shear fatigue test may stress the components as much or perhaps more than what was seen clinically.

Evaluation of Sealed Joint Performance for the Selection of Sealants Suitable for Use in Autoclaved Lightweight Concrete Panels

Abstract The strength of autoclaved lightweight concrete (ALC) is evidently lower than that of normal concrete. Therefore, when movement occurs at a sealed joint between ALC panels, the sealant is required to deform and remain intact without damaging the ALC substrate. However, there is currently not sufficient information to permit evaluation of the expected performance of sealants applied to ALC substrates. In this study, static and dynamic tests were carried out in order to obtain an index that could be used to select the modulus of a sealant that can be expected to provide long-term performance when applied to an ALC substrate. To develop this index, an initial study was carried out in order to clarify actual joint movement between ALC panels of buildings; the expansion and contraction at the joint were measured, and shear joint movement was calculated based on the expected story-to-story drift of an external wall due to earthquake loads. Thereafter, in a subsequent stage of the study, five types of two-component polyurethane sealant products, of different elastic modulus, were subjected to tensile and shear tests from which the relationship between stress and the type of joint fracture was determined. The results from these tests revealed that when the stress is greater than 0.6 to 0.7 N/mm2, the ALC substrate is more easily fractured than the sealant. In a final stage of the study, the cyclic fatigue resistance of the same two-component sealants was evaluated using tensile and shear fatigue tests. Results from the fatigue tests indicated that the high modulus sealants lost adhesion from the ALC substrate at an early stage in the test. As well, the fatigue resistance of test specimens with joints having three-sided adhesion was lower than that of specimens having normally configured joints with adhesion on two sides of the sealant. Therefore, on the basis of results derived from all the studies, it was determined that a suitable sealant for use on ALC substrates is a sealant having a low modulus that is applied in the normal fashion as a two-sided joint.

Fatigue life evaluation of anisotropic conductive adhesive film joints under mechanical and hygrothermal loads

The shear fatigue lives of Anisotropic Conductive Adhesive Film (ACF) joints were evaluated experimentally and theoretically under different testing conditions. The shear fatigue tests of ACF joints were performed with different loading amplitudes. It is found that the fatigue lives of ACF joints decrease with increasing loading amplitudes and Basquin’s equation is fit to predict the fatigue lives of ACF joints. Hygrothermal aging and thermal cycling tests were conducted to investigate the shear strength and lives of ACF joints. The results show that the shear strength and lives of ACF joints decrease with increasing hygrothermal aging time, however increase firstly and then decrease with increasing thermal cycling time. The fatigue life model considering aging damage is proposed and the predictions of the fatigue life agree with the experimental results at different aging time for ACF joints.

A fast test technique for life time estimation of ultrasonically welded Cu–Cu interconnects

In this research the quality of the interconnects of the ultrasonically welded Cu terminals to the Cu substrate in the IGBT-module has been investigated. An ultrasonic resonance fatigue system in combination with a laser Doppler vibrometer and a special specimen design was used for shear fatigue testing of these large ultrasonic Cu–Cu welds (about 0.5 cm 2). Fatigue life curves up to 10 9 loading cycles were obtained in a very short period of time. Using this technique it was possible to evaluate the fatigue strength of these interconnects for the first time. The microstructural features of the interconnects were characterized and their crack growth behaviour was studied. Fracture analysis of the fatigued specimen shows that failure occur due to the propagation of the crack beneath the welding interface into the copper substrate. Additionally performed finite element simulations offer an insight into the stress and strain concentrations during the mechanical fatigue tests. As this method is not restricted to the welding geometry, material joints with larger interconnects can be tested likewise. Thus this new technique can be used as a practical and valid fatigue testing method for evaluation of various interconnects.

Experimental investigation of tack coat fatigue performance: Towards an improved lifetime assessment of pavement structure interfaces

This paper focuses on investigating the bonding fatigue performance between two asphalt concrete (AC) layers. For purposes of this experimental campaign, a customised double shear testing device was designed. Two interface conditions have been analysed herein: with and without a tack coat. Moreover, the corresponding fatigue behaviour has been analysed at two temperatures: 10 °C and 20 °C. As expected, the absence of a tack coat leads to a decrease in bonding fatigue performance. Since fatigue tests are highly time-consuming, a method that allows predicting the conventional interface fatigue law from accelerated shear fatigue tests has been proposed. Other novel findings on interface fatigue behaviour will also be discussed. In addition to these fatigue results, an interface failure model is proposed to evaluate the interface lifetime. Incorporating interface fatigue performance into pavement analysis proves to be a key parameter in describing in situ pavement conditions and assessing pavement durability.

Enhancing Fatigue Performance of Sandwich Composites with Nanophased Core

We report fatigue performance of sandwich composites with nanophased core under shear load. Nanophased core was made from polyurethane foam dispersed with carbon nanofiber (CNF). CNFs were dispersed into part‐A of liquid polyurethane through a sonication process and the loading of nanoparticles was 1.0 wt%. After dispersion, part‐A was mixed with part‐B, cast into a mold, and allowed to cure. Nanophased foam was then used to fabricate sandwich composites. Static shear tests revealed that strength and modulus of nanophased foams were 33% and 19% higher than those of unreinforced (neat) foams. Next, shear fatigue tests were conducted at a frequency of 3 Hz and stress ratio (R) of 0.1. S‐N curves were generated and fatigue performances were compared. Number of cycles to failure for nanophased sandwich was significantly higher than that of the neat ones. For example, at 57% of ultimate shear strength, nanophased sandwich would survive 400,000 cycles more than its neat counterpart. SEM micrographs indicated stronger cell structures with nanophased foams. These stronger cells strengthened the sub‐interface zones underneath the actual core‐skin interface. High toughness of the sub‐interface layer delayed initiation of fatigue cracks and thereby increased the fatigue life of nanophased sandwich composites.

Fatigue Degradation Properties of PCM-concrete Interface

Stress analysis of RC structures that have been retrofitted by an externally bonded layer of Polymer Cement Mortar (PCM) based materials requires the development of a constitutive model of the PCM-concrete interface under static and fatigue loading. In this paper, the bending fatigue and shear fatigue tests were conducted to determine the interface fatigue degradation properties by using the J-integral method based on the energy equivalence. Substrate concretes with four different compressive strengths and interface roughness were applied to understand the effects of substrate concrete and interface roughness on the fatigue degradation properties. It was found that the failure characteristics of the PCM-concrete interface is similar to those of cementitious material and the failure modes of PCM-concrete interface has an important effect on the interface tensile and shear degradation relation and S-N relation under fatigue loading. The degradation relation is similar in the case that the failure mode is identical, regardless of the type of substrate concrete. The fatigue resistance of the PCM-concrete interface is inferior to that in the concrete cohesion layer.

A novel method for evaluating fatigue properties of bonding layers used in bridge deck pavement

A new method was used to evaluate the fatigue properties of the bonding layer used in the bridge deck pavement. The shear fatigue test of three bonding layers was conducted on a dynamic shear rheometer(DSR). The fatigue formulas were gained for these layers. The experimental results indicate that, at the same torque level or at the same frequency, neoprene latex asphalt bonding layer exhibits excellent fatigue performance when compared to other two bonding layers.

Subsurface microstructural alterations during sliding wear of biomedical metals. Modelling and experimental results

Underneath contact surfaces under sliding wear distinct microstructural changes have been found in biomedical materials. These are attributed to the nature of the contact stress (and strain) field. The experimental investigation of subsurface areas of retrieved metal-on-metal hip joints and laboratory specimens revealed that the worn surfaces of these fcc CoCrMo alloys in general consist of a nano-crystalline (nc) layer with a thickness of up to 200 nm. This layer is chemically modified by mechanical mixing, which introduces the interfacial medium (e.g. proteins) into the subsurface volume. Below 200 nm one often finds a nc-layer of the same grain size but having only the chemical composition of the base material. Thus, the interface between the mechanically mixed nc-layer and the underlying one cannot be distinguished by grain size, but by chemical composition. In comparison to shear fatigue tests, these materials show a distinct tendency for ratchetting and they depict the same lattice defects as in a siding wear stress field. This contribution shows that computer simulation and experimental validation can support each other in order to understand the complicated interaction of wear mechanisms under sliding wear qualitatively. But there is no general description available and any aspect requires its own simulation method.

Comparison of fatigue behaviour between resistance spot and friction stir spot welded aluminium alloy sheets

Tensile shear fatigue tests have been performed using resistance spot welded (RSW) joint and friction stir spot welded (FSSW) joint of aluminium alloy sheets. When fatigue strength was characterised in terms of applied load, RSW joint showed higher fatigue strength than FSSW joint in the entire load range, while the fatigue strength normalised with respect to the nugget area was higher in FSSW joint than in RSW joint. Friction stir spot welded joint exhibited a very small scatter of fatigue life compared with RSW joint, indicating that FSSW is a very stable and reliable joining method. Macroscopic fatigue fracture modes were similar in both joints: nugget shear fracture in high applied load region and parent sheet fracture in low applied load region. It was indicated that geometrical factors around the weld zone played a dominant role in determining the fatigue strength and fracture mechanism of the joints.

Experimental investigation of fatigue performance of spot welded dual phase sheet steels

Spot weld fatigue performance of dual phase steels is of great interest to worldwide automotive manufacturers due to their expanding use in automotive industry. Given that the majority of the fatigue life is spent propagating the crack through the microstructure, changes in microstructure of welding steels could result in significant changes in spot weld fatigue life compared to that of low carbon steel spot weld. In the present study, tensile shear spot welds of DP600GI, DP780GI with different thickness were used for fatigue test under various amplitude tensile loads. For comparison tensile shear fatigue test was also conducted for spot welds of low carbon steel. Microhardness was measured for spot weld of dual phase steels to study the hardness change across the weld nugget. Failure mechanism and crack propagation path of dual phase steel spot weld was studied. For spot welds of low thickness, the fatigue strength of dual phase steel spot weld is higher than that of low carbon steel specimen in high cycle fatigue test. When thickness increases, the fatigue strength of dual phase steel spot weld and low carbon steel spot weld are almost the same, and fatigue strength of dual phase spot welds also increases with the thickness. And it is also shown in the present study that static tensile interfacial fracture of spot weld does not necessarily lead to interfacial fracture of high cycle fatigue tests. Crack propagation path of tensile shear spot weld of dual phase sheet steels under fatigue test was examined. Crack initiates at the faying surface around the weld nugget, and then passes through the thickness of sheet, which leads to the failure of specimens.