Cracks In Sheets Research Articles

Effect of Heat Input on Tin Bronze-Induced Intergranular Cracks During Arc Cladding Process

This work aimed to figure out the effect of heat input on the characteristics, formation, and elimination of liquid tin bronze-induced intergranular cracks in steel sheets with a thickness of 2 mm. Tin bronze cladding layers were prepared using an arc cladding technique on the steel. A statistical method was adopted to analyze the severity of intergranular cracks. Microstructures and intergranular cracks were characterized by SEM and TEM. The tensile experiments were carried out using an electronic universal testing machine. For the bare steel sheets, the intergranular cracks originated from the cladding layer and propagated into the interior of the steel along the grain boundaries. The intergranular cracks could evolve into macrocracks and lead to the failure of steel. With the increase in heat input, the maximum temperature, maximum stress, and contact time between steel and liquid tin bronze increased. The severity of intergranular cracks was also increased, and the longest crack reached 520 μm. The mechanical properties of the steel sheets decreased with the increase in heat input. For nickel-plated steel sheets, intergranular cracks were eliminated under low heat input, and a transition layer with a nickel content of 12.32 wt.% was generated. The intergranular cracks generated under high heat input and nickel content in the transition layer were only 1.34 wt.%. The strength of the nickel-plated steel also decreased drastically, and the ductility was almost zero.

Study on the fatigue properties of SPR-bonded aluminum-steel sheet joints

This study deals mainly with the influence of adhesive layer on the fatigue behavior and fretting of self-piercing riveted (SPR) joint joining differing thicknesses of AlSi10MnMg aluminum and DP590 steel sheets in lap shear geometry. Fatigue life, failure modes, crack propagation and fretting behaviors of the SPR and SPR-bonded joints were investigated and compared. The results showed that the static strength and fatigue life of SPR-bonded joints were significantly enhanced than that of SPR joints, but the fatigue failure mode of SPR-bonded and SPR joints differed. The SPR-bonded joints all failed in a rivet tail pull-out mode at all tested loads, which accompanied with small cracking in the aluminum sheet in contact with the rivet tail at lower test load. However, the failure mode of the SPR joints shifted from the aluminum sheet cracking to rivet tail pull-out as the fatigue test load increased. And during the aluminum sheet cracking failure, the fatigue crack originated from the faying interface of aluminum and steel sheet at the vicinity of the rivet shank and propagated along the width direction of aluminum sheet. Fretting wear analysis showed that the overall extent of fretting decreased and the location of fretting areas varied due to the adhesive bonding. Fretting of SPR joints mostly existed at the faying interface between aluminum and steel about 1.5mm away from the rivet shank and resulted in fatigue crack initiation, while the fretting region of SPR-bonded joints shifted to the faying interface between rivet tail and aluminum sheet.

Quantitative characterization of granite failure intensity under dynamic disturbance from energy standpoint

Abstract Quantitative evaluation of rock dynamic disaster intensity is a challenging and difficult task in the field of earth science. In this article, the dynamic compression tests of granite under different impact velocities are carried out, and the energy evolution characteristics of the dynamic failure process of granite are analyzed. The dynamic fracture characteristics of granite were studied by using computed tomography and section scanning equipment. The results show that the energy dissipation and energy accumulation mechanism of granite under dynamic loading are fundamentally changed with the increase of impact disturbance strength, which leads to the transformation of the failure mode from the tension-type sheet crack under low-speed impact to the complex network crack coupled by tension and shear under high-speed impact. At the same time, the greater the impact velocity, the larger the macroscopic crack density, the more uneven the particle distribution on the fracture section, the greater the roughness, and the higher the rock mass fracture degree. In accordance with the results, the energy distribution ratio is proposed to quantitatively characterize the coupling effect of energy dissipation and energy accumulation in the dynamic failure process of granite and to reflect its dynamic failure intensity. The higher the energy distribution ratio, the stronger the energy coupling effect and the more intense the dynamic failure of the rock mass.

Newly discovered diamictite and cap carbonate couplet in the southern Alxa Block, northwestern China: Implications for stratigraphic correlation and Marinoan glaciation

Neoproterozoic glaciogenic diamictite and cap carbonate couplets have played a pivotal role in understanding glacial-interglacial cycles and establishing regional stratigraphic correlation. The Alxa Block in northwestern China preserves a sequence of Neoproterozoic diamictites along its southern margin, but the age and origin of the succession remain debatable due to the lack of discovery of cap carbonate. We report newly discovered cap carbonates that overlie the diamictites of the Shaohuotonggou Formation in the Longshoushan region in the southern Alxa Block. Based on detailed geological investigations, we identified massive diamictites, stratified diamictites, and cap carbonates in the lower part of the formation. The presence of ice-rafted dropstones, bullet-shaped and facetted clasts, glacial striations, and relatively low chemical index of alteration values of sedimentary matrix support a glaciogenic origin of the diamictites. The 2- to 2.6-m-thick cap carbonates are mainly composed of thinly laminated microcrystalline dolomites and show sheet cracks, cemented breccias, and tepee-like structures at the basal part of the unit. These features and their consistently negative δ13C values (−5.2‰ to −2.2‰) are characteristic of Marinoan-age cap carbonates (ca. 635 Ma). The quasi-continuous deposition of the massive diamictites, stratified diamictites, and cap carbonates suggests that the formation of this couplet was closely related to the Marinoan glaciation and subsequent deglaciation. We propose a three-stage depositional model for the glaciogenic succession and recommend that the diamictite and cap carbonate couplet in the Alxa Block provides a credible mark of the Cryogenian−Ediacaran boundary for further stratigraphic correlation and investigation.

Influence of heat treatment and forming cycle on the precise forming of AZ31 magnesium alloy sheet

Precision forming of 3 mm thick rolled AZ31 magnesium alloy sheet at 90° results in severe cracking and a considerable rebound angle. The effects of different sheet heat treatments and changes in the forming cycle on the value of the forming angle were investigated using 90° precision forming tests. The reasons of sheet cracking were examined using tensile tests and numerical simulations. Microscopic analysis and characterization techniques such as metallographic experiments, SEM observations, and EBSD tests are used to clarify the mechanism of improvement and control of the forming angle value. The results indicate that annealing treatment exhibits high sensitivity to controlling sheet cracking, but low sensitivity to controlling rebound. Among them, after heat treatment at 250 °C+1 h, the sheet no longer cracks during forming. In incomplete annealing, the more small grains produced by recrystallization and the greater the number of dimples in the fracture, the closer the forming angle is to 90°. Full annealing can result in a small reduction in the forming angle value compared to incomplete annealing treatments. After extending the forming cycle for 1 h, the increase in the ratio of dual tensile twin boundaries and low angle grain boundaries resulted in a significant decrease in the value of the forming angle and no cracking of the sheet. The increase of recrystallized tissue on the tensile side and the increase of the KAM value led to the decrease of the forming angle value to the minimum value at 300 °C+1 h heat treatment condition.

Finite element modeling and analysis of the self-piercing riveting forming process with the ball-shaped die

Self-Piercing Riveting (SPR) technique faces challenges as it expands to low ductile materials. In this paper, the ball-shaped die is suggested to prevent the formation of cracks in sheets during the SPR process. The SPR model with the ball-shaped die was developed using the finite element method, and simulations of the joint forming process and tensile test were conducted. The influence of die depth and diameter on SPR forming process and quality was analysed. The simulation results showed that as the die diameter increases, the undercut decreases, and the remaining thickness of bottom increases. The undercut and the remaining thickness of bottom decreases with the increase of the depth of the die. When employing a ball-shaped die with a 1 mm depth and 10 mm diameter, the SPR joint with tight interlock and excellent mechanical properties can be obtained. The results of the simulation and experimental tests are consistent.

Initiation and growth of fatigue cracks in sheets with U-shaped notches in the first and mixed modes of fracture

Initiation and growth of fatigue cracks in sheets with U-shaped notches in the first and mixed modes of fracture

Crack Width Recognition of Tunnel Tube Sheet Based on YOLOv8 Algorithm and 3D Imaging

Based on the tunnel crack width identification, there are operating time constraints, limited operating space, high equipment testing costs, and other issues. In this paper, a large subway tunnel is a research object, and the tunnel rail inspection car is an operating platform equipped with industrial cameras in order to meet the requirements of the tunnel tube sheet crack width recognition of more than 0.2 mm, with the measuring instrument to verify that the tunnel rail inspection car in the state of uniform motion camera imaging quality has the reliability through the addition of laser rangefinders, the accurate measurement of the object distance and the calculation of the imaging plane and the angle of the plane to be measured, to amend the three-dimensional cracks. The pixel resolution of the image is corrected, the images imaged by the industrial camera are preprocessed, the YOLOv8 algorithm is used for the intelligent extraction of crack morphology, and finally, the actual width is calculated from the spacing between two points of the crack. The crack detection width obtained by image processing using the YOLOv8 algorithm is basically the same as the value of crack width obtained by manual detection, and the error rate of crack width detection ranges from 0% to 11%, with the average error rate remaining below 4%. Compared with the crack detection error rate of the Support Vector Machine (SVM), the crack extraction model is reduced by 1%, so using the tunnel inspection vehicle as a platform equipped with an industrial camera, YOLOv8 is used to realize the recognition of the shape and width of the cracks on the surface of the tunnel tube sheet to meet the requirements of a higher degree of accuracy. The number of pixels and the detection error rate are inversely proportional to each other. The angle between the imaging plane and the plane under test is directly proportional to the detection error rate. The angle between the vertical axis where the lens midpoint is located and the line connecting the shooting target and the lens center point is αi and the angle θi between the measured plane and the imaging plane is reciprocal, i.e., αi + θi = 90°. Therefore, using the inspection vehicle as a mobile platform equipped with an industrial camera and based on the YOLOv8 algorithm, the crack recognition of the tunnel tube sheet has the feasibility and the prospect of wide application, which provides a reference method for the detection of cracks in the tunnel tube sheet.

Hidden correlation between rheological dynamics and crack formation in water-based slurry

Cracks generated in sheet coating of water-based slurries are an increasingly important concern in the development of diverse material science, such as fine ceramics, Pt catalysts, and Li transition metal oxides, from an environmental safety perspective. However, a comprehensive understanding of crack formation remains elusive due to the intricately entangled interplay among various characteristics of slurries. Here, we systematically ascertain the causes at work in crack initiation by analyzing the physical parameters of a series of aqueous alumina slurries using machine learning. The analysis reveals a strong correlation between rheological hysteresis and sheet cracking. As a verification of the correlation, the crack suppression by controlling the rheological hysteresis is experimentally confirmed. Furthermore, we visualize the microstructure in the slurry that induces cracks with a liquid-phase scanning electron microscope, clarifying the rheological dynamics. These results disentangle that rheological hysteresis is a good indicator directly reflecting microstructural durability against drying stress.

Visual and IR Inspection Analysis of PV Modules Installed at the Desert Climate of Qatar

This study presents the results of visual and infrared (IR) inspection of photovoltaics (PV) technologies installed at the Qatar environment and energy research institute (QEERI) outdoor test facility (OTF) at Qatar Foundation (Doha, Qatar). Silicon based PV technologies which have been operational in the field since 2014, have been investigated for various failure modes. The visual inspections were carried out for all the PV modules from the backside however, the inspection from the front side was not possible for some modules due to heavy soiling. The visual defects which were identified during this study include, cracking of the back glass, yellowing of the encapsulant material, cracks formation in the back sheet, and pits formation in the back sheet. The visual inspection revealed that around 19 % of the total modules have back sheet cracking and discoloration, 8 % have yellowing of the encapsulant, and around 4 % were having pits in the back sheet. Moreover, one module was detected with back glass cracking. The IR inspection was also done both from front and backside for all the silicon PV modules to detect hot spots. The IR inspection has revealed that hot spots were generated at different locations of the PV modules. 39 % of the modules have hot spots at the location of junction boxes, around 6 % of the modules have hot spots in junction boxes and around 1 % have hot spots at the locations away from junction boxes. The visual and IR inspection has revealed that the dominant failure modes which have been observed for silicon-based technologies at OTF are the hot spots generation at junction boxes and the back sheet cracking, and its yellowing.

Taguchi Optimization of Geometrical Factors of a Polymer Composite Patch in Crack Repair

For the repair of a crack in thin aluminium sheets, polymer composite patching is one of the better repair techniques. During service, when the load acts, the patch separates from the substrate due to the stresses developed at the interface. This separation of the patch from the substrate largely depends on the geometrical factors of the patch, i.e. length, width and thickness. The optimum geometrical factors need to be incorporated for the effective and economical repair of the cracks. In this work, the optimum combination of the geometrical factors, i.e. length, width and thickness of the polymer composite patch, is obtained using the Taguchi technique with the help of the results generated in the numerical analyses.

Performance and reliability of crystalline-silicon photovoltaics in desert climate

Performance and reliability of photovoltaic (PV) systems are important for the deployment of PV in desert climate. In this study, we investigate the performance and reliability of multi-crystalline, mono-crystalline and silicon heterojunction PV arrays operating in the field for 5-years from 2014 to 2018 under desert climate. From data monitoring and performing visual inspection at the field, a drop in the energy yield and the presence of various visual defects were observed and therefore further in-depth analysis was required to identify the potential of main cause of the performance losses. For the (Multi_D), (Multi_E), (Multi_F), (Mono_G), and (SHJ_H) arrays a degradation rate of −2.65 %/year, −1.91 %/year, − 0.14 %/year, − 1.59 %/year and − 0.62 %/year, respectively, was calculated using the RdTool. From each array, all modules returned from the field to perform indoor current–voltage (IV) measurements at Standard Testing Condition (STC) and at different irradiance and temperature operating conditions. The electrical parameters of these modules were analyzed and the degradation rate was estimated by comparing the STC values provided by the manufacturer with the STC values measured after 5-years exposure in desert climate. From the seven difference manufacturers, multi-crystalline silicon (Multi_A), (Multi_B) and (Multi_E) showed the lowest annual degradation rate below 1 %/year. Multi-crystalline silicon (Multi_D) and mono-crystalline silicon (Mono_G) showed the highest PV module power degradation of −3.0%/year and 6.3 %/year, respectively. Further, Encapsulant yellowing, back sheet cracking and cell cracking were the most prominent failure modes observed during the first 5-years of operation in the field.

Sedimentology of the Ediacaran barite‐bearing cap dolostone from Gaolan, northern Three Gorges, South China

AbstractWhile Ediacaran cap dolostones research is a hot topic, detailed sedimentological analysis of barite‐bearing cap dolostones remains scarce. Here, new data are presented from Xiangerwan in northern Three Gorges, South China, to illustrate the sedimentary characteristics, depositional environment and formation mechanism of the barite‐bearing cap dolostone. In ascending order, the succession is divided into: (i) pebbly dolostone; (ii) dolostone with unusual sedimentary structures (for example, sheet cracks and tepee structures); and (iii) barite‐bearing facies. The gravels of the pebbly dolostone record the slow relative sea‐level rise during post‐glacial transgression, with a local terrestrial influence. Sheet cracks and tepee structures represent water escape structures in the supratidal and upper intertidal zone, and gently wavy stromatolites in barite‐bearing facies are deposits typical of the upper intertidal zone. In addition, primary radial length‐slow dolomite cements were originally precipitated at the seafloor. In general, the cap dolostone was formed in a shallow‐water ramp environment. The form and sedimentary characteristics of barites indicate a primary (syngenetic) origin and help to divide the barites into bladed (Type I) and needle‐like (Type II) variants. With the ongoing melting of the Marinoan glacier and water density stratification, the cap dolostone was gradually precipitated, accompanied by exotic gravels input. The stratification persisted, and special sedimentary structures were widely developed. Phosphorus and barium ions were brought up from the deep basin by upwelling, indicated by the flourishing stromatolites and barite fan deposition. Above the sediment–water interface, the Type I barite first grew upward from substrates, then the Type II barite could grow either in the reverse ‘V‐shape’ cavities between and within the Type I barite clusters, forming rhythm layers with bedded dolomite, or scattered in the laminae of stromatolites or surrounding dolomite. Finally, the formation of barite fans indicates the end of cap dolostone deposition and deeper water sedimentation.

Molecular dynamics modeling of cracks in dry clay sheets at the nanoscale

Clay is a nanomaterial by nature. The cracking in clay at the nanoscale can provide significant insight into the cracking mechanism in clay at the continuum scale. This article is devoted to understanding the atomic-scale mechanism of the formation of cracks in a dry clay sheet through molecular dynamics with a general force field for clay. We simulate the formations of mode I and mode II cracks in intact dry clay sheets under tension and shear loading conditions, respectively. The numerical results show that the mode I and II cracking in a clay sheet is brittle and strain-rate dependent. The notion of critical bond stretch is adopted to model the breakage of bonds between atoms in clay. The critical bond length for crack formation is determined by the radial distribution function and the force curve between a pair of atoms. We investigate the crack initiation under mode I and mode II loading conditions from the bond breakage analysis. We interpret the cracking mechanism in terms of the type and number of broken bonds in mode I and mode II cracking. We present the stress intensity factor and cracking energy release rate under both cracking modes. The numerical results of the stress intensity factor and cracking energy release rate are quantitatively comparable to the experimental and numerical data in the literature.

Refined conodont stratigraphy at Martenberg (Rhenish Massif, Germany) as base for a formal middle/upper Frasnian substage boundary

The famous Martenberg section of the eastern Rhenish Massif, Germany, type-section of classical Frasnian goniatite and conodont zonations, has been restudied in order to document the microfacies development and to refine the conodont stratigraphy around the global semichatovae Event/Transgression, the proposed level to define a future upper Frasnian substage. More than 8.000 platform elements were identified and include new taxa. Palmatolepis jamieae is subdivided into the subspecies Pa. jamieae jamieae, Pa. jamieae savagei n. ssp., Pa. jamieae rosa n. ssp., and Pa. jamieae ssp. δ. Another new species, Pa. adorfensis n. sp., was previously partly identified as Pa. jamieae, while Pa. descendens n. sp. has previously been described in open nomenclature from Inner Mongolia. Morphotypes are defined in Icriodus symmetricus, Pa. ljaschenkoae, and Pa. proversa. A global literature survey shows that the eustatic semichatovae Event can be recognised in more than 20 regions of all continents with (sub)tropical Upper Devonian outcrops. At Martenberg, the transgression is preceded by a thin but distinctive interval with unconformities, microbial mats, sheet cracks, and currents that brought in the regionally youngest volcaniclastics. The new conodont data confirm that no typical Pa. jamieae (sensu the holotype) occur in the two beds originally supposed to represent the jamieae Zone in its reference section. We fully support the conclusion of Ovnatanova and Kononova (2020) that the jamieae Zone should be abandoned. Early Pa. jamieae subspecies and the related new taxa enter at Martenberg and in a few other regions in the globally easily recognisable Frasnian Zone 10 (= plana Zone). Frasnian Zone 11 (feisti Zone) is subdivided into subzones FZ 11a (= feisti Subzone) and FZ 11b (= nasuta Subzone). The base of the latter coincides with the semichatovae Transgression, the semichatovae Subzone of more shallow shelf settings, and is proposed to define in future the upper Frasnian substage base. On a global scale, the Martenberg section is currently the best bed-by-bed documented section for facies changes, conodont and goniatite biostratigraphy at the middle/upper Frasnian transition. Therefore, it is a prime candidate for a future GSSP selection. A global literature survey identified more than 20 other pelagic conodont successions that have the potential for precise correlation and a better understanding of the environmental changes associated with the semichatovae Event.

Effect of process parameters on porosity defects in Al-Si alloy hot rolling

Hot-rolled Al-Si alloy sheets are used to be formed Al alloy welding additions and cladding materials that are widely used in the aviation, automotive, and air conditioning industries. However, if parameters of hot-rolling process are not properly selected, porosity defects during casting will lead to cracks or fractures in Al-Si alloy sheets. This study based on meso-damage theory and established a damage equation describing porosity defects in the hot rolling process. The parameters of GTN (Gurson-Tvergaard-Needleman) void defect evolution, including the volume fraction of voids in different periods, the plastic equivalent variation of void nucleation, the standard variance of equivalent variation of void nucleation, and the correction coefficient of the material, are determined in this study. A finite element model of the porosity defects is developed based on the determined parameters. The finite element method is used to analyze the effect of different process parameters on the porosity defects and cracks in Al-Si alloy sheets during hot rolling, then we performed the hot rolling test to validate the results. The results show that the void stress and diameter are reduced and the quality of porosity defects is improved by decreasing rolling reductions and increasing the temperature. The optimized process parameters were a 20% depression and a temperature of 550°C.

Facile ultrasonic aided green reduction of graphene oxide by Doum palm fruit

This work describes a novel, facile, green, and one-step sonochemical method for reducing graphene oxide (GO) using Doum palm fruit. The successful transformation of GO into reduced graphene oxide (RGO) is confirmed via several techniques. FTIR confirmed the removal of most oxygen functional groups from GO and conjugation between Doum and derived reduced graphene oxide (GRGO). From XRD, the GO sharp peak was disappeared upon reduction and replaced by a wide broad peak. X-ray photoelectron spectroscopy (XPS) studies revealed an increase of the (C/O) ratio in GRGO compared to GO. The crumpled morphology of GO occurs upon reduction noticed from HRTEM. Corrugation and cracks in GO sheets are observed after the reduction process, FESEM revealed. The thermal stability of GRGO is higher than that of GO. These findings illustrate that this method is promising for the mass production biosynthesizing nanoscale oxides conjugated to reduced GO for medicinal and biological applications.

Effects of a stainless steel interlayer on the interfacial microstructure and bonding strength of Cu/Al clad sheets prepared via the powder-in-tube method

Cu/Al clad sheets with a 304 stainless steel foil (SUS304) interlayer are successfully fabricated by the powder-in-tube method. The influence of SUS304 thickness on the interfacial structure, elemental diffusion, and peeling strength of the clad sheets is studied. Experimental results indicate that the initial Cu/Al interface is partially transformed into a Cu/SUS304/Al interface after introducing the SUS304 interlayer. The proportion of SUS304 fragments at the bonding interface is shown to increase with thickness of the SUS304 interlayer. Differences in deformability between SUS304 interlayer and Cu/Al matrix promote the occurrence of shear deformation at the bonding interface via the cladding process, enhancing atomic diffusion at the Cu/SUS304/Al interface. Peeling tests reveal that interfacial cracks in clad sheets with an SUS304 interlayer propagate along the Cu/SUS304 and Cu/Al interfaces. Under combined effects of interfacial transfer and large shear strain, the interfacial strength of clad sheets is apparently improved. Clad sheets with the thickest SUS304 interlayer (30 μm) exhibit highest peeling strength (30.9 N/mm), demonstrating 73.6% improvement over clad sheets without an interlayer. These findings provide novel insights into the innovative design of clad sheets possessing extraordinary interfacial strength.

Recognition of crevasses with high‐resolution digital elevation models: Application of geomorphometric modeling and texture analysis

AbstractCrevasses—cracks in glaciers and ice sheets—pose a danger to polar researchers and glaciologists. We compare the capabilities of two techniques—geomorphometric modeling and texture analysis—to recognize open and hidden crevasses using high‐resolution digital elevation models (DEMs) generated from images collected by an unmanned aerial system (UAS). The first technique includes derivation of local morphometric variables; the second includes calculation of the Haralick texture features. The study area is represented by the first 30 km of a sledge route between the Progress and Vostok polar stations, East Antarctica. The UAS survey was performed by a Geoscan 201 Geodesy UAS. For the sledge route area, DEMs with resolutions of 0.25, 0.5, and 1 m were generated. Models of 12 morphometric variables and 11 texture features were derived from the DEMs. In terms of crevasse recognition, the most informative morphometric variable and texture feature was horizontal curvature and inverse difference moment, respectively. In most cases, derivation and mapping of these variables allow one to recognize crevasses wider than 3 m; narrower crevasses can be recognized for lengths from 500 m. For crevasse recognition, the geomorphometric modeling and the Haralick texture analysis can complement each other.

Energizing ASTM lap joint fracture standards.

Several ASTM standards on the fracture of glued and welded joints need attention because they do not consider the Griffith energy criterion of cracking which was proposed a century ago. It is almost as if Griffith never existed because the ASTM definition of failure is the stress criterion postulated by Galileo in 1638 in which stress at failure (i.e. strength = force/area) is defined as the determinant of fracture. Irene Martinez Villegas (Villegas, Rans 2021 Phil. Trans. R. Soc. A 376, 20200296. (doi:10.1098/rsta.2020.0296)) shows in this volume that attempts to use ASTM D5868 to standardize welded composite (carbon fibre reinforced polymer, CFRP) lap joints reveal major problems. First, the test is a low angle bend-peel test; not shear. Second, the energy required to break the joint is not emphasized so that joints may have high strength properties but also low toughness; third, the fracture force is not proportional to the lap joint area so the concept of strength independent of sample size is false; fourth, as the CFRP panels are made thicker, the strength rises at constant overlap area so the strength can be any value you want; fifth, the strength of larger joints goes down; this is the size effect noted in many bend-cracking tests, much as Galileo suggested for bent beam fracture in his famous book 'the larger the machine, the greater its weakness'. The purpose of this paper is to demonstrate that poor ASTM 'shear strength' standards should be replaced by a definition of welded lap joint performance based on Griffith's energy conservation argument in which fracture surface energy is the main parameter resisting failure. The foundation of this Griffith-style lap joint analysis for long cracks goes back to 1975 but has been largely ignored until now because it does not fit the Griffith equation for cracked sheets, has no 'stress intensity factor', and travels at constant speed, not accelerating like the standard Griffith tension crack. This study of tensile delamination shows that a long lap crack is not driven by stress near the crack but by changes in stored elastic energy in the stretched strips remote from the crack tip, while strain energy release rate is negative. It would be more appropriate to call this lap failure a tensile delamination crack. This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.