Dome Failure Research Articles

Influences of Weld Nugget Shape and Material Gradient on the Shear Strength of Resistance Spot‐Welded Joints

Resistance spot‐welded joints containing press‐hardened steels are seen to exhibit a fracture mode called total dome failure, where the weld nugget completely separates from one steel sheet along the weld nugget edge. The effect of weld nugget shape and material property gradients is studied based on damage mechanics modeling and experimental validation to shed light on the underlying influencing factors. For a three‐steel‐sheet spot‐welded joint combining DP600 (1.5 mm)–CR1900T (1.0 mm)–CR1900T (1.0 mm), experiments under shear loading reveal that fracture occurs in the DP600 sheet along the weld nugget edge. In subsequent numerical simulation studies with damage mechanics models whose parameters are independently calibrated for every involved material configuration, three variations of the geometrical joint configuration are considered—an approximation of the real joint, one variation with a steeper weld nugget shape, and one variation with a less pronounced gradient between weld nugget material and heat‐affected zone material properties. The results of the finite‐element simulations show that a shallower weld nugget and a more pronounced material gradient lead to a faster increase of plastic strain at the edge of the weld nugget and promote the occurrence of total dome failure.

Atom Probe Tomography Analysis of Exsolved Mineral Phases.

Element diffusion rates and temperature/pressure control a range of fundamental volcanic and metamorphic processes. Such processes are often recorded in lamellae exsolved from host mineral phases. Thus, the analysis of the orientation, size, morphology, composition and spacing of exsolution lamellae is an area of active research in the geosciences. The conventional study of these lamellae has been conducted by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and more recently with focused ion beam (FIB)-based nanotomography, yet with limited chemical information. Here, we explore the use of atom probe tomography (APT) for the nanoscale analysis of ilmenite exsolution lamellae in igneous titanomagnetite from ash deposits erupted from the active Soufrière Hills Volcano (Montserrat, British West Indies). APT allows the precise calculation of interlamellar spacings (14-29 ± 2 nm) and reveals smooth diffusion profiles with no sharp phase boundaries during the exchange of Fe and Ti/O between the exsolved lamellae and the host crystal. Our results suggest that this novel approach permits nanoscale measurements of lamellae composition and interlamellar spacing that may provide a means to estimate the lava dome temperatures necessary to model extrusion rates and lava dome failure, both of which play a key role in volcanic hazard mitigation efforts.

Dome Collapse Interaction With the Atmosphere

AbstractDome collapse is a dramatic volcanic process, yet the dynamics and evolution of dome collapse still present open questions. Observational data are rare, and this limits our ability to interpret the evolution of this phenomenon in terms of risk assessment. We show how the partial dome collapse of Soufrière Hills Volcano on 2010 evolved in less than 45 min and was characterized by five main different episode of dome failure process. Time and amplitude of seismic and infrasonic records associated with successive pyroclastic density currents show a nearly quadratic temporal trend suggesting a self‐accelerating process increasing in intensity up to the failure limit. Each episode generated gravity waves in the atmosphere, representing the first evidence of internal waves formed due to propagation of density currents in stratified fluids. Finally, we use gravity waves to estimate the total erupted mass and the plume height of the Vulcanian explosions triggered by the decompression induced by the collapse.

Investigation of the Failure of Advanced High Strength Steels Heterogeneous Spot Welds

Nowadays, environmental regulation encourages carmakers to reduce the global vehicle weight. Steelmakers develop grades with high performance (Advanced High Strength Steels, AHSS) and fine steel sheet assemblies are used in car body structures, with an optimized thickness in each part. However, unusual fracture modes are sometimes observed during the mechanical tests of heterogeneous AHSS welds, made of dissimilar steel grades and sheet thicknesses. Weld fractures can occur with a strength lower than expected. This study aims at understanding these fracture mechanisms and focuses on two common steel grades joined by Resistance Spot Welding (RSW): DP600 (a dual phase steel) and Usibor®1500 (a martensitic steel). The parameters affecting the failure modes and load bearing capacity are investigated during two common types of tests: the Cross Tension and Tensile Shear tests. The positive effects of heterogeneous welding with respect to the corresponding homogeneous configurations are discussed, as well as the consequences of a so-called Dome failure occurring at the weld nugget boundary.

Dynamic Stability and Failure Probability Analysis of Dome Structures Under Stochastic Seismic Excitation

The intrinsic relationship between deterministic system and stochastic system is profoundly revealed by the probability density evolution method (PDEM) with introduction of physical law into the stochastic system. On this basis, stochastic dynamic stability analysis of single-layer dome structures under stochastic seismic excitation is firstly studied via incorporating an energetic physical criterion for identification of dynamic instability of dome structures into PDEM, which yields to sample stability (stable reliability). However, dynamic instability is not identical to structural failure definitely, where strength failure can be experienced not only in the stable structure but also when the structure is out of dynamic stability. It is practically feasible to decouple the stochastic dynamic response of dome structures to be a stable one and an unstable one according to the generalized density evolution equation (GDEE). Consequently, the global failure probability can be investigated separately based on the corresponding independent stochastic response. For unstable failure probability assessment, the failure probability is the unstable probability if the dome's failure is attributed to instability, whereas inverse absorbing is firstly implemented to get rid of the stochastic response before instability and a complementary process is filled in the safe domain immediately to finally assess the probability of strength failure after dynamic instability.

Character, mass, distribution, and origin of tephra-fall deposits from the 2009 eruption of Redoubt Volcano, Alaska—Highlighting the significance of particle aggregation

The 2009 eruption of Redoubt Volcano included 20 tephra-producing explosions between March 15, 2009 and April 4, 2009 (UTC). Next-Generation radar (NEXRAD) data show that plumes reached heights between 4.6km and 19km asl and were distributed downwind along nearly all azimuths of the volcano. Explosions lasted between <1 and 31min based on the signal duration at a distal seismic station (86km). From Moderate Resolution Imaging Spectroradiometer (MODIS) imagery and field data, we estimate that over 80,000km2 received at least minor ash fall (>0.8mm thick), including communities along the Kenai Peninsula (80–100km) and the city of Anchorage (170km). Trace ash (<0.8mm) was reported as far as Fairbanks, 550km NNE of the volcano. We estimate the total mass of tephra-fall deposits at 54.6×109kg with a total DRE volume of 20.6×106m3.On March 15, a small (4.6km asl) phreatic explosion containing minor, non-juvenile ash, erupted through the summit ice cap. The first five magmatic explosions (events 1–5) occurred within a 6-hour period on March 23. Plumes rose to heights between 5.5km and 14.9km asl during 2- to 20-minute-duration explosions, and were dispersed mainly along a NNE trajectory. Trace ash fall was reported as far as Fairbanks. Owing to a shift in wind direction and heavy snowfall during these events, field discrimination among many of these layers was possible. All deposits comprise a volumetrically significant amount of particle aggregates, yet only event 5 deposits contain coarse clasts including glacier ice. The most voluminous tephra fall was deposited on March 24 (event 6) from a 15minute explosion that sent a plume to 18.3km asl, and dispersed tephra to the WNW. Within 10km of the vent, this deposit contains 1–11cm pumice clasts in a matrix of 1–2mm aggregate lapilli. A small dome was presumably emplaced between March 23 and March 26 and was subsequently destroyed during 1–14minute magmatic explosions of events 7–8 (March 26) that sent plumes between 8.2km and 19km asl. Ash fell along a broad swath to the ESE, covering communities along the Kenai Peninsula with up to 1mm of ash. Proximal deposits are largely composed of aggregate lapilli of 1–2mm with very little coarse juvenile material. Events 9–18 (March 27) sent plumes between 5.2km and 15.5km asl during <1–11-minute-long explosions. Ash clouds dispersed along trajectories to the NE, ENE and N and event 17 deposited up to 1mm of ash on upper Kenai Peninsula and Anchorage. A moderate-size dome was emplaced between March 29 and April 4 and was subsequently destroyed during event 19 on April 4 which lasted 31min and sent ash to 15.2km asl. The proximal deposit is principally composed of dense dome rock, unlike earlier events, indicating that event 19 was likely caused by dome failure. The cloud dispersed to the SE along a narrow trajectory and up to 1–2mm of ash fell on the lower Kenai Peninsula.Particle size data showing a preponderance of fine ash, even in the most proximal locations, along with the abundance of aggregate lapilli documented in most samples, confirms that particle aggregation played a significant role in the 2009 eruption and induced premature fallout of fine ash.

Prediction of Failure in Thin-Walled Hemispherical GRP Dome Subjected to Static Internal Pressure Based on a Failure Factor

Failure analysis of one-ply thin-walled hemispherical GRP dome internally pressurized was checked via analytical approach and finite element simulations using ABAQUS and MATLAB software. Tsai-Wu failure criterion was employed during analysis. The failure factor against changes of dome’s geometrical parameters was investigated. Subsequently, laminated hemispherical GRP dome failure behavior was theoretically analyzed using MATLAB software. During the analysis some geometrical parameters were assumed to be constant. Moreover, symmetrical laminations were taken into account. The Tsai-Wu failure factor was checked based on changes of applied internal pressure, ply thickness, dome’s internal radius and ratio of dome’s internal radius over ply thickness. The behavior was determined to be linear and quadratic both.

Limit dome height and failure location of stainless steel tailor-welded blanks

Forming limits of stainless steel tailor-welded blanks (TWBs) are investigated through both testing and numerical simulation. Limit dome height (LDH) tests were performed for 1.2/1.0 mm TWBs with 0°, 90°, 45° weldment orientations and various blank widths. Numerical simulation of the LDH test was conducted with LSDYNA. Since TWB is, in reality, a structure, the forming limits of TWBs in terms of the LDH and failure location should be characterized rather than the conventional forming limit diagrams (FLDs). A localized necking criterion based on the vertex theory was employed to identify the failure sites of TWBs. The localized necking criterion was compiled into a computer program, which processed the output data from LSDYNA. The LDHs and failure locations were computed for various combinations of blank thickness and weldment orientation. The predicted LDH and failure locations were compared with the test results and found to be satisfactory.

Catastrophic lava dome failure at Soufrière Hills Volcano, Montserrat, 12–13 July 2003

The lava dome collapse of 12–13 July 2003 was the largest of the Soufrière Hills Volcano eruption thus far (1995–2005) and the largest recorded in historical times from any volcano; 210 million m 3 of dome material collapsed over 18 h and formed large pyroclastic flows, which reached the sea. The evolution of the collapse can be interpreted with reference to the complex structure of the lava dome, which comprised discrete spines and shear lobes and an apron of talus. Progressive slumping of talus for 10 h at the beginning of the collapse generated low-volume pyroclastic flows. It undermined the massive part of the lava dome and eventually prompted catastrophic failure. From 02:00 to 04:40 13 July 2003 large pyroclastic flows were generated; these reached their largest magnitude at 03:35, when the volume flux of material lost from the lava dome probably approached 16 million m 3 over two minutes. The high flux of pyroclastic flows into the sea caused a tsunami and a hydrovolcanic explosion with an associated pyroclastic surge, which flowed inland. A vulcanian explosion occurred during or immediately after the largest pyroclastic flows at 03:35 13 July and four further explosions occurred at progressively longer intervals during 13–15 July 2003. The dome collapse lasted approximately 18 h, but 170 of the total 210 million m 3 was removed in only 2.6 h during the most intense stage of the collapse.

Mechanisms of lava dome instability and generation of rockfalls and pyroclastic flows at Soufrière Hills Volcano, Montserrat

Abstract Between 3 January 1996 and 1 December 1998 at Soufrière Hills Volcano, Montserrat, there were 27150 seismic signals attributable to rockfalls and pyroclastic flows. Large (1-4 x 10 6 m 3 ) and major (&gt;4 x 10 6 m 3 ) dome collapses began to occur after the extrusion rate reached 2 m 3 s -1 and the lava dome exceeded 30 x 10 6 m 3 in volume. Large to major collapses occurred on 26 occasions and were usually associated with periods of elevated extrusion rate (6 13 m 3 s -1 ), intense hybrid earthquake swarms and/or inflation-deflation cycles of crater-rim ground deformation. During these cycles, gas-rich pulses of magma, 140 000 320 000 m 3 in volume, were intruded into the dome and, soon thereafter, dome collapses from the headwalls of shear lobes were generated. Large dome collapses also occurred after 10 March 1998, when magma extrusion ceased, but these had no seismic precursors. These events represent structural failures from over steepened canyon-like walls and were followed by intense degassing, suggesting that gas pressure build-up within the relict dome may have played some role. Rockfall counts and durations established from seismic data show variations that correlate with extrusion rate. Using pyroclastic flow runout and rockfall duration data as proxies for event magnitude, power law relationships between frequency (total number of events) and magnitude have been found. Seismic signals associated with rockfalls and pyroclastic flows commonly comprise both high-frequency and long-period components. Intense degassing from the dome is interpreted as the source for the long-period component. These results indicate that rockfalls and pyroclastic flows generated by dome collapse at Montserrat are not simply the result of passive dome failure, but are intimately related to discharge of pressurized gas and pulses of magma extrusion. Pyroclastic flows were usually sourced from lobe headwalls, where lava was hot and gas-rich and where fragmentation of the micro vesicular andesite lava occurred more readily.

The explosive decompression of a pressurized volcanic dome: the 26 December 1997 collapse and explosion of Soufrière Hills Volcano, Montserrat

Abstract Abstract: We calculate the gas flux through a pressurized and permeable lava dome as magma slowly ascends to the surface and degasses. This provides an estimate of the mass of gas and the associated energy that may be released following the explosive collapse of such a dome. We estimate that during the 26 December 1997 dome failure of Soufrière Hills Volcano, up to 10 16 J of energy was released. We then develop a model of the dome break-up driven by the pressure jump across a fragmentation wave. We predict that the fragmentation front advances into the dome at a speed of order 10 ms -1 , while the gas and solid fragments issue from the dome at speeds of order 50-60 ms -1 . This fragmented material forms a dense fountain of gas and solid fragments. This may rise 100-200 m above the dome and then spread out to form a dense pyroclastic density current, with initial density of order a few hundred kilograms per cubic metre. We anticipate that such flows will become stratified in density and mean grain size. Some new experiments on stratified gravity currents illustrate that the flow propagation speed is similar to a well mixed current of the same total buoyancy, although the flow tends to become laterally stratified, with the dense lower region out-running the fluid higher in the current.

Instability and collapse of hazardous gas‐pressurized lava domes

An important type of gravitational lava‐dome failure involves significant internal gas overpressure that influences the failure process. For the first time, this paper presents a rigorous analysis of the mechanics of gas‐pressurized dome failure. We develop diffusion models to calculate gas overpressures in a lava dome, and embed these pressure data into stability analyses to demonstrate how gas pressurization can initiate instability. The results bear on the mechanistic understanding of hazardous dome failures. Gas pressurization can promote deep‐seated failure, and the timing of conduit pressurization can control the timing of dome collapse. Theory explains why dome collapse can be delayed for cases of oscillating effusion. Dome collapses and explosive events linked to collapse of lava domes can be hazardous. Monitoring criteria are considered to anticipate whether or not such collapses are likely to be explosive.

Statistical forecasting of repetitious dome failures during the waning eruption of Redoubt Volcano, Alaska, February–April 1990

The waning phase of the 1989–1990 eruption of Redoubt Volcano in the Cook Inlet region of south-central Alaska comprised a quasi-regular pattern of repetitious dome growth and destruction that lasted from February 15 to late April 1990. The dome failures produced ash plumes hazardous to airline traffic. In response to this hazard, the Alaska Volcano Observatory sought to forecast these ash-producing events using two approaches. One approach built on early successes in issuing warnings before major eruptions on December 14, 1989 and January 2, 1990. These warnings were based largely on changes in seismic activity related to the occurrence of precursory swarms of long-period seismic events. The search for precursory swarms of long-period seismicity was continued through the waning phase of the eruption and led to warnings before tephra eruptions on March 23 and April 6. The observed regularity of dome failures after February 15 suggested that a statistical forecasting method based on a constant-rate failure model might also be successful. The first statistical forecast was issued on March 16 after seven events had occurred, at an average interval of 4.5 days. At this time, the interval between dome failures abruptly lengthened. Accordingly, the forecast was unsuccessful and further forecasting was suspended until the regularity of subsequent failures could be confirmed. Statistical forecasting resumed on April 12, after four dome failure episodes separated by an average of 7.8 days. One dome failure (April 15) was successfully forecast using a 70% confidence window, and a second event (April 21) was narrowly missed before the end of the activity. The cessation of dome failures after April 21 resulted in a concluding false alarm. Although forecasting success during the eruption was limited, retrospective analysis shows that early and consistent application of the statistical method using a constant-rate failure model and a 90% confidence window could have yielded five successful forecasts and two false alarms; no events would have been missed. On closer examination, the intervals between successive dome failures are not uniform but tend to increase with time. This increase attests to the continuous, slowly decreasing supply of magma to the surface vent during the waning phase of the eruption. The domes formed in a precarious position in a breach in the summit crater rim where they were susceptible to gravitational collapse. The instability of the February 15–April 21 domes relative to the earlier domes is attributed to reaming the lip of the vent by a laterally directed explosion during the major dome-destroying eruption of February 15, a process which would leave a less secure foundation for subsequent domes.

Seismological aspects of the 1989–1990 eruptions at redoubt volcano, Alaska: the SSAM perspective

SSAM is a simple and inexpensive tool for continuous monitoring of average seismic amplitudes within selected frequency bands in near real-time on a PC-based data acquisition system. During the 1989–1990 eruption sequence at Redoubt Volcano, the potential of SSAM to aid in rapid identification of precursory Long-Period (LP) event swarms was realized, and since this time SSAM has been incorporated in routine monitoring efforts of the Alaska Volcano Observatory. In particular, an eruption that occurred on April 6 was successfully forecast primarily on the basis of recognizing the precursory LP activity on SSAM. Of twenty-two significant eruptions that occurred between December 14 and April 21, eleven had precursory swarms longer than one hour in duration that could be detected on SSAM. For individual swarms, the patterns of relative spectral amplitudes are distinct at each station and remain largely stationary through time, thus indicating that one source may have been preferentially and repeatedly activated throughout the swarm. Typically, a single spectral band dominates the signal at each seismic station: for the vigorous one-day swarm that preceded the first eruption on December 14, signals were sharply peaked in the 1.9–2.7 Hz band at the closest station, located 4 km from the vent, but were dominated by 1.3–1.9 Hz energy at three more distant stations located 7.5–22 km from the vent. The tendency for the signals from different swarms recorded at the same station to be peaked in the same frequency band suggests that all of the sources are characterized by a predominant length scale. Signals from the precursory LP swarms became weaker as the eruption sequence progressed, and swarms that occurred in March and April could only be detected at seismographs on the volcanic edifice. Onset times of precursory LP swarms prior to eruptions ranged from a few hours to about one week, but after the initial vent-clearing phase that ended December 19 these intervals tended to become progressively shorter for successive swarms. These trends in the relative onset times and intensities of successive precursory LP swarms are consistent with an overall depressurization of the magmatic system through time. In general, each of the swarms had an emergent onset, but the intensities did not always increase steadily until the eruptions. Instead, as the time of an eruption approached the intensity usually increased more rapidly before peaking and then declining prior to the eruption; for three of the swarms, two distinct peaks in intensity were apparent. The time intervals between final peaks in swarm intensity and ensuing eruptions ranged from about 2 hours to almost 2 days, but the peaks always occurred closer to the eruptions than to the swarm onsets. Both the onset of LP swarm activity and a decline in intensity prior to an eruption may represent critical points in the process of pressurization that drives the flow of fluids and gas in a sealed magmatic system. A notable exception to this pattern is the eruption of March 9 which lacked a detectable precursory LP swarm, but was followed by an unusually long period of strong LP seismicity that may have been stimulated by a depressurization of the magmatic system resulting from dome failure. On both December 14 and January 2, the spectra of early syn-eruptive signals have peaked signatures much like those of the spectra of precursory LP activity from shortly before the eruptions; these similarities may indicate that the source of precursory seismicity continued to be active during at least the early part of each eruption. In syn-eruptive signals from March and April recorded at stations on the volcanic edifice, the dominant spectral energy progressively shifts with time during the eruption to lower frequencies; at least part of the energy in these signals may have been generated by the debris flows associated with dome failures.